today i will be eating mostly Y axis

[louie]

Hi all,
In the latest design for the troublesom Y axis for my plasma table i am using two 25mm end supported round rails, one above the other for the Z axis to locate to, but with a strech of 1500mm I wonder if i'm asking a bit much of them,of course it all depends on the weight of the Z axis 5 or 6 kg sound ballpark? The other consideration being the depth of pocket v length of arm.
Any sugestions/opinions welcome.

louie.

[routercnc]

6kg at the centre of 2off dia 25mm rails of 1500mm length is about 0.5mm sag (at the centre of the span). Fairly easy to calculate.

The question then is how important is this amount of Z sag for a plasma? How critical is the variation of distance to the workpiece when cutting?

Also, if the load is offset then the rails will twist. This will rotate the plasma away from 90deg to the material. Again, how important would it be if the cut angle was a few degrees out? I suspect the problem would be a slight chamfer on the edge of the workpiece.

I'm sure some Plasma expert can help you out with these further questions.

[louie]

Thanks, Z sag i don't like the sound of, but the torch hight control would take care of that?. Twisting is something else though, can't have that! i'll have to think again.

[Jonathan]

Couldn't you avoid any twisting by balancing the Y axis....i.e. put a suitable mass the other side of the rails to the plasma torch so that the centre of mass falls directly between the two rails. Admittedly that's going to make it even heavier, but still if twisting is worse than sagging then that's ok...