[sperman]

A conversation in another thread made me decide to checkout how well the TTS collet fits into the spindle. I've seen this mentioned on the forum before, and since I've had tools pull out from time to time, I decided to see if this was part of the problem.

First I took an R8 collet from work (only marking is Taiwan) and checked the engagement on a bridgeport clone we have. It's hard to see much of a pattern, because it appears to contact evenly all the way around the collet. (Hopefully these pictures aren't too bad. The flash created some glare.)





Then I put the Tormach collet in the machine at work. Most of the contact appears to be at the splits in the collet, and at the bottom of the collet





I then took both collets home and did the same procedure on my 1100.

The Taiwan collet showed contact in larger areas, but still in only 1 spot on each of the three fingers.





Finally is the Tormach Collet in the 1100.





I'm tempted to try and remove the pin from the spindle, and lapp the collet into the spindle. The only other way I can think of is to stone the high spots away until it makes more even contact all the way around. That sounds like a lot of work, and would be easy to make things worse instead of better.

[SCzEngrgGroup]

There's a thread on the Novakon forum from 6-9 months ago, pretty sure it was posted by "Hirudin". He spent quite a bit of time looking into the collet/spindle taper fit, and the fit of the TTS holders on his Novakon machine. He then spent more time actually hand-sanding all the bits to get MUCH better contact patterns, and also to reduce tool runout. You should take a look at what he did. It didn't look to be a fundamentally difficult undertaking, and I certainly would not think doing it just to improve the collet fit would be a very big deal. Nice thing is, the collet only really fits in the spindle one way (well, two ways if you have one of the newer Tormach collets, with two alignment grooves).

That said, I'd be surprised if improving the contact pattern made very much difference in tool retention. I still believe that boils down more to lack of adequate drawbar tension that anything else. I've used a number of different collet, both Tormach and Brand X, and never once experienced pull-out, even when making cuts that I've been told by Tormach users are beyond the capabilities of the Tormach machines. But it would be interesting to clean up the contact pattern and see if it helps or not.

Are you also going to check the contact pattern between the toolholder shank and the collet? It would be nice to see a before and after of that as well, to see if improving the collet-to-spindle fit gets you better toolholder-to-collet fit. I tend to think it won't - the collets are not very flexible in the are of the taper.

Regards,
Ray L.

[mike sr1]

Scott,
Your collet to spindle fit appears better than mine, the wear on mine is the bottom 1/8" of the collet. I read a couple threads on another forum and their fix was to have the spindle taper ground to correct the problem. This thread was a couple years ago and the cost was around 100 dollars if you take the spindle to the shop.
I dont have enough problems with it to justify the machine being down for a period of time. Not that I run production on it but it is my main playtoy and I just dont want to do without it for a period of time when it isnt any worse than it is.
I checked my Bridgeport spindle on collets that I use often and it has a nice even wear pattern top to bottom. I have had pullout with this machine too, running a 3/4" cutter hogging 304 stainless.
I am sure that a proper fit would sure help though, and lapping the collet would be one solution, but when another collet is needed the problem would still be there.
From reading those threads, I know at least what the problem is, getting "roundtuit" is another thing ha!