otish, How would you make these spacers by friday afternoon?

alonzo83 · Sep 3, 2015

I need to make fifteen of these spacers shown below.

The part holds a 1.250" ball bearing on each side. We are going to use uhmw.

First problem I think I am going to have is keeping the radi consistent. I believe I have about .005 or less tolerance to hold on the distance as they are some sort of out dated spacers for ball bearings in a crane. A ball bearing goes in each end.

The second issue I am having is my form tool I made is chattering. It cuts well but I don't know how to stop the chatter. This is the first radiused form tool I have made so I am just winging it.

Thank You for reading, Thoughts, and suggestions are appreciated.

Edit I also forgot too mention I don't a 1.250 ball end mill

Milland · Sep 3, 2015

I don't see an image...

Now they're there.

alonzo83 · Sep 3, 2015

sorry I forgot too add them

Milland · Sep 3, 2015

No worries, just concerned I was going blind (gotta cut down on the wood alcohol).

No top rake on the form tool, give it some serious top rake, smooth all the edges with a fine stone. Closer to a polish the better, but don't lose form or round the edge. If you're holding the part in a three-jaw, see if you can make a single-split sleeve from Al to allow collet-like support of the material. Better to have the tool a tiny bit below center than above. Should cut nice and smooth...

Edit: you may have to recontour the radius on the form tool after putting the rake on it to get the correct shape in the part. If you could take a tiny grinding wheel to the top surface and grind in a radius right behind the curved edge that would work, but would be tricky as heck to do by hand without nicking the edge.

I'm a little surprised the form has to be held so closely, if you had two of the bearings you could do a final "press" in a vise to imprint the shape into the pocket, as UHMW will cold flow.

spiningwheels · Sep 3, 2015

Seems to me that the tool is sticking out way to far out of the toolholder.
Keep it as short as possible

Philabuster · Sep 3, 2015

How would you make these spacers by friday afternoon?

I would knock them out on the CNC lathe.

Milland · Sep 3, 2015

spiningwheels said:
Seems to me that the tool is sticking out way to far out of the toolholder.
Keep it as short as possible

I really don't think that's the issue here, or it's the least critical link on the chain. It's a big tool, not that far from the holder. It's much more likely the material is moving, at least in my opinion. That's why my recommendation for an aluminum split sleeve if he's holding the blank in a three jaw. UHMW is soft, will cold flow, and is slippery, all of which makes three jaw chucks problematic. If he's got a six jaw, that should be good enough.

alonzo83 · Sep 3, 2015

I am going to give the sleeve a try milland. The test part I made to try out my cutter really moved a lot and scarred the od. didn't think that would be the source of my chatter but I imagine you are correct on this one.

alonzo83 · Sep 3, 2015

Philabuster said:
I would knock them out on the CNC lathe.

ah yes, if such a thing existed in our humble repair shop. . .

Milland · Sep 3, 2015

alonzo83 said:
I am going to give the sleeve a try milland. The test part I made to try out my cutter really moved a lot and scarred the od. didn't think that would be the source of my chatter but I imagine you are correct on this one.

Sounds good. Make it long enough to bottom in the chuck, or use most of the jaw length. A shoulder inside will make your life easier by giving you a constant registration and preventing "push back". Double check that the heel of the lathe bit isn't rubbing against the lower part of the radius as you bury the tool. The diameter is so small that you need to treat that part of the tool bit as if it's a "bearing ball" itself to avoid contact. You can put some ink or Dykem on the underside of the tool to see if there's contact.

alonzo83 · Sep 3, 2015

Just got this pic.

I think the job will go better and have a better product if I cut a bit oversized and have them cold form on sight with a vise. I dont have the ball bearings here to form them.

What do you guys think?

Limy Sami · Sep 3, 2015

Another point Alonzo ............from the pics that tool is NOT SHARP think fine india or Akansas stone top and front clearance honed like a sharp wood chisel.

Plenty of front clearance too at least 10deg

+ 1 on less over hang,

+ 1 on support sleeve for material.

Milland · Sep 3, 2015

I like the fractional reading on the caliper - now, that's precision!

Don't leave them too long, no more than .005 - .010 or so I'd guess. It will cold flow, but too much and you'll distort the OD of the part. If the parts go into a bolted joint, it's possible that leaving the spacer a touch long and letting it set in the assembled joint will be OK, but get their approval first.

Otherwise, just rework the lathe bit and machine the parts to spec.

CalG · Sep 3, 2015

Soft jaws instead of the sleeve so you can control the depth on each side without really thinking about it after set up.

Use a Dremel tool to cut in your "chip breaker". ( top rake)

Dead sharp!

How much the tool sticks out ? You will know by how it sounds, but that is a lot of tool in the cut.

DavidScott · Sep 3, 2015

If all else fails you could use your vertical turning center, aka VMC. It's what I do when I need a cnc lathe.

alonzo83 · Sep 3, 2015

I will keep the tolerances close milland.

Limey I am glad I caught your attention after reading your previous posts I know you have a lot of experience in this area.

I will catch up tomorrow morning before I head out to the shop.

Thank you all for the replies. Off to bed for now.

Milland · Sep 3, 2015

Just want to correct something I said in #4 - " Better to have the tool a tiny bit below center than above." should be above center, not below. Just noticed I made that mistake and wanted to make sure it was clear what I intended.

Sorry!

stephen thomas · Sep 3, 2015

It goes pretty quick on a BP. You would not even need a rotab, just a DH. Like a 4:1 Hardinge with a 5c pot collet closer. Or worst case a 5c import spindex mounted to an angle plate. The principle is the same. With the boring head, the dia can be dialed in as close as needed.

PM'r Alwyn making CI tooling for high end optics.

These are bigger parts than you need, but does OD just as well:

All work courtesy of PM'r Alwyn B.

FWIW, I have used the process to make a bunch of 4" OD wooden balls for a millwork project.
I have also actually made the parts you are working on, but only needed one pair. They enclose a ball/heim type joint on the airlifter for my planer. But I just made them tapered cups, more or less, for that app.

smt

norb · Sep 3, 2015

For the finish just turn the chuck by hand to eliminate the chatter

lionelt · Sep 4, 2015

This guy made a similar forming tool.

See the top rake.

Around 11.44 and 19.60

http://youtu.be/8sEuyRtMslk

otish, How would you make these spacers by friday afternoon?

Stainless

Diamond

Stainless

Diamond

Aluminum

Diamond

Diamond

Stainless

Stainless

Diamond

Stainless

Diamond

Diamond

Diamond

Diamond

Stainless

Diamond

Diamond

Cast Iron

Stainless

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