FYI: Super X3 mill head weight. If you need a counterweight

[cjdavis618]

I am in the process of building a counterweight system for my x3 mill and wanted to share the info I have found.

I took the head off (this does include the gib mount) and weighed the individual pieces, but all of them together add up to:

100.9 lbs or 45.7 Kg

[neilw20]

What about an air cyclinder with an air balance valve to give it the constant 45KG required.
Thats what I am collecting parts for. Thanks for weighing it for me!

[skmetal7]

Any problem with using a gas spring/ air shock that is mounted in the column? I guess it could be kind of hard to compress it to install. The only thing I don't like about them is their dampening characteristic when it extends (assuming a cnc conversion, could slow down upward travel speed)

A counter weight is a good idea but it adds mass

[neilw20]

On the X3, the strut stops the head going down at least 100mm or so.
When the head is rotated, you sometimes need to remove the gas strut.
You need a special tool to keep it (the rat trap) compressed.
Using a balance cylinder will not increase the inertia much.
Where the strut is it interferes with the job you are machining quite often.
I am going to balance mine above the head, inline with CG of head assembly.

[LeeWay]

I don't think you need one that will hold the full weight of the head. That would make driving down much harder than it really needs to be.
I don't have the X3, but rather an X2 head on a fairly heavy Z axis. Fairly heavy is kind of relative actually and is only maybe 75 pounds right now. Perhaps a little more. I used a 30 pound rated gas strut.
All I really wanted was to eliminate spin down when the power was cut and to assist in raising the spindle. Mine is on a ground ball screw and linear ways though so it would spin down rather easily before. With the power off now, I can raise and lower the Z by hand equally well in either direction.
I don't think the dovetails would need any higher rating on the springs than about half the weight of the Z. Maybe even a little less.
You could rig up a pulley system on the temporary to find out what the ideal helper weight would be for your machine using barbell weights or large sinkers. Anything heavy of known weight that you could attach. Very little is needed to counter the spindown, but more is needed to assist in raising the Z.

[cyclestart]

Originally Posted by skmetal7 A counter weight is a good idea but it adds mass

How big an issue is that ? Something about inertia ? Physics was never my best subject back in school, never could figure out that sliderule

Those struts bring back bad memories of a few hatchback cars. What kind of lifespan to expect?

Otoh counter weights would be a pita if the machine needs to be moved.

[cjdavis618]

Originally Posted by skmetal7 A counter weight is a good idea but it adds mass

Yes it does. But by using the counterweight, I can get close to a perfect balance between upward and downward pressure. I have a vmc that also uses a counterweight system. It's weight is stamped 900lbs. I can take one hand and push up and pull down the mill head. I don't have it running yet, but it is rated at 550 ipm.

Even though the mass is increased, if the system is balanced well, it will not be a problem. I would need to adjust my Mach acceleration though to compensate.

I would rather have 150lbs of perfectly balanced system vs 100lbs of downward force on the stepper.

[ViperTX]

cyclestart.....well you have good reason to be concerned about the lifespan of the gas springs. I used 2 from MSC or McMaster Carr.....anyway.....they were being used within the temperature range specified and were properly sized based on the manufacturer's recommendations and mounted as required....you know the body higher then the moving shaft...or something like that....don't have the part in front of me.......well used one season in an outdoor sheltered environment.....they lasted 9 months.

[blades]

That's extremely poor lifespan for a gas strut, considering ones used to hold up the hatch in my 1990 Camry wagon with 375k miles are still operational. I was considering a gas strut for my X2. Maybe I'll scrounge one from the boneyard instead of buying a new one.

[DonF]

I wouldnt let a bad strut scare you off. I have used them for lots of stuff and they last years not months. Its posible Mcmaster got a faulty batch.

[LeeWay]

I bought the ones I am using from Surplus Center. They appear to be good quality. Time will tell, though.

[cyclestart]

Originally Posted by blades considering ones used to hold up the hatch in my 1990 Camry wagon with 375k miles are still operational.

Our experiences are very different. Maybe it's the temperature extremes that do the automotive struts in here. -40F to 100F. The -40F being the more likely culprit. I see a lot of local hatches held up by sawed off broom handles. I do plan to test out the LMS strut.