Mill crank handle interface ?

[jcfx]

I want to make two to replace the ones that came with my PM 932 mill with round ones and possibly gain
a little Y travel with an extended one since my new vise is bigger than the one I was using.
Tubal cain has a video on making one for a Bridgeport, but he doesn't go into the math much.

There has to be a name for it, and info on how to calculate the cuts for the segmented finger thingy
on a mill crank handle that interfaces with the one that's on the knee /Y axis depending on the mill.

[GlennW]

Divide a circle into equal parts, which in your image is 60°.

Set it up on the rotary table and align the edge of the end mill with the center of the circle.

Mill all the way across the part. Rotate the table 60° and do it again.

Repeat until it looks like the part you need!

I probably have something wrong there because I make similar spline wrenches fairly regularly, but have never had to explain how to do it...

[Russ Hanscom]

There is probably a maximum size of end mill indicated.

[Bill Shields]

It looks like the faces of the fingers are on the radius ..but nothing says that they have to be.

Put a narrow straight edge...like a piece of keystock..across the flats and see if they are radial.

[jcfx]

Divide a circle into equal parts, which in your image is 60°.

Set it up on the rotary table and align the edge of the end mill with the center of the circle.

Mill all the way across the part. Rotate the table 60° and do it again.

Repeat until it looks like the part you need!

I probably have something wrong there because I make similar spline wrenches fairly regularly, but have never had to explain how to do it...

Is it really that simple ? Kinda thought there might be more to it.
That's pretty much what Tubalcain demonstrated in his video.
I swear I had found the correct terminology for this crank interface thing but can't seem to find it again
a spline wrench search just results in ... spline wrench.

Russ - yep he had to do extra passes because of the width of the spaces between the fingers / splines

Bill - Not sure what you mean, the mating faces are all flat.

[rmac]

I think Glenn has the right idea, but (as he suspected) he didn't get the explanation quite right. This is one of those things where a picture really helps:

Here, the red lines indicate the path of the end mill. Note that (as Glenn said), one side of the cutter always aligns with the center of the pattern.

After an initial first cut, the part looks like #2, where the areas that were cut away are shown in gray.

Now rotate the part 120 degrees (not 60) and make another cut exactly like the first. #4 is the result.

Rotate by 120 degrees again and make a third, final cut, again exactly like the first. #6 is the result.

Now nibble away the three little triangular bumps that are left to arrive at #7, which is what you want.

If you used a wider end mill, you wouldn't get the triangular bumps, but if the end mill is too wide, then it will start to cut away the inside surface of the teeth. I don't see any way to know how wide is too wide without knowing the actual dimensions of the part.

Depending on the part on the mill that the wrench has to mesh with, it might also be necessary to offset the cutter slightly from the exact center of the circle in order to provide some wiggle room. If both parts were made exactly as described, there wouldn't be any clearance between them and you'd need a hammer to install the wrench and Godzilla to get it off. Probably not what you want.

Tubalcain has a video on making one for a Bridgeport, but he doesn't go into the math much.

Tubalcain made this far more complicated than it needs to be. By using the procedure we're talking about here, except with 40 degree rotations instead of 120, he could have done the job with nine settings of his rotary table instead of the 27 he showed in the video. There's a discussion of all this in the comments for Part 2 of the video series.

-- Russell Mac

[GlennW]

Thanks for sorting that out, Russel!

[rmac]

Thanks for sorting that out, Russel!

You're welcome. Sometimes you just gotta draw the picture.

[jcfx]

+ 1 Thanks Russell, your drawing pretty much matches up with mine.