Made the other half of the valve arm linkage.
Still need to radius the lobes, which I shall do on the belt sander once I have made a rod to hold on to it. On future engines I'll use a radius cutter or some other technique to properly radius the ends of these kinds of parts, for now a gentle hand applied radius will do.
Nuts!
Well, cross slide nut.
I also made the hex locking nut for the piston rod. No pics of that - a simple enough part.
So, family shot as it stands now, including the ghost of Engine Past - my beloved Elmer Number 14, and at least one scrap item I see.
These are awkward little parts.
I putzed around for a while trying to come up with various half baked approaches to holding the castings, getting ever impatient, but managed to reign myself in, decided to just take whatever time was needed and make some sort of holding fixture.
The techniques I have seen for making these parts include super gluing them to aluminum bosses, and pressure turning. I don't want to use those approaches, I prefer mechanical holding, so that was my approach.
First off, cleaned the casting gates off.
Then started scratching up some ideas, based on some measurements from the actual casting. I have a bunch of 1" diameter aluminum slugs laying around, all 5/8" long. These were thrown out by a previous employer. No idea what they were for, but they do come in handy from time to time.
The idea initially was to make essentially a holder in soft material so that I could turn the holder as well as the part. I was at first considering the pressure turning route.
Since I already had the collet chuck mounted and trued, this gave me a nice way of getting in close to the part.
It was at this point that I decided to add four tapped holes for set screws to clamp the part. I wish I had decided on that first, it would have been better to tap the holes on the circumference before boring the recess.
Anyway this meant making use of the new dividing head, in order to add 4 tapped holes around the circumference. This is just a pic of the head getting trued up.
So the tapped holes went in wonky because of course I was drilling into half thickness material at some points. But it still worked.
After machining to size on the lathe, this left only the two screw holes for clamping the gland to the steam chest - so another advantage of this little fixture was that I could transfer the part to the dividing head chuck and maintain concentricity of the boss and through hole to the OD of the fixture.
I used a gauge pin in the collet holder to center the spindle axis to the part, then moved the table to position the gauge pin at 1/4" distance from the center, and simply rotated the dividing head, visually aligning each lobe to the pin - obviously moving the pin from one side to the other. Then clamped the dividing head, changed over to the #41 drill, and drilled the two holes.
When all was said and done, the part came out well. The one side does not look centered, but that's a result of my over clean up on one side.
Up close it looks a bit rough, and does need a debur - but dimensionally it is spot on and fits the steam chest perfectly. So whereas I am usually lamenting about things not going right, this time it turned out, and I'm happy with it.
I made a start on some test assembly.
Very pleased to find that I can turn the crank over with my fingers, and the piston rod slides nicely in and out of the inboard head. Very, very pleased with this. Just need to stay the course now - it's finally looking kinda sorta like an engine.
I made another holding fixture for the cylinder gland. This time I got the sequence right, and drilled and tapped the set screw holes before boring / drilling. I also put them in at a slight angle (about 1°) so that when tightening on the part, they force it down into the fixture. That was the idea anyway, and it seems to have worked.
The bore was made to tightly fit the largest diameter of the gland, to help hold it concentric to the center axis.
I did have an oops. Tool dug in - I must have tried to take too much off.
I t dug into the part and made it look ugly - but happily there was a fair bit of stock still to come off, so it cleaned up OK.
Off to the mill - centered using a gauge pin,
then rotated the part back and forth until a gauge pin looked even on both ears, and then drilled the holes.
Rotten finish on the front. It buffed up OK though.
I had been working on a follow rest system for supporting small diameter shafts for turning and single point threading. It was way too complicated, and a complete failure. Based on something I saw Joe Pie demonstrate on youtube, and also on a thread on this very forum, I modified the follow rest and made it much simpler, and a lot more effective.
Essentially, I am just using my lathe follow rest, but I had made a new adjusting shaft and a bracket for it. The original idea was to use a couple of very small ball bearings to support the shaft.
In the end though, it's easier to bolt a piece of material (in this case a piece of phenolic) to the bracket, and just use an end mill in the chuck to drill a hole in situ, so that the support is perfectly centered.
It's then very easy to position the cutting tool close to the support for whatever work you need to do.
I used the "upside down tool" approach for single point threading, so that the cutting tool moves away from the headstock.
And it works a treat.
So I'm well pleased with that - no need for expensive dies for cutting small threads. Just as well, because the cheap dies are awful, I have had no luck with them at all - a waste of money. But this follow rest approach works really well.