Gallery, Projects and General > Project Logs
The Return of No. 83, a Hot Air Engine
vtsteam:
I finished drilling and boring (not shown) the new plug, giving it an I.D. equal to the I.D. of the stainless cylinders. Formerly that hole was equal to their O.D. I also drilled and tapped 4 mounting holes for a new flanged cylinder
I then started a third cylinder and press fitted it into an aluminum flange (which will provide additional cooling sink). The flange was drilled for four fixing screws. It's shown here fastened to the newly sleeved and bored bulkhead. The previous two cylinders are sitting next to it for comparison.
The new one will be shortened so that the overall length including the bulkhead is the same as the other two. I haven't capped it yet-- I've left it open to be able to see how the displacer is riding in the bore.
I'm happy with today's work and the new cylinder mount. :ddb:
vtsteam:
I shortened the third displacer cylinder, brazed a cap on it an then thinned the walls to .014". It's mounted here on the aluminum cooler/bulkhead. This time I used copper instead of stainless steel as the cap.
vtsteam:
The brass displacer rod guide is somewhat worn/oversized and the displacer can sometimes contact the bottom of the displacer cylinder if things aren't adjusted to compensate for the droop. That's not ideal, since the displacer is then no longer parallel with the cylinder, and there's not a lot of leeway for this -- the cylinder is ~ 3" long, and the clearance is only .073".
The wear is in the brass guide, not the rod. Guides on a horizontal displacer hot air engine receive a lot more wear than a vertical.
Another detriment due to wear here is pressure leak. There's no seal other than a good fit over its 3/4" length. As built, the guide was permanently brazed in place. I've decided to make it replaceable by drilling and threading the existing guide 1/4 -28 to take a screw-in bushing.
I've got some sintered bronze material in the scrap box, and I think I'll make a guide bushing out of that. That material should reduce wear and friction compared to brass, and obviate the need for oiling.
Here's the guide, now opened up and threaded:
tom osselton:
:beer:
vtsteam:
Thanks, Tom :beer:
I spent time in the shop today adding a motorized spindle to a milling attachment I had once built for my old Gingery lathe. I found that the milling attachment does mount onto my newer homemade lathe with T-nuts in the boring table.
That was a fun, overdue project -- I've had the spindle for a year. The milling attachment was built in 2002. Neither had seen service on my present lathe until now.
I had planned to use this new rig to mill down the top of No 83's valve guide socket, since the new threaded bushing will have a head that would otherwise increase it's height. Seemed like a good reason to make up the tooling.
Got the rig working and set up, but :wack: I found I didn't have a 1/4" end mill to fit the spindle. All my 1/4" end mills have a 3/8" shank. The new spindle has an ER11 collet system which only handles up to a little more than 1/4". I thought about mounting a 1/8" end mill, but the one I had turned out to be too short to clear the power piston cylinder.
So in the end I went with the old fashioned way: I chucked an oversized drill bit in the drill press, and drilled out most of the way down on the valve guide, then finished up with a file to square the top off.
Oh well, glad to have the new powered milling attachment made up. I've ordered some 1/4" end mills with 1/4" shanks.
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