yoopertool, another option is to reduce the speed, and possibly the acceleration, of your Z axis. Stepper motors produce their best torque at zero speed, and the torque available (to a first approximation) decreases linearly with speed. Even if you are planning to counterbalance the Z axis, this is a bandaid you can apply immediately. (Of course, that will reduce the speed of your whole machine if you are doing 3D contouring (like carved signs) but if you're doing 2.5D work (pocketing etc.) it will not slow things down much.)
How heavy is your Z axis? Constant-force springs have a finite lifetime in terms of extensions/retractions, and can get quite large in order to support a load with a reasonable lifetime.
I have a pair of Ametek (Hunter) Neg'ator SK18P47 springs rated for 13,000 cycles. They support 5.7 lb each, are 1" wide and use a hub of 2.4" diameter. The largest spring in the range, a SK31U68, supports 19.6 lb, is 2" wide and uses a hub of 4.12" diameter.
If you are willing to accept a shorter lifetime, 2500 cycles, the springs are smaller. An SH20S47 will support 19.8 lb, is 1.5" wide and uses a 1.75" diameter hub. I used a pair of SH10K29 (2500 cycles, 5lb each) to counterbalance my Sherline mill's head for a while, but stopped using them since they really didn't make a big difference.
The springs are definitely much lighter than a counterweight, so from that standpoint they will give less load on the X and Y axes if your machine is a gantry.
Best regards,
Randy  |