Minor repairs on lathe spindle threads on my American Beauty

[Eric Gourieux]

I have an American Beauty with spindle threads that have some minor damage. I'm not sure why/how this happened, but that could be a topic for a different thread (pun not intended). Brent from Robust recommended a die from McMaster-Carr, but I'm having trouble determining which die. I purchased a die that has the specifications: 1 1/4-8 UN. The threads on my AB are 1 1/4 - 8 threads. This die is too small. On the McMaster website, they list dies as UNC and UNF, and from what I can determine, these stand for "coarse" and "fine". I purchased this particular die, since it was the only one I could find that was 1 1/4 - 8. I don't know anything about machining, and my only experience with using a tap was to make my own vacuum chucks with the Beall tap. Can anybody help me with this nomenclature on the dies? Has anybody else had experience with repairing the threads on their lathe spindle?

[Steve Schlumpf]

Eric, the UN means unified threads and a 1.25 x 8 should fit. A photo of the die would help. In my experience, one side of the die has a slight cone shape to it and allows you to start the die onto the bolt or in this case, the spindle. I would also expect it to be really tight and most likely end up cutting ever so slight as you thread it onto the spindle.

Not knowing how much damage you have to your threads - any chance you can use fine files to fix things?

[Leo Van Der Loo]

If the damage is small and not over the whole length of the treaded end, I would use a Thread file, they are designed to do these repairs.

It shows the different files here.

A local machine shop should have them, maybe even lend you one

https://www.amazon.ca/Nicholson-Thread-Repair-Single-Square/dp/B001T4KRHC

[Leo Van Der Loo]

Leo, the thread files you linked to are for external threads only. There is a repair file made for internal threads made by JAWCO but they are difficult to use if the thread damage is anything more than minor.

That is what the OP needs it for, as he says, "I have an American Beauty with spindle threads that have some minor damage."

[Bruce Page]

Leo, you are right, I misread his problem. :o A small triangular file would also work to clean up the thread. Everyone should have at least one in their tool box.

Eric, does the die you purchased have an adjustment screw on the side? You can use this screw to open up the die so it will take less of a cut. First mark the screw slot with a pencil or Sharpie so you can adjust it back to its original setting.

[William C Rogers]

Eric
a picture of the damage would be helpful. Also HF carries a small file set called needle file.

[Steve Schlumpf]

You know, the spindle is hardened, so a die might be really hard to use. One other option would be to use a 1.25 x 8 nut and just thread it on to straighten the threads.

[Dale Miner]

Just to clarify, 1-1/4" x 8 tpi is neithe NC (UNC) or NF (UNF).

1-1/4" x 8 tpi is a NS (UNS) thread.

Make sure your die is clearly marked 1-1/4 x 8 tpi. If it is marked 1-1/4 x 7 tpi it is the wrong die.

A 1-1/4" NC is 7 tpi. Trying to use a 7 tpi die on a 8 tpi spindle will make it appear the spindle is to large and destroy the spindle in the process.

If the damage of the thread is confined to a small area, a 3 corner file would be your best bet with trying the chucks frequently during filing until they run on without any noticeable difference from before the damage occurred.

UNS chart. http://www.gewinde-normen.de/en/unified-special-thread.html

UNC chart. http://www.carbidedepot.com/formulas-tap-standard.htm

[Sid Matheny]

If this is the die you got I think it should work.

https://www.mcmaster.com/#25585a12/=15j05xu

[John K Jordan]

I would also far prefer to use a thread file for restoring damaged threads. A thread restoring die, tap, or file does a better job than a die or tap made for cutting threads.

Many times I have used this kit for metric and SAE threads:
https://www.amazon.com/gp/product/B000P6UNHEged threads.

This kit doesn't have files for an 8 tpi UN8 thread found on lathe spindles, but if I could find one I'd use it rather than a thread restorer die unless the threads were SERIOUSLY damaged. It would probably be a lot cheaper, too. But I agree - a file should make quick work of minor thread damage.

JKJ

[Eric Gourieux]

Thanks for all of your replies. I ended up running a 3 corner file over the problem area and it works great. There was only some minor damage, so it didn't take much. I'm all up and running again.

[Tom Albrecht]

Great.

Now I would like to hear what you think caused the problem. I have my suspicions, but I'll wait for now.

[Leo Van Der Loo]

Great.

Now I would like to hear what you think caused the problem. I have my suspicions, but I'll wait for now.

You don’t think it was chuck grub screw only tightened lightly, do you ?? :eek:

[Doug Rasmussen]

It's probably very good that you didn't use the die on your spindle. In fact, as you say it appeared too small, I doubt you could have turned the die. It takes a horrendous amount of torque to turn a die that size if it's removing even a small amount of material, especially on a heat treated spindle.

There are tools specifically designed for thread repair. My favorite for situations like a spindle repair would be this one from McMaster #2630A12. @ $105. (https://www.mcmaster.com/#2630A12)

[Perry Hilbert Jr]

I also get leery about using a die on such threads. There is so very much more than just the outer diameter and threads per inch. Had a rifle permanently ruined by a jerk gunsmith who thought all 1x14 threads are the same. Turns out there are different angles for the peaks and valleys of the threads. A British 1x14 is not compatible with an SAE 1x14 even though both are "v" threads and the same number of threads per inch. Different angles of the "v"

[Mark Greenbaum]

Eric: You might want to contact the manufacturer and tell them what has happened. They'll probably understand and offer a replacement spindle at reasonabale cost (or free). After you replace the spindle, you can repair the damaged one correctly, and have a spare for future use.

[Joe Kieve]

Just to clarify, 1-1/4" x 8 tpi is neithe NC (UNC) or NF (UNF).

1-1/4" x 8 tpi is a NS (UNS) thread.

Make sure your die is clearly marked 1-1/4 x 8 tpi. If it is marked 1-1/4 x 7 tpi it is the wrong die.

A 1-1/4" NC is 7 tpi. Trying to use a 7 tpi die on a 8 tpi spindle will make it appear the spindle is to large and destroy the spindle in the process.

If the damage of the thread is confined to a small area, a 3 corner file would be your best bet with trying the chucks frequently during filing until they run on without any noticeable difference from before the damage occurred.

UNS chart. http://www.gewinde-normen.de/en/unified-special-thread.html

UNC chart. http://www.carbidedepot.com/formulas-tap-standard.htm


Very interesting...never knew there were so many different thread configurations. Thanks for that information as it might save some of us headaches in the future.

[William Bachtel]

I had some problems screwing faceplates , chucks, etc on my American Beauty also, but I am very careful. I have owned other lathes like 3520 b Powermatics and never had any trouble whatsoever.
Not sure about why? I believe this should come from the factory ready to use without it needing a wear in period. Thats my 2 cents worth. Hope this helps. I turn very big bowls.

[Eugene Dixon]

Just to clarify, 1-1/4" x 8 tpi is neithe NC (UNC) or NF (UNF).

1-1/4" x 8 tpi is a NS (UNS) thread.

Make sure your die is clearly marked 1-1/4 x 8 tpi. If it is marked 1-1/4 x 7 tpi it is the wrong die.

A 1-1/4" NC is 7 tpi. Trying to use a 7 tpi die on a 8 tpi spindle will make it appear the spindle is to large and destroy the spindle in the process.

If the damage of the thread is confined to a small area, a 3 corner file would be your best bet with trying the chucks frequently during filing until they run on without any noticeable difference from before the damage occurred.

UNS chart. http://www.gewinde-normen.de/en/unified-special-thread.html

UNC chart. http://www.carbidedepot.com/formulas-tap-standard.htm

I was curious and looked. Didn't see a 1-1/4"X8 UNS in the chart. I do need to visit the optometrist, however.

[Eugene Dixon]

Had to chase the threads on a spindle on the car once. Thought it deserved a new nut also. Suggest you check for damage on the mating piece. You could chase those threads also. Grub screw penetrations sometimes come with burs as added, no-charge, factory features.

[Doug Rasmussen]

I had some problems screwing faceplates , chucks, etc on my American Beauty also, but I am very careful. I have owned other lathes like 3520 b Powermatics and never had any trouble whatsoever.
Not sure about why? I believe this should come from the factory ready to use without it needing a wear in period. Thats my 2 cents worth. Hope this helps. I turn very big bowls.

Are the difficult faceplates, etc from the lathe maker or other brands? If the various screw on things are from the lathe maker then they've got a manufacturing problem they should correct. If from others, what you're experiencing is not so uncommon even in precision metal working machinery. There are no "standards" on spindle nose threads even though they may be made to a common nominal size like 1 1/4-8.

1-1/4-8 is a standard thread size with quite an allowable +/- tolerance range off of the nominal thread size. A lathe maker might choose to have his screw on accessories with a snug fit on his spindles. If the lathe makers chooses his threads to be on the high side of the allowable tolerance range then faceplates made by another company who has chosen the low side of the allowable tolerance might not fit. The obvious solution would be for everyone to make their spindle threads as small as possible within the tolerance range and their faceplates as large as possible within the tolerance range. The problem with that scenario is everything would have a loose or sloppy fit.

[Tom Albrecht]

You don’t think it was chuck screw only tightened lightly, do you ?? :eek:

Yep that's what I thought. Ask me how I know.

[Eric Gourieux]

I'm not 100% sure how I damaged the threads, but I suspect it is from removing chucks one handed while using the lathe in reverse to unscrew the chuck. I never use lathe power to screw the chuck onto the spindle, but it seemed quicker to unscrew with lathe power at very slow speed. A few times I felt the chuck "tip" toward the ways just before reaching the end of the spindle particularly if there was a turning mounted in the chuck. I think this action damaged a few threads. I did talk with Brent at Robust, and he was extremely helpful. After examining the spindle further, I was able to file off the irregularity and my chucks screw on just fine. In no way do I feel like this was a manufacturing problem, as all of my chucks worked fine with the spindle until I damaged it. Thanks for all of the recommendations and feedback.

As far as a grub screw causing damage, they certainly can cause damage. However, I do not use a grub screw.

[Dale Miner]

I was curious and looked. Didn't see a 1-1/4"X8 UNS in the chart. I do need to visit the optometrist, however.

Well,

Your comment made me take another look. For years I thought everything above 1" with 8 tpi was a UNS. Turns out everything above 1" with 8 tpi is a 8UN series.

http://www.portlandbolt.com/technical/thread-pitch-chart/

I have worked quite a bit with 8 tpi in larger sizes. Some as large as 3" 8tpi.

[Eugene Dixon]

Always enjoy a quick fix. Wait, that has undertones, overtones and semitones. Any way, great news for you. Congrats.

[Thomas Canfield]

A friend bought a 1 -1/4 x8 die from auto parts store to clean up his Laguna thread and loaned it to me to clean up thread on my Powermatic 3520. It was a hex form and a large adjustable wrench was used instead of the normal die handle and I think about $30. The clean up was minor in both cases and not like cutting full threads.

[Joe Bradshaw]

My girlfriend and I both have Robust Liberties. I have found that some accessories screw on really tight. We have some Rubber Chucky products and they would not screw all the way on the spindle. I had to chase the threads. I was told that Robust spindle threads were cut to tighter tolerances. As a side note, my girlfriend had problems screwing her chucks on, until I cut a piece of 2x6 to sit on the ways and hold the chuck at the proper height to screw on. It worked great.
Joe

[Jim Barkelew]

I think the 8 threads per inch thread is for high pressure applications where different thread diameters need to be used in plumbing connections. The same TPI makes a stronger high pressure connection. The 1-8 UNC thread happens to match the pressure thread so it's a great "standard" size. My spindle is 1-1/2 -8 and adapters or nuts are hard to find.

As to the tight tolerance on the spindle I would guess the Robust spindle is made to near the max material condition (MMC) in the tolerance band. Or near the largest diameter tolerance to get a nice un-sloppy fit. A spindle thread cut to the minimum material condition will result in a sloppy fit even though it was made to a tight tolerance. The same thing can be said about what screws onto the spindle. Parts made to the minimum material condition to a very tight manufacturing tolerance will have a sloppy fit. Sorry to ramble, I used to teach a class in geometric tolerancing.

+1 on the triangular file. Works on most any size common thread.

Hole Tapping Tip: To determine the tap drill size, subtract 1/TPI from the screw size. Example: 1/4-20 thread, 0.25 - 1/20 =0.2 No chart needed. You just have to find the drill.

[Ronald Blue]

Here is a good tool to have around and it won't break the bank and it can be used on most thread pitches that you might need to repair. It's a knife edge file and unlike a regular triangle file the angle is much flatter and you can concentrate on the damaged area better. Here is a link for one.

https://www.mcmaster.com/#4236a21/=15l4t10