Z-Axis Backlash

[ger21]

If using a 1/2-10 acme leadscrew for my z-axis with a bronze nut, would the weight of the router, clamps and bearings (probably 8 to 12 lbs) eliminate the backlash due to always being loaded, or would I be better off with a homemade plastic antibacklash nut. If I use a plastic nut, it would probably need to be replaced periodically while the bronze nut would probably last quite a long time. Thanks,

Gerry

[balsaman]

The weight will take care of backlash unless you are going the do heavy cutting. Delrin nuts lasts a longggggg time.

Eric

[HuFlungDung]

Would it be worthwhile to rig up a spring to over-counterbalance the weight of the Z components? This would pull the nut up against the "under" side of the screw thread. It might also improve Z axis performance since sometimes a little bit of binding, plus the weight could cause a stepper motor (if that is what you are using) to loose a step or two.

[ger21]

I'd need a big spring to lift 10 lbs and apply upward pressure. I've got a 250oz-in stepper, and I'll be using 1/2-10 acme rod. I'm goint to try a 7lb constant force spring to carry most of the weight, and I'll probably go with the delrin nut. Thanks.

Gerry

[balsaman]

My z axis weighs at least 10 lbs. I used a 1/2"-10 acme rod, a delrin nut and a spring. The spring overcomes all the weight of the axis for most of the travel, a little less than the weight of the axis when its all the way up.

How are you cutting the 1/2" threads in the nut? Do you have a 1/2-10 acme tap? I made my own tap from a bit of the acme rod after I found out how much the acme tap costs...

Eric

[ger21]

I'm going to make a tap. I'll probably order the rod this week. I'm cutting parts and assemling my gantry and z-axis right now. (If I could stay in the garage). I'm also going to try to make a 8tpi, 2 start tap for the x and y drive nuts. But I won't get to that for a while yet, too many things to do around the house.

Gerry

[bhdavis]

Use gas shocks instead of springs. They maintain constant force whereas a spring applies more force as it compresses.

Gas shocks are available from McMaster-Carr (http://www.mcmaster.com/).

BH Davis

[HuFlungDung]

There's a good idea, BHDavis. I was even thinking about using some kind of a counterbalance on my lathe cross-slide, to take up a little backlash, but a gas shock would be ideal, if I can find something that isn't too stiff to operate.

[ger21]

If you look, I said constant force spring. It's like a tape measure. Actually, I did look for a shock at McMaster-Carr, but couldn't find one to fit my application, so decided to go with the spring. Thanks, though.

Gerry