Z-axis design - help sizing materials please!

[Ross77]

Hi Johnathan

personally I wouldn't go for that length of travel on unsupported rail. The calculation you need is for a cantilevered beam, just you have it mounted vertically. As a rule of thumb I look at third points, so for a cantilever of 400mm you would need a 1200mm rail with the mounts 800mm apart. (not very feasible)

If this is a router then I guess this will then be mounted on a y axis gantry and needs moving as well so overall weight will be an issue. Is there a reason you need such a long z or could you just change the bed height

[Jonathan]

Hi Johnathan

personally I wouldn't go for that length of travel on unsupported rail. The calculation you need is for a cantilevered beam, just you have it mounted vertically. As a rule of thumb I look at third points, so for a cantilever of 400mm you would need a 1200mm rail with the mounts 800mm apart. (not very feasible)

600mm is about as much as is practical allready. I read somewhere a rule of 2:1, i.e. if the bearings are 200mm apart then it's acceptable to have the force (of the cutter) 400mm away.

If this is a router then I guess this will then be mounted on a y axis gantry and needs moving as well so overall weight will be an issue. Is there a reason you need such a long z or could you just change the bed height

Yes it's a gantry router. I can think of things I'd like to make which need that long a Z, maybe not quite 400mm but close enough.
With regards to accelerating the mass of big Z axis/gantry I should be ok as on the X-axis I'm using two 3Nm steppers @ 70V for the and spinning the nuts, not the screws. The nut is currently held between two tapered roller bearings with a pulley in between.