View Full Version : Machining hardened ballscrews

16-07-2009, 10:34 AM
Machined my ballscrews last night and after hunting around and finding hardly any info on speeds, feeds, tools etc (should have asked John!)thought I would share my findings.

Ballscrew - Hardened rolled 16 x 5mm from Zapp
Lathe - Trusty old Leinen LZ4 S - using collet to hold ballscrew
Tools - Carbide insert turning and threading tools

Started with my Z axis screw as it was about 100mm too long and gave me some experimenting room. I needed to turn and thread 30mm on the end so put it in the collet with 35mm sticking out, set speed at 1100 (guessed) and faced the end with a large tipped carbide tool. Faced off fine no problem at all so then decided to work on the diameter, needed to get it down to 12mm for a couple of angular contact bearings.

Started with a 0.25mm cut and a steady feedrate (another guess, better safe than sorry) which seemed to work ok so the next cut went for 0.5mm and upped the feedrate which again was ok so decided to stick with 0.5mm. Ballscrew was getting a bit warm when cutting so flooded it with coolant when machining, this kept temp down nicely.

After 4 cuts checked the tip, pretty worn already so changed the tip and slowed spindle down to 550. Same depth of cut and feedrate but no coolant needed, result - much better. Took it down to about 0.1 oversize and then finished with emery by hand until the bearing fitted nicely with a little force.

Screwcut 10mm length on the end with a M12 fine thread using normal lathe screwcutting methods and a carbide tipped threading tool as now the hard stuff has gone and machines quite nice once you get under it.

First one took me 1 hour! Mainly pissing about trying different things but once I found what worked then the next 2 took about 15mins each.

Conclusion -

Speed - Keep it around 500RPM
Turning tool - Carbide insert tool with a nice big tip (i used a PDJN)
Depth of cut - 0.5mm
Coolant - No need when turning dia, just use when screwcutting.
Feedrate - Can't read the legend plate that tells me what it is set at but it looks and sounds about right!

Not as difficult to do as I thought it was going to be!

16-07-2009, 12:29 PM
How even was the hardening on your ballscrew?

First 2 i did were ok, the last one was a bit unevenly hardened, down at 12mm dia i still had a hard section about 15mm from the end and also near the shoulder. A bit of emery soon sorted that out though.