ER collet bearing nut type A? plus TIR question

Hello. I am awaiting the arrival of a 2.2kw air cooled spindle. I read an interesting thread on collet nut torque here:

My aim is to mill metal (aluminium, bronze, brass plus mild steel if it is possible) with the right cutter. While the Makita trim router cutting aluminium did a fair job to tolerance of ±0.001", it has been running for as long as nine hours at a time. With small DOC and avoiding 100% cutter engagement, the cutters stay sharp and relatively cool. The Makita gets a little warm after prolonged activity, even with relatively small cuts.

First question: Is there any advantage to using an ER ball bearing collet clamping nut over a standard nut? My (possibly faulty) understanding is that the ball bearing nut cuases less friction at tightening and promotes a more secure grip by permitting higher torque values to be applied. It is said that it creates less wear on the components so collets may last longer.

Second question: I have been offered a set of ER20 collets with a claimed TIR of 5 microns. I guess that empirically speaking, a smaller TIR value is better than a larger one. Is there any disadvantage to using a higher precision ER20 collet?

Any assistance in answering these two questions would be very much appreciated.

Given the price difference I went for a low runout set

I’ve not found myself having any issues with these.

As for the nuts, be careful to get high RPM balanced nuts, the bearing nuts tend to be for low RPM heavy mills where the out of balance doesn’t matter, on a small spindle they shake quite spectacularly…

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Excellent answer! Thanks Liam. I had already earmarked the APT set as representing good value for money. I had not realised that the bearing nuts are usually for low RPM heavy mills.

Do you use a torque wrench to tighten the collet nut? I managed to obtain torque settings from REGO-FIX:

RFAG_TD_Anzugsdrehmoment_EN_0.pdf (296.4 KB)


Neither had I until I put one on and heard it spin up :frowning:

I don’t, just two large halfords spanners

Setting them up so you can squeeze the spanners together to tighten or loosen the nut means you’re not putting too much force on the spindle or the CNC.

No reason not to use a torque wrench, but remember to use the crow’s foot at a right angle or compensate for the offset in the torque


Good old Halfords. I bought several of their sets.

The image of you using the spaners is exactly how I would use them too. I had considered whether the use of torque wrench would place too much lateral load on a spindle/spindle mount.

Thank you for the cautionary note. Something I had not included in my deliberations.

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This is the torque wrench which I was considering - It will apply the required axial load on the collet nut while introducing an unwanted lateral force on the spindle and mount. Your two spanner approach appears to be utilising an improvement in mechanical sympathy to the spindle and mount, than a single lever could. Confusion reigns. :upside_down_face:


Well it looks like a very nice torque wrench, however it also looks quite single purpose, doesn’t look like you can put regular sockets or anything else on it.

I don’t see why you couldn’t use a wrench like this in place of the larger spanner in my pair, but I’ve not had any issues with bits slipping or collet coming loose tightening to ‘reasonable squeeze’ in one hand. Unless you’re really keen on tightening to book torque, I might start with a couple of spanners and see if you have a problem with the collet coming loose.

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Yes, you make a fair point.

I will just use the spanners for now and see how that goes. After buying the HDZ Z axis upgrade, the ER collets, the Edge Pro Mini Tram, a 300mm square by 10mm thick piece of float glass, the spindle, VFD and dustboot, additional V wheels and Gates belts, I am hoping to save some money. :rofl:

As expensive as this upgrade is, it is approximately one third of the money I would have spent on the Stepcraft machine I was considering. Now is the good time for the upgrade so that I can move ahead with my CNC machining objectives and a new chapter in my CNC journey.

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I think you’ll like the HDZ, when I got mine I wasn’t sure whether to install it or just put it in a nice display case :wink:


Yes, it is a nice solid piece of engineering. Almost reminiscent of the Victorian penchant for over engineering and it certainly seems very fit for purpose. I am looking forward to using it.

Great engineering engenders that feeling of wanting to display it. I can remember taking my 7 year old son along to Farnborough Air Sciences Trust museum some17 years ago. One of the exhibits was a Rolls Royce jet engine. Visitors could gently push on one area to rotate the engine. It was so well suspended and virtually frictionless, that it turned and could continue its revolutions for some time after the push from a child’s hand. That made me want to take it home and display it. It was a very impressive pinnacle of the engineer’s art.

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