[peteeng]

Hi TJ - I was thinking in diameters not turns. So its small to big. So should be somewhere around 96kgf so your losing some force somewhere... but you now have the drift so onward.. Peter

Ballscrew Force =( torque x 2 x PI x efficency) / (9.81 x pitch) = kgf

pitch in meters, torque Nm, efficiency of ballscrews is about 0.9, leadscrew efficiency can be quite bad depends on the pressure angle...

[tjbaudio]

Hi TJ - I was thinking in diameters not turns. So its small to big. So should be somewhere around 96kgf so your losing some force somewhere... but you now have the drift so onward.. Peter

Ballscrew Force =( torque x 2 x PI x efficency) / (9.81 x pitch) = kgf

pitch in meters, torque Nm, efficiency of ballscrews is about 0.9, leadscrew efficiency can be quite bad depends on the pressure angle...

It's even worse than that, its .5 lead, 2 start. so .25 pitch. https://www.applied.com/c-brands/c-n...ut/p/101640711

So I should have just over 400lb (180kg) - friction at my disposal in Z. Given I measured about 1/4th of that I must have something really wrong! Time to strip it down and see where my fault is. I'm guessing mechanical. The counter weight spring and lead screw are on opposit sides of the ways. Maybe that's inducing a twist. I could also have some shmoo not visible from out side.

Any way, thank you for putting me on the path to the real problem. How much force would you guys expect the z axis to take to move with relatively tight gib adjustment?

[cncuser1]

tbaudio: .5" lead and 2 starts... that is the ssource of the problem with lack of ooomph in Z. Any decent ball screw with .2" lead, 1 start! will give you everything you need in Z ( force and accuracy and speed).
Bonus points if you install ball screws in X and Y also.

[tjbaudio]

tbaudio: .5" lead and 2 starts... that is the ssource of the problem with lack of ooomph in Z. Any decent ball screw with .2" lead, 1 start! will give you everything you need in Z ( force and accuracy and speed).

So 300lb of friction does not sound excessive to you? According to the math I should be generating 400lb screw to head stock but only have 110 lb spindle to vice of down force.

[cncuser1]

300lb of friction does seem like alot. These mills have many sources of problems, this might be one. First off I'd ask if the ways get hot? That much friction in a peck drill operation must generate alot of heat?

But regardless of the friction, which you'll want to look into, the Z lead screw is just plain old wrong and will be the cause of continual grief.
If you do change the lead screw it will be a good opportunity to look into the fit of the head to the column, gibs etc and to verify if in fact you have the friction your numbers show. For example if you lay the column flat on a table and slide the head, do you in fact get 300lbs of friction? Is the gib jamming?

To my mind on the one hand you are not getting the performance oyu want or should be getting on Z. On the other hand you have the wrong lead screw. The shortest distance between two point is a straight line.

Good luck, curious how things turn out.