[WB-1]

Hi, what do you guys think about not having the ballscrew evenly spaced between your linear rails.

On my X-Axis I have nothing to attach the ballscrew supports to, so was going to put them on the lower 8020. Meaning it will be off set.

The distance between the linear rails is 330mm.

Is there going to be a problem of binding if I try to cut aluminium?

Damn I missed a 'w'

[JerryBurks]

Not sure if you mean the gantry when you say "x" I don't understand the picture.

Anyway, no matter which axis the screw will only be balanced (i.e. not apply forces/torque to the rails) when the bit is actually machining along the screw center. Obviously that is not possible, but the further the bit is away from a screw, the longer the leverage is and the higher the torque (resulting in forces) that must be taken up by the linear bearings. Assuming a distance of 24" and a machining force of 10 pounds that will generate a sizable torque of 20 ft-pound that has to go somewhere. The actual forces applied to each of the linear bearing depend on the design but overall it is helpful to space your linear bearings apart as far as you can.

Assuming a moving gantry that means to have the screw centered for X (long axis) or better have 2 screws to avoid that "racking" torque in the first place.

For the Y-axis (i.e. on the gantry) it means to have the lead screw as far down (close to the bit tip) as possible, not in the center between the rails. I am not aware of machines that use 2 parallel screws on the gantry although that may not be such a bad idea, at least for machines with tall z-axis.

Z-axis is normally not a problem because the spindle/bit center is quite close anyway.

[WB-1]

Hi I think the new picture might help to explain a little better.

I'm worried that the yellow line (ballscrew) is not in between the linear rails.

I would rather it was higher but I don't know how to fix in place

[WB-1]

After reading all of your post:

For the Y-axis (i.e. on the gantry) it means to have the lead screw as far down (close to the bit tip) as possible, not in the center between the rails.

I think you have answered my question!
I would have thought the ballscrew centered between the linear rails would have been better...

[RomanLini]

No, evenly spaced between the 2 rails is the worst place to have it! Ideally the screw should be as close as possible to the primary rail, which is the rail closest to the load force (ie closest to the cutting tool. The secondary rail is much less critical as the forces on it's bearings are very low compared to the primary rail.

Even putting the screw outside the 2 rails and very close to the load force can be better still.

[WB-1]

hey thanks for the reply. I would have completely got that wrong, but it does make sense now that you say so. Cheers.