Hello my name is Kent. This video demonstrates the Precision Matthews PM-25MV
milling machine and the excellent CNC conversion kit from David
Clements of ArizonaVideo99. A link to David's channel is in the video
description. I've been using the converted mill for making parts for my
business. If you'd like to see more examples, check out other content on my
channel. I upload videos about my milling successes and failures regularly.
Subscribe if you like to follow along. This Precision Matthews mill is from
August 2014 and I received the CNC conversion kit from David during
January of 2016. The installation of the kit only required a
weekend. It simply bolted on without any modifications. The finish on the
conversion kit is quite high.
All the parts of the mill that needed to be removed are light and I could lift
them solo. Electronics, LinuxCNC, and other general fiddling have taken a lot longer.
The stepper motors I'm using are Leadshine ES-M32320 with ES-D508 drivers on
all three axes. The motors are NEMA 23 closed-loop stepper motors from Leadshine's
Easy Servo line. With 283 ounce-inches of holding torque, these are
smaller than what others are using on similar CNC conversions.
However, I've not had a problem other than when I had over tighten the angular
contact bearings on one axis.
I have roughly 0.001 of backlash, but with LinuxCNC compensation, backlash is practically
non-existent. This amount of backlash is better than my skill level. Also when
taking large cuts the column headings assembly seems to flex more than this.
And as one learns their machine, workaround are found for machine related errors.
To demonstrate that the small motors work fine, we can examine the following
error from the z-axis motor, which should be the hardest-working axis. I've written
software for doing this on Linux but similar software is available from
Leadshine for Windows. Also, monitoring the current delivered to the stepper drivers
show they are not close to the current rating. The combined need for all three
axes generally remains below 100 watts at 48 volts. In these graphs the x-axis is
time and the y-axis is the following-error or the difference between commanded
location and actual location. The error is measured in steps and there are 4000
steps per revolution and each revolution is five millimeters to travel. If the
system was otherwise perfect, each step would be an absurd 49 millionths of inch.
Clearly the following-error is very low.
The following-error also quickly stabilizes near zero once an axis
stops moving. If the following-error grows too large or cannot be recovered,
the axis stops and is treated by LinuxCNC as an e-stop.
This is a warm-up routine that I run before milling part. It simply exercises
the axes.
We'll run the program at various feed rates.
Feed-rates in excess of what is reasonable are also possible. I believe even higher
feed-rates are possible if the acceleration was reduced. While higher
velocities may be possible there may be no point. Most of the mill's time is
spent at much lower velocities. The higher velocities create a lot of
momentum that has to be bled off by the motors.
I hope this video is helpful to
those planning their own CNC conversions or considering the
Precision Matthews PM-MV25 milling machine, and
David's CNC conversion kit. While I have no hesitation recommending the mill or
the CNC conversion kit, I'm not necessarily recommending that everyone
use the smaller motors. More experience with them would first be necessary. After all,
larger generic motors are similarly price. However, there are advantages of
closed-loop motors worth considering.
Thank you for watching and I hope you'll be back for the next video.