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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.
Maker of Fine Kindling, and small metal chips on the floor.
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Originally Posted by Dale Miner
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.
"When the horse is dead, GET OFF."
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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.
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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.
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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.
Last edited by Eugene Dixon; 12-19-2016 at 3:24 PM.
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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.
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Yep that's what I thought. Ask me how I know.You don’t think it was chuck screw only tightened lightly, do you ??
[OP]
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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.
Last edited by Eric Gourieux; 12-19-2016 at 3:30 PM. Reason: Additional comment
Member
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/technica...d-pitch-chart/
I have worked quite a bit with 8 tpi in larger sizes. Some as large as 3" 8tpi.
Contributor
Always enjoy a quick fix. Wait, that has undertones, overtones and semitones. Any way, great news for you. Congrats.
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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.
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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
Contributor
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.
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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
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