Have you any photos of the 3D printed motor mounts etc? Direct drive or belt driven? The 3Nm implies size 23 so I'll guess direct drive. John
> -----Original Message----- > From: Chris Albertson [mailto:albertson.ch...@gmail.com] > Sent: June-14-21 8:41 AM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Spindle Control > > 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 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
