Vertical hit and miss engine

[Brian Rupnow]

So here I am, using up a butt end of cast iron that was originally part of a longer piece which was used for an air cooled cylinder. The o.d. has been turned and polished with 200 grit sanding strips, until it "just about" slides into the cylinder (which you can see setting on the lathe bed). It actually just starts to enter the cylinder but won't slide all the way in. the round counterbore has been put in in this set up, and next step will be to cut the two ring grooves, still in that same set-up. Then the piston will be parted off for other operations.--Have also included a pic of the engine without cylinder on it.

[Brian Rupnow]

This is the finished piston fitted to an arbor and held in the lathe chuck. The piston is coated with 600 grit aluminum oxide paste and with the lathe set on its lowest speed (Which is really quite slow) the cylinder is gradually worked back and forth until the entire piston will fit thru the cylinder. This is not for the faint of heart. You have to be able to let go of the cylinder very quickly if it "grabs",  then stop the lathe and work the cylinder loose before starting again. This makes an extremely good fit between piston and cylinder. The method works very well, and it doesn't take very long at all.

[Brian Rupnow]

Today was con-rod day at the Rupnow Ranch. Cast iron piston from yesterday, 6061 aluminum con rod from today. I have found that the rings I purchased (and which call for a 0.094" wide slot in the piston) are such a very very close fit into a 0.094" slot that tomorrow I will put a bit of 600 compound on a sheet of glass that I save for things like this, and "dress" the width of the rings just a tad.

[Brian Rupnow]

There comes a point in every build where one must machine the horriblest, awfullest scariest part. And that for me is the crankshaft. I have made any number of these one piece crankshafts, using 1144 stress-proof steel. Some turned out perfect. Sone turned out mediocre, and some were downright awful! I put the same amount of care and breath holding into every one I make, but the results are never consistent.  Far as I know, the only things left to machine are the crankshafts and counterweights, so here we go--

[Brian Rupnow]

First step with crankshaft is to cut it to length (allowing 1/2" extra at each end where it will be center-drilled.) Second step was to set it up in the three jaw lathe chuck and square up the ends. Third step was to set it up in the vice, paying particular attention that it is setting parallel to the bed of the milling machine. The material is 1 1/2" diameter, but the crank has a maximum width of 1/2" at the crank throws, so 1/2" of material was machined away. Trust me, at 0.015" depth of cut, that's a lot of travelling back and forth.

[Brian Rupnow]

Now that you have one truly flat milled side on the round piece of round 1144 steel, you can scribe a line 1/2" over onto the uncut portion and clamp it to a piece of wooden 2 x 4. Then cutting "close to the line" you can cut off a lot of the excess material with the bandsaw, then finish up in the milling machine, to end up with a piece of flatbar.

[mike mott]

Brian, Yes cutting as much as you can with a saw does save a lot of the "back and Forth " as you say. I like the block of wood trick.

Mike

[Brian Rupnow]

And here we are, finishing up that rough sawn side on the mill. Note the way the part is supported on dolly blocks at both ends and is not supported by the vice at all. This ensures that when milled to finished size, the two sides will be perfectly parallel. All the vice is doing is providing gripping power so the part doesn't move. Tighten vice lightly, whack each end of part to make it lay flat against the dolly blocks. Tighten vice some more, whack the part some more. When vice is fully tightened and dolly blocks are held tightly against mill table by overhanging ends of part, then its time to start milling.

[Brian Rupnow]

So here we are, all ready to rock and roll. The cad model shows the crankshaft overlayed on the material which it will be cut from. The crankshaft will actually be 1/2" longer at both ends to match up with the raw material. Then it will be trimmed to length after all turning is completed to get rid of the countersunk ends. The picture shows the 1144 stress proof all ready to go into the lathe. I am going to spend some time tomorrow making a new lathe dog that doesn't rattle back and forth between the chuck jaws. That scares the Hell out of me.

[crueby]

Excellent start on the crankshaft.   

[Brian Rupnow]

Thanks Chris.--- First section of crankshaft is turned between centers. I kept checking it with my con rod until I was happy with the fit. Last evening I had all kinds of ideas for a new, super duper lathe dog that would fit on both sides of a chuck jaw. This morning I looked at what I had, and decided to just drill and tap another 1/4"-20 hole in the opposite side of the machinists clamp. Now I have a bolt setting on each side of a chuck jaw, so it doesn't rattle back and forth between chuck jaws. Works great!!!

[Brian Rupnow]

So there we have it gentlemen--a crankshaft at 95% finished. I still have to trim the ends and do a little clean-up, but that is a full days work. I really liked the way my new improved lathe dog worked. Now my back hurts from standing at the lathe all day, and I still have to go for my "fat mans walk". That blob in the center is a spacer glued in place with hot melt glue to keep the center gap from closing up when I tighten the tailstock center.

[Johnmcc69]

 
 Awesome work Brian!

 John

[Brian Rupnow]

Thanks John. The crankshaft is finished except for the keyway, which I will probably cut tomorrow. The main thing that I don't like about turning between centers, is that you can't readily check the size you've turned to by sliding the bearing over the shaft. You just keep checking with your micrometer and praying you don't turn undersize. In a perfect world, I like to leave about 1/2 a thou on the shaft and take that down with 200 grit carborundum paper.  In this case, I must have guessed right, because a 3/8" bearing will just start to slide onto the shaft ends. A bit of sanding should bring things right. 1144 stress-proof steel does move a little when machined. Not anywhere near as much as cold rolled or even A36 steel, but it still moves some. The crank as shown has about .010" total indicated run-out. If that poses any problem when I assemble the engine, I will set one end up in the 3 jaw chuck and whack it with a dead blow hammer. These little one piece crankshafts are amazingly flexible.

[GordonL]

What kind of tool do you use to get square corners on the center throw? I always have a problem with leaving a fillet in one or both corners or having a step in the journal if I change tools to RH or LH.