One ring to rule them all?

[routercnc]

Any thoughts on an under slung gantry? I'm just thinking if i'm using 200 or 250mm box section and mounting to the top of the gantry then the Z axis is effectively 200mm + rail / cartridge height before its even descended at all.

It might be a little tricky to mount the rail, i'd have to jack it up off the bed I suppose. The gantry could be epoxy leveled upside down.

It crossed my mind too as you are right there is much less Z offset doing it that way. I did sketch something up but the problems I encountered were:

> Side rails cannot easily be supported back down to the bed as the gantry and rails are in the way. The supports down to the bed would have to be outboard of the rail which puts in a bit of an offset.

> Rails and ballscrews are exposed to swarf and potentially clamp collisions which is not ideal.


I looked at the commercial machines and they were on top so I went that way. If it helps the box section for the gantry could probably be much smaller as with 2 of them you significant reduce the twisting. I would expect 2off 50x50 sections to be twice as good as 1off 50x50 for bending in X and Z, but importantly, significantly better than x2 for twisting. This is where the advantage is with 2 beams on the gantry.

I also looked at rails on the inside faces, which is what Jonathan did on the 'sufficiently stiff machine', which is a bit more out of the way and has less Z offset. Downside is it spaces the beams out a bit further for loss of gantry travel. Not a deal breaker if you can make the machine longer.