Z Axis Counter weight. How much weight??

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rlaury
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Z Axis Counter weight. How much weight??

Post by rlaury »

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
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Re: Z Axis Counter weight. How much weight??

Post by Gary Campbell »

Go for "neutral buoyancy" then tune the servos to deal with the mass
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Re: Z Axis Counter weight. How much weight??

Post by cnckeith »

i always like a little downforce to control backlash and make it easier for the axis drive to control.
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Re: Z Axis Counter weight. How much weight??

Post by rk9268vc »

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.
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Re: Z Axis Counter weight. How much weight??

Post by rlaury »

Thanks all!
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Re: Z Axis Counter weight. How much weight??

Post by cnckeith »

cool counter weight design is here.
https://centroidcncforum.com/viewtopic.php?f=57&t=3376
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
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Re: Z Axis Counter weight. How much weight??

Post by RJS100 »

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
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Re: Z Axis Counter weight. How much weight??

Post by tblough »

I actually prefer an air cylinder over gas struts. The force is adjustable and more importantly, constant, over the entire range of motion.
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Re: Z Axis Counter weight. How much weight??

Post by ShawnM »

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.
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Re: Z Axis Counter weight. How much weight??

Post by suntravel »

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
Last edited by suntravel on Thu Oct 06, 2022 1:55 pm, edited 1 time in total.
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