I’d like to add some Z axis height to my MPCNC so that I can work on thicker wood and have the ability to set up jigs on the table.
I’ve read the " the Z axis has the largest effect on rigidity . For a Primo MPCNC, 81mm is the shortest and I highly recommend that." on the cut calc - but does this apply to the Z axis dropping down from the core, or from the uprights supporting the rails, or both?
What I’m thinking is elevating my rails on some 40x40mm aluminium extrusion which will be super stiff. I can then either block the extrusion, or have the whole thing height-adjustable.
I’ll still have my tool hanging quite low from the core though.
Any comments or suggestions about how to raise the Z height?
What that means is that the Primo is at its most rigid the closer that the cutting is to the core. In this case, the higher up it is, the more rigid. Since the kinematics of the machine lower the cutting tool from the core, the taller you make the machine itself, the less rigid that it will be cutting the lowest point.
So you CAN have it deal with thicker material, if you don’t try to cut all the way to the bottom.
Many people make the spoilboard surface so that it can drop down, or raise the legs of the machine over that surface. This can allow a thick piece to be put in the machine, provided that you aren’t trying to cut more than 3" or so into it. Since the vast majority of the bits that we can buy are less than 1" cutting depth anyway, this likely isn’t a problem.
So it’s really that the further away from the top of your machine’s travel you go, the less rigid the machine is. So you can make the machine as deep as you need it to be, but you should probably limit the cutting depth to about the 3" or so.
I’ve had two different solutions for a higher Z height:
I made a taller machine and had two different heights of spoil boards bolted to the base board. When I wanted more height, I removed the tall spoil board, and installed the shorter one.
I drilled holes a bit larger than my legs below each leg to allow the legs to pass through the base board and the “workbench.” When I want more height, I loosen the machine screws on each of the legs and pull the machine up. I use 3D printed spacers that clip to the legs to assure that each leg is pulled up the same amount, and the spacers provide structural support beyond the clamping of the leg mount.
Note that both solutions require longer legs and a taller Z axis. I’m currently using #2 because it is faster to make the change. With #1, I found that once I had adjusted for a higher Z, I was inclined to leave it at that height because of the work required to swap spoil boards…but that is my personality since the change wasn’t that much work.