5c collet chuck not flat

[leeko]

Hi all

A couple of months back, I bought a cheap scroll-type 5c collet chuck from eBay. I just got around to fitting it to a backplate, and noticed that it didn't sit flat on the machined register. I took it to a surface plate, and the back of the chuck isn't flat. I tried stoning any burrs, but the issue is that the rear surface of the chuck isn't flat - it's a little convex.

I took the chuck apart, and found many large burrs. I think the issue is that one or more of these burrs got in the way during final assembly, and when they screwed the two halves of the chuck together it forced a bow in the rear section as it was clamped to the non-flat surface.

I spent a couple of hours deburring, cleaning and reassembling today, but the chuck still rocks on my surface plate.

I'm thinking I can put a 1" bar between centers and tighten the collet chuck onto it, then remachine the backside register of the chuck. It is hard, but not so hard I couldn't cut it with a file.

Does anyone have any suggestions for a better way to tackle this? I figure at this point it's worth spending a.little more effort on it before it goes in the bin...

Thanks,

Lee

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[JimDawson]

What you suggest is exactly how I would do it.

 

[leeko]

Thanks Jim. Good to know I'm not way off in my thinking!

Lee

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[Ulma Doctor]

I second the motion to restore flat in this manner.
(that and $4 will get you a coffee at Starbucks )

 

[Alexander McGilton]

There is an article on CNCCookbook describing exactly this. The one change I would do is is instead of machining down a piece of round bar in the 3 or 6 jaw chuck to a concentric shank, or placing a mandrel between centers small enough to put within a collet. I would instead take a piece of 1.5in dia about a foot long or longer bar of CRS, place one end in the four jaw or three jaw (which ever is heavier and holds firmer), and center drill and live center the free end. Then machine a 5c profile on this bar stock with thread and 1-1/8inch dia tang to the right of the thread a few inches long. This is the largest and most ridged possible mandrel that can fit down the collet chuck. More concentric as it can be machined in one clamping and has only one contact interface instead of the two that a given collet would introduce. Just remember to remove the key way pin. In the CNCCookbook article he mentions an error in eccentricity first time he mounts the chuck and collet for a test. I belive this can be remedied with having a more ridged setup and not a cantilever.
When you are done you will have not a piece of scrap but a 5c arbor with a machinable end.

https://metalartspress.com/howtos/r8-and-5c-collet-dimensions#

5C Collet Chuck for Lathe & Ball Bearing Spinner Key

Why use a 5C Collet Chuck for a Lathe? If you consult our Total Guide to Lathe Workholding, the advantages of a 5C Collet Chuck become clear very rapidly:

www.cnccookbook.com

 

[leeko]

Thanks guys. Alexander, that's a great suggestion and I'll save it for next time

I machined the chuck back flat last night, on the 1" arbor. It went quite well, though I had to run the speed way down as I was getting sparking. I guess this material is harder than I first thought!

Next step is to properly counterbore the through holes in the chuck face, as they're slightly conical at the moment. I have no faith in this chuck's concentricity, for obvious reasons, so I intended to mount it as a bump-true type with a smaller boss. I found that even with socket head cap screws, the conical seats for the screw heads would cause the chuck to shift as I tighten the screws.

Hopefully after all this, I'll have a useable chuck!

Lee

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