Install ball screw into PROXXON MF70?

General CNC CNC Routers
1

Hello dear forum,

I’ve read the

post from 2020 dealing with MF70 modification, and one user noted that the conversion to a ball screw is recommended to mitigate backlash.

switching your axes from trapezoidal lead screw to ball screws

Sadly, there are no instructions to do so in the internet, or at least I cannot find them.
Is it a complicated process that involves machining own parts? Or is there an assembled package not specifically for MF70 that can be installed into the MF70?

Thank you for any answer

2

That was me. I don’t have PROXXON experience, just milling experience.

Have you measured your backlash?

3

Sadly, I don’t know how to properly do that.

4

I don’t know where you are in your journey of learning machining, nor do I know where you are in your journey of buying tooling to use with the machine tools. It’s proverbial that the machines seem expensive until you start buying all the associated tools for using the machines.

You can measure backlash by putting an indicator on the table and pushing it back and forth and measuring how far the table actually travels, and doing this on each axis. Alternatively, you can estimate it by looking at the wheel index and seeing how far it turns sloppily without moving the table (such as with the table locked, if the PROXXON has locks.

I’ll note that the CNC conversion package linked to from that post in 2020 doesn’t change from trapezoidal lead screws to ball screws. It may be that many folks doing this are not making that change.

If you use lead screws for a CNC conversion, some software has backlash compensation. For example, in LinuxCNC, each JOINT has a BACKLASH setting which will cause it to rapidly turn the leadscrew through the “deadband” where it changes which side of the lead screw engages the lead nut.

You’ll also be limited in some of what you can do in ways that might not matter to you. For instance, you will be limited in where you can apply climb milling. You may find that you need to mostly stick with conventional milling with trapezoidal lead screws. It’s the use of ball screws in CNC machines that has enabled widespread use of climb milling.

You might also find that you have some surface artifacts near corners from the time it takes to do backlash compensation.

What kind of work do you plan to do with this machine, and what is driving your decision or consideration to modify it from manual to CNC?

5

Hi,

I’m the starter of the topic you refer to.
At the time I was looking for a CNC controller or information concerning a conversion to CNC. Shortly after my last posting I found a ready build CNC controller, including stepper motors for my Proxxon MF70. (see: http://www.kofex.net/ )
I too searched for some time for ball screws for my machine, but I couldn’ t find a ready made kit either, so I use the original lead screws.
I’m using the machine for more than two years now and it serves me well. I’m a railroad and wood modeler and I use the machine mainly for milling wood and XPS in 1:160 scale. I don’t experience any form of backlash. Still I can make very small cuttings with a precision of < 0,1mm.

Should you want to use your MF70 for milling non-ferro material ore steel, you should look for a more robust machine.

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