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lapping internal taper?

Posted: Thu Sep 27, 2018 8:09 am
by TRX
I need to make an internal taper to take a collet.

According to my reference books, this type of thing should be hardened, then ground to final size on OD and ID.

I don't have a toolpost grinder. I could fake it pretty good on the OD with some flat stock and sandpaper, but the inside has me stalled.

Assuming I get a reasonably good surface finish on the OD, is this something that a lap could finish up? Or would I just wind up with a bunch of concentric grooves in the tapered surface?

Re: lapping internal taper?

Posted: Thu Sep 27, 2018 8:19 am
by SteveM
You should see if you can borrow a TPG.

Lapping removes so little, you probably couldn't measure it.

Steve

Re: lapping internal taper?

Posted: Thu Sep 27, 2018 8:47 am
by earlgo
If yours is not a production shop, you could get away with making your collet holder from 4x40PHT material and not grind, but polish the finish. A standard brake cylinder hone will do for the cylindrical section. At least it did for a 5C. It may not collapse small enough for an R8 and definitely not for the smaller Ericson collets.
--earlgo

Re: lapping internal taper?

Posted: Thu Sep 27, 2018 10:50 am
by John Hasler
SteveM wrote:
Thu Sep 27, 2018 8:19 am
You should see if you can borrow a TPG.

Lapping removes so little, you probably couldn't measure it.

Steve
You can measure it (or at least detect it) by bluing up a known good taper. You can't use a split collet for this, obviously, but if you have a known good socket you can make a gage to fit it and then use the gage to measure and also to lap your new socket. Note that concentircity is more important than angle. I was able to make an adapter to adapt my 3PN collets to my 5C spin indexer without worsening the runout by more than .0002" (that's as close as I can reliably measure).

Re: lapping internal taper?

Posted: Thu Sep 27, 2018 11:28 am
by SteveM
John Hasler wrote:
Thu Sep 27, 2018 10:50 am
You can measure it (or at least detect it) by bluing up a known good taper.
Yes, detect would be the proper term for that.

If what you are looking at is 5C, you can probably pick up a 5C arbor, or some other 5C tooling where it is not a collapsing unit, and use that as a gauge.

It's not a true gauge, but it may be suitable and better than nothing.

Something like this would work (and when you are done, you could use it for something because now youc an use 5C):
Image

If you have something else that is a socket (like a spin indexer) you could make a plug out of brass to fit the socket (see John's bluing comment) and use that as a lap.

I assume this is a spindle adapter and the same goes for the outside taper - blue to check your outside taper. Turn or grind the outside taper between centers so that you can remove / replace as you check the fit in your spindle.

Steve

Re: lapping internal taper?

Posted: Thu Sep 27, 2018 2:47 pm
by TRX
Well, how important is the ground finish, then? How about honing? Could I just make a few strokes with a ball hone and call it good? Or will any finish do as long as it's not too rough?

Re: lapping internal taper?

Posted: Thu Sep 27, 2018 2:56 pm
by John Hasler
I think a ball hone would tend to make a taper bellmouthed.

Re: lapping internal taper?

Posted: Thu Sep 27, 2018 3:58 pm
by SteveM
A ball hone will just put a cross-hatched pattern on a surface without materially affecting the existing dimensions.

Steve

Re: lapping internal taper?

Posted: Fri Sep 28, 2018 7:01 am
by TRX
Well, does the finish of the internal taper even matter, as long as the collet isn't grunchy when you pull it in?

Re: lapping internal taper?

Posted: Fri Sep 28, 2018 11:10 am
by John Hasler
TRX wrote:
Fri Sep 28, 2018 7:01 am
Well, does the finish of the internal taper even matter, as long as the collet isn't grunchy when you pull it in?
Good question. Spindle manufacturers seem to claim taper surface roughness of Ra < 0.001 mm (.00004").

Re: lapping internal taper?

Posted: Fri Sep 28, 2018 11:28 am
by SteveM
John Hasler wrote:
Fri Sep 28, 2018 11:10 am
Good question. Spindle manufacturers seem to claim taper surface roughness of Ra < 0.001 mm (.00004").
Probably to avoid causing wear to the collet taper.

A nice finish certainly won't hurt.

Steve

Re: lapping internal taper?

Posted: Fri Sep 28, 2018 12:47 pm
by ctwo
I have clamped my Dremel to my tool post for a few grinding sessions. I ground my chuck jaws that way, and I perceived it worked just fine. I think Shadon HKW (BarZ guy) used an air die grinder in place to bring his R8 mill spindle back into spec.