Spindle thread breakage

Hey all,

I experienced something new tonight and was curious if anyone else has had a similar experience? I went to remove my collet nut and found that it had locked onto the threads pretty good. I used some WD-40 to get it loose, but it appears that part of my thread broke off and obstructed the nut from coming off, which ended up welding the broken off portion into the threads during the removal process. The nut was NOT overtorqued or cross-threaded. It appears that there is a second set of threads going from the collet nut attachment location into the actual spindle. I’m hoping that I can just get another set of threads and change it out to get back up and running. Any help would be very appreciated. I’ve already sent a ticket in to get some support from the staff.

Thanks in advance!

Usual preface, I’m with PreciseBits so while I try to only post general information take everything I say with the understanding that I have a bias.

We’ve seen this more times than I’d like. It’s usually due to material being stuck in the threads of the spindle or collet nut when tightening it down. Can also be caused by over torque, corrosion, metal flakes from component wear, and a number of other things. As such it’s recommend to at a bare minimum blow out the spindle, collet, and collet nut between every bit change. It’s better to actually clean them.

Worst case you can clean the threads of the spindle up with some needle files. As long as you have at least 2 full threads left it shouldn’t effect the system too much. If you go that route make sure that you taper off the lead in thread so it doesn’t catch.

I know you said that you didn’t over torque the nut. However, most people aren’t aware that there are torque maxes listed for the setup (ER size and nut type) in addition to a recommend torque for the bore size of the collet. As an example an ER16 with a UM/A/Hex nut has a max torque of 41 ft-lb. However, here’s the recommend torque base on bore diameter:

  • 1.0mm-1.4mm - 6 ft-lb
  • 1.5mm-3.9mm - 15 ft-lb
  • 4.0mm-4.9mm - 30 ft-lb
  • 5.0mm-10mm - 41 ft-lb

The above numbers also come from pricey industrial spindles (HSD, Columbo, Mechatron) and matching grade nuts. If either are hardened wrong, made from the wrong steel, lack proper lubrication, and/or aren’t clean they may not hold up to the maxes.

One last thing. Collets and collet nuts are consumable parts. Each cycle wears them and can effect runout, clamping force, and the material of the components. In your pictures your nut is past it life. I say this from the groove that has been ground at the end of the chamfer. In general once you get a groove or spalling material in the chamfer the nut needs to be replaced. At this level I would also check the collets. If they also have grooves or transferred material from the nut they should be replaced regardless of any other factors. This is due to the fact that they will damage or accelerate the wear of the new nut.

Hope that helps. Let me know if there’s something I can help with or expand on.

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Thank you very much for your response! Ironically, I bought a new collet nut and 1/4” collet online and they arrived in the mail the same day that this breakage occurred because I’d noticed there was unusual wear on the collet. Are you aware of any torque wrench options that will work on a horizontal orientation? I have inch/lbs and ft/lbs torque wrenches, but they are for typical 3/8” sockets. I am also still waiting to hear back from support about being able to get new set of threads and taper. It looks like there are holes for a special wrench to hold the spindle still while unscrewing the threads from the spindle motor.


No problem.

Wrenches depend on the nut type and I don’t know what you are using. In general though you can usually find spigot end wrenches that will let you rotate the head to different orientations. Norbar is the one manufacturer I know of off the top of my head for those.

I don’t know what you mean by getting a new set of threads and taper. The part that holds the collet is the armature and it goes through almost the entire length of the spindle. It sits inside of multiple bearing sets that would need specialized tooling to remove and remount without damage. In rare cases I’ve seen things called spindles that have a removable chuck. No real spindle I’ve seen has that though. Closest you get is an ATC spindle and those are real pricey.

Let me know if there’s something I can help with.

This is an extreamly helpful response. Thank you for taking the time to help us all here on the forum.

@AndrewSwann There are “Crows Foot” wrenches which work well in a torque wrench. I bought mine at Harbor Afraid… I mean Freight (lol)…

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No problem. Glad it was useful.

If there’s something I can help with here or in another topic let me know (@ or email me). I usually try to check the forum a couple times a week but there’s not been much that I can address over the last year or so. I have a pretty broad knowledge of cutters their use and associated parts. I have to be careful about comparisons and brand specifics though as I don’t want to be advertising or marketing.

You might try a product called Musclechuck. Should solve thread problem and provide quicker bit changes.

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@AndrewSwann Was Inventables able to help you? I have the same problem, and I’m curious about replacing the threads on the spindle. It does look like they are designed to unscrew from the spindle.

Hey Adam, Inventables was not able to offer any information or assistance on the matter. The response was essentially, “The spindle assembly is not sold as individual parts, so you have to buy a whole new spindle (~$250 if I recall correctly)”. They look like they should have threads that make the taper portion removable, but the tech I was conversing with couldn’t verify anything. Also, they don’t know anything about what torque is recommended for their spindle. :roll_eyes: I bought an adjustable digital torque wrench that I have set to 16 ft/lbs, and that feels comfortable so far. I don’t want to get a muscle chuck, mentioned in a previous comment recommendation, because it reduces the height of material you can cut. Use some small files to clean the threads out so that you can thread the collet nut on without much trouble. I’d also strongly recommend getting a new collet and collet nut, because I’m sure that if your threads broke off, they damaged the threads on the collet nut as well.

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Thanks for getting back to me. I have a support request in now. I’ve had disappointing encounters with support before, and I was hoping your experience would prove that my past experiences weren’t the norm.

To be clear, I don’t think that it’s because support doesn’t want to help; I just think there’s some aspects of the machine that were streamlined (particularly on the Pro) so that it ships with less pieces to try and tinker with to get to work properly. This seems evidenced by the fact that the gantry comes fully assembled with the spindle attached. The folks who originally designed the setup aren’t the same ones who are troubleshooting problems, so I think they are doing the best they can with the information available to them. I was just really disappointed that they couldn’t offer something as simple as the torque recommendation on their spindle. That seems like something that should have been part of the tech-specs to keep the “average consumer”, such as myself, from inadvertently damaging something and needing to get it fixed. Customer service has been great in my other interactions. My hose for dust collection was kinked in packaging, and they sent me a brand new one express shipping at no cost.

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That’s nice to hear.

I’m just following up with the results of working with customer support. It was a very good experience. She was quick and friendly. I need to be more careful about making support critique comments on forums. Forums are forever, but these are real people we are dealing with, and they deserve better than to be immortalized in negative ways.

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