[MPBeng]

Hi all.
I have a Lagun ML3-A Vertical Knee mill that I have bought and pulled down for repairs to the feed mechanism. A questionable design has allowed any coolant that found its way between the ways of the "Y" axis to enter into the knee; thus contaminating the gearbox oil and making a general mess of most of the feed gears. When I opened it up there was sludge and rust everywhere and no discernible oil to be found. Some repairs have been done by the previous owner but I guess it was put in the too hard basket and hence sold off...to me. Yes I got it cheap and the ways are quite good.

I've purchased new generic gears and would need to machine them to suit their intended purpose. But since I used to work and program CNC's about 25 years ago I started to think about the logistics of upgrading to ball screws and steppers. After finding this forum I've started to research and get more serious about it all.

The "X" axis has a 32mm Acme lead screw fitted. The "Y" axis has a 25mm Acme lead screw fitted, and the "Z" axis has a 63mm Acme lead screw fitted. I have researched the ball screws and will have no problems installing up to a 40mm ball screw in the "X" axis, and capturing the nut in the existing mounting provisions. I'll use two opposed flanged ball screw nuts to eliminate backlash (the old mechanism has provision for three nuts). The "Y" axis requires a little more modification but I don't envisage too much difficulty getting a 32mm ball screw in there. By removing the clutch dogs for the "Y" axis I'll have sufficient room to install apposed nuts here too and not lose any travel. Now the "X" and "Y" axes will have fixed ball screw nuts with steppers mounted on one end of each of the 10mm lead ball screws.

But the "Z" axis isn't so easy. There's minimal room in the knee to mount a decent stepper let alone the Nema 42 monster I want to use. There is plenty of room under the knee at full drop. But this requires using a rotating nut which is going to take some thought to sort out. My main concern before I start buying components is whether this is at all feasible? I'm not the sharpest tool in the shed and am having trouble getting my head around whether the Nema42 4200 oz/in steppers will have enough power to drive the axes under the loads of cutting steel. I'm still using the original dovetail ways. Add to this fact that the bare knee and table weight would have to be pushing 600 lbs (total machine weight is 4620 lbs). Then I'll have the work and clamping/vise to add to that so no more than 800 lbs total weight on the "Z" axis plus friction from the dovetail ways.

I've pretty much sold myself on 10mm lead for the "X" and "Y" axes, but I'm wondering should I use 5mm lead for the "Z" axis. This should reduce the torque required to move everything and the total travel in "Z" is only about 300mm usable once a tool is loaded. A bit slower on the "Z" axis is better than no power. Now 5mm lead will limit me to a 50mm ball screw. The reference charts for 50mm ball screw with 5mm lead state Dynamic Load C(kgf) of 2700 and Static Load Co(kgf) of 11940. I take it that means I'll be using only 13.46% of the total load carrying capacity of the 50mm ball screw?

With the space restriction under the knee I'll have to run a belt drive for the rotating nut. Should I use 63mm ball screw and the resultant reduced the helix angle to free up some more power? Should I use 10mm lead and a 2:1 reduction in the belt drive to achieve the same power requirements as a 5mm ball screw?

I guess everything boils down to will the Nema42 steppers be sufficient to drive all three axes? If no then I'll rebuild the manual feed mechanism and put this idea to rest. Thanks everyone for your time and sorry for the epic write up and many questions.

Cheers,
Chris.

[geast1967]

I'm doing the same thing in my ML3. Here are some pictures.Attachment 412472