Did my first cuts this morning with the Primo. I had pretty play in the Z-axis, so I tightened all the bolts with a torque wrench with 3Nm.
Well, now I remembered that when I was assembling the whole thing, I did loosen the bolts, that the X & Y came below 2Kg (~4lbs) pulling force.
After tightning all the bolts with 3Nm, the Z-axis, has no more play, however XY pulling force goes up to 4Kg, and movements are not very smooth.
I did some test runs in “thin air” with increasing speeds, about an hour in total. Temperature of the steppers went up to 45°C, which I guess is OK.
Unless someone has a better idea, my next step will be loosen all bolts again and tighten them with 2Nm in the hope, that the play in the Z-axis does not come again, and reducing the XY pulling force.
Torque wrenches and special tools make us feel precise, but I believe they will cause more harm than good here.
We use torque wrenches when we need to stretch bolts or to apply a specific clamping force via bolt threads.
For plastic parts that flex, like these, we definitely aren’t stretching bolts, and the clamping force on the plastic good from “pretty good” to “ah crap” in about a quarter turn.
For parts with bearings, snug the adjuster up until the bearing touches the tubes, then call it good. If you’re feeling aggressive, maybe an think of an 1/8 turn and go HALF of that…but still better not to.
For any parts that clamp, like the legs, just snug the bolt until the clamped part stops spinning. Think about the forces on the tubes…nothing pulls out of the clamps, only against them. Your grandma with arthritis could get those tight enough.
Overtight bolts will lead to parts being misaligned, plastic pieces cracking, or…if you’re lucky enough to avoid those…the parts eventually flowing under the pressure of the bolt and working their way loose anyhow.
Good luck.
I’ll have to add one thing. Check your bearings before each job as a preflight check. Nylock nuts, contrary to popular belief, do loosen up over time.