Suggestions on Y axis counter weight

[MH1]

First here is my machine so far:


table is 10 foot by 5 1/2 foot. I tired searching for something similar, however most are short travel on a z axis. I see people have used gas shocks, air shocks, even a bag of rocks hanging from the ceiling. All of which I have far too much travel for my 5ish foot y axis. Only thing I was kinda looking into is a constant force spring, which the only one I could find that had one big enough and strong enough (at least i assume haven't actually weighted the trolley with a router and motor on it yet) is only good for 4000 cycles, which will wear out really quick. When i was sitting in my garage yesterday, I looked at the garage door springs and thought hmm... but didn't look into if that was actually My other option is probably rethink my table and possibly make it roll out flat and then make it roll up when not in use (still want to keep as much floor space in the garage as possible) but I kind of like the idea of it staying the way it is. so I wanted to see if anyone had any other suggestions before I start rethinking it.

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[wizard]

The first thing that came to mind is load balancers used with heavy tools. Generally these are devices seen on production lines so should be rather rugged. I'm not sure though that they can respond well to a fast moving CNC axis.

The second thing is to use a pneumatic balance. The long stroke on your Y implies a long cylinder but you may be able to address that with pulleys and a belt. Set up right a pneumatic system can prevent a rapid fall if power is cut to the machine. This does imply an air compressor set up to supply make up air and a few other pneumatic components. With the right engineering I've sen such counter balances run for decades.

Another possibility is simply a large servo with a brake. You still have gravities impact but the brake would add safety. Your CNC controller though needs to implement such functionality which is an issue with low end solutions.

[Jim Dawson]

........

The second thing is to use a pneumatic balance. The long stroke on your Y implies a long cylinder but you may be able to address that with pulleys and a belt. Set up right a pneumatic system can prevent a rapid fall if power is cut to the machine. This does imply an air compressor set up to supply make up air and a few other pneumatic components. With the right engineering I've sen such counter balances run for decades.

I agree with wizard, pneumatic spring, I have been using one on my mill for years. With proper ''gearing'' the cylinder extended length need not be longer than the Y axis length.

[Goemon]

For my education, why do you need a counter-weight for the Y-axis? I thought they were only used on the Z-axis to take some of the spindle weight off the ball nut. I bought a gas spring from LMS for this purpose but I never considered looking for anything like that for the X and Y.

Is it a backlash reducing measure?

[Jim Dawson]

For my education, why do you need a counter-weight for the Y-axis? I thought they were only used on the Z-axis to take some of the spindle weight off the ball nut. I bought a gas spring from LMS for this purpose but I never considered looking for anything like that for the X and Y.

Is it a backlash reducing measure?

The Y axis in this case is the vertical axis, see the picture in post #1

[Goemon]

The Y axis in this case is the vertical axis, see the picture in post #1

Oh, I thought it was just resting on it's side while you were working on it.

I guess building it that way allows a large work envelope without taking up a lot of floor space. It's probably better for chip clearance too. someone needs to figure out how to mount one on the ceiling.

[Jim Dawson]

Oh, I thought it was just resting on it's side while you were working on it.

I guess building it that way allows a large work envelope without taking up a lot of floor space. It's probably better for chip clearance too. someone needs to figure out how to mount one on the ceiling.

That was my first thought also, until I saw It was bolted to the wall and noticed it has a support rail on the bottom.

[Goemon]

That was my first thought also, until I saw It was bolted to the wall and noticed it has a support rail on the bottom.

Good eye. I didn't catch that.

I like the "out the box" ideas like that. If you think about it, traditional CNC table designs are a horribly inefficient use of space if the machine could have gone on the wall.

If I ever needed to build a large work envelope machine, I'd convert the walk-in store room in my basement and mount rails to the walls (on steel plates). When not in use, the gantry could go against the back wall so a 5' x 10' machine with a 5' Z axis would take little to no floor space.

On the counter weight thing, I have seen large VMCs with a 48" Z axis. What do they use as a counter weight? Some of them look like they use hydrolic or pneumatic cylinders and both are available in large sizes.

[Jim Dawson]

On the counter weight thing, I have seen large VMCs with a 48" Z axis. What do they use as a counter weight? Some of them look like they use hydrolic or pneumatic cylinders and both are available in large sizes.

Some just use a counterweight hung on a cable, the down side of this is that it adds mass to the system. I have always liked pneumatic springs, constant pressure over the entire travel and low mass.

[Goemon]

Some just use a counterweight hung on a cable, the down side of this is that it adds mass to the system. I have always liked pneumatic springs, constant pressure over the entire travel and low mass.

You could achieve constant pressure with a counterweight too.

I wonder how necessary a counter weight is on a CNC router like that with a large heavy steel frame and a fairly lightweight spindle. I can see the need on large bed mills where the spindle traveling up the Z axis is heavy enough to tip the machine over and / or drastically shorten the life of the ball screw and rails. What value would it add here?

I bought a gas sping for my Z axis because I bought a 35-40lb spindle with a 12" x 12" x 1" cast iron surface plate for the spindle mount and I was originally planning to use acme lead screws with nuts that had a 25lb limit. I have since upgraded to large ball screws so I am not sure if I will bother to install the spring.