Thanks very much for looking in All
Vince, the small bits aren't all that bad; it just takes a bit more planning to do the machining - especially for work-holding. Oh, and not dropping them; that's instant shop-monster food. Actually I'm enjoying making the small bits; except for the smaller threads, these are of a similar size to quite a few parts I've made for the various versions of Elmer's engines I've built - though Elmer had a knack for simplifying the small parts a bit.
Don, yes; they do take time - as today's progress might show!
Marinus & Jim, thank you; that's high praise, but I don't consider myself a skillful model engineer. I'm still learning every step of the way, and in this build there are a lot of "firsts" for me.
Jan, yes, the screws are small - and some horological tools would be a boon. In fact, my list of "tools-to-make" still keeps on growing, and a lot of it especially for smaller parts. After this engine is completed, I'll spend quite a bit of time doing some tool-making jobs.
Eric, your 2 cents run through the exchange rate is worth a whopping 19 Namibian cents today, so I'll gladly take it
On to some more small bits. The disk arms are the smallest parts on the engine, and I'd been puzzling over how to make them. If I made them from three separate pieces each like on the plans, I'd have to single-point thread the spindles either M1.4 or M1.6 as I don't have dies for those sizes. That would have been a nice challenge; I'm one of the few people around who actually likes screw-cutting on the lathe, and even though these are very fine threads, I'm pretty certain I can do them with a razor-sharp honed toolbit. What I couldn't figure out was how to make the eight arm ends with the tooling I have...
"Arnold" is derived from "Eagle" - so it's with great trepidation that I sully my majestic avian namesake with what's to follow...
I turned "lazy" mode on, and decided to make the disk arms as single pieces. There were still some machining issues to overcome, but a plan was hatched and off I went.
Things started off with short sections of 5mm hex brass rod - much longer than needed, as I needed a way to hold things later on:
I turned a 2mm pip about 4mm long at one end of each of the pieces. My Myford's 3-jaw chuck is pretty badly off center at this size, so I marked the flat that lied between the #1 and #2 jaws so that I could later on chuck up the workpieces again and keep the best possible centering on the pip I turned. Then it was off to the milling machine with the tooling plate mounted in the vise, and I set things up so I could repeatably drill the workpieces with the 14.7mm distance between the holes. A bit of scrap aluminium plate served to both lift the workpieces a bit so the clamps didn't foul on the cap screws at the back and prevent proper clamping, as well as prevent drilling into the tooling plate:
After drilling the holes, I switched to an 8mm cutter and set it to height to mill off 1.25mm. Things were a bit tight between the clamping spaces on the tooling plate, but it worked:
As always, between milling each side of the workpieces, I followed that golden rule that Mr Philip Duclos mentions so often in his writings. Clean away the chips and de-burr the workpiece.
With the milling done, I ended up with this lot:
As you can see, there's the 2mm spigots I turned on each workpiece, and on the left, on the faces facing the camera, the permanent marker markings I mentioned earlier that corresponds to the opening between the #1 and #2 jaws of the Myford's three jaw chuck. Also, the metal-munching rat left it's hallmarks in the middle of the cut-outs; I didn't worry about that. Boring really, but there's a little method to this madness...
Back to the lathe with the workpieces, and a type of set-up I'd never used before. All the boo-hah about the 2mm pip at the end of the stock and marking the place to re-mount in the chuck now came into play. I wanted to turn down a section between the holes drilled into the workpieces to 1.5mm. I could have used my small revolving center for support at the tailstock side, but that puts an axial load on the end of the workpiece, and when things get this small, it could just buckle it up. So a bit of 2mm inner diameter tube chucked up in the the small drill chuck in the end of the big tailstock drill chuck, with a drop of oil added would provide a running center without adding axial tension to the workpieces. After digging around all my HSS cutting tools, I selected a suitable toolbit; this one was originally shaped to cut the worm gear from back when I made my rotary table:
With a drop of oil on the spigot at the end I shoved it into the bit of tube in the tailstock chuck. Some turning followed. Very carefully. The joys of turning brass with a nice sharp toolbit with zero rake manifested itself; with 10 thou initial and later 5 thou in-feeds as things got smaller, everything turned out well. The shaft of the workpiece is 1.5mm, and the steps up from that is 2mm:
I have to say, most of the turning was just eyeballed - I just used the same settings on the cross-slide for in-feed for all the bits, but no measurement for the shoulders or the distances to the holes.
The bits were just hacked off the parent stock with a junior hacksaw, and then I started cleaning them up on the mill and with files. All too soon, shop time ran out, but I managed to mostly finish off one bit after a lot of loving care with a needle file after rounding it over on the mill. One done, one partly done, and the rest to go... Well, that's some progress of sorts anyway:
The small bits can be a bit tricky, but it's a lot of fun. I'm really enjoying this
Kind regards, Arnold