Ballscrew Mileage

[Geof]

The X axis ballscrew on our 2002 SL10 died yesterday; or I should say it suddenly developed a death rattle. My guys took it out and we found a section on the edge of the ball track had spalled off and I guess it is now all munched up in the nut; also on closer inspection we could see micro-spalling all along the ball track. The replacement ballscrew arrived today by airfreight so we will be up and running without much loss of production and a reasonable $3500 bill.

Just for fun I checked how many toolchanges the machine has done; more than 1,600,000. I figure each tool change represents about 12 inches of travel on the X axis which calculates out to about 310 miles of travel. Is that good mileage?

[Donkey Hotey]

Hmmm...that doesn't sound so good to me. Is the screw lubricated with pressure-fed oil like the mills or is it greased like the toolroom machines?

[Vern Smith]

Wouldn't you consider the number of accel/deaccel's harder on the screw and nut than the distance traveled with the load in relative steady motion?

Vern

[Geof]

I am quite happy with the life we got out of it; we did check and the lube oil is flowing normally. As Vern mentions it slams several inches one direction at 1000ipm then several inches the other way every tool change. I don't know what the life rating for these ballscrews is but in the past I have seen numbers in the tens of millions of inches at rated working loads in ball screw specs. The part I find interesting is that it is a classic ball race failure; micro-spalling which builds up to a major failure. If these ball screws were not in an environment that creates metal chips you would be able to monitor their life by analysis of the wear particles in the lube oil.

I just did a quick calculation; this machine does a tool change about every 27 seconds, on average, when it is running.

[mactec54]

They do a lot of work, but what has happened is not that normal for a screw to peel metal off the ball tracks, you may have had some ware & the balls went though the case & peeled the metal up.

Do you have a photo

[Geof]

I don't have pictures and I am off on two weeks vacation on Sunday; I will see about getting a picture when I get back.

The wear is typical for a ball race, spalling out of minute fatigue fragments.