How Do I Crown This Wheel?

You have failed to indicate the radius of the "crown" or if a manual machine or under NC control.

Depending on your proclivity for self abuse a reasonable radius may be made (with flat surfaces) from the compound. I can produce the angles and moves for you in a CAD drawing with a spreadsheet, this will likely not make you happy.
 
Seeing as its a drive wheel for a belt grinder being made by a "relatively inexperienced" operator I doubt very much if it is going to be an auto machine.
And seeing as how most suggestions have been for a couple of passes with the compound at differing angles before blending the cuts with a file or grinder I doubt that CAD spreadsheet would be of much use

Cheers Phil
 
I understand, yet the often stated quest for .0005 accuracy would preclude filing and off hand grinding would it not?
 
I also just make an angled pass on either side of the crown-to-be. I frequently use a freehand HSS wood lathe tool for finishing off the crown. One with a square face on it. I just clamp a length of square bar stock on the Aloris tool holder,and use that for a rest. I do have a good eye,and this is needed for freehanding a crown. They always work fine when I'm finished.
 
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Maybe taking a clue from how to do this on a wood lathe would help. Mark each 1/4 or 1/2" on your part. Using a parting tool, plunge in at each mark the required depth then machine the waste away. File smooth then finish with some emery paper.

(George was posting while I was typing )
 
Wreck™Wreck said:
...the often stated quest for .0005 accuracy...
Click to expand...
I've not actually seen that stated here very often. In any case I've found that crowned pulleys work fine with just a 2 degree slope on the outer thirds and a flat in the middle. To make it pretty knock the corners off with a file and then sand.

Or, to do it the farmer way, put two wraps of duct tape around the middle third.
 
Thanks everyone for your ideas.

Wreck, my machine is an old Enco with no CNC and I don't think I'm capable of those tolerances but I don't think they are required. I believe the Machinist's Handbook states 1/8" per foot so for my wheel would need about .020 taper.

I'd rather not freehand this if I can avoid it. I don't mind putting the finishing touches on freehand. For the 3" idler, I made a jig with a 20" radius that bolted to the cross slide and I just swept it back and forth taking small cuts creating a nice radius. It worked very well but I didn't think it was very solid so didn't want to do it again on this more expensive piece of aluminum. If I pushed down too hard it would be off the center of the work piece and cut less than it should have. After multiple finish passes the wheel turned out to be within a couple of thousands in symmetry. I wanted to try the compound this time maybe using 1 or 1 1/2 degree as described above. Although I'm not sure of how to properly set that up either.

My real pressing question should have been about the order of the cuts and how to hold the piece keeping it concentric. I just wasn't sure what the proper order was so I didn't screw up the next step. I have decided to use the arbor idea and super glue it on while working on it (thanks jpfabricator for that idea).

I appreciate all your input and will post a pic when it's done...its my last wheel to do. Maybe this drive wheel doesn't even need to be crowned at all?
 
JH, I think a small flat is even better than a radius, but don't know that for a fact.
 
Anything will work,as long as it is lower at the edges. But,when I think about what the shape of the crown might do to belt wear,stretching in places and causing distortion to belts,I have to think that a smooth rounded crown is the best. Think about it: All of the old time machine makers used a smooth,rounded crown form. They did not use pieced together crown surfaces,though pieced ones would have been easier and cheaper to produce.

Those guys had loads more experience than we will ever have with flat belts. I'm going with their lead.
 
I found the hand file to be too slow and inefficient on the large wheel so I went to the angle grinder with the lathe running and it worked great. Only one wheel in the system needs to be crowned. My drive wheel is crowned.
My drive wheel has a boss on the inside without a recess. I cut the crown opposite the boss first and then flipped it around to grip the boss. My chuck has a runout of less than .0002 so flipping was not a big deal. As Wreck implied this is not close tolerance work anyway.
R
 
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