After 4 months since I first thought about building my CNC router, here we go. I'm still at brainstorming/CAD phase so if you have any thoughts and ideas I would love to hear them.

Working surface will be 150x100cm and 18cm Z height (60"x40"x7"). I'm aiming at aroung 10m/min (400IPM) cutting speed (or more if I manage to solve the ballscrew whip problem).
I intend to cut hardwoods and some aluminium. Budget is around 3000€.

Since I have a welding workshop and have access to a milling machine I'll be making the router from steel. I'll mating surfaces and surfaces where I'll bolt linear rails will be machined.

I'm making the Y axis beams from 120x40mmx3mm tubing and I'll weld a strip of 30x15mm steel to have more meat for threading into. My idea is to make the router easily removable from the frame. I'll be bolting the Y beams to the frame with 4 bolts on each corner. Hopefully that will also give me enough room to shim the rails to be in the same plane and in a way disconnect the router from the frame so I'll have to worry less about the welding distortion in the frame. After the router is done I'll resurface the table and any discrepancy in the frame will be solved by that (I hope that is).

I'll probably use 25mm rails since I've got 25mm carriages for cheap.

I thought to use 1610mm ballscrews but since the price isn't that much higher I'll use 2010mm screws. That gives me around 1000rpm before I hit the critical speed in a fixed-supported system. And this is where I have a couple of questions for you guys.

Since the ballscrew is so efficient and almost "friction-less", does it really heat up that much during heavy use? I have no access to a router in a real world so I can't check for myself. The reason I'm asking is if the screw doesn't heat up significantly than it won't expand much and fixed-fixed mounting is possible and that give me 1500rpm before critical speed. Can you give me any feedback on this please.

Another idea I've found here on the forum is to make a spring actuated plastic support for the screw in the middle to prevent it sagging (I attached photos bellow).

I don't intend to hit critical speed but it would be good if I could make even faster machine although it isn't crucial for me.

For X axis beam I'll use 200x80x5mm tubing. In another thread someone mentioned I should use square tubing instead because the cutting force is pushing against the narrower part of the beam. That makes sense but using 200x200 tubing will eat up router space pretty fast. That made me experiment with Fusion360 simulation workspace.

I don't have any idea how high the cutting forces are but I've found on the forum someone mentioned 300N so I used that. In my static simulation where the Z axis is in the middle of X axis and it is at it'slowest point I've got around 20 microns of deflection. I was getting around 30 microns before I've added some diagonal bracing inside the 200x80 beam and side support for spindle mounting plate. (30 micron is 1 thou)

Is this "acceptable" deflecton or should I consider going with 200x200 tubing? At this point the gantry will be over 50kg (110lbs) so I'm afraid to add even more weight.

The Z axis is 25mm aluminum plate and for the spindle mounting plate I'll bend sheet metal around the spindle and bolt it to the plate to make it more rigid.

I found some hybrid NEMA34 8Nm motors (~1000oz/in) and I'll use 2 on the Y axis, one on X and maybe one NEMA 23 4Nm for Z axis since I'll use 1605 screw for it. On MYCNCUK forum I've found spreadsheet for calculating motor size and for 60kg/120lbs gantry I need ~4Nm or torque and since I'm using double 8Nm motors I think I'll have some headroom. (the calculation DID include acceleration load but it is hidden inside the spreadsheet formulas and I can't find what value for acceleration they've used)

I thought about connecting motor with a belt. That would allow me to make a 2:1 reduction since these motors only have 3Nm of torque at 1000rpm and almost 5Nm at 500rpm.

This is it for now. If you had enough patience to read all through this than thank you. If you have any questions/ideas feel free to share. Thanks again.

This is the stepper I intend to use: https://www.vallder.com/en/c/292/38/...hnical-details