Z-axis design - help sizing materials please!

[Ross77]

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.

As far as I know thats for friction bearings like the igus or dovetails like a mill/lathe. and is to stop/reduce binding, not for resisting the cutting force.....

The thing to remember is that all machine design is a compromise, and as such it will be designed for a specific task, if you need 400mm of travel then you will have to put up flex and vibration at certian points and reduce feeds and speeds accordingly.

The other point is that it will only be as good as the weakest bit....theres no point in have expensive powerful motors and drives and then using unsupported rail... it just dosnt make sense.

I hope I dont seem negative or put you off but rather offered some pointers to another route.

[Jonathan]

As far as I know thats for friction bearings like the igus or dovetails like a mill/lathe. and is to stop/reduce binding, not for resisting the cutting force.....

I've just checked the Igus datasheet and that is indeed the case.

The other point is that it will only be as good as the weakest bit....theres no point in have expensive powerful motors and drives and then using unsupported rail... it just dosnt make sense.

I've already got the expensive powerful motors and drivers on my milling machine. I intending to use those motors on the router and put some 1 Nm ones I've got lying around on the router.

I hope I dont seem negative or put you off but rather offered some pointers to another route.

On the contrary - you're not putting me off, yet!