Do nuts and leadscrews always have to be replaced together?

[Friendly non murdering Sword]

So I will probably do an overhaul of my old Deckel FP1 next winter and I've already some parts on my list that need replacement... Two of which are the bronze nuts for the X and Y axis. They have 0,02" and 0,015" of backlash, respectively. That amount of backlash is not too terrible for the age of the machine in my opion but since I'm able to turn replacements on the lathe I'll probably replace these nuts too when the mill is disassembled anyways.

What I was wondering... Should the leadscrews always be replaced together with the nuts? I've heard of uneven wear of the leadscrews in the center of the axis compared to the ends. Then again I checked and the backlash is constant to 0,002" from center to the ends. The Deckel leadscrews are pretty pricey in my country... ~700€/piece. So replacing two of those will almost cost me the same as the machine itself.

What is your opinion on this?

 

[jmkasunich]

Then again I checked and the backlash is constant to 0,002" from center to the ends. The Deckel leadscrews are pretty pricey in my country... ~700€/piece. So replacing two of those will almost cost me the same as the machine itself.

What is your opinion on this?

If the backlash is consistent over the length of the screw I'd only replace the nut. Especially if the screw is that expensive!

 

[C-Bag]

Are you sure the nuts are not adjustable for lash? My cheap Chinese mill/drill is.

 

[woodchucker]

Even if the nuts are not adjustable, sometimes you can slit them and put a screw in to pull them tighter to remove the backlash...
that 0.002 is not much backlash if you are indeed referencing inches. quite acceptable. The 0.015 well, on my machine that's not bad.. on a Deckel.. well... I guess.

if you had ball screw you can almost be perfect. but with a regular screw, I think 0.002 is as perfect as it gets for me. it's still precision and if you know you have it you can still hit tenths.

 

[projectnut]

I'm willing to bet the backlash can be adjusted out. Neither is bad in the commercial world. I have seen working machines with .035" or more backlash on one or both axis. That's where the DRO comes in handy. I'm not sure what the factory spec is for a Deckel, but a Bridgeport comes from the factory with between .003" and .005' in both the X and Y axis when equipped with an acme lead screw and bronze nut. Anything tighter would cause premature wear on the nut. My Bridgeport had about .025" backlash in both axis when I got it. I was able to adjust both down to .005". Almost 20 years later it's still .008" on the X and .006" on the Y.

I am considering a new X leadscrew and nut which are both original. Only because the machine originally came with an F6 power feed from the factory. Part of the feed mechanism was under the table so I have 2" less X movement than the manual machine of that era. I have long since replaced the missing power feed with one on the end cap. I had to fabricate an extension to mate with the shorter lead screw. It would be nice to have the full travel of the table. If I remember correctly a new lead screw from H&W is around $300.00 and a nut is around $40.00

 

[benmychree]

.005" is generally accepted as normal backlash with a new screw and nut. Save your money.