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Mf 70 Proxxon Mill Spindle Mod to take ER11 Collets from 1mm to 7mm

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I’ve been looking for a solution to the Proxxon 3.2mm max shank size limitation for some time as there are very few standard profiles available in this size and I didn’t want to try and turn down shanks given the hardened metal alloys they are manufactured from.


I recently came across a replacement Spindle kit manufactured by a German Firm Usovo which will accept ER 11 collets – 1mm to 7mm - have purchased and installed the new Spindle and very happy so far.


The install is very straightforward but I had one gotcha involving the removal of the original Proxxon drive collar. The collar is retained by a 3mm Phillips Head which rounded first try and had to be drilled out.

This isn’t really a problem as the intention is for the original spindle to be discarded but I used an 2mm easy out to remove the remaining part of the screw after I removed the original spindle so as to retain it as a spare.

When fitting the new spindle, I used a new 3mm Hex socket head machine screw to replace the OEM Phillips Head - just a heads up as it isn’t part of the kit. The offending screw is shown in the instruction sheet photo step 5.

Photo 1 - Instruction sheet – see step 5 and 10 for a better view of the retaining screw and drive grommet.

Photo 2 - shows the original Proxxon Spindle, bearings and the Drive collar. I was pretty disappointed to note the pitting and rough machining of the original spindle in what is a new and not inexpensive machine, especially when compared with the kit spindle machining shown in photo 3. 

Photo 3 - Kit contents – note the lower ball race is already pressed in place on the new spindle. Also note the instructions don’t mention the obvious ie that the old bearings have to be removed.

Photo 4 - shows the Hex Head Machine screws used to retain the motor so why didn’t they use one for the drive collar retainer instead of a Phillips head??

Photo 5 – Comparison of Collet holders and old bits removed. The black plastic drive collar is shown but there is a more flexible grommet not shown which press fits over the top of the drive collar

Photo 6 - New spindle installed with collet holder and a 5mm collet. The first run was noticeably quieter with no discernible runout. Very happy so far.

Photo 7 – Range of ER 11 collets 1mm – 7mm. Bought these on line for just under $40 and despite the homey labels they were nicely machined and supplied in individual oil filled plastic bags. Comparison of the 3mm Proxxon to the 3mm ER11 collet.

When using the larger mill bits, one has to have regard to the limited torque available and take shallower cuts but to me this is a easy limitation to accept for the far greater Type and range of standard milling bits available to the ER11 collets than the 3.2mm Proxxon max.

The link to the spindle kit is https://www.usovo.de/en/c/cnc-technology/proxxon-mf70-accessories they were great to deal with and while not cheap at 99 euro for me it offered value for money. There are two versions available for mill serial numbers above or below serial 22852.

They also offer a beautiful planetary reduction gearbox for the earlier serials to give more torque for the larger mill bits – would love one for mine, a later serial, but not in the works at the moment unfortunately.

I have no financial nor any interest in the firm just posted as a heads up for many of us that have the machine. Hope this is of use to others. Cheers Pete.

01 Spindle Replacement Instructions r.jpg

02 Original Spindle and bits r.jpg

03 Replacement Spindle Kit contents r.jpg

04 Removing the motor r.jpg

05 Both Collet nuts r.jpg

06 New Spindle with 5mm Collett fitted r.jpg

07 ER11 Collets r.jpg

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  • 2 weeks later...
On 10/16/2022 at 7:55 AM, PeteB said:

Range of ER 11 collets 1mm – 7mm. Bought these on line for just under $40 and despite the homey labels they were nicely machined and supplied in individual oil filled plastic bags.

Hello Pete


I have bought a number of these cheap sets but have never found them to be too accurately made. Where did you get yours from?



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Hi Keith - mate I bought them off evilbay just to see what they were like, at $35au they aren't .005 tolerance but for my purposes that isn't needed. As mentioned I used the Mark 2 eyeball and not a dial gauge to measure runout but to the eye and a trial step cut with the 3mm, 5mm and 7mm into Swiss Pear it looked ok to me. There were quite a few stating they were within a .005mm tolerance for not a lot more. Cheers Pete




Edited by PeteB
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The original bearings are pressed in and there is a sleeve in between them so I have no idea how to get purchase to pull them out. How did you remove them?



Figured it out. You start by removing the topmost bearing; place a bit of something on the table then lay a long bolt or rod slightly diagonally so it goes through the bottom bearing and notches below the topmost bearing. Then you lower the mill with the screw on top until you start moving the bearing a bit. Raise the mill head, reposition the long bolt or rod opposite to where you last were and do the same thing and repeat that until the top bearing pops out. 

Now you can remove the sleeve and then you're left only with the lower bearing and that's the complicated one to remove.


I placed a plastic tube that is larger than the bearing right under the head then a metal bar across that tube and in that metal bar there's a hole. You just slide a washer in a bolt, place the bolt down from the top so that the washer lays on top of the bottom bearing and the bolt passes through the metal bar's hole which is against the tube underneath the head and then you just place a big washer and some nuts on that bolt and tighten. You will be squeezing the metal bar against the tube which is pushing on the bottom of the mill head while the bolt you're tightening is pulling the bearing down. Tighten until the bottom bearing pops out.

If all that text is a bit unclear, look up videos on homemade bearing puller for bicycle. It's more or less the same principle.

Edited by Borrokalari
Found out how
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On 10/16/2022 at 2:55 AM, PeteB said:

there are very few standard profiles available in this size

Is this still a problem?   I see a lot of 1/8 shank milling tools out there.  Are they not considered standard?

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Thank you for sharing it with that level of details!

Just curious - what kind of larger cutters do you find useful at this scale? Any tips and experience to share?

That mill has a pretty limited capacity.. 😊

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