Model Engine Maker
Engines => From Kits/Castings => Topic started by: Allen Smithee on June 20, 2022, 12:28:27 PM
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Last week I picked up a job lot of stuff from a friend who is clearing out a lot of model engineering and aeromodelling stuff because he has realised that the number of years he has remaining is almost certainly less than the man-hours of projects he has been hoarding. Much of this I will be looking to pass on, but that's another thread.
Amongst this hoard was this box containing a Stuart S50 kit:
(https://i.postimg.cc/cJQ9Hk0w/1.jpg)
I thought it was incomplete, but I've checked it off against the BoM and it's all there (screws and small metal parts are in those two film tubs). As you can see it has been started, but I'd estimate it's about 20% finished. I'm really just an aeromodeller who dabbles in the dark arts, but for some reason this one has caught my imagination and I think I may actually finish it off. So if people can bear yet another S50 thread I will document my amateur attempts for all to laugh at.
Doing some reading around I note that these were very prone to chilled-casting syndrome, especially in the steam chest and the steam-chest cover. If you look at the photo you may be able to see that this steam chest casting is actually bronze rather than iron, so perhaps this was a response. The steam chest cover is still iron, but if that turns out to be chilled it's a shape I can always mill from a bit of mild steel if I need to.
I regard the silly practice of quoting all sizes in fractional inches as a deliberate challenge; proper metric dims would be ideal, but if you're wedded to inferial dims what's wrong with thou FFS!! At this moment I'm wondering whether it will be simpler to do a quick redesign to allow me to use my existing metric taps/dies/drills/reamers or just to buy in a few inferial tools and hide them when they're not needed... ;D
Actually I do have a box of assorted BA taps an dies that I was given, so the fetish with 5BA and 7BA may not be a problem. But I've never owned a 3/32 reamer and I don't intended to start now!
Looking closely at it I think there are a few things I'll change. The connecting rod and even the crankshaft run steel-in-cast-iron, and I think I want to bush these with brass or bronze on principle. There's no oil hole in the big end, which seems sub-optimal but easily fixed. And the niggardly piece of 1/4" x 3/8" MS bar supplied for the connecting rod has almost no machining allowances, so I'll probably make it from 1/2" round bar stock instead. I might also replace the cast-in dummy nuts with real ones to look nicer (if I can be bothered). They supplied a big chunk of mild steel bar to make the crank web from, but it seems over 80% of it would end up as swarf and as it's essentially just a shape with two tapped holes in it I'm thinking of cutting it from 1/8" plate instead, and making a flanged bush which I'd silver solder into the middle to provide the support for the shaft. Or something.
I've never done a steam engine before so may I as a typical clueless newbe question? I'm looking at the steam valve which is supplied as a tiny bronze casting. I can see how it is actuated by the pushrod from the eccentric, with the end of the pushrod screwed into a bit of brass that sits snuggly between the pillars on the back of the valve. Am I correct in thinking that the valve block itself just floats, being pushed onto the face on the side of the cylinder by the incoming air/steam pressure? If so I presume I just need to get the seating face flat on some wet&dry and then possibly lapped onto a piece of glass (or something) mor is there a precision fitting aspect that I'm missing?
TIA,
AS
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Hi Pete,
Stuart models normally provide good quality Cast Iron and you rarely find hard spots (they had a bad period but seem to have improved since then ::) ). Having seen this kit I think you have a good set :)
Cast Iron is actually a good bearing surface against steel as long as it is well lubricated.
Yes the valve block floats and the air/steam pressure will hold it against the valve face. You will get both surfaces smooth enough rubbing them on wet and dry on a flat plate.
May I suggest you try making the bits to drawing before you try modifying them or making improved ones. ;)
Jo
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yes the valve needs to be able to lift off the port face slightly to allow any trapped condensate to escape and avoid a hydraulic lock. Just some fine wet and dry on a flat surface to rub the casting on should do, i don't always bother with that but will depend on the finish on the casting if it has already been machined.
M3 and M2.5 would be OK preferably with smaller than ISO hex sizes and you could get away with drilling the valve rod hole 2.4mm and cut a M2.5 thread onto the supplied 3/32" material.
When the drawings were first bone most would have been working with a steel rule and firm leg callipers so fractions suited those methods.
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Hi Allen,
Looks like a very nice acquisition indeed. I don’t think anyone ever complains about another steam engine build on this forum. I for one am looking forward to it.
I also try and stick to metric tooling and dimensions, but have found that occasionally, the gaps between rational metric dimensions are just too big and something old fashioned just seems to fit better. But many times, nearest metric sizes work fine. Just need to check clearances, and importantly the gaps between features to ensure that the small differences in dimensions do not accumulate in an unfortunate way. So I have purchased a set of ME taps and dies. I also occasionally resort to a drill size from a set I purchased many years ago.
As Jo suggests, I have just used wet and dry agains a sheet of glass for the valve face and my engines run fine, though I have to admit that I am not sure how I could determine if it was passing too much unless it was so excessive that the engine would not run. Allowing the valve to lift means that the cylinder can discharge condensate instead of locking up on the condensate that accumulates when warming up from cold.
Getting beaten to post faster than I can type, so better post anyway.
It won’t fly but I am sure you will enjoy it anyway.
MJM460
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May I suggest you try making the bits to drawing before you try modifying them or making improved ones. ;)
Invoking MIL-TFD-41?
Where's the fun in that??? ;D
AS
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That's a very nice acquisition - looking forward to seeing your build.
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No more Mil specs please that time in my life is passed ::) Make It Like The F**kin’ Print for once
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For the uninitiated - we had a shop floor senior manager who didn't like to see any concessions rejected by Engineering because it implied his lads had tried to ship stuff that was unacceptable. So if a concession/permit request wasn't approved the engineer woukld write "Rework in accordance with Mil-TFD-41".
Mil-TFD-41 = "Make It Like The F'ing Drawing Four Once"
AS
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There was quite a detailed build article in Model Engineer some years back by "Tubal Cain" which is still available on the ME website and may be helpful for your build. Just change the PDF number at the end, there are about 10 parts.
https://www.model-engineer.co.uk/sites/7/documents/sally-1.pdf
This photo of the bed casting being marked out gives a good idea why fractions were used as you can't find many steel rules marked in 1/1000ths
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I was waiting for paint to dry on my current project, and it was too windy to go flying, so I thought I'd make a start on this (but this will be a sporadic "when I'm not doing other stuff" build so don't hold your breath). I've never built a steam engine, never build from castings and my metalworking skills are (by the standards of this community) rudimentary at best. But the best learning is by doing, so here goes...
I looked at the drawings and the con-rod took my fancy. As I said previously, the kit includes a miserly piece of gash 1/4"x3/8" bar for this and I had already decided that was too much like hard work, so I found a piece of 1/2" EN1a round in the stock box and used that instead.
(https://i.postimg.cc/WzxYSg2K/2.jpg)
It's a simple-enough part with some taper-turning, but it's infuriatingly dimensioned - measurements from random features rather than picking a datum and referencing everything to that. But why do things properly when you can waste everyone's time doing it strangely...
(https://i.postimg.cc/7h5Qgmy0/3.jpg)
The books always talk about setting-over the tailstock for mild tapers, but I hate doing that so I put my better boring head in the tailstock instead. I'd forgotten that I'd made a dead-centre for it, but it was there in the box waiting for me:
(https://i.postimg.cc/1R7kfNZD/4.jpg)
The setup is a bit strange because my QCTP gives me limited access near the tailstock, so initially used the whole 12" piece of bar and started taking the round part of the rod down to 7mm dia before doing the final taper turn. Despite the unsupported length it cut nicely even without a steady:
(https://i.postimg.cc/QMDPRQpZ/5.jpg)
Then the feck-up fairy dropped in for coffee. The centre in the boring head suddenly started to smoke, and then burned out completely. That's when I remembered that I had machined the centre, but hadn't hardened it...
Looking around the workshop my eye fell on a small live centre in my Unimat 3 box. It wouldn't fit into the nice Jones & Shipman boring head, but my other boring head took larger cutters so I quickly turned up an adapter sleeve and I was back in business. I also played around with the position of the compound slide and toolholder to allow me to taper turn on a shorter length:
(https://i.postimg.cc/SNwHGFRs/6.jpg)
Then it was just a matter of moving to the mill to face off all sides to dimensions, pilot-drill little and big end bores and trim off the surplus length I'd left on the bar so I could hold it in the chuck. This is still around 0.1 oversize on thicknesses to allow for cleaning up after I drill and bush the bores. The phone's flash exaggerates the machining marks (that's my story and I'm sticking to it):
(https://i.postimg.cc/QxBR5xXw/7.jpg)
(https://i.postimg.cc/2yyg0Cnq/8.jpg)
(https://i.postimg.cc/CK4tYRNB/9.jpg)
(https://i.postimg.cc/1Rdd9hpH/10.jpg)
So here's the roughed-out part - I've left the ends square while I decide how to round them. I think once the big-end is bushed I'll make a little jig with a pin that I can stick in the milling vice and round it against an end-mill. But the little end will probably have to be hand-filed because the bore isn't concentric with the radius for some obscure reason.
(https://i.postimg.cc/FRWBdwwh/11.jpg)
Incidentally - this is my part sitting next to the piece of gash material that Stuart suggests you could make it from. No doubt an experienced machinist could do it, but why? Is an extra 1/2" of material at each end to give you something to hold it by really too much to ask...
(https://i.postimg.cc/vTKkjCv0/12.jpg)
To be continued...
AS
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Then the feck-up fairy dropped in for coffee.
Yea - don't you just hate some uninvited guests :facepalm: :Mad:
Nice part so far :ThumbsUp:
Per
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Looking good!
I can't help thinking that the kit suppliers have a right old laugh when they think about what bar they supply for parts. Seems like more often than not the kit stuff goes in my offcuts box while I find something more suitable.
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Then the feck-up fairy dropped in for coffee.
Yea - don't you just hate some uninvited guests :facepalm: :Mad:
Sadly she's a regular visitor...
AS
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I’m pretty sure that little beach lives in my shed somewhere.
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Hi Allen,
I feel your pain, I am currently building the Hemingway knurling tool (nearly finished),
Some the the tooling called up is
BA taps, Metric, and Imperial??
I will be onboard following S50 your Build,
Gary
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If you did want to mill the radius on the small end it could have it's width reduced to 1/4" and just put an 1/8" radius on the end.
If you are bushing the little end then you may need a bigger radius to leave enough metal around the bush but then you get into needing to modify the crosshead so the slot is deeper and then there is a knock on effect with piston rod, slide bars etc.
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Looks like you are a natural Model Engine Maker Pete :)
One of the great things about making model engines (rather than flying them and conducting the odd bit of impact testing ::) ) is you can do it in the relatively dry/warmth of the shed.
Jo
P.S. Eric has lots of Stuart 10Vs if you feel the need next time you visit him ;)
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Far from having a laugh I would have said Stuarts gave good thought to what they supplied. You need to remember the S50 is aimed at the beginner who may well have quite basic machines/tooling and probably just a lathe. Far better to provide them with rectangular stock than round and there is enough length to hold there.
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Not sure I agree. To turn the taper at least one end has to be on a centre with(say) a 4-jaw at the other. I felt there was just not enough excess material on that piece of flat to drill a centre with enough depth to support the steel during turning that would not still be a hole in the finished part. At least at my skill level, anyway!
YMMV,
AS
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A small size 0 BS ctr drill does not go in far and there is always the oppertunity to make use of the hole to get oil to the big end bearing. An 1/8" over finished size would have been more than enough material for the hole not to show.
The need for a large ctr hole could also have been considerably reduced if the topslide had just been set over to cut the short taper, using such a long length of bar you would have had to offset 3-4 times as much and with the other end in a 4-jaw rather than between ctrs means the bar has to be bent which probably added to the over heating problems
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The need for a large ctr hole could also have been considerably reduced if the topslide had just been set over to cut the short taper,
The geometry didn't work - I couldn't do that without the topslide fouling on the tailstock, and the saddle would be off the front of the bed if I tried it the other way.
using such a long length of bar you would have had to offset 3-4 times as much and with the other end in a 4-jaw rather than between ctrs means the bar has to be bent which probably added to the over heating problems
I don't understand that. Surely the angular bend is the same regardless how long the bar is? I probably should have done it between centres, but I don't own a lathe dog (let alone a catchplate) so it wasn't an option.
AS
[edited because I misunderstood what you were saying - apols!]
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Others seem to do it OK on a Myford with a big 4-way toolpost
https://www.model-engineer.co.uk/sites/7/documents/sally-7.pdf
Angle will be the same but as you are having to offset the tailstock ctr a lot more the bending force is greater which increases the risk of a small ctr poping out.
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The geometry didn't work - I couldn't do that without the topslide fouling on the tailstock, and the saddle would be off the front of the bed if I tried it the other way.
That is often a problem when working with tailstock support. My solution was the extended toolholder shown here: http://www.charleslamont.me.uk/iqc_toolpost4.html (http://www.charleslamont.me.uk/iqc_toolpost4.html)
BTW, Your Myford should have come with a catchplate as part of its standard equipment.
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You may be right, but with the combination of tool holder, compound, saddle and tailstock that I have I couldn't find a geometry that worked until I accepted that I'd have to swing the compound and the QCTP (which I was reluctant to do).
Anyway, further progress. My eye fell on the flywheel. This had been started (almost finished) by the previous owner, but it had some witness dents which suggested to me that it may have leaped out of a chuck at some point. The centre bore is supposed to be a fit on the 1/4" silver steel crankshaft, but it was a very slack fit (I measured the bore at 6.47mm - I did wonder if these issues were connected. I had choices - I could rebore it to the next size up in silver steel (probably 7mm) and adjust parts accordingly, or I could plug/bush the bore and redrill the hole at the right size. I chose the latter because I didn't want to wait for the new material to arrive and I didn't have a 7mm reamer so I'd have to buy one.
So I carefully set the flywheel in my more accurate chuck and clocked it, tapping gently until it was running within 0.02mm of true at the rim and centre-drfilled, drilled and reamed it 1/4"leaving it a light push fit on the shaft.
(https://i.postimg.cc/YCvk9583/13.jpg)
I then gingerly bored the hole out to 7.8mm before reaming it to 8mm. There were some hard lumps in the middle of the casting and I had t switch to a brazed carbide boring bar to cut through them - I wonder if that's what caused the oversized hole and impact damage. Ayway at this point I realised I was an idiot - I should have made the plug first so that I could fit it without disturbing the chuck setup! So I took the chuck off with the flywheel still in it(!) and used a collet to turn an inch of EN1a bar (the same bar I was using yesterday) down to 8.02mm. The finish cut was less than 0.02mm and was done at 2,800rpm to get a decent finish, and then I cut gentle lead-in with a fine file and polished it with some wire-wool before parting it off. The resulting plug was a mild press-fit but I gave it a hint of bearing lock as I pressed it home. I then refitted the chuck with the flywheel, reclocking it to check drilled.reamed it th 1/4"
(https://i.postimg.cc/SRVq2qwZ/14.jpg)
(https://i.postimg.cc/9XBcNtrG/15.jpg)
I then started to turn the bush down to length, but it started moving in the chick. Clearly gripping it on the centre boss wasn't firm enough, so I moved it to my other chuck (for which I have outside jaws) to face off the two sides of the centre boss to length and clean-up the centre boss casting a bit.
(https://i.postimg.cc/FsshtdLw/16.jpg)
There are still a couple of dings on the flywheel, but I think I might leave them there as "character" to give it an artistic "weathered/used" look. Its fit on the sfat is just a smidge tighter than a running fit - if it was a moving joint I'd give it a light lapping before use. But it's not a moving joint so it's pretty near perfect by my standards. At some stage I have to drill and tap into the hub for a retaining grubscrew, but that can wait.
Of course there's no point in having a flywheel on a shaft if you have nothing to spin it on, so I was forced to go back to the main body casting. Whilst some work had been done on this the bores for the crank hadn't been drilled. So I clamped it to an angle-plate and set it up in the mill (apols - I forgot to take pictures of this bit). Like most castings the measurement datums are infuriatingly vague, but I found if I clamped it so the top edge clocked horizontal a square sitting on the mill bed visually lined up with the centres of the cast-in dummy nuts on the bearing chairs on both sides (and also the cast-in dimples for the oil-cups on the tops of the dummy bearing caps). I centre-drilled the "top" side and then went straight to a 5.5mm drill to drill through (slow speed, with lube) because it's a fairly rigid drill. I found that if I was gentle it was quite happy to drill into the "lower" bearing and establish its own centre without wandering. I then followed through with 6.3mm drill and 1/4" reamer. I appreciate that this was probably "bodging" - I should probably have accurately datum'd each side separately and centre-drilled in the measured positions on each side. But I felt that with my skills the "proper" approach was fraught with opportunities to screw up so I was happy to bodge it and just hope there weren't any had spots on the casting that might throw the drill off track. Fortunately the feck-up fairy was having her post-tiffin nap, so it all worked well enough:
(https://i.postimg.cc/HL5g0bq8/17.jpg)
(https://i.postimg.cc/2SgYB0Kf/18.jpg)
(https://i.postimg.cc/yYQs71hx/19.jpg)
To be continued...
AS
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That is often a problem when working with tailstock support. My solution was the extended toolholder shown here: http://www.charleslamont.me.uk/iqc_toolpost4.html (http://www.charleslamont.me.uk/iqc_toolpost4.html)
I have a Dickson QCTP - the extended toolholders are sometimes advertised but seem to be like hens teeth if you actually want to buy one!
BTW, Your Myford should have come with a catchplate as part of its standard equipment.
I bought my Myford pre-owned from the proverbial "little old lady down the road". It came with many things and was excellent value for the price I paid, but amongst those things there were zero catch plates - I counted them (twice)...
One of these days I'll make one from one of the chuck backplates or faceplates (I have several of both) but that will only happen when I get motivated to buy a lathe dog. We're strictly a 1-dog household so that will have to wait until Charlie stops working from home:
(https://i.postimg.cc/P55X6hx1/IMG-20220526-112553537.jpg)
It's a dog's life...
AS
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Thats one relaxed dog!
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RDG (Myford) usually have the extended holders in stock, that's where my one came from not that I use it much. A 10mm square DCMT tool gets in better even with a revolving ctr in place.
https://www.myford.co.uk/acatalog/Myford_Quick_Change_Toolpost_and_Accessories.html
3mm dia valve stem with ctr drilled hole and tailstock support turned right to the end with a Dickson post
(https://hosting.photobucket.com/albums/v156/jasonballamy/Engineering/RMC/.highres/20200208_094321_zpsvqlkglix.jpg)
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Looks like things are progressing in good order for you Allen, although I have to say that I am a bit put-off at seeing that drill chuck key hanging out there while the machine is running. Shame on you. :hellno:
Jim
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Looks like things are progressing in good order for you Allen, although I have to say that I am a bit put-off at seeing that drill chuck key hanging out there while the machine is running.
Guilty as charged, although I would say that it wasn't there while I was actually cutting. That shot was posed because when I went to remove the reamer I realised I'd forgotten to take a photo, so I popped the reamer forward and switched on again at 100rpm for a few seconds to take the shot (forgetting to remove the key).
But having said that...
Until a few days ago the tapers in the spindle and tailstock were getting weak, so the tailstock chuck was prone to slipping and I got into a habit of leaving the tailstock chuck key in and keeping a hand on it to hold the drill, tap or WHY against slipping. I'd been tolerating this for a while because my main focus had been on a non-machining project:
(https://i.postimg.cc/rpDJwy6N/215.jpg)
(https://i.postimg.cc/gJNtxSSv/202.jpg)
But when I started the Stuart I decided to address that before starting, so I gave both spindle and tailstock tapers a thorough clean-up with a double-ended MT2 reamer. It's been very effective and both now stick like a minister to a partygate excuse.
AS
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(https://hosting.photobucket.com/albums/v156/jasonballamy/Engineering/RMC/.highres/20200208_094321_zpsvqlkglix.jpg)
Thanks for that Jason, and I'll look at it again when I'm next in the workshop but I think before I can get anywhere near that close the saddle or the topslide will foul on the tailstock.
AS
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Today I had to hand over wads of cash to order a selection of inferial reamers and BA/ME taps & dies rather than rework the drawings to use the metric sizes I'm tooled up with. So it looks like the rest of the build will be more or less to the drawings, although I'm tempted to make the cylinder caps from brass rather than steel as it would look cute.
Having said that I'm still tempted to make the crank web from a bit of 1/4" steel plate rather than the 3/4" length of 1-1/2" bar provided:
(https://i.postimg.cc/RqxNsTmv/image.png)
I'm struggling to see the reason for all that scrap steel! My other thought was to dig out my keats fixture and machine the web with an integral crank pin. I probably won't, but we'll see how I feel when I get to it!!
AS
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I'm struggling to see the reason for all that scrap steel!
Can't have it both ways. In an earlier post you were asking for more material to hold now you are saying it's waste :LittleDevil:
Why not saw off a 1/4" slice and machine from that and save the "waste" for something else, the EN1A round stock will be nicer to machine than a bit of unknown plate
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The crank web drawing is (for me) remarkably unhelpful because while the dimensions might describe the part they don't give me anything I can actually machine to for the two angled faces. No doubt Jason will tell me that they are perfectly adequate because a real machinist will turn the round features and then mark out the angled faces on the back of an apprentice for hand filing or shaping with a stone club or something, but I have a lathe and a (sort of) mill and that's what I want to use.
So the first task was to redraw it in Fusion 360:
(https://i.postimg.cc/8P9dCxpz/image.png)
This allowed me to extract meaningful dimensions:
(https://i.postimg.cc/HkBC104H/image.png)
I even extracted this useful dimension which would mean I could mount the part in a rotary table at the defined distance and use the angle directly for the two cuts:
(https://i.postimg.cc/Rhmvs306/image.png)
...although that's a hard way to do it so I think I'll just centre it in the rotary table and use that 425thou dimension on both sides (and I can drill/tap the crank pin hole at the same time without changing the setup). But this exercise does how that CAD can be useful as a measuring tool!
I need to do some pondering about this, because this built-up crank inherently means milling and turning on large offsets from a thin 1/4" shaft - probably need more attention to shallow cuts at correct feeds and speeds than I normally bother with...
AS
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Modelling the part is a good approach - it can give you a sort of electronic dry run to help think through the machining sequence. For what it's worth, I think you're doing a great job on this engine and I am enjoying your build.
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School boy geometry really.
Scribe lines to the large and small dimensions, and join where they intersect with the outside of the stock, no need to know the angle. hacksaw just clear of the line and then set line level in the mill vice and mill to the line. And to think someone said I was making things complicated :Lol:
If you are playing with CAD work out what you need to space a pin in the crank pin hole off the vice jaw by and use that to set the angle
(https://hosting.photobucket.com/albums/v156/jasonballamy/Engineering/Oscillator/.highres/DSC02371_zpsnoiuzep3.jpg)
(https://hosting.photobucket.com/albums/v156/jasonballamy/Engineering/Oscillator/.highres/DSC02372_zps1gpfyqua.jpg)
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The crank web drawing is (for me) remarkably unhelpful because while the dimensions might describe the part they don't give me anything I can actually machine to for the two angled faces. No doubt Jason will tell me that they are perfectly adequate because a real machinist will turn the round features and then mark out the angled faces on the back of an apprentice for hand filing or shaping with a stone club or something, but I have a lathe and a (sort of) mill and that's what I want to use.
Best to just do it your own way and have the satisfaction of the end result. If someone chooses to openly laugh at you rather than offer positive encouragement they are best ignored. In doing it your way, you may decide as you go that there was an easier way, or a quicker way, or whatever, but that really doesn't matter when your own approach works. You may afterwards decide that in future you'll use another method, but that doesn't matter either. I am looking forward to your successful outcome.
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Ah, I see.
I don't want to mark lines and mill to them by eye - I have machine tools with calibrated dials so that I can machine to dimensions. What's the point in having a machine that will hold to less than a thou if you just use it to visually line up with a scribbled scratch?
The model took less than 10 mins to do and it produced data that allows me to just mount a rotary table to do two accurate cuts without disturbing the setup. In only a little more time I could have produced the same data using a pencil and "schoolboy geometry". The point is that data only needed to be developed once - if the drawing had been done properly those dimensions would already be there. The scabby drawing with non-useful dimensions just makes work for every builder.
I've been looking at S50 build logs and videos, and it seems this issue has arisen several times. It also seems that the cut-outs aren't really there to form a counterweight (although that's useful). Their main reason for being there is so that the crankshaft can be fitted over the edge of the base casting to run in the enclosed trough. So the dimension is actually very simply defined:
(https://i.postimg.cc/Zn3R1fn5/image.png)
The desired clearance over the edge of the casting (A) will need an easily measurable dimension for the tangential distance between the flat and the centre (B). Then for a given counterbalance (or just visual) effect there will be a required angle between the flats (σ). To machine the part the builder needs just A and σ to be able to rattle of both flats datumed to the shaft centre. Add one further dimension for the crank throw and the true position of the crank pin hole can be drilled at the same time without moving it from the fixture.
I used to read riot acts to draughtsmen (and a few draughtswomen) about dimensioning shop drawings USEFULLY so that the drawings contained the information needed to make the part. To do this the draughtsperson had to think about how the part would be made, and if this involved getting off their stool and heading down to the shop floor to ask how it would be made then that's just another school day in their education which might ultimately lead to fewer un-manufacturable drawings being sent down.
Apols for the rant, but it's a hobby-horse of mine. The purpose of a drawing is to communicate a design intention, not to document a designer's thought process. A drawing which amounts to an exam question (requiring further working and a slide-rule or calculator) before the part can be made is like a broken pencil - utterly pointless.
Not that I feel strongly about it or anything...
;D ;D ;D
AS
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I have that same conversation with my engineers routinely. They have a habit of just slapping any old dims on a drawing to get the job out to the floor. Hoping to work them through that a bit. Getting them to talk to the shop is the key - and they are getting the hang of it, happily. Why is that so hard? My favourite part of the day is going to the shop and talking to the machinists and welders.
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Personally, I'd have used marking blue, marked out the shape with scriber lines and light punch dots, sawn to shape, filed to line, finishing with draw filing, and 'breaking' the edges just enough to remove any trace of the punch dots. Estimated time for a component this size, 10 -15 mins beginning to end. Each to his own
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I'm not in that environment any more, but 30ish years ago I was a process engineer in a company making electronic connectors and associated goodies (I was introducing Statistical Process Control approaches). I would expect my guys & gals to walk the floor at least twice a day, and on the last working day before Xmas I would give them all ties (purchased from charity shops) that they had to put on before heading down to run the gambit of the assembly women. Anyone who came back with an intact tie (not cut off, stolen, shredded, dipped in bonding agents or stapled to shirts) clearly didn't have a close enough working relationship with the staff, and got re-educated (one of my guys usually came back de-bagged and covered in lipstick, but he was one of nature's babe-magnets).
But I encouraged the women on the shop floor to come up to the engineers who created the drawings and seek a personal explanation of what they meant. It was always educational for one or both of them. When it came to the toolroom I encouraged engineers to invite toolmakers into the discussions on both the designs and the manufacturing techniques because I was fed up with seeing un-manufacturable designs leave the office. One of my favourites from an even earlier job in the underwater business was a sonar pressure fitting which had a pin to release a ball-valve. It was a phosphor-bronze part with a phosphor-bronze pin and three O-rings that looked something like this in cross-section:
(https://i.postimg.cc/ZRS3kGnq/image.png)
The pin was 2.5mm dia in a 2.8mm bore. Quite how those undercuts for the O-ring cavities were to be made doesn't seem to have occurred to the designer, let alone how the specified 5x3x2 O-rings were going to get in there afterwards...
AS
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As I said earlier the drawings are old and were done for makers who had little more than a basic lathe, no mill, no micrometers not Rotary table and certainly no way to measure angles to much accuracy. So would have been marked out and made as per the above post and what I said earlier. They are of their time, fair enough if you want to move on and have better equipment but there are still beginners who will just have basic machines and tools which are who the model is aimed at.
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The pin was 2.5mm dia in a 2.8mm bore. Quite how those undercuts for the O-ring cavities were to be made doesn't seem to have occurred to the designer, let alone how the specified 5x3x2 O-rings were going to get in there afterwards...
AS
That's a corker!
I'd like to pretend I'm immune, but just a couple of weeks ago I was reviewing one of my own designs when I realized it wouldn't go together. Glad I caught that before it went out anyway.
Yesterday I had a really fun conversation with the programmers figuring out how we are going to fixture a huge steel weldment I designed, as well as getting into the GD and T on it. I love that kind of collaboration. Actually climbing up on the mill table to look at it when it gets there will be even more fun.
Makes me feel a bit silly when I'm twiddling the handles on my little mill. ;D
But this is why, as you do, I try and machine by the numbers. Just trying to emulate what I see at work, in my own small way.
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Apart from summer jobs in small sub contract machine shops in the West Midlands when I was a student, I haven't worked in production engineering, but did spend a lifetime in the construction industry. You probably wouldn't believe how complicated the reinforcing can be in a bridge deck, especially at the ends where the bearings are. My first boss in the design office used to make us bend up scaled down links and bars from big paperclips just to check that it would all fit together on site. Later, on site, which is where I spent most of my career, I've lost count of the times I've had to have reinforcement redesigned 'on the hoof' and rebent in order to make it possible to fit all the links and bars together.
I used to get really angry if sent an updated drawing which just carried the note 'Generally revised', but didn't give any indication of what exactly had been changed.
I used to try to insist that any change was 'bubbled' (cloud shape drawn round it), but it didn't always happen.
I'd been well trained in technical drawing at school by a teacher who had spent 30 years in railway drawing offices before changing career to become a teacher of technical drawing and lower school maths.
I had a friend who did a lot of 1 off prototype work, and he would sometimes build the prototype from a series of back of envelope sketches, and only do the 'proper' drawings once he'd made sure the thing could be built, and would work.
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Two practices I learned early and carried through my career: when going on to any shop floor, my first habitual action, as a safety precaution, was to tuck my tie inside my shirt; and the largest words on any drawing were "IF IN DOUBT, ASK".
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Plus 'DO NOT SCALE'!
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Plus 'DO NOT SCALE'!
I think this is the crucial one. I was always taught that the lines on a drawing are "indicative pictures" to show what the part looks like; only the dimensions on a drawing are "accurate" unless explicitly stated otherwise. I'm now in the aircraft industry and we take this concept further in that a drawing which could be used as a physical template isn't called a drawing - it's called a "loft foil" to clearly differentiate it from a "drawing". The process for producing a Loft Foil includes lots of rigorous check of the physical dimensions before it is released for use. The same applies to the films used where the drawing is photo-etched onto the material for large and complex machined parts with lots of features (whole fuselage frames for example) - I think this process was invented by Grumman to speed up F6F production in WW2. Even then these projections include numerous reference datums so that the sizing and positioning can be checked when the material is put in the machine before any metal is cut.
I guess once you see these practices you tend to assume they're universal.
PDR
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Next query - the steam chest. I was looking at the drawing, and the internal cavity dimensions are not defined:
(https://i.postimg.cc/7YXJyd1T/image.png)
The actual casting looks like this:
(https://i.postimg.cc/L5Fc8ypc/image.png)
In the as-cast form the internal dimension is typically 1/2":
(https://i.postimg.cc/9FZ5RwFd/image.png)
The valve block drawing calls for the valve itself to be 1/2" wide:
(https://i.postimg.cc/9FfZzcQB/image.png)
I get that the length of this cavity is not important (it just needs to be long enough for the valve to pass the ports), but what about the width? I looks like I'm not supposed to leave it rough cast, but does it need to be a close, working fit or just a clearance fit on the valve?
AS
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Any clearance is fine actually - the valve is guided and located by the valve rod, and forced against the sealing surface by steam ( or air) pressure. So you can just clean the inside to allow the balve to slide without let or hindrance, so to speak. If yhe valve fits in the frame and slides without obstruction, no clean up of the internal frame needed. A good fit between the valve and the little block that holds it to the valve rod is more important.
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A good fit between the valve and the little block that holds it to the valve rod is more important.
That's a sliding fit so that the valve is free to move onto the port face. :)
Jo
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Yes. That would make it a good fit. A tight fit would be bad. I assumed the drawings specified the tolerance in that area, but looking back at the valve they don’t at all, they leave it to the maker to figure out. I suppose that’s part of the fun. :thinking:
Using a term like “ good fit” isn’t much help without some other information to say “sliding”, “transition”, “interference” or whatever, I freely admit.
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In the day the slot may have been described as a "full" 1/8" and the nut possibly a "bare" 1/8" which it may well be anyway as the extruded brass is seldom spot on. Main thing is the nut can slide about in the slot but not so loose that it knocks as direction changes. Also be careful to get the thread nice and perpendicular to the nuts face as a wonky thread will twist the nut and stop the valve floating. I'd mill it with a 3mm cutter and then open up until the nut just goes in. Latest Stuarts are now coming with these valves CNC machined.
You can just file out the chest casting to clear the nut. Some engines have quite a bit of space, others like this not much so provided it is clear the engine will run.
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Thanks peeps. So I can just make it a clearance inside the chest.
The slide valve itself is supplied as a casting:
(https://i.postimg.cc/D01V8mFC/image.png)
(https://i.postimg.cc/cH5CRzQ2/image.png)
There's not much spare metal on it, so I think it will just get a surfacing skim around the four sides and then facing along the seating face (perhaps with some light lapping onto 600/1200g wet&dry if it needs polishing. If that allows it to fit inside the steam chest without touching the sides then maybe I'll leave the cavity as-cast.
The parts list says the valve casting is gunmetal, but then the parts list also says the steam chest is cast iron. Both castings are a yellow metal, but the valve is a lighter yellow than the chest. Perhaps the chest is just brass?
PDR
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They are actually some form of pressing or forging hence the round marks from the ejector pins and nice smooth finish.
Seems the new owners can no longer get the pressing done or it is not cost effective so they are supplying CNC machined ones along with things like the 10 series conrods. As Bridport have CNC facilities I assume they make use of the machines for the machined and ready to run kits and just stop the program part way through to provide the part machined ones that go into the "casting" kits
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It is more likely that the steam chest is gunmetal. At one time, several of the small parts, including, I think, the valve, were hot-stamped rather than cast. You won't really be able to tell until you get a fresh surface. Brass is yellow, gunmetal has a distinctly pinkish colour, and most bronzes are somewhere in between.
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Hi Allen
I’m building a engine about the same size as this one.I started it few yrs ago, then got busy with other stuff & it got shelved.
Recently started it again, yesterday I finished the cylinder/steam chest.
I will be doing the valve today (hopefully) & found this discussion on valves, how apropos.
BTW, I noticed a book by Vonnegut in one of your pics. Been a favorite author of mine for 50 odd years.
Cheers, GT
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I grabbed it at random from the shelf in the study. On my Fournier project I was messing with 3d-printed pilots and needed similar support - only afterwards did I realise the slightly eclectic selection of books I'd used:
(https://i.postimg.cc/Zq90PLnD/image.png)
(https://i.postimg.cc/XJ4qM6xt/image.png)
That's my well thumbed copy of Abbot & von Dienhoff's "Theory of Wing Sections", an equally well-thumbed copy of Neil Williams' primer on flying aerobatics and a basic maths textbook from my university days.
:-[
AS
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I have just extracted from the bookcase about 4 feet away my identical copy of the maths textbook by Jeffrey. Apparently it cost me £3. I see the book is still available, for about £50.
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Anyway, back to the build. I got a few minutes to start the crankshaft. This seems pretty straight forward even for me - a 1/4" silver steel rod with 7/32" of 2BA thread and a 1/32" undercut at the base of the thread. Put it in my better chuck and clocked it, then turned it down to 4.8mm for 7/32". I put a small centre drill into the end for use as a datum when I moved the crank to the mill, and put a chamfer in the thread before tapping it in situ.
(https://i.postimg.cc/G9014mxM/20.jpg)
I used two different dies for this, because my toolsteel 2BA die has lead-ins at both ends. It cuts a lovely thread but doesn't get close enough to the shoulder. So I then used an old carbon-steel die which I've ground flat on one side so that it cuts all the way. I want to be sure that the shaft would screw into the web and clamp down on the shoulder rather than just getting tight in the thread.
I had a 0.8mm grooving tool I made for something years ago (can't remember what) and I decided that would be fine for the undercut:
(https://i.postimg.cc/rwX8mQh8/21.jpg)
So there was the threaded end done. Not brilliant, but it will do.:
(https://i.postimg.cc/yNnBLB7d/23.jpg)
The material is overlength (the crank pin also comes out of this piece of stock) but I'll cut the shaft to length when I've made the crank web just in case I find that I've got something wrong and have to start again!...
(https://i.postimg.cc/DwT8Dv3d/24.jpg)
I can't start the web until my M5 taps and dies arrive - I was hoping for today, but it seems that free postage is slow postage >:(
So in the mean time I've been looking at my setup for milling the angled faces on the webs. This rotary table was a cheap one Jo found for me at a bring & buy. I've added a Warco Myford adaptor and a cheap Myford-thread to ER32 collect holder. The holder came from RCM and it's not brilliant (it has more runout than my 3-jaws) but it's probably adequate as a milling fixture. The whole setup is a bit tall for my baby mill, but the head gibs are just as smooth at the top end of the column so I hope it will be OK:
(https://i.postimg.cc/7hJkP20G/26.jpg)
I think the rotary table was made from a Hemmingway kit (looks very similar) but if so it was never finished - it lacks any means to lock the table for milling. I'll have to see whether the friction alone is sufficient; if it isn't I'll just have to pause while I make a locking clamp. I also need to decide whether it would be better to mount it flat on the table (as in the above picture) and trim the crank webs with the side of and end mill, or mount it vertically on an angle plate and cut using the end of and end mill (if you see what I mean). I can see pros and cons for both approaches. Mounting it flat will allow me to also mark, drill and tap the crank pin hole very accurately using the mill's DROs and the rotary table. Mounting it on an angle plate would bring the milling height down. I will have to mount it that way anyway so that I can use the rotary table to accurately place and spot-drill the pip location for the eccentric's grub screw that sets the valve timing.
At the moment I'm leaning more towards milling the flats with the RT clamped flat to the bed and the crankshaft axis vertical. I'll probably get a better cut down-milling with the side of the end mill, and it should be less bothered by the thin web being milled while mounted on a central shaft. At least that's mu theory!
AS
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Just be careful that the leverage of the cutting forces (which can be considerable) don't act to unscrew the web from the shaft during machining.
Personally, I'd mark out the shape of the web then cut off the bulk of the waste with a hacksaw in the vice, and either finish it by hand methods, or put the web in the machine vice and end mill the flats down to the marked lines.
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For what it’s worth, I’m not a fan of hand methods - not that they don’t work - that’s not it, I just like to machine everything and locate surfaces rather than mill to scribed lines. It’s AN approach, not necessarily THE approach.
Allen, I generally try to end mill where I can. Side milling works, but consider tool deflection and allow for a spring cut (recut with little to no extra nominal material removal) to achieve squareness.
That’s what I do. But I ‘m still learning, so take my advice at face value.
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If you don't want to use a scribed line and don't like filing then these pictures better describe the method I mentioned earlier.
First turn the boss on the end of your bit of 1.5" stock and tap the hole. No worries about turning it while on a thin shaft or interrupted cuts. A bit of 1/4" plate could also be held by its outer edge not screwed to the shaft.
(https://hosting.photobucket.com/albums/v156/jasonballamy/Engineering/Muncaster%20No1/.highres/20200221_174150_zpsjbuxchdb.jpg)
Saw off from the 3/4" length and face the saw cut leaving it a little over thickness 5-10 thou
Then hold the work boss upwards in the mill vice or WHY, locate ctr and then position the crank pin hole.
(https://hosting.photobucket.com/albums/v156/jasonballamy/Engineering/Muncaster%20No1/.highres/20200221_184250_zpslsunozgt.jpg)
This one was reamed and loctited but if you screw in your 1/4" shaft and screw something into the pin hole you can use those two diameters in CAD to work out what packing goes under the pin to mill one side and then move it so the pin is to the left and mill the other side. Height can be worked out by touching tool on 1/4" shaft and raising as required from there. You can just see I'm using a drill bit resting on the fixed vice jaw as my packer
(https://hosting.photobucket.com/albums/v156/jasonballamy/Engineering/Muncaster%20No1/.highres/20200221_185303_zpsvuoriulq.jpg)
When there is no more work to do to the shaft or crank screw the two tightly together and don't take apart again. Then hold assembly in the lathe and with either a sharp HSS tool or an insert for aluminium take light cuts to bring the web to final thickness. This final stage ensures the face of the web is 90 deg to the shaft just in case any threading was a fraction off. Different engine but same setup
(https://hosting.photobucket.com/images/v156/jasonballamy/DSC04430.JPG)
Some people like to round the corners which can be done by filing, do this before final assembly
(https://hosting.photobucket.com/albums/v156/jasonballamy/Engineering/Muncaster%20No1/.highres/20200223_094251_zps0gfanguw.jpg)
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Just be careful that the leverage of the cutting forces (which can be considerable) don't act to unscrew the web from the shaft during machining.
Personally, I'd mark out the shape of the web then cut off the bulk of the waste with a hacksaw in the vice, and either finish it by hand methods, or put the web in the machine vice and end mill the flats down to the marked lines.
It's a concern, certainly. It's my intention to fit the shaft with loctite and then drill/fit the pin before machining the flats - I'm hoping that will stop it unscrewing:
(https://i.postimg.cc/7Lyc5w7H/image.png)
The drawing calls up a "mills pin" which I think is what I call a "roll pin" - it doesn't seem to be supplied in the kit so I'm thinking of using a short length of 16 or 18swg piano wire instead.
AS
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Looks like Jason has finished milling your crank webs for you Pete ::)
I thought that rotary table cost an arm and a leg.. or was it a couple of quid :noidea: Clamping the web in a vise with a spacer under something in the crank pin hole to mill either side to the same angle may be easier.
Yes they have just pinned the crank with a bit of round bar and not a roll pin.
Jo
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Just offering a method for anyone who prefers machining to filing or working to a line. Another option that may not suit you with that small dingy anchor if you are limited for head room would be to have it horizontal with a chuck mounted to it, you can then hold the provided extra length of 1.5" bar in the chuck, mill the two sides and then saw it off with the advantage of less sawing.
I would go for something softer than piano wire for the pin should you find the need to skim the web face as PW is a bit hard.
Wonder if the pin is even needed as the CSK on the web is intended for peining over the end of the shaft like a rivit, that combined with Loctite should hold. I often just loctite these smaller engine webs onto plain shafts.
Mills pins are a solid pin that has had grooves swaged along its length which stick out around their edges making the pin a bit bigger at these points so it holds in a hole. Bit OTT for us so mild steel pin and loctite will be fine if you do feel the need to pin.
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I use piano wire because I have plenty of it in stock - but for this sort of application I'd usually anneal it first. I have a pair of grooved aluminium blocks that I use to grip piano wire for annealing so that only the end gets softened* without ruining the whole piece.
I don't own a collet large enough to hold the crank web by the OD and I don't like the idea of holding a thin disk in a vice or V-block. I do have spare 1-1/2 bar so I will be able to have several goes at this if needed!
AS
* I used to use this so I could tap the end of a 10swg undercarriage leg on an FAI-F3D pylon racer to take my "low-drag" internal wheel collets
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You can simply clamp it to the mill table to drill the pin hole, have the hole over a tee slot
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It all sounds painful with the repeated removal from fixures and re-datuming. I'm hoping to be able to essentially machine the front of the web, trill and tap the centre hole, loctite the shaft into it and then part/saw it off. Turn it around it the chuck and grip it square on the outside edge (using a hole in a stopper as the centre datum) to face off the rear edge to thickness. Then move to the mill, mount it in the RT collet set to zero degrees and bore/fit the locking pin. Then drill/tap for the crank pin and then rotate +/- 18.75 degrees to mill the sides down to 425 thou from the centre. If it works it just means simple setup changes with minimal need to faff about re-datuming.
But you could be right and the whole thing could be too floppy to cut nicely. I guess we'll find out...
AS
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More progress - I finished the crankshaft (perhaps, but more on that later)
They provide a length of 1-1/2" mild steel bar which has lots of meat on it (as previously discussed), although it is barely a thou over the required size, so I took the view that no one will notice if I skimmed about 0.2mm off the OD to get a nice machined surface (I hope we can keep this between ourselves - you won't go ratting on me will you). I started by drilling it 4mm and tapping it 2BA - I tapped it all the way through with a plug tap in case I wanted to have a second attempt with the left-over material:
(https://i.postimg.cc/gJ1nTpDz/27.jpg)
ThIs photo shows I'm lazy and impatient because I use the VFD in revers at low speed to wind the tap out again, and I do it fast enough for the tapping oil to get thrown outwards...
(https://i.postimg.cc/LXJJD5jQ/28.jpg)
A quick trial fit with the shaft showed all was well.
(https://i.postimg.cc/52mQNZxg/29.jpg)
Next came turning the front face with the raised central boss:
(https://i.postimg.cc/DzyJWB0T/30.jpg)
And then it was ready to cut off. The web is only 1/8" thick, so there's a lot of material to lose. I resisted the temptation to reverse it in the chick and remove the excess as swarf(!), but because I'm lazy I was reluctant to use a hacksaw. So I decided to start parting it to get as far as I could before it got chattery - received wisdom is that parting off this amount in a Myford is likely to be problematic, but I thought I'd give it a go. This parting tool is the one ArcEuro sells - a 2mm blade holder with a GTN2 carbide insert. I've found then to be very good in steel (but I've wrecked a couple in cast iron when the hard lumps tear the insert out of the holder). I locked the saddle and started at 1,100rpm with a little lube brushed on and started parting. I kept the feed slow but steady - keeping a constant pressure on the blade, backing out periodically to remove chips and refresh the lube. After the first 3/8" I backed the tool out, moved it 0.2mm closer to the chuck and widened the groove before returning the blade to it's original position to continue.
(https://i.postimg.cc/13SNS9Z4/31.jpg)
As the cut got deeper and the diameter smaller I progressively increased the speed to around 1.800rpm
(https://i.postimg.cc/xjWzsvxv/32.jpg)
I'm confident that I could have fully parted it without trouble, but I stopped when I got to here because I had visions of the part leaping off and making a dash for Mordor. So I hacksawed this last bit.
(https://i.postimg.cc/kXKtL2zk/33.jpg)
Et voila, I had my shaft and duly loctited it in place before grabbing some lunch:
(https://i.postimg.cc/Y0ghcPn1/34.jpg)
On returning from lunch I realised that the Feck-up Fairy works weekends - I had loctited the shaft before trimming it to length. I didn't want to start heating things to soften the bond so the only way I could see the fix this was to turn it as-is using a steady, which worked successfully. I was thinking about this afterwards and I'm fairly sure this is the first time I've used it:
(https://i.postimg.cc/P5dNc2mw/35.jpg)
With that done I reversed it in the chuck, and gripping it by the shaft withe the centre boss pushed up to the jaws I was able to face off the rear of the crank (and the excess shaft protruding through it) to the required thickness without difficulty:
(https://i.postimg.cc/28R1dzyT/36.jpg)
I then transferred it to my "mill" - it's a cheap and cheerful Seig X2p benchtop machine with a few mods - when you know its limitations you can do stuff with it, but it's cutting performance has been likened to a cold knife through granite. But nothing ventured...
I set it up in an ER32 collet on the RT and registered the centre in the back of the shaft, setting my cheap DROs to zero. With the RT set on zero I moved out 5/8" to drill the tapping hole for the crank pin:
(https://i.postimg.cc/Bv6bZb7Z/37.jpg)
I also drilled a 1mm hole and loctited in a short length of 39thou music wire as a "mills pin". Now to the controversial bit...
The angle between the flats was 37.5degrees, so I rotated the RT through 18.75 degrees (half). The distance from centre for this flat was 0.425", so there was about 8mm to cut off [this mixture of metric and inferial units will be a feature of this build - in fact it's about to get worse, so bite me!] so I toggled the DRO to inferial and moved the table 425thou, and then zero'd the DRO. I then looked through my cutter collection and selected a nice sharp (unused) 8mm 3-flute cutter. I have several of these and they work well. So I took off the drill chuck and fitted an ER32 collect chuck with the 8MM cutter. I then toggled the DRO back to metric, advanced it a further 4mm and zero'd it again. If I had done this all correctly the zero position on the DRO would mill the required line. But I shared concerns raised by others that the whole setup would be too floppy, or that the part would move in the RT. I marker a couple of tell-tale lines across the part and the collet nut so that I could see if the part moved in the collet, and I clamped it up very firmly. Then I hedged, but setting the depth of cut to half the thickness of the web (1/16" cut), set the speed to 2,500rpm (this machine loves to run fast) and I did a series of light, slow cuts, typically 1mm at a time with the final cut being 0.2mm away from my zero line. It all went like a dream - nothing slipped, nothing chattered, it just cut cleanly. I did wonder if I could take deeper cuts, but decided that experiment could wait for another day:
(https://i.postimg.cc/3JTw4nfc/38.jpg)
So I dropped the cutter a smidge over 1/16" and repeated the process, before making the final 0.2mm cut across the whole depth:
(https://i.postimg.cc/G3Y2mZKD/39.jpg)
I rotated the RT to -18.75degrees, moved the table by 0.850", zero'd the DRO, switched to metric and then moved it another 8mm to set the new zero, and then repeated the process for the second side. In this picture you can more clearly see the half-depth cut and (more to the point) those sharpie tell-tales!
(https://i.postimg.cc/6qd5bvqc/40.jpg)
And that was essentially that:
(https://i.postimg.cc/xd4CXQBv/42.jpg)
I swapped back to the drill chick, moved the table to the DRO location for the crank pin hole then slackened the collet so that I could raise the part by half an inch and (with a reversed drill in the chuckand fet through the hole) I clamped it again. Then I tapped that hole 5BA, lightly deburred the back of the hole and the part was finished:
I made the crank pin. I'm going to gloss over that because I'm not very happy with it and I'm probably going to make another one, but it allowed me to do a trial assembly:
(https://i.postimg.cc/BnNtGHgw/43.jpg)
(https://i.postimg.cc/903QBpmz/44.jpg)
It also allowed me to try out a setup for cutting the screwdriver slot, although Feck-Up Fairy clearly stopped for coffee and cakes before departing as I made a complete hash of the calculation for the Z dimension (more obvious in the final picture). This is just an Arc 50mm slitting saw (0.8mm) which cut very nicely despite my arbor being 1/2" instead of 13mm:
(https://i.postimg.cc/15r3pwL5/45.jpg)
That concluded the days activities, but I couldn't resist a quick trial assembly:
(https://i.postimg.cc/0NW67DKJ/46.jpg)
To be continued...
AS
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Looking good Allen - coming right along.