Horizontal Mill Engine
We're getting smaller. I found the plans by Elmer Verburg for this little reversible mill engine. It's 4" long and 1-1/2" wide. Pretty small parts!
I always start with what I believe will be the hardest part to make. In this case it was the cylinder block.
The quarter in the picture is for scale. It has two 1/8" milled slots in the top that lead to 35 degree angled hole to each end of the cylinder. Working without a milling machine that was challenging. I milled the slots by shimming the block to center in the tool post of my lathe and chucking a 1/2" end mill in the chuck. To drill the angles holes I indicated the tool post to 35 degrees and chucked the drill bit up in the chuck. Hey, it worked!
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Next toughest part in my mind was the steam chest.
The parts are all aluminum or brass. The steam chest bolts to the top of the cylinder and contains the valve that slides in and out to supply air or vent pressure from each end of the cylinder in turn.
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OK I thought those would be the hard parts. This one proved to be the real P.I.A.
It is the connecting rod that will run from the top of the eccentric strap to the air valve. It's .093" in diameter between two 1/8 X 3/16" blocks. I made it from 1/4 square brass stock. I'd get the center area turned down to around 1/8" and it would break. It took 3 attempts, but I finally got a usable rod.
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The eccentric was a simple item. .156" throw.
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Now the strap. It was a lot of work for what it is.
First it was laid out on a sheet of 1/8" thick brass, then the holes were rough drilled. It was then chucked up in a 4-jaw chuck in the lathe and bored for .002" clearance on the eccentric. Saws and grinders brought it to it's finished shape.
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Now I needed to make the shoulder bolts for the crankshaft, eccentric strap and connecting rod.
Simple but small. They were turned on the lathe, threaded with a 2.5mm die, cut off and slotted with a cut-off wheel on a Dremel Tool.
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I couldn't find screws small enough to bolt the steam chest to the cylinder, so I made them as well. All totaled I ended up with this.
It took another evening of tinkering to get the valve timing just right, but it came to life. Here are two videos. The first one shows it running in reverse, and the second one shows how it reverses.
If you'd like to try it you can download the plans here.
