Scotch All Round

[PaulR]

I've been drawing up 2D CAD plans for my next build and although the plans aren't quite finished yet I think the essential dimensions are all ok so I made a little start on the frames. If it comes together it'll be a double-acting twin cylinder engine with spool type valves with Scotch yokes turning the crank and controlling the valves. It' be a simple 'blocky' bar stock build using just the lathe and a rubbish drill press with dodgy machine vice and definitely no adhesive or soft soldering like last time!

I'd forgotten how difficult it is to get a series of holes lined up without a mill or some other traversing device. I was fighting a machine vice that doesn't want to hold anything parallel to the drill table and a quill that seems like it's a bit wobbly or misaligned too! Anyway, in the end they didn't come out too badly, only one is a fraction adrift (well two because I stuck the frames together and drilled them in one go) and given that they're clearance holes for screws or non-critical parts to be soldered in they'll stand a little fettling if necessary. For scale, the steel is 1/2" x 1/4" thick and 134mm long.

This could be the most boring photo on the entire forum but I have to start somewhere 

[PaulR]

Faced the 4 cross-member/steam passage things to length and turned down the ends of the first one.

[paul gough]

Sounds interesting. Hope to see a sketch soon. Regards, Paul Gough.

[wagnmkr]

Ya had me at "Scotch"   

 

[PaulR]

Sounds interesting. Hope to see a sketch soon. Regards, Paul Gough.

I think my CAD skills are a bit lacking/unconventional but if it's a runner I'll definitely post the plans here... I'd rather make sure it works before encouraging anyone else to start making swarf! 

[PaulR]

Ya had me at "Scotch"   

Best lay off that while in the workshop 

[PaulR]

Did just a little more today, finished turning down the ends of the cross members, now they just need the through holes drilling. Also drilled and reamed the holes for the bearings after the photo was taken. Started making the bearings but ran into an issue with a blunt drill bit which, when went badly wrong when I tried to sharpen it on one of those bench-top multipurpose grinders. Don't think I can rescue it by hand so will need to order another.

[PaulR]

Chopped the valve chests (well just open ended cylinders) down to size and used that side of the frame to mark out the holes for the steam pipes (cross members) and the securing screw on one of them. The projections on the end of the pipes go inside the valve cylinders which stops them rotating so only one securing screw is needed. Hopefully 

Really should have done something to protect the work in the 4 jaw but repeatedly having to take the part out to check its length was tedious enough, I don't trust the backlash in the top slide to rely on that for measurement when facing off a mm or so in 1/8mm increments.

[MJM460]

Hi Paul, I find the trouble with removing the work from the chuck is that you then lose any reference distance to the cutter, much better to leave it in place.

I first note the measurement, then mount the workpiece in the chuck then measure from the face to be cut to a suitable reference such as the face of the chuck, (not the face of the jaws) with calipers using the depth function or preferably a depth micrometer.  Then wind the top slide away from the cut two or three turns and approach the cut from there.  After the first cut to make a good surface for measurement, you can re measure to the chuck face to calculate how deep you have cut.

The other trick is to set up a dial gauge against a face of the top slide where it will be not too much in the way, set it to zero and use that to measure how fat you move the top slide.  It’s a good compromise for lengths within the dial gauge range until you can add a digital scale or DRO.

I am sure more experienced members will have even better ideas, but the dial gauge trick works for me.

Looking forward with others to seeing the arrangement develop.

MJM460

[PaulR]

I first note the measurement, then mount the workpiece in the chuck then measure from the face to be cut to a suitable reference such as the face of the chuck, (not the face of the jaws) with calipers using the depth function or preferably a depth micrometer.  Then wind the top slide away from the cut two or three turns and approach the cut from there.  After the first cut to make a good surface for measurement, you can re measure to the chuck face to calculate how deep you have cut.

The other trick is to set up a dial gauge against a face of the top slide where it will be not too much in the way, set it to zero and use that to measure how fat you move the top slide.  It’s a good compromise for lengths within the dial gauge range until you can add a digital scale or DRO.

Thanks for these tips. The first one sounds like a good idea and more accurate than using the scale on the topslide - I'll give it a try next time I don't think the second idea is a 'goer' for me as it's already very cramped in the working area. I managed to get both pieces down to within 0.04mm of the target, it just took much longer than necessary using my hokey cokey method!

[PaulR]

Made some more holes and a threaded hole in the other valve cylinder, turned and reamed the bearings and cut a piece of steel ready for the crankshaft. These run of the mill (well, lathe!) operations don't really deserve photos but here's a random pic of parting off one of the bearings just to show I am actually making this stuff and not buying it ready-made off eBay 

I've been trying to work out how I could bring steam/air into the valve cylinders via the fixing screws (and not use pipe unions) and still make it possible to disassemble the entire thing but it has me beat. So I'll be bringing it in via connections under each one. It won't look as neat but hey ho. It'll also leave more space for connecting the supports to attach it to the base. I'm itching to get those cross members soldered in place but I can't until I have the cylinders (3/4" bar) cut to size as I need to spot through the holes in the frame.

[crueby]

Not sure where the steam/air inlets will go, but if its at the screw, how about a banjo type fitting? Here is a link to that type on Wikipedia:
https://en.wikipedia.org/wiki/Banjo_fitting#/media/File:Banjo_Fitting_Schematic3.jpg

[PaulR]

Not sure where the steam/air inlets will go, but if its at the screw, how about a banjo type fitting? Here is a link to that type on Wikipedia:
https://en.wikipedia.org/wiki/Banjo_fitting#/media/File:Banjo_Fitting_Schematic3.jpg

Never seen that type of fitting before, thanks! If I was just hooking up two silicone tubes for air I could replace the screw with a simple inlet fitting - I might still do that instead of making yet more holes - but I was trying to get clever and incorporate air passages in the stand/base with one inlet connector and maybe even a simple reverser. Will cogitate for a day or two while other bits are being made

[PaulR]

Not sure where the steam/air inlets will go, but if its at the screw, how about a banjo type fitting? Here is a link to that type on Wikipedia:
https://en.wikipedia.org/wiki/Banjo_fitting#/media/File:Banjo_Fitting_Schematic3.jpg

Thinking about it, this banjo fitting is basically one of the options I'd already considered albeit with a series of holes or slots in the screw in case the single hole doesn't line up with the flow (hope you get what I mean?) and I hadn't considered using washers. Anyway, I decided it would make the screw too fragile as it's only M3 brass. However I guess I could make it in steel and shorten it as required to make sure it does line up. It would certainly make things neater, need to ponder if there are any ramifications...

EDIT: this is basically the same idea with cross holes, from a little feed pump I was sketching out.

[crueby]

The way that Kozo used banjo fittings on his train designs was to turn a groove on the inside of the ring, so the alignment of the cross holes did not matter. Or, if the ring is a loose fit on the post, with the washers making the seal, then no groove needed.