The Millathe: A CNC story

So a long while back I managed to acquire an Emco maximat 7 machining center. It has been my goal to make it a CNC machine, however it has been sadly sitting in my living room waiting for me to finish busscooter, but now that that is done (besides a few safety features which need to be added). I've turned my sites to making this CNC dream a reality and things are finally starting to happen.

So hear's the deal: this machining center, or the millathe as it is has been nicknamed, is like 75% lathe 25% mill and 100% heavy, seriously the millathe isn't that big but weighs well over 100lbs.  Unfortunately I don't have pictures right now and am other wise not at home so those will get posted later. It also happens to be Austrian and metric which is wonderful because if you know me I tend to shun 'standard' units (really? Who calls 'units standard' when only a small fraction of the planet uses them?). The lathe portion of the millathe seems fully operable except for the lead screw; which is linked through a mess of gearing to what appears to be a cracked plastic press fit gear, so  cant be turned automatically by the spindle motor. The lead screw does have a knob so you can turn it by hand, but this project is about avoiding that. Unfortunately most of the gears in the lathe system seem to be of phenolic materials but they're functional for now, perhaps some time in the future I will rebuild the power part of the spindle drive but that's another project and another thing to add to the list of fixes.

Currently the plan is to make lathe portion CNC before turning to what ever may be wrong with the mill section of the machine. The list of key action items for modifying the millathe in no particular order  looks like this:

•  Replace lead screws (I might not replace them but they look a bit wonky).
• Add Backlash compensation, because no one loves backlash in automated systems.
• Acquire steppers for driving the Z and R axis screws giving control of the lathe port.
• Create method of supplying power to said steppers in order to control the system.
• Create control system for the steppers.

At the moment I've started looking at the control side of things.  The plan is to stream through USB to an arduino nano which can act as a buffer and send the signal out separately to each stepper driver synchronously. I plan on using the Allegro A4989 stepper motor driver to control all of these shenanigans. It will require that each motor needs 2 outputs from the arduino, one for step and, one for direction.

 The outputs from the A4989 generally go straight to the gates of transistors but, it's tempting to instead direct them to some gate drives to allow them to drive larger fets for larger stepper motors. I haven't really done any calculations to justify this but it seems like it would be nice thing to have a one size fits all solution to driving steppers even if it is over kill. A pair of LM5109A gate drivers per stepper driver seem perfect for this task since they have inputs that can be driven separately allowing for whatever sort of control method the stepper controller feels like. 

However last night I began to experiment with methods of sending arduino data over usb and had moderate success in getting LED's to count synchronously according to their appropriate digital out ports rather than by using the normal digitalWrite commands. This was kind of  interesting since apparently pyserial only sends data as strings and chars. Which to me this seems weird and inefficient but I'm not that experienced with data streaming techniques. Hopefully it will be able to send data at a pace appreciable enough to make it work other wise. I'll talk more about messing around with this in the next post.

I don't have any pictures of the millathe to post at the moment but I always feel bad not posting a picture so here have a repost of the  tool post holder I made for the millathe a while back. It is currently mounted on the millathe and works just dandily. yaaay reposts.