Dyno compression ignition

[tangler]

I think it was Dickens who said "Procrastination is the thief of time".     The next job is the con rod.  I couldn't make up my mind which way to do it - on the milling machine or in the lathe.    The problem is that I need to ream the little end and that isn't very straightforward in the mill because many of my reamers are on 1MT tanged shanks which tend to fall out of the spindle when reversing.  And I don't much like using my 4" rotary table either.  And I'm not very happy with the crankpin.  After 10 days vacillation I've finally made a decision  .    Re-do the crankpin but make the con rod first with the bearing in the big end, then make the new crankpin to fit the bearing.

 I've got a couple of lengths of H15 so the first job was to slice a bit off



I then mounted the slice in the milling vice on a pair of parallels (since removed), milled to slightly over the correct thickness and drilled a hole for the big end bearing and a pilot hole for the little end bearing.



This lump of ally usually sits on the rotary table.  The hole through lathe faceplate is too big for this sort of job since there is little support for the workpiece.  I've drilled a small clearance hole in the middle that will allow a reamer to pass through.  I actually took this picture after I'd finished and remembered to skim the outside so that I can set it up centrally again.



I'm using the Headstock Dividing Attachment as a rotary drive and I've got a 1/4" slot drill in the milling spindle, which is sitting on centre height.



I centred up the big end hole and milled round for the boss



Then turned the workpiece around, centred and reamed the little end



I milled all 4 bosses and rounded the end, leaving a sliver to come off on the base.  Transfer to the mill and cut the waste away for the taper from the big to little end.



Finally mill way the waste between the bosses



The big end bearing is made from a scrap of cast iron, reamed to size (I've only got a hand reamer for this)



And the OD turned  0.001" bigger than the big end hole in the con rod and parted off



Then pressed in.  There's quite a bit of hand work left to make it looking nice(ish)



More later 

[tangler]

I re-centred the crankpin in the Keats fixture



Turned the old pin away and drilled a hole



I then turned up a piece of silver steel to be a loose fit in the hole and over size for the pin



The pin has been parted off and is sitting on a ring of silver solder, liberally anointed with flux



After heating with a torch



Then returned to the lathe and the pin turned to a much better finish.  The con rod is looking a bit nicer now as well.



Cheers,

Rod

[tangler]

I seem to be on a bit of a roll -

The spinner nut:  This took a bit of thinking about  

I drilled a piece of ally tapping size for the end of the crank shaft 25mm deep and then counterbored this 15mm deep so that I could get the tap in to cut a thread in the bottom 10mm



I then turned it down to the maximum OD, used the parting tool to cut the decorative groove and cross drilled for the tommy bar hole



I then turned the blank end for end and re-centred it in the 4 jaw independent chuck



After parting off the end I mounted the George Thomas hand rest



and used the graver to hand turn the shape



The graver chattered over the tommy bar hole so I had to use the topslide to cut a straight taper over this bit but it looks OK.  Several grades of wet 'n dry brought up a pretty good surface.  I put a bit of polish on it but I will probably end up with a brushed finish from a fine Scotchbrite.  I the parted off 1.5mm behind the groove.

Rod

[Jasonb]

Looking good Rod, you obviously spent the weekend in the workshop.

J

[Ramon Wilson]

Nothing like a good session to put a smile on your face eh Rod 

Nice reclaim on the pin  and nice coverage of the process - never silver soldered a pin in myself so will be most interested to see how it stands up.

You must be getting close to the end now - looking forwards to seeing that first run.

Regards - Ramon

[tangler]

Guys,

Thanks for your interest.  Unfortunately I often find that some little doubt or problem stops me dead in my tracks.  If it wasn't for sharing with my friends on MEM I don't know when progress would have resumed.

 

Rod

[tangler]

More progress    I mentioned that I wanted to use a prop driver with a separate collet.  The Zinger prop has a 1/4" hole in the hub and I wanted to avoid opening this out if possible.  Things were a little tight to get the tapered collet to fit in the prop driver without breaking through and collet itself might be a bit small to give adequate grip on the crankshaft but I thought I'd give it a go.  The brass collet is drilled through to be a snug fit on the crank shaft, then I turned the taper with top slide set to 13 degrees and, after parting off,  slit the collet with a piercing saw.  The prop driver was drilled through to fit the crankshaft and then turned down to fit through the prop.



My normal knurling tool is the calliper type but I extracted one of the wheels and its screw to put in this lump of steel.  Unfortunately, as you can see, I was only able to get the tool to knurl the periphery.  I ran the lathe backwards top get the knurl to have the grip going in the "right" direction (I don't actually believe it will make any difference)



I then parted the driver off, turned round and mounted it in a collet to turn the tapered hole for the prop collet.  Here we see the collet on the shaft and the finished driver. 



I made a temporary assembly to see if there was sufficient grip.  I still have the extra length on the end of the crankshaft so I can't use the spinner nut so used an ordinary hex nut and washer instead



Somewhat to my surprise the prop seems to be rock solid   

Rod

[Ramon Wilson]

There could be a bit of competition here Rod to see whose gets finished first - I've had a good couple of sessions too - Only joking I'm not really up for that sort of thing 

This method of locking the prop driver is well tried and tested and gives, as you remark, a rock solid 'lock' - much better than having to make 'D' shaped holes 

Just a point that may be useful - when knurling the drivers I usually make the land where the knurl is going to be formed slightly proud (about half a mil) then just tweak the edges with a chamfer tool after knurling - makes for less strain and a neat finish. Also means the knurl embeds into the prop better

The knurl doesn't need to be retained in a holder either - it works just as well on a spigot and then you can get the knurl much closer to the hub should you desire (taking a look here will give you the idea -  post 96 http://www.modelenginemaker.com/index.php?topic=1334.90)

If I can get the rotors finished tonight that only leaves the con-rods before the pistons and lapping 

Regards - Ramon

[tangler]

Ramon,

Good points, filed for next time 

Pistons tomorrow.  I need to do some homework tonight,  looking back at your threads.

Cheers,

Rod

[tangler]

Some progress over the last week:

I need a lap for the cylinder.  This length of mild steel  had a 6 degree included taper turned on it and then the end was threaded M4.



Then a piece of ally was bored with a matching taper



before transferring to the mill and slitting partially through the radius for 2 cuts and all the way through for the other.  The lap was assembled with a nut to push the lap up the taper and increase the diameter as required.



Here's my collection of SiC powder together with some mixed with oil in the little jars.  The 220 grit is too coarse for anything but the other 2 seem to give a satisfactory result on the Flexispeed spindle.



Basically following Ramon's method I lapped with the 400 grit until the bore was parallel and all turning marks had disappeared.  Then I used the 600 grit to get an even , finer finish all over before concentrating on the lower half to get a taper as far as the flange.



More later...

[tangler]

For the piston, the smallest  diameter cast iron I've got is 1 1/4" but as the smallest you can seem to buy is 1" anyway,  I made do with what I had.



Turned down to a more manageable size for the bore which is a nominal 12mm.  There should be enough to make the contra piston as well.



The piston is conter-bored to give a skirt and then has a 5mm slot milled in it for the con rod clearance.  I drilled 5mm first



then opened out the slot with a 5mm end mill using the milling spindle and the HDA to lock the lathe spindle.  The long travel dial gauge (with the comedy large dial for the hard of hearing) is mounted on a magnetic base stuck to the drip tray and acts as a depth gauge.



I then re-mounted the milling spindle at 90 degrees and used the HDA to index the piston a quarter of a turn to drill the gudgeon pin hole.  The gudgeon pin is going to be 5/32" (4mm) silver steel so the drill is 1/64" less so that I can follow it with a reamer.  On no it isn't.  I picked up the drill from the wrong side of the rack - 1/64" larger.     No way back from this, I'm constrained by the size of the hole in the little end of the con rod.  So, turn the end off the blank and do it again (actually only took about a 15 minutes).





But now I've only got a stub end to make the contra-piston.



My solution was to thread the hollow section of the contra-piston 3/8" 32tpi  (This next picture is especially for you, AS)



Then make threaded stub to mount it on from, it turned out, the nastiest bit of steel it's ever been my misfortune to try and turn.



With the contra-piston now screwed on to the mandrel I turned it to size



And then attacked it with a dead smooth file, a flat India slip stone and then a white Arkansas slip until the contra piston was a very firm push fit at the top third of the cylinder.

In order to hone the piston I made another arbour.  I turned a parallel section that was a snug fit on the piston skirt



Then milled the end to fit into the piston slot







The piston was honed using the same tools as the contra piston.  At present it's pretty tight at the top of the stroke and may need easing off a little more but I can't really tell until I've assembled it and found where the top of the stroke actually is.  I've also made a compression screw - simple turning and cross drilling.



Cheers for now

Rod

[Jo]

  That is three of us that have had "challenges" with our pistons on engines of late: I managed to machine my baffle plate on the Stentor at 90 degrees to where it should be, Tug has just had to remake his for the Italians when he got the undercut and the holes in the wong place and now yours. As things come in threes does that mean it is now safe for me to try doing the Titan piston 

Rod: I promised you some of my CI, The initial firings didn't get hot enough so the sash weights are still hard so they are going to have to have another go. At this rate I might be bringing them to Guildford next year  .

Jo

[Ramon Wilson]

Nice work Rod - I'm about to go forth and do likewise  .

Ever since making that same classic mistake - taking the drill size for granted - when someone had put the drill in the wrong slot  and turning a lot of work into a scrapper I developed, and still have, the habit of checking the drill size as soon as I take it out of the rack


Sash weights eh Jo - bet they're nice and homgenous 

Not wishing to rub it in - well not too much  - mine came from a slice of SG iron which machined beautifully to a fine finish. A limited resource though so shame about the two that now grace the bin 

Ramon

[Allen Smithee]

I know it's very easy to second-guess with 20-20 hindsight, but rather than scrap the piston would it not have been worth trying brass or bronze bushes in the oversized gudgeon pin holes?

AS

[Jo]

Sash weights eh Jo - bet they're nice and homgenous 

Not wishing to rub it in - well not too much  - mine came from a slice of SG iron which machined beautifully to a fine finish. A limited resource though so shame about the two that now grace the bin 

Morning Tug, I have a 12" stick of 1" white Iron sitting with the Titan bits on the dinning room table But having been given these couple of dozen over sized sash weights it seems a shame not to try to reuse them and pass them on to other who may have a use for free CI. Having cut the ends off a couple they didn't have any inclusions  , they are just still a bit hard.

Jo