DRO compensate for backlash fix?

I was looking at an XLO 602 vertical mill at a dealer while the mechanic was working on it. The bearings in the head had been replaced and he was going to work on the table bearings. From what I could tell there was about .050" backlash in the X axis. I called about it today and it was all done. The salesman said they didn't do work on the table backlash as the machine has a Fagor 3 axis DRO. I'm wondering if it is still better to have some work done on the table to tighten things up or does it really matter with the DRO?
I don't know much about machines but when I see a machine with a DRO, .050" backlash and the head needing new bearings, I'd say the machine has seen alot of use. Does a DRO really compensate for .050" or maor backlash in the table?
Still, I'm sorely tempted to buy it but still cautious enough to consult this knowledgable group.

the DRO is independent of the lead screw arrangement.
there is a scale and a reader head that reads the scale and translates the actual movement...jim

As Jim has stated the DRO doesn't "compensate", it just a measuring device that only reads when the table moves.

Thus while the leadscrew is spinning thru the arc associated with .050" of lost motion and essentially doing nothing, the DRO still maintains the same reading.

An important consideration is if the table locks work. You can have all the DROs you want but if the table begins to drift from the position where you thought you locked it during a cut you will have poor results. This would seem to be more of a possibility with a mill which has seen more use. However, if they lock, and hold, you're in good shape.

Personally, if you can run the mill under power (bring own collet, endmill, stock, agree to shop-vac it clean at the end) and do some test cuts that would be a great confidence builder, or "decision maker".

You can work with a machine with 0.050" of backlash and a DRO but its going to be a pain in the rear. That's an extra half a turn of the handle every time you reverse position. Its possible that the nut may be adjusted or reworked to get rid of some of the backlash, but unless you are getting a great deal on the machine I'd keep looking.

When checking the backlash, check it both at the extremes and in the center, this will show you how much the lead screw is worn. Personally I wouldn't buy a used machine with any more than 0.020" backlash on both axises unless you enjoy repairing machine tools or working on sloppy ones.

Also take an indicator with a magnetic base, put in on the table and indicate on the inside taper of the spindle. Rotate the spindle slowly by hand. You should see less than 0.001" of total runout, and I like it to be way less. Any more and the spindle is either bent from a crash or worn on the inside taper. Spindles can be reground, but figure $300. to $500. to do this.

Run the machine and listen to it carefully, and as suggested above, make a cut if you can. Listen to any abnormal noise from the spindle bearings, which are at the very bottom of the spindle. If its a vari-speed machine, run it through the speed range and listen for any rattles, which shows wear in the vari-speed. This is fixable, but for non-Bridgeport machines parts can be a hassle.

Engage the quill power feed and see if it seems to work. Unfortunately the power feed units on these type of machines are often abused and have worn out clutches. Not to bad to replace on a real Bridgeport, a possible hassle getting parts on a copy machine.

See how much slop is in the quill handle as you switch from down to up motion of the quill (put light drag on it with the lock). Too much slop here makes the machine a pain to use and can cause chatter when drilling. You can get around that by putting a little drag on the lock, but again it makes the machine more a pain to use.

You can also put the indicator in the quill, indicate on the table surface and get an idea of how much the ways on the machine are worn by moving the table back and forth in both directions.

Typically when you find the right machine (used in a model shop or prototype shop, not production) you can tell right off the bat by looking at it that its going to pass all these tests. Those are the machines to find. I learned this the hard way, the first mill I bought as a younger man had been used in production and was pretty beat but I didn't know how to check it back then. I've still got it and use it for "2nd op" jobs but on my new mill I knew what to look for and got a good one.

Good luck-

Paul T.

Thanks folks. I think I'll pass on this machine. I'm going to copy the above advice and use it.

Well what are you going to use the mill for? hobby shop?

You always take the backlash out when you turn the handle go past and come back , always clockwise.

even if the machine is brand new, thats just me.

Everthing on my mill looked good to me. What I missed was that the saddle way was worn. This showed up when I locked the saddle the digital would jump a couple thou. So check at both ends of travel and in the middle. normally a well used mill will get tighter at the travel extremes. loosening up the gib will hide this. If it is too loose the table will shimmy around as you crank it and affect the accuracy.That doesn't make it unusable since most work is near the middle, but you may have to loosen it back up for full travel (and lose a little accuracy_