lapping internal taper?

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John Hasler
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Re: lapping internal taper?

Post by John Hasler » Fri Sep 28, 2018 1:29 pm

Yes but how good a finish is actually necessary? .8 micron seems to be common, which surprised me. I expected a much smaller number.

Another question never addressed anywhere except in one research paper I don't have at hand is the lay of the finish. It should be parallel to the axis but you can't get that with an ID grinder.

TRX
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Post by TRX » Fri Oct 05, 2018 7:55 am

I was looking at the lapping section in my 1940s Audel's machinists manual and found a comment that taper laps were sometimes made, but they recommended against their use. They didn't say why, though.

I also found a comment from someone who had a tailstock with a badly damaged socket. He cut the tang off an old drill, glued very fine sandpaper to it, and used that to remove enough of the bumps and scars to get it to hold a drill. One could do something similar to get a specific surface finish.

[yeah, not collets, but it's still "finish of internal tapers"...]

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GlennW
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Re: lapping internal taper?

Post by GlennW » Fri Oct 05, 2018 8:48 am

TRX wrote:
Fri Oct 05, 2018 7:55 am
I was looking at the lapping section in my 1940s Audel's machinists manual and found a comment that taper laps were sometimes made, but they recommended against their use. They didn't say why, though.
Tapered lapping isn't too good because the lap will wear with a pattern in it that matches the surface being lapped.

You need to be able to move the lap axially while it is rotating in order to even out the wear pattern.

Same with honing to achieve a straight bore or the honing stones will wear to match the surface being honed.
Glenn

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John Hasler
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Re: lapping internal taper?

Post by John Hasler » Fri Oct 05, 2018 10:10 am

I've done limited lapping of Morse sockets with sandpaper glued to a presumed-good taper. I did not do the obvious thing and trim paper to completely cover the tool: that would remove more material at the large end. Instead I left a triangular gap with an angle matching the taper. I stopped frequently to replace the paper, clean out the socket, blue it up, and test it with my "gage".

As a next step I located high spots with my gage and then tried to work them down by taping a patch of sandpaper to the tool at the spot matching the high spot (with upside-down paper taped elsewere on the tool to keep it centered) and then "lapping" just that spot. It worked, but it was very slow. It also risked introducing runout.

As for finish, I use fine sandpaper manually to try to give sockets and tapers an axial scratch pattern because there are plausible arguments to the effect that friction is lower parallel to the scratches than perpendicular to them. I havene't found much on how fine those scratches should be, though.

TRX
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Post by TRX » Fri Oct 05, 2018 10:57 pm

John Hasler wrote:
Fri Oct 05, 2018 10:10 am
It worked, but it was very slow. It also risked introducing runout.
I'd think you'd have to work pretty hard to get any detectable runout. My concern would be introducing low (high?) spots that would reduce the grip on the tool.

On the other hand, if your socket is buggered and the proper MT taper reamer isn't in the cards, you do what you have to do.

John Hasler
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Re: lapping internal taper?

Post by John Hasler » Sat Oct 06, 2018 8:05 am

My goal was to *remove* high spots. That's why I checked frequently with the gage. With drawbar-type MT collets in a mill spindle you don't want grip (rotation will just tighten the drawbar). You want concentricity and straightness and you want the taper to pull into the socket with minimum friction to maximize collet clamping force. I lubricate collets with antiseize.

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Richard_W
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Re: lapping internal taper?

Post by Richard_W » Sat Oct 06, 2018 2:09 pm

I would cut the bore with a cermet insert at a high RPM. It will give a nice finish. I made an adapter for a cylindrical grinder that had an ID attachment built on the back. They wanted me to make it for a 1/4" shank. I had suggested making something with that had the male taper for the grinding spindle on one end, but instead of a 1/4" bore on the other. Make it to hold a 32ER collet. In that way if they needed another size they could just get the correct size ER collet for their need in the future. They consulted the manufacturing engineer and with his blessing I made one. They needed it in a hurry and later that day they had it in their hand. All tapers fit perfect with no lapping. Although I did have the mating taper to set the lathe compound to. When checked on the ID spindle it was with in a .0001 run out. All done on the lathe with no grinding or lapping. Material used was 4140 HT off the shelf and a spare ER32 collet nut.

TRX
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Post by TRX » Sun Oct 28, 2018 5:05 am

I found this company: https://triaticinc.com/tapered-diamond-hones/

They look like steel spindles impregnated with diamonds. I'd call them laps, they call them hones.

There's also a company that makes a "taper honing machine". Their web site is the usual Flash and Java infected mess, but best as I can gather they reciprocate a straight hone in at an angle. Looks reasonable, but much more trouble than I'm prepared to expend.

I'm now wondering if honing would be useful for cleaning up an internal taper. The tailstock socket in my old lathe probably beyond what lapping could fix, but one that's less buggered might be fixable by lapping.

John Hasler
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Re: lapping internal taper?

Post by John Hasler » Sun Oct 28, 2018 7:46 am

TRX writes:
There's also a company that makes a "taper honing machine". Their web site is the usual Flash and Java infected mess,
but best as I can gather they reciprocate a straight hone in at an angle. Looks reasonable, but much more trouble than
I'm prepared to expend.

I'm certainly not prepared to buy a machine but the technology sounds interesting: IMHO that's the right way to finish a taper. Do you have a link?

BTW the NoScript Firefox plugin deals quite well with the Flash and Javascript garbage (though I deal with Flash by simply not having it installed at all).

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