Thunderhex and Thunderhex Bearings

Has anyone else seen fitment issues with the Thunderhex and the Thunderhex bearings after you tapped the end of the shaft. Another mentor brought this to my attention. The thought is the end of the Thunderhex shaft is deforming out when tapped which causes issues in trying to install it into the Thunderhex bearing. The mentor plans to try Hex bearings, but I think he will have the same issue.

Take the Thunderhex and clamp it in a drill. Then take sand paper and wrap it around the Thunderhex. Spin the Thunderhex while moving the sand paper up and down it. It will wear away the paint on the rounded edges making it easier to fit in the bearing.

I did notice last week that one of our shafts was a little harder to get in the bearing than I expected, and we had tapped that end of the shaft. It still fit, though, so I didn’t really think much of it.

Try taking a file to the end of the shaft. Maybe there’s a small burr there from cutting the shaft?

This warning is in red on the thunderhex page itself

Note: Due to a manufacturing variance, our current inventory is slightly out of tolerance. The diameter of our ThunderHex Stock is oversized by (on average) 0.0003". This results in a press-fit into ThunderHex round bearings. Users who need a looser fit should gently sand the rounded corners of the hex.

I’m assuming the removed burrs, but will check tonight and will have them try sanding them down. Some of the shafts are long, so we will probably clamp in our lathe and run some emery cloth on them.


Isn’t that an old warning from last year? When our bearings and shaft first arrived we checked the fitment and it was smooth. So thats why we suspected the tapping operation.

Our team has always had issues with the thunderhex being oversize enough where bearings, sprockets, ect won’t slide on easily. As others have said, take some sand paper and put it in a drill to remove some of the paint. This usually lakes care of it, but sometimes you have to file down the actual sides.

Thank you!

Because of these issues our team has stopped using thunderhex as axles, only using leftover materials as cool-looking standoffs.

Last year was thunderhex hell for our team

Have you found another option when using hex shaft? We bought some from McMaster-Carr last year and had issues with the tolerance on it vs. the tolerance of the Hex Bearings and had an extremely difficult time installing the shafts on our climber. So we decided to go with the Thunderhex this year.

Last year we almost always used thunderhex axle with regular hex bearings. This allowed for the ease of tapping but also an easier operation of getting the shaft into the bearing.

Thanks we plan on testing the regular hex bearings tonight to see if their is a difference.

Personally, I think dealing with Thunderhex being a little oversized is a lot easier than dealing with regular hex being oversized. At least with Thunderhex we can toss it on the lathe and take a couple thou off, and once you dial in the amount you need, it’s pretty easy to run down an entire shaft. Heck, in the few cases where we feel a need to use solid hex (instead of Thunderhex with the hole in the middle), we turn it down to fit in thunderhex bearings. It’s just easier to slide the shafts in and out of thunderhext than it is trying to get the shaft prperly aligned with the inner race of a hex bearing.

We haven’t noticed any fitment issues after tapping our thunderhex, but it certainly seems possible. What size tap are you running, 1/4-20?

The batch of thunderhex we bought before this preseason had no fitment issues, we love it.


Yes it is 1/4-20. No issues seen before tapping, but was found after.

I agree

Just throwing this out there - when your shafts arrived, were they left outside in the cold before opening? The tolerance is so close that a shaft below room temperature will smoothly fit, but they will be too tight if you don’t do that.

Anyhow, for us it’s now a standard practice to take some emory cloth and shaft stock and run it on the lathe for a second or two before fitting into bearings. Just enough to strip the anodize layer off should do it. (We also use the “tight press” bearings because they are so cheap in 11-packs)

ThunderHex is way, way, way better than regular hex. I’ll never go back to regular hex bearings - they are a pain to fit, a pain to align, and they are far harder to fix the shaft for if they fit too tightly.

They were not left outside.

Thanks for the feedback. I’m leaning this way myself. Hearing confirmation from others is re-assuring.

I have used shrinking to fit thunderhex into bearings before. I used liquid nitrogen(-320 F) to do it, but dry ice(-109 F) should do just fine and a lot of grocery stores carry it.

Aluminum shrinks/expands ~0.001"-0.0015" per inch per 100 degrees F, which you can get about 1 thou shrink with dry ice or about 2 with liquid nitrogen.

Andymark offers 7075 hex shaft that our team now uses for drivetrain axles (but works for anything else). If anything, however, this shaft is a little too thin. There’s a small degree of play in our wheels that are mounted on it, but we haven’t noticed a loss in performance as a result.
It could even just be our wheels too. I’ve been too busy with other parts of the robot to address the seemingly trivial problem that is axle size. We’re just happy we didn’t need to slice of faces of the shaft on a mill this year

We also get hex shaft from a local metals warehouse, Discount Steel. They may or may not ship to your area… but if you have a local metals warehouse I’d imagine they would have hex shaft. If you do have a shop nearby bring hex bearings and test them on the shafts before you buy them