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Worn nuts for mill leadscrew

G

Gennady

Super User
Hello folks.

My King USA mill started to act erratically for some time. I decided to have a look and yesterday removed table and started diagnosing. To my utter disappointment I discovered that nuts (there are two to take up a slack) are worn completely. I am not sure how this is happened - mill was always generously lubricated, anyway - here is a picture

1751812308917.png


I will have to rebuild it, so several questions -
1. Is that leadcrew 5 TPI or 6 TPI ? Seems to be right handed? I am a bit confused...

1751812445972.png


2. OD if this leadscrew is 1.129" - is there closest standard leadscrew. Nearest fractional size is 1 1/4 - does it look right to you, folks ?
3. Regarding fix - would be OK to bore internal diameter, have some decent wall thickness and then to make a threaded insert? OD of the threaded part is 1 3/4". Make a sliding fit, then to solder insert in pace ?
 
Looks like 5 tpi to me. What markings are on the handwheels for measurements?
 
This link might help you with common (commercially available) ACME sizes. Maybe its 1.125x5 assuming its an inch graduated machine? Some folks cut their own leadscrews & nuts, some throw some $ at the problem & buy them, all depends on your tooling & abilities & aspirations. Try to find a machine parts/manual, online or otherwise. It will probably state the size there too for confirmation

www.roton.com

Acme Lead Screws - Roton Products Inc.

Roton Products is a manufacturer of lead screws, ball screws, & more. View our acme screw engineering data & shop online for your power transmission needs.
www.roton.com

A more accurate way of measuring unknown threads is encompass as many threads as you can. Then just count the threads encompassed & divide by whatever the measurement reading is. In this machine you probably have a pretty good idea to narrow it down, but I'm talking generally if you aren't sure its maybe even metric. Now if you have significant wear, obviously this isn't going to be 100% accurate but maybe you can traverse outside of that wear range.
1751816090705.png
 
I think you could do a sleeve when I did the one on my old mill I had to redo it all.
I have both an acme 29 degree pitch gauge and an acme 29 screw gauge if you plan to make a cutter with hss.
If they are of any help let me know I am happy to lend them to you.
IMG_0461[1].JPG
 
combustable herbage said:
If they are of any help let me know I am happy to lend them to you.
Click to expand...
Thanks a lot . I just happened to order these for myself today. :) But thanks again for the offer.

Folks. I am starting to collect bronze scrap to make a cast. If somebody in Ottawa and vicinities has bronze scrap - even smallest pieces - and willing to donate it :) please, LMK.
 
Gennady said:
1. Is that leadcrew 5 TPI or 6 TPI ? Seems to be right handed? I am a bit confused...
Click to expand...

I agree with David. Looks like 5 to me. Peter's method is very exact.

I think your confusion about whether it is 5 or 6 comes from counting teeth vs counting cycles (tooth and valley).

Gennady said:
2. OD if this leadscrew is 1.129" - is there closest standard leadscrew. Nearest fractional size is 1 1/4 - does it look right to you, folks ?
Click to expand...

I'd guess that 1-1/8 is close enough given that 5tpi was so exact. It seems strange for something to be 4 thou bigger than that, but when I take into account that its an acme thread, it is possible. Not only that, but its the nature of an acme thread to be less sensitive to pitch diameter and overall diameter.

Gennady said:
3. Regarding fix - would be OK to bore internal diameter, have some decent wall thickness and then to make a threaded insert? OD of the threaded part is 1 3/4". Make a sliding fit, then to solder insert in pace ?
Click to expand...

Not what I'd do, but I see no problem doing it.
 
Gennady said:
To my utter disappointment I discovered that nuts (there are two to take up a slack) are worn completely. I am not sure how this is happened
Click to expand...
Does your mill have a power X drive?
It is easy to forget to unlock the gib locks and then use the power X. The power feed can overpower the gib locks and (hidden by background noises) you may not even notice - BUT this is stressing the leadscrew/nut and greatly increases wear.
 
Gennady said:
Yes it does. I am starting to belive that it is my fault and not going to blame previous owner (as usual :) ) .
Click to expand...

Ya, @CWret has a great point.

Another potential cause is our efforts to reduce backlash. I constantly read about others adjusting their backlash to zero or at least as low as they can. I adjust mine to minimum at its tightest locations which is usually the two far extremes of travel. That can leave significant backlash at its loosest location which is usually the middle of its travel. With just normal wear, that can mean 20 or 30 thou of backlash or more. While that might strike mortal fear into the minds of many hobby machinists, it does not bother me. I simply take it into account when I am using the machine.

Just like the power feed, trying to adjust to zero backlash on a slightly worn leadscrew can easily generate forces that can rapidly wear a leadscrew nut.
 
All my mills have 10-80 thou backlash. frankly it isn't worth adjusting the nut for 80 thou. it holds more oil that way!! Backlash only is a problem in climb milling, which I don't do often. when I do, I use the locks to minimize jumping of the table, and only take very tiny cuts, .001 thou or so.
 
I replaced all of my leadscrews (mill and lathe) with ballscrews. Economy ballscrews are not very expensive anymore.

Backlash in a CNC machine is problematic, especially if servo driven where the loop is closed with linear scales because the servo hunts trying to get to zero but the number of ticks to get to zero becomes nonsensical with a lot of backlash.
 
Susquatch said:
Ya, @CWret has a great point.

Another potential cause is our efforts to reduce backlash. I constantly read about others adjusting their backlash to zero or at least as low as they can. I adjust mine to minimum at its tightest locations which is usually the two far extremes of travel. That can leave significant backlash at its loosest location which is usually the middle of its travel. With just normal wear, that can mean 20 or 30 thou of backlash or more. While that might strike mortal fear into the minds of many hobby machinists, it does not bother me. I simply take it into account when I am using the machine.

Just like the power feed, trying to adjust to zero backlash on a slightly worn leadscrew can easily generate forces that can rapidly wear a leadscrew nut.
Click to expand...


Susquatch said:
Not what I'd do
Click to expand...

Good point, @sasquatch. BTW - what method of fixing nut you had in mind?

slow-poke said:
I replaced all of my leadscrews (mill and lathe) with ballscrews. Economy ballscrews are not very expensive anymore.
Click to expand...
Interesting idea, but I afraid it will involve substantial machine modification. I have no plans to convert this mill into CNC... yet.

BTW. were did you source your ballscrews and nuts?
 
Gennady said:
Good point, @sasquatch. BTW - what method of fixing nut you had in mind?


Interesting idea, but I afraid it will involve substantial machine modification. I have no plans to convert this mill into CNC... yet.

BTW. were did you source your ballscrews and nuts?
Click to expand...
From various sources, Amazon, eBay, Ali.

Some vendors will finish the crank end to your specifications.

Often you can just use different bearings to match the ballscrew outside diameter and your machines inside diameter. Before I did the first one I was fretting about mounting ect. After doing one, piece of cake, the fear of the unknown is always worse than the actual doing especially for us industrious types with all of our tools.

I did need my mill to make the nut mounting bracket.
B85B5808-6E2B-46D0-B1D3-E753E11681FD.jpeg1AAA56E6-C802-4D30-ACFD-DA72C13F5F66.jpeg
 
Just an example.

Note if you need to machine the crank end, you will need carbide these ballscrews are very 'hard"

You might need left hand thread version for crossslide (doesn't matter for CNC), just flip the bits.

 
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