Bog's Paddleduck Engine

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kvom:
Today I decided to make the upper plate, as I had limited shop time available. I started with a 4"x4" piece of .25" thick brass plate that had been flycut on one face. After squaring the sides I used a 1/8" endmill to saw the short side, then used an endmill to bring to the final dimensions.

Since all of the holes are or can be referenced from the center, drilling them was an exercise in cranking the handles and watching the DRO. I drilled all of the mounting holes to take 6-32 screws. The large holes for the glands needed to be slightly over 1" in diameter. I used a 3/4" end mill (my largest) to make the initial hole, and then the boring head enlarged them to ~1.05 (loose fit arounf the gland).

I didn't make any cutouts as I want to see how the plate looks when mounted before deciding on any blingification.

As I was taking the photo UPS arrived with my 3/8" drill rod, so machining the valves may be the next task.

bogstandard:

--- Quote ---One other factor that makes this build enjoyable is the nice mix of milling and turning.
--- End quote ---

Actually Kirk, the first proviso on the build was that it could be machined completely on a lathe with a vertical slide. Having a mill would be a definite advantage, but not essential. Hence no difficult angular port drilling normally associated with an engine of this type.

On your last post, don't forget to give yourself a bit of 'wobble' clearance on the crosshead support holes. I was a little lax in getting my crosshead holes in the right positions, and needed that adjustment to get the engines to run.

John

kvom:
A full afternoon's work in the shop resulted in exactly one useable part:

The two other valves that I started ended up in the scrap bin because of various operator errors. On the positive side I did learn the best way to turn this rod to get a better finish, and I can probably make a valve in less than half an hour if I don't mess up.

I decided that the lathe karma was lacking, and decided to move to the mill for a "simple" piece, the blanking plates. Well I messed up there somehow as the holes didn't end up centered. So I figured it was time to call it a day.

As for wiggle room, I think I need to plan for that on the steam chest/blanking plates. I drilled the holes with a #20, which is a close fit for an 8-32 screw. Using the DRO to drill the holes for the plate, I found that the screws would "just" go through the plate and the steam chest. I plan to enlarge these holes by a couple of thousands so that when attached to the block I will be able to wiggle them slightly in case the bores on the block and steam chest are not perfectly aligned.

bogstandard:
Kirk,

There is no shame in making wiggly holes, as long as they are not seen in the finished article.

You can sometimes strive too much for precision fits. On mundane items like mounting holes, give yourself a break.

John

kvom:
Here's the summary pic of today's progress:

Got the other valve made, although it took longer than the hour I estimated yesterday. I also reamed the steam chest bore to .375" to match the valves. Of course now it's a press fit at best, so some lapping is due there.

The same is true for the block, where I re-reamed the bores to .5" to remove the burrs caused by drilling the steam holes. I then drilled the holes on each end for attaching the steam chests. The afternoon finished with turning the pistons, which are likewise a press fit and require lapping.

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