How would you make a one piece model crankshaft

[GLW]

Im assuming you would use a 4 jaw chuck with the appropriate offset but I thought I would ask the experts.

[Doug_C]

Not an expert, but I have slept in a Holiday Inn.

It could be done with a 4 jaw or a piece of round stock with proper offset holes to mount one end of the crank in.

Another way is to produce the crank out of flat stock. Leave the ends on it with center drilled points at each end to use as turning between centers in the lathe. Then cut off the excess once the journals and bearing surfaces are completed.

Keep the tool pressure low to avoid part deflection. This is done with a bifurcated tool point. Like this one Bob W. posted recently.

DC

[Anonymous]

The standard method is turning between multiple centers. Typically a flat bar is squared up and the ends centerdrilled with centers for the main bearing journals and the rod bearing journals. The excess metal can be sawn or milled away before turning to make make the job easier. Because the blank is fairly flexible, sharp tools and low cutting pressures are required. A tool post grinder is very handy to finish the journals to required size and a nice finish. After all the machine work is completed, the remains of the centerdrilled ends are cut off.

[Mosey]

Certain I'm not an expert, but anyway, I used the flat bar with 2 centers in each end turned between centers. When I realized that there are to be 2 holes tapped into the journal sides for counterweights, I just bolted a little flat bar across the offset part of the crank to stiffen it while I turned the bearing surfaces. No flex this way.
I turn the journals to within a thou. and finish to size with emory strips down to 500 grit. Then diamond polish.

[Bob_W]

Just one other thing I did with the larger crankshafts: When beginning to turn the second end of the main shaft, the interupted cuts could cause the 'dog' to slip on a finished surface, potentially damaging the shaft. Instead,I roughed the first end to within .025" of final diameter or so and then remove the shaft and clamped the dog to the just completed 'rough' surface. Now turn the second end to the finished diameter. Remove the dog and re-clamp on the finished end, with some brass or copper strips if desired, and finish off the crank. I have had a dog spin even on the rough cut, but it didn't cause any damage since I still had the finish cut left. Could be I just needed to clamp a little harder.

Bob W

[emb]

You would use a Keats angle plate. This is no mare than a Vee block which can be clamped to the lathe faceplate. The Vee block has substantial clamps to hold the journal of the crankshaft, and the whole job is offset on the faceplate to allow turning the pin. If I could figure out how to do it, I would post a picture of a Keats.

Using a 4 jaw will not work ar you simply cannot get the offset. For small engines a round block with a precicely drilled off-centre hole can be held in the 3 jaw. If the journal is then clamped in the hole, the pin will be the correct amount off-centre for turning.

There is plenty of literature available on engine building. I would hope that this forum could address the kind of questions for which answers are not readily available.

I wish you luck with this forum
emb, of MBI

[gastrap]

I thought of turning a one piece, but went with 5 piece on this 4.25X6 inch hit & miss.
http://img.photobucket.com/albums/v242/ ... itmiss.jpg

[SpinDoctor]

One of the recent issues of Hot Rod has a piece on just how aftermarket manufacturers make billet crank shafts. Check there [img]/ubb/images/graemlins/wink.gif"%20alt="[/img]

[DIX]

I'm machining a three piece crank right now and my question is how would you machine the rod journal when the throw is 1 1/2" and the width of the journal is 1/2"? I don't have a tool post grinder so this is strictly single point cutting tool business. Assume you figured out how to support the tool sticking out about 2" from the tool post. How do you machine the surface of the journal when there isn't any room sideways?

Dick

[Bob_W]

Dick

You may have already completed your crank but I just finished machining the center throw on a 1/4 Galloway crank and thought I would pass on the info for what ever it is worth. As you can see I still have most of the work ahead but thought this might be of interest. Many ways to do this, but I chose to use a modified P3 style (1/8 wide x 1/2 high) cutoff tool that I ground to cut on the outside corners. Roughed in the throw with serval tools for turning the left, middle, and right sections. I made up a quick and dirty steady rest since mine was too small and the carriage would have been in the way. I finished with the lathe running real slow, about 50 RPM (.500 dia), to prevent any chatter. The finish shown is right after the cut

To get the two corners cutting at the same diameter, I set a test bar in the lathe and brought the points against a previously trued section. Then stoned the longer point in place by hand until they both touched at the same time.

So, this way worked for me and maybe it and the other suggestions may be of some help

Bob

[Bob_W]

I attached a a view of the previous operation, zoomed out a little bit so you can see a little more. The tool is hanging out a little over 1 1/2".

Bob

[mrb37211]

It isn't exactly internal combustion, but the Village Press book by Kozo Hiraoka on "Building the Shay" describes converting a single piece of steel into a crankshaft with three cranks 120 degrees apart and six eccentrics spaced for the cranks.

The book was based on a series which appeared in the magazine "Live Steam" during the mid-1970s, with the engine sections in 1975.

Another series by this author on building a Shay was started by Live Steam in the 1999 July/August issue.

Charles