I like the color photo from e-bay! I hadn't thought about how it should be painted until seeing this. The book says the articles are from Live Steam so the story lines up. It's cool to see interest in this little engine. I hope some of you make one too! I'd love to see that, and to be honest, it wouldn't hurt for me to see how some parts might be machined
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I made the first part this past weekend...so here goes some build logging...
The Crosshead TrunkThe print calls for the crosshead trunk is machined from 1.375" high x 1.5" x 2.625" brass. I didn't have that on hand, and I coughed a bit when seeing how much brass would cost, so I took some 1" x 1.25" bar of 1018 steel to start. I suppose it would help with understanding how this could possibly work if I posted the drawing. The crosshead trunk is actually only 1" wide, but has feet that spread it out to 1.5". The book suggests these could be fabricated as bars soldered into grooves at front/back of the trunk. I took it one step further and decided the whole "base" of the trunk could be made of 0.25 x 1.5 steel and I'd solder the trunk on top of that. Hopefully, this will make sense when I actually make that part and show it in this build. But I thought I should point this out immediately for anyone who has the article in hand and is going "huh?"
I squared up this block on the mill, and bored 0.75 for the crosshead. I got to use my spiffy new boring bar. When I dialed it in in the 4-jaw, I made sure the three sides indicated the same.
As the article suggested, I drilled/tapped two holes on the underside (the thick offset side) for grub screws. These will allow it to be attached to a 0.75" mandrel.
Now I need to round over the top of the trunk, so here's my setup. The article suggests an indexer, which I don't have, but I do have an RT that can run vertical with a tailstock. But just for giggles, I decided to try a setup with V blocks instead. You'll note the crosshead trunk has the mandrel installed with the set screws and this is sandwiched between V blocks so it can't shift along the X axis. I had an
ah-ha moment and dropped a rod in the t-track to help with alignment of the V blocks. The rod wasn't quite big enough, but I pushed on the V blocks (in Y) when I did the final tightening of the clamps holding the blocks to the table. I was a bit shocked that when I dialed in with the DTI, it was already perfectly aligned! It's cool when things work out like that.
Now it was just a matter of rotating the trunk, tightening down the clamps onto the mandrel, and taking a pass on the mill. This was a bit tedious, but I set the mill's depth stop to be close (but not all the way) to the final depth. It was just a matter of going around and making sure I don't go too far where it should be flat on the sides.
When I got to the sides I'd use a square like this to set a starting point, and then (by hand) would rotate it slightly away from square in the right direction to make those last passes. You can see it's already pretty round over the top in this photo.
I took it to this point with the idea that I could file off the facets to finish it off.
Next, it was time to cut out the side opening. I decided to go with the book's idea to cut into the mandrel. In hindsight, I really don't think the rotation helped at all. The cut along the top is at such a small angle that I believe anyone making this engine could simply place this part in a vice and mill out a rectangle instead. But I followed the book. So I ran the end mill off the edge to touch it down to the mandrel and set the depth stop, and then went at it.
I undersized the cut slightly in X so I could clean it up later. My setup didn't allow me to rotate the part during a cut, so my plan was to do the final cleanup while the part's XY plane was parallel to the table. Here's where it ended up before this final cut. About at this point I was realizing the end mill was cutting rather difficult (and rough) and was dull.
Here it's mostly done. Just a little filing remains.
And now I have this part.
And finally I needed to turn the ends in for 0.125". I did this between centers just because I could, and it also meant I could take out the part for inspection or to flip it end-to-end without additional setup. Note my poor man's "DRO." I just purchased a magnet for the base of that DI and it worked incredibly well, though on that side of the carriage it was reading backwards. But 0.125 was only a full rotation and a quarter of the DI so this wasn't confusing.
And there's the main part of the crosshead trunk. I've done a little filing for this photo, but a bit more needs to be cleaned up.
Next I think I'll make the "base" part of the crosshead trunk, and then I'll make the front/back heads for it.
Todd