Stuart No 4 Steam Engine

[f350ca]

Thought I'd start a thread on another project. Might be slow progress as time dictates.
I find it easier to put a finish on parts before machining rather than try and mask off the shinny bits at the end.
Paint works fine doing this, we'll see how powder coat works, might chip at the edges?
Gave them a light going over in the sand blast cabinet and coated them, liking the finish the powder coat gives, this is only my second attempt.

[Pete O]

Didn't think it would take you long to get started Greg!
I read recently that in the manufacture of Bridgeport milling machines, they do the machining after the painting. Apparently they used to do it the other way around but often found that the finished machine might be .0005" out of spec somewhere, they'd strip it down and find a .0005'-thick bit of glue or something from the masking.

[f350ca]

There's lots I should be doing but gave in and started machining my new toy.
This part houses the cross head (I think thats what its called) that restrains the piston rod. The top face has to be perpendicular to the bore or the piston rod would bind in the packing. The bottom of the legs has to be perpendicular or the connecting rod would bind as the crank rotated.
To get a reference surface I cleaned up the bore and made an expanding mandrel to hold it, then machined the top and bottom face. The mandrel seamed to work well but there was a hard spot on the edge of one of the legs. The interrupted cut on the legs must have shifted the raw bore on the mandrel, saw a couple thou runout on the top face after finishing the bottom. 





To bring the two faces back parallel I ground them.


With the faces parallel and the OD available to dial it in I mounted it on a tooling plate and cut the bore for the cross head. Have a slight chatter at the top but left a half thou to finish the bore with a lap.


Drilled the necessary holes while it was mounted.

Pleased with the powder coat finish, no chipping at the edges where I machined.

[f350ca]

Keep stealing time to play.
Made an adjustable lap to finish the bore where the cross head runs.
Have some reamers for tapered dowel pins, thought that would be a good taper, found one with straight flutes, figured I could chuck it up and adjust the taper attachment to it. Wrong, turned out to be a Brown and Sharpe taper, hence the mandrel I made didn't quite match the tapered hole I did in my blank using the actual spiralled tapered reamer. So then I needed to make a mandrel to run between centers to set the taper attachment and adjust the taper by offset to z travel to match the 1:48 taper.
The lap worked but was too adjustable, had to clamp one end to get it to stop sliding up the mandrel and slipping on it.


Working the bore using valve lapping compound.



Got the finish I'd hoped for, smooth but not gloss that wouldn't hold oil.



Forgot to take pictures when I was machining the base and crank case. Now need to make some studs and scaled nuts.



Next will be the bearings. Started the caps. They're cast bronze. Machined them to size and reamed the mounting holes to fasten them together with dowel pins while I turn the outer profile.

[f350ca]

Wet snow here, so a great time to play in the shop.
Finished the crank bearings, well sort of the bore is 3/8ths right now, they need to be opened up to 7/16ths. Haven't yet decided how that will happen. Seams odd listing dimensions in fractions but thats how the drawing was made.



Thought the crank was cast iron, wrong, some low carbon cast steel that machines horribly. Tryed several different cutter profiles in HSS and a couple of inserts, nothing gives a great finish.
Roughed it to 1/2, leaving some room if it warps a bit when machining the throw.




Didn't even mill nice.

[TomG]

Looking good Greg.

You must have got the high performance model with the steel crank.

Tom

[f350ca]

Will have to fire the boiler with nitros Tom to get the benefit of the steel crank.
Made a jig that the crank fit with a light press fit, this put the throw with a 5/8s offset on the center line of the lathe. Used an aluminum lap to bring it to final size. Then machined the ends, couldn't get a nice finish so took the last thou off with a file and emery paper and lapped to final dimension.


I clamped a piece of scrap to the mill table then drilled and reamed to 3/8ths to match the dowel pin in the bearings. With a collet in the spindle I positioned the crank case using the dowel pin between the collet and the reamed hole. Then brought an angle plate up against it and clamped. Drilled and remed to final size.



Had a 1 thou over reamer and lapped the shafts to 2 ths under, giving me 0.0012 clearance, (If the caps are perfectly aligned) Will that give enough room for oil?

[Hawkeye]

Lost the last two pictures, Greg. Looking great otherwise.

[TomG]

I would think that would be enough clearance, as long as the alignment is good. Even if it isn't, bronze and steel are excellent bearing surfaces and the rpm's are low, so nothing bad can really happen.

Tom

[rleete]

(10-30-2018, 09:59 PM)f350ca Wrote: Had a 1 thou over reamer and lapped the shafts to 2 ths under, giving me 0.0012 clearance, (If the caps are perfectly aligned) Will that give enough room for oil?

If you use a light oil (like light machine oil, or 3 in 1), yes.  If you use a thick oil like way oil, then probably not.

Why not fit small lube cups to the top of the caps?  You can either make them, or purchase from PM Research or eBay.