Centroid Community CNC Support Forum

Hi All:
I have the precision Matthews 728 converted to CNC with Acorn 4 with Clearpath Servo's. I have fitted the machine
with a dual chain lift counter weight system. My question is, the weight of the counter weight. If the weight is equal
to the head weight, can the inertia unbalance the servo loop and cause the system to be unstable. My gut tells me it should
be somewhat "less" than the the head weight so the over shoot is all ways on the head side of the load. Any one have any
experience with this?

Thanks

RonL

Go for "neutral buoyancy" then tune the servos to deal with the mass

i always like a little downforce to control backlash and make it easier for the axis drive to control.

on my PM-30 build with upgraded motor and power drawbar, I just chose a capable servo for Z axis, and just dont use a counterweight or air strut. Head weight helps with backlash as mentioned above. Teknic SDHP servo is more than capable of 400in/min with no counterweight. Just get an inline brake so when powered off, the head doesnt drop.

Thanks all!

cool counter weight design is here.
https://centroidcncforum.com/viewtopic.php?f=57&t=3376

Here is a low-cost alternative. I used two gas struts on either side of the column from McMaster Carr. They range from 100 to 140 lbs over their range of motion. The head etc. is about 325 lbs. I used double ball nuts and have less than .001 backlash. Most important, my 1700 oz. closed loops stepper moves the Z-axis with easy and no brake is needed.

Thanks... Richard

I actually prefer an air cylinder over gas struts. The force is adjustable and more importantly, constant, over the entire range of motion.

tblough wrote: ↑Mon Oct 03, 2022 8:04 pm I actually prefer an air cylinder over gas struts. The force is adjustable and more importantly, constant, over the entire range of motion.

I agree with this. My last router, a Biesse Rover, had two air cylinders to counter balance the very heavy Z axis. It had a regulator with a relief valve right next to the axis and you could easily dial in the exact pressure needed to counter balance the head. Much more accurate than gas struts but I guess anything would be better than nothing.

On this size mill, I had only gas struts with the Acme screw, after change to ball screw I removed the struts and used a bigger CL stepper.

IMHO there is no need for support if there is no backlash and the drive is overpowered.

Uwe