Milling tool removal: advice required

[Rob Meades]

I have a small (High-Z/S-400T CNC (https://www.cncstepusa.com/high-z-standard)) milling machine with a Suhner (UAD 30 RF (https://www.cncstepusa.com/cnc-router-spindle-suhner)) milling motor (picture attached). The motor has a 17 mm-threaded collet chuck with collet nut and the selection of collets that came with the motor (picture of the nut and a few of the collets attached); the machine is used only occasionally, probably less than once a year, but part of the reason for this is that it is difficult to use and I'm looking for advice on either (a) what I'm doing wrong or (b) what to change to fix it.

The issue is that the milling tools are an utter pain to remove. The collets aren't held very well in the collet nut: there is _some_ snap-in, but not a lot (the collet is easily removed from the nut again by hand), and the collets never come out with the collet nut when it is released, I end up spending some considerable time with a mole grips on the shaft of the milling tool and a large flat screwdriver between the shaft and the extraction groove of the collet persuading them both to come out. The shafts of the milling tools fit nicely into, e.g., the 6 mm collet before the nut/collet/tool assembly is screwed onto the machine, they just never want to leave.

The whole lot was purchased together (7 years ago) so there shouldn't be any compatibility issues.

What might I do to ease the situation, including dumping the Suhner motor for something else if that is a sensible option? Might the collet nut be damaged somehow? Could I be fitting things wrongly?

[Muzzer]

I would consider buying a replacement collet nut, possibly from a different source, although this may be tricky, as they have omitted to specify the collet system they are using. As you suggest, they are supposed to extract the collet, since taper seats with such a narrow taper angle are not inherently self-releasing.

I take it you have oiled the chuck before tightening and the collets are clean and unblemished? Do you leave the cutter in place when trying to release the collet -- this might prevent the collet from contracting and give you just enough engagement with the nut to make a difference.

I notice the instructions don't address removal of the collet. Your problems may be simply the result of poor design and/or quality control (it's probably made in China anyway) - German and Swiss manufacturers love to trade on their supposedly superior engineering when reality often results in a different experience. Speaking as the owner of a 4 wheeled money pit.

[Rob Meades]

Thanks for the response!


I would consider buying a replacement collet nut...

Yes, that was my feeling also, I've just sent the UK agent where I bought the machine (prototools.co.uk) a message asking if they can supply one. It seems an incredibly simple tool retention system, little that can go wrong in what is, after all, just a nut/taper. And you're right that the manual only shows tool insertion, not tool removal, which I always thought was a bit bizarre.

I have not tried oiling the chuck, will do that, but I have tried the procedure with a collet from the supplied set that I happen not to have used, fresh from the sealed baggie, and the situation is the same, so the problem does not appear to be collet damage.


Do you leave the cutter in place when trying to release the collet -- this might prevent the collet from contracting and give you just enough engagement with the nut to make a difference.

In order to have any chance of releasing a collet I have to pull the milling tool free with a mole grips, which is already hard enough.

I will report back here with how I fare in fixing this.

[Rob Meades]

Instant reply from Prototools; you were right: turns out that the collets did indeed change to being of Chinese supply which, over time, drifted away to a different fit to the original Suhner nut. Me having bought my first milling machine in 2016 didn't know it was all meant to be a lot easier to use, didn't know to raise the alarm :-).

Prototools now only supply collets with nuts to avoid any possible confusion. They are going to send me a Chinese nut FoC.