MF70-CNC

Proxxon MF70 mill CNC conversion

This project is for my conversion of a Proxxon MF70 mill to CNC. The contents will be mostly config files, scripts, improvement designs, as well as a list of various information I found useful.

This is mostly for my own use, but I hope somebody else will wander into it and save some time.

Why

It's small and cheap, that's really about it. Before spending the time, effort and money on a larger, much heavier and expensive machine, I decided to start small and see whether I like this stuff at all. So far I do.

It has to be said that the mill is tiny and extremely limited in what it can do. But it can be made work.

Conversion process

The mill was converted using the 3D printed parts from the "Bubblegum CNC" project, and can be found at https://www.thingiverse.com/thing:33799

There are assembly videos at https://www.youtube.com/watch?v=zhckeUoXwuc&list=PLYxf6JVpXtyO_PyjGGxkbttEl6JiWM5uO

I found both to work fine without much of an issue.

I didn't particularly like the idea of gluing endstops to the plastic -- seems flimsy, but it does work.

The plastic parts proved sturdy enough to resist the mill trying to exceed the travel limits -- which is good, but probably not a great thing for the Delrin nuts the machine uses.

Things I learned

1. CNC coordinates are different from 3D printer coordinates. 3D printers always use positive X, Y and Z coordinates. CNC machines have a 0,0,0 in the center of the table, and positive at one end, and negative at the other. https://www.autodesk.com/products/fusion-360/blog/cnc-coordinate-system-made-easy/
2. You must have endstops on both sides -- so six of them.
3. Make sure the end stops and the movement directions are correctly wired and set -- if during homing towards +X, the motor runs backwards and hits the -X endstop, it will keep trying instead of stopping.
4. For safety, the endstops should be of the normally closed type -- but a common arduino CNC board has revisions that don't support this
5. While 3D printers have long been self-contained machines with a microcontroller that does all the work, it's still common to have a PC make the actual decisions about moving the motors. The microcontroller based solutions like GRBL and Smoothie are less developed.
6. Linux software for microcontroller based CNC is sub-par, and needs improvement. I'm currently trying bCNC.
7. When homing, move the Z axis upwards first, to make sure it doesn't crash into anything
8. Milling is a good deal more work than 3D printing.

Smoothieware

I mostly went with Smoothieware because it runs on a higher end board -- making more room for CNC functionality, which is more complex than a 3D printer. Unfortunately it's not as well supported as the Arduino based GRBL.

TODO

1. Rewrite the machine to use NC switches. Currently using NO mostly due to a previous conversion attempt.
2. Fix bCNC to work properly with Smoothieware.
3. Figure out manual tool changes.
4. Try to extend the Y axis by milling replacement parts: https://0xfred.wordpress.com/2012/04/17/extending-the-mf70s-y-axis/
5. Buy a bigger machine.