Here we go again . . . MK4

[Boyan Silyavski]

Now thats the most out of the box z design i have seen recently. No shame in using 8x Hiwin bearing blocks and 4x rails plus a couple of motors apart from the Hf spindle. How would you align all that stuff in place? Each piece must be carefully machined to a tight tolerance.

Ok. I know that you will patiently make it. Obviously not your first machine 2 questions:

1. Wasn't it simpler and better using BT30 spindle and servo motor on a fixed gantry?

2. So much effort in all places but gantry will slide on round open cage bearings? No square supported ones?

[routercnc]

Now thats the most out of the box z design i have seen recently. No shame in using 8x Hiwin bearing blocks and 4x rails plus a couple of motors apart from the Hf spindle. How would you align all that stuff in place? Each piece must be carefully machined to a tight tolerance.

Ok. I know that you will patiently make it. Obviously not your first machine 2 questions:

1. Wasn't it simpler and better using BT30 spindle and servo motor on a fixed gantry?

2. So much effort in all places but gantry will slide on round open cage bearings? No square supported ones?

Thanks Boyan. This is probably about version 5 of the Y/Z axis design with all sorts of combinations tried out, some with single Z ballscrew, some with pulley driven ER straight shafts, and other options. Eventually the desire to have the option of pulley driven spindle (for lower speed, higher torque), much larger cutting bits, and the ability to add a PDB drove me to this design.
I wanted to make the stiffest Z axis I could as it is all won or lost here. The 4 rails and 2 ballscrews is as stiff as it can be (in concept terms) so went with that. I thought a lot about the alignment of the bearings as you cannot just machine everything and bolt it together. The Y axis box structure has slip planes to allow it to be pre-loaded up to the bearings to squeeze them together. I'll let you know if this plan works !

1. I agree fixed gantry would be even stiffer, but I needed to maintain a very large cutting area for wooden panels. If it was just smaller metal parts then you are correct. So this requirement has forced a compromise. Fixed gantry would have a very large working footprint and I don't have that space.
I also looked at lots of spindles including buying off the shelf BT30 etc but they are very expensive with PBD. In the end I decided to allow fitment of direct drive WC spindle (the hole is 80mm diameter), with the option of making a spindle later.

2. As Zeeflyboy has pointed out this has already cost a lot to make, plus there is more cost to come (more Z axis rails, more aluminium plate, more steppers and drivers, pulley hardware etc.) so the ~£200 profile rails on X will have to wait. Agree it is a weak point, and will also give some loss of accuracy. For now they will have multiple blocks per side, not the usual 2, to get the best out of them. But the rail supports which they run on has already been spot drilled ready for profile rail. A simple adapter plate to the gantry will then allow the upgrade.