You can buy in line speed reduction gearboxes for most standard stepper motor sizes. If you buy a stepper that turns out to be underpowered then adding a gearbox is a relatively minor mod that will increase the available torque at the expense of speed. I would not think speed is that important for raising and lowering the Z axis.

Martin C

The small Raglan mill is delightfully light to use, both traversing and raising the knee. But I think raising the head on a wm18 might need a bit more oomph than traversing the table on the little Raglan.

At least the head is a fairly constant weight, not like raising s table with a heavy item loaded onto it.

I think I would investigate the assister rams, to lighten the load, before deciding on the size of the motor required.

What torque rating is your current Nema 23, may be easier to just get one with higher torque which should fit the existing installation rather than make up new brackets etc for alarger 34

You can get them upto 4.5Nm, that is what CNC4You use on their conversions of the WM18

I've got 6Nm on the KX-3 but may be larger

Edited By JasonB on 05/04/2023 10:50:17

I just put a torque wrench on my WM18 and lifting the head takes less than 20Nm. Unfortunately that's the minimum torque my wrench can measure so the answer isn't conclusive. A 12Nm Nema 34 is definitely in the right ball-park, but an 8Nm uncertainty is a shade more than I would care to risk £70 on.

I'll have a think about how to measure the torque needed from first principles. I'll have to bodge something because I don't have a suitable spring gauge or a set of weights.

An alternative is to fit a gearbox to the motor, like this NEMA 17 example on Amazon:

With a 1:5.18 ratio, the gearbox would deliver 23.21Nm from a 4.5Nm NEMA17 motor – more than enough to lift mu WM18's head. It would take 5 times longer to lift the motor though! May be acceptable. The stepper will probably turn at 200rpm without bother, and a 5:1 gearbox would spin the Z hand-wheel at about 40rpm, which is a comfortably moderate manual turning rate. 400 or 500 rpm from the motor isn't inconceivable, and 80rpm on the hand-wheel is a fairly quick manual turning rate.

Also possible to buy stepper motors with built-in gearboxes.

Dave