Author Topic: Stuart S50  (Read 7056 times)

Offline Jasonb

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Re: Stuart S50
« Reply #15 on: June 26, 2022, 07:05:13 AM »
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.

Online Jo

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Re: Stuart S50
« Reply #16 on: June 26, 2022, 07:25:08 AM »
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  ;)
Enjoyment is more important than achievement.

Offline Jasonb

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Re: Stuart S50
« Reply #17 on: June 26, 2022, 07:38:08 AM »
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.

Offline Allen Smithee

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Re: Stuart S50
« Reply #18 on: June 26, 2022, 09:16:40 AM »
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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Offline Jasonb

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Re: Stuart S50
« Reply #19 on: June 26, 2022, 10:32:38 AM »
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

Offline Allen Smithee

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Re: Stuart S50
« Reply #20 on: June 26, 2022, 12:06:47 PM »
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.

Quote
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!]
« Last Edit: June 26, 2022, 12:30:52 PM by Allen Smithee »
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Offline Jasonb

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Re: Stuart S50
« Reply #21 on: June 26, 2022, 01:15:31 PM »
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.

Offline Charles Lamont

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Re: Stuart S50
« Reply #22 on: June 26, 2022, 04:48:17 PM »

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

BTW, Your Myford should have come with a catchplate as part of its standard equipment.
 

Offline Allen Smithee

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Re: Stuart S50
« Reply #23 on: June 26, 2022, 05:55:15 PM »
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.



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"





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.



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:







To be continued...

AS
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Offline Allen Smithee

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Re: Stuart S50
« Reply #24 on: June 26, 2022, 06:05:59 PM »
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

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!

Quote
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:



It's a dog's life...

AS
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Offline crueby

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Re: Stuart S50
« Reply #25 on: June 26, 2022, 06:19:09 PM »
Thats one relaxed dog!

Offline Jasonb

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Re: Stuart S50
« Reply #26 on: June 26, 2022, 06:22:55 PM »
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


Offline Bearcar1

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Re: Stuart S50
« Reply #27 on: June 26, 2022, 06:40:22 PM »
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

Offline Allen Smithee

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Re: Stuart S50
« Reply #28 on: June 26, 2022, 11:04:44 PM »
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:





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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Offline Allen Smithee

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Re: Stuart S50
« Reply #29 on: June 26, 2022, 11:09:54 PM »


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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