Still waiting to be able to get a Super X2 Plus mill for conversion so I've been doing a bit more reading and planning.

I've read that a number of people have reported problems with the Z axis on both the X1 and X2 mills. The general opinion seems to be that you need to rig up some sort of counterbalance system to offset the weight of the head. I am thinking that the problem isn't so much the weight of the head as the tilting force created by the leadscrew not being vertically in line with the centre of gravity of the head.

What torque is needed to raise the weight of the head? Torque is given by:

Torque = (W x g x P)/2 x π x η)
where W = weight of head
g = acceleration due to gravity
P = leadscrew pitch
η = leadscrew efficiency

For the X2 mill with an 18 kg head and a 5 mm pitch ballscrew this works out at 0.15 N.m. With a 2 mm pitch acme screw (50% efficieny) we get 0.11 N.m. This should be well within the capability of an NMEA 23 motor, so driving the weight of the head is not a problem High acceleration could cause lost steps as a result of the inertia of the head but a counterweight can only increase the inertia and people report a definite improvement with the counterweight.

I think the problem lies with the design of these small mills. If you look at big mills with a rising table the lifting screw is always centred under the table for good reason. In these small mills the screw or rack is well behind the centre of gravity of the head. With the X1 it is even situated behind the column! The lifting force from the leadscrew combined with the weight of the head will create a considerable tilting force on the head. This must be countered by forces on the dovetails which will tend to lock things up.

So I am considering using a Z leadscrew fixed as nearly as possible above the C of G of the head. This will probably require modification of the motor and belt drive to accommodate it.

What does anyone think? Is this a silly idea or might it work?

Russell.