Experiences with Thunderhex/regular hex in a hex 5c collet

We are looking into getting a 5c collet system for our lathe and are wondering what experiences other teams have had with this system when using it on Thunderhex/regular hex purchased from an FRC supplier.

Works great! Collets make it super easy.


We’ve used MSC products 35505965 and 35506054, cheap and certainly accurate enough for our needs… snap ring grooves don’t need to be very concentric.

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For general operations, hex collets are great as you do not have to worry about rotational slip. If you need to turn something very concentric however you likely do not want to use a hex collet and/or regular hex stock as the hex collets are never perfect, very good but never super low runout. 1678 uses an Emergency Collet that we drilled and bored to 13.75mm round, the boring is very important as it will ensure the hole you now have in your 5C collet is perfectly aligned with your lathe spindle. If you want to go full paranoia mode, buy some 5C collet blocks to use with your set and put the collet+block in a 4 jaw and make it perfect every time. Learn to love your dial test indicators!


While I love everything about this - is this level of precision needed for frc purposes.

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If you are making custom gearbox shafts that do not rely on the Thex or hex profile it is required if you want it to run smoothly. Also the collet block in a 4 jaw is about the only way to make regular hex shaft shouldered down to Thex perfectly concentric unless you get really lucky with the collet you got and how it fits in your machine.

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Rather than going through this whole process would purchasing the nearest larger 64th inch collet work? It would be a 35/64 collet which is about 5 thou larger than the specced 13.75mm of the 1/2in thunderhex. If so we will likely pick up that and one for 3/8 thunder hex along with the regular hex colelts for regular hex shaft.

I shoulda also say that a big part of moving to this system is the speed of it vs the the accuracy of it. The lathe we use is the one that the metalshop class in our school uses and all of the 3 jaw chucks there are all beat up. Each of the chucks has a large amount of runout which results in the need to shim and indicate any hex stock put in the jaws which takes time. A 4 jaw would be amazing but again its a time thing. You can do it fast but you need decent bit of experience.

We do have a few reasons for looking at a 5c system over a 3 jaw for a robotics only chuck. One is a safety thing. If we ever need to sand something down its a lot safer to have it held in a collet chuck vs a 3 jaw with regards to getting clipped by the jaws. Another things is as the above picture says one round stuff for something like a shooter we’d really want to get it perfect as something spinning at high speeds on a badly balanced shaft is just scary. And third tbh is it just seems cool to try out a 5c system.

I have 5C setups for half my lathes, and honestly we keep the 3 jaws on all the time. It’s just a lot more convenient. Also, if a student hits something (which does not happen often but does happen) I’d rather they not hit my ~$1000 5C collet chuck.

We are set up on one lathe with a pneumatic closer which is nice when running production spacer part off jobs, but that’s not often.

The one time I certainly did use a 5C was to drill some 12mm precision linear rod that I didn’t want to gouge.

Also, we’ll use 5C in a vertical fixture in the mill, or on the 4th axis. Those see some use a couple times a year.

These are more expensive than Lyndex-Nikken collets on McMaster (which are primo).

No. Collapsing a collet more than .001 or so will cause it to permanently deform and introduce runout.

a 5C collet chuck is infinitely safer for students than a 3 jaw chuck.


I don’t disagree on that. I’d just rather they not wreck a nice set-tru collet chuck or in the case of one of our lathes, the spindle nose taper (5C sleeve inside spindle) So, the 3 jaws stay on most of the time.

I would like to note that you can get a 5C collet from Shars.com for around $7 for common round sizes and hex sizes for about $20 each.


Going deliberately oversize on a 5C style collet is a horror show. If you do manage to get a grip, you’ve probably damaged your collet (as another post mentioned) and even in that case, the design of the 5C would only be gripping it at the very front edge which would allow the part to pivot since it’s gripped in only a small area.

The design of ER-style collets allows them to support a wider range of sizes and still clamp down evenly as an alternative - lot’s of different collet holders out there to adapt to your machine.

While I have a few dozen 5Cs, I’m going to make the move to ERs for their flexibility.

– Chris Herzog - Joliet Cyborgs #4241