Yes, I thought about reverse engineering the spindle motor controller and fitting it with a conector for external PWM input but my goal with this CNC conversion was to try and do the lowest cost and easiest possible conversion and document it. So at every decision point I take the simplest route that costs the least and most importantly, they anyone reading my instructions could follow. As soon as I suggest modifying a controller board, I've lost 90% of the machinists who might be following my instructions.
To that end I've 3D printed almost all the parts needed for CNC conversion. People usually use metal but the stepper motors I use only only produce less them 3 Newton meters of torque. The the maxim force the motor mounts will ever see is 3 Newton meters. I don't need cast iron for that, plastic works. My goal is to do the complete conversion including motors and a ball screw all for under $400 with an assembly time of no more then one day of work, not counting the time needed to print the parts. I looks like I'll meet these goals. I use a dial indictor to measure deflection under load of the plastic parts and there is one part on they-axis that needs to be redesigned into the more organic-looking shape with compound curves. I find this is the "secret" for making strong 3D printed parts, It is the same reason car fenders don't bend, even though that are made with thin sheet metal, It is the compound shape. Printed parts are like that, they are made of a thinn skin of solid plastic over a light foam-like core and all the strength is in the skin. Flat slabs of printed plastic are not very strong or ridgid. I does not impress me much that someone can build a CNC milling machine for $10,000 and 6 months of work. Anyone can do that. What I want is "under $400 and one day". After about three attemps I'm getting closer to that. When I get there I'll write it up on the web and publish the design files. So, back to my spindle speed controller. This device will literally replace the knob on the pot and cost about $6 to make. On Sun, Jun 13, 2021 at 11:09 PM Gregg Eshelman via Emc-users < emc-users@lists.sourceforge.net> wrote: > How old is that mill? Those Chinese mini mills and lathes have had PWM > spindle motor controllers for many years. I used to have a Grizzly mini > lathe with a low 3 digit serial number, probably from the first batch they > imported. I was at least the 3rd owner and I had to fix a lot of issues, > both original and from prior owner abuse. One fix was resoldering one end > of a big resistor on the primitive and very noisy motor controller. > You can buy a new PWM motor controller and potentiometer to upgrade. > http://benchtopmachineshop.blogspot.com/2017/01/mill-speed-controller.html > On Sunday, June 13, 2021, 2:30:15 PM MDT, Chris Albertson < > albertson.ch...@gmail.com> wrote: > I have a Harbor freight mini mill with the dumbest possible spindle > control. The mill comes from the factory with a variable resistor to > control speed. My idea was to connect a variable resistor to a $5 model > airplane servo. So the PWM output from LinuxCNC drives the servo and the > servo turns the pot which controls the spindle motor. I would never be > able to do rigid tapping with this setup. > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
