What does a high end cnc machine have for a counterweight?

[slashmaster]

For my counterweight, I've got a rope going from the head, through 2 pulleys on the ceiling to a bag filled with junk.. What does a high end machine do for a counterweight? Can't really see because it's all enclosed. They would never use those gas struts that hatchbacks use would they? Also, is it best to have the counterweight exactly as heavy as the head or should the head be a little heavier so it takes up the leadscrew slop?

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[Browellr]

I don't think high end machines need counterweights, they have ballscrews with zero play, big motors, and a rigid setup that doesn't bend around.

What kind of machine is it? if there's angular play in the axis, it will move no matter how you counterweight it. If there's slop in the leadscrew, it will chatter more with a counterweight because there will be less downward force at the tool while cutting.

[atomarc]

I don't think high end machines need counterweights, they have ballscrews with zero play, big motors, and a rigid setup that doesn't bend around.

What kind of machine is it? if there's angular play in the axis, it will move no matter how you counterweight it. If there's slop in the leadscrew, it will chatter more with a counterweight because there will be less downward force at the tool while cutting.

Au contraire..many, if not all vertical machining centers have counterweights. I've seen a naked Haas, and the older models had huge cast iron counterweights. Do a google search on vertical machining center counterweights. Super fast rapids and a heavy spindle casting would require some type of counterbalance.

Stuart

[Miz]

I've worked on older cnc routers with large drilling units that use standard air cylinders, adjust the air pressure to suit the weight. Newer machines have just the motor and ball screw.

[underthetire]

Au contraire..many, if not all vertical machining centers have counterweights. I've seen a naked Haas, and the older models had huge cast iron counterweights. Do a google search on vertical machining center counterweights. Super fast rapids and a heavy spindle casting would require some type of counterbalance.

Stuart

Most do NOT use Counterweights. As posted, large servo motors and rigid setups. Counterweight systems are no good for high speed, they can induce bounce. Haas is neither high end, nor do they use counterweights in the last probably 10 years, and they used to use counterbalance with nitrogen cylinders. 30 years ago, high end machines used hydraulic counterbalance, but the need for speed has all but eliminated them with the exception of large slow moving machines.

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[Browellr]

In my mind's eye I was picturing a diy CNC router, not a HAAS lol. Whatever you've built must be awesome

[awerby]

The "gas struts like hatchbacks use" work fine for me, on my less-than-high-end router build. I had to use a couple of them to counterweight a big spindle, but it seems better than having heavy weights swinging on ropes.

[slashmaster]

Thanks for the replies guys! I wonder if any of the high end machines use springs to help pull the head back up like a garage door? If not are the z-axis rapids going down always faster than up? It would surely quickly wear out a leadscrew on any of our benchtop machines if we don't have some kind of force pushing the head back up wouldn't it?

[Al_The_Man]

Some Mazak lathes that had a vertical saddle/X axis were extremely heavy, these used a hydraulic counterweight system.
When powered down a pin was released to hold the axis up, otherwise it would back-feed down and crash.
Most use hydraulics of some kind.
Al.

[slashmaster]

The "gas struts like hatchbacks use" work fine for me, on my less-than-high-end router build. I had to use a couple of them to counterweight a big spindle, but it seems better than having heavy weights swinging on ropes.

Tell me something, have you ever owned a vehicle that had these gas struts? The struts don't last long. Hatchbacks are one thing because of little room for anything else, but greedy automakers like Volkswagon currently put them on non-hatchbacks for the trunk and hood to make you pay when they lose pressure! Be sure the ones on your spindle don't lose too much or you'll lose steps going up but not any going down!

[atomarc]

The pulleys and ropes work fine but you have to use metric rope and all the ballast in the gunny bag must be in grams or kilograms...imperial won't work...unless your machine is made stateside.

Stuart

[Kenny Duval]

That's bull****. I have fractional marbles in the Crown Royal bags of my German made BF20L. They work fine. You just have to do the metric to imperial conversion in the G-Code to cover the differences.

[CitizenOfDreams]

Tell me something, have you ever owned a vehicle that had these gas struts? The struts don't last long.

I don't think it's that big of a deal to go to Advance Auto and buy a couple of $20 struts every 3 years or so. Compared to having a sack of metric marbles hanging on a rope from the ceiling...

[Browellr]

I find an M24 X 10 rope works great! Keep in mind the pitch changes over time once you factor in the friction of the pulley, and the inevitable constant; the weight of the sack! HA!

[Kenny Duval]

I can't find a place to sell me metric rope in the states.

[Layman94]

The Optimum Bf20l is manufactured in China.

[RCaffin]

I find a gas strut works fine.
Dunno about the lifetime though.
Cheers
Roger

[DICKEYBIRD]

It's going to be a while before my new machine is ready for the Z-axis but I've been pondering a counterbalance system. Someone suggested modifying an automobile shock absorber or strut and convert it over to air pressure. Sound like a great idea to me. Has anyone actually done this and if so, did you save any pics on how to do it?

[CNCMAN172]

We had a Fadal in our shop and lost a bearing in assembly that attached to a huge counter weight. The counter weight was attached to the spindle via a large flat chain that went over a few cog type gears and the bear that went bad was in the cog assembly. The machine would make a thump noise when moving up and down due to the bad bearing. They actually designed the counter weight system so you could raise the spindle to a certain point where a steel rod could be pushed into the machine through the counter balance to support the weight so you could work on the the chain or other aspects of the z axis. The spinde was the 15HP type and was very heavy thus they needed a counter balance.

Russ