Andymark Hex Bearing Trouble

Has anyone else had any issues with the 3/8" Hex bore bearing from Andymark? (p/n am-0439)
I’d like to here about both successful and unsuccessful implementations.

I’ll start with my experience:
4 total Bearings supporting 2 winch drums. Half of the bearings were standard 3/8" ID flanged shielded, the other half were the AM 3/8" Hex. Both hex bearings’ inner races were destroyed. The -static- load on the system never exceeded 160 lbs. IMHO there was no more than slight, if any at all, dynamic loading due to system configuration.

Our bot this year is using the hex bearings. We have yet to have any damage done to the bearing what so ever. The problem may be over use of the bearings consistently. That’s my biggest assumption.

It would be interesting to hear how the races were destroyed - that is, describe exactly what they look like - or post a decent photo. I bet Andy & Mark would like to get those bearings for analysis, too.

We used these in several places in the drivetrain without mishap, 2 regionals so far.

Can we see a picture of the mechanism they were in?

We are realizing that the inner race of this bearing is very thin, and cannot handle a heavy side load very well. We are working on this issue now, and will give some feedback this week.

Andy B.

This was my guess as to their failure method. Upon receiving the bearings I realized the inner races were similar in size to normal 3/8" inner races, just with a hex bore; I expected to see a thicker inner race to support the material cleared by the hex cutout. The hex as Andy has pointed out causes six points of very low wall thickness. The first bearing to go failed under normal operation with winch drum in place with minimal side loading. The second bearing failed once the drum was removed for a reduction in wrap diameter to provide more torque. With the bare axle exposed the rope stacks as it is wound and is contained side to side by the bearing itself, thus causing side loading. I had assumed that the forces involved would not be enough to damage the bearings, I was partially correct. The standard 3/8" ID bearings were fine, AM inner race in pieces.

I can grab pics once I’m in the lab this Tuesday.


Here’s some photos of how these bearings were used on 228’s 2010 robots.

Here’s our swerve module; we had assembled nine of these: four for competition robot, four for practice robot, one spare/pit display demo.](

The internal gearbox had a 10.204:1 ratio (about 9.5 ft/sec normal) accomplished by a first stage 50:14 reduction (with a 28t idler to act as a spacer), and a 40:14 second stage reduction. The first stage reduction was accomplished between the inner CIM mounting plate and the outer U-shaped gearbox housing plate. The second stage reduction was done on the inside, between the CIM mounting plate and the Colson wheel. To get the torque through the cluster shaft from the first stage on one side of the CIM mounting plate to the second stage on the other, we used one FR6ZZ-Hex bearing.

After about about forty minutes of use, this is what a typical failure looked like.

To fix this issue, we disassembled the gearboxes and modified the cluster shafts. We left the hex on the inside to keep the shaft sandwiched between the two flanged FR6ZZ bearings, but turned the shaft from the bearing outward into round and milled a 3/32" keyway into it. This allowed us to retain the 50t 3/8" hex bore gear from the first stage, but excluded any use of the 14t 3/8" hex pinions for the second stage. Luckily, AM uses 14t gears for standard CIM pinions; we took four of these, bored them out from 8mm to 3/8", and broached them for a 3/32" key. After this, we’ve had no bearing problems of any kind.

It has taken us a while to fix this bearing issue, but I do believe that we have this nailed.

As we found out last year, that inner race for the FR6ZZ-Hex bearing (the dreaded am-0439) was too thin and can only handle light loads. This this revelation, we have been able to get a new bearing made. This time, the outside diameter is 1.125", which leaves plenty of room for a very thick inner race.

Thank you to everyone regarding this issue. Your patience and detailed information was very much appreciated.

So, without bearing any further load on this, I introduce to you our FR6ZZL-Hex bearing, am-0692.


Andy, I am rolling on the floor after that one, but shouldn’t the product code be “am-2B4” ?

Looks MUCH beefier now. Thanks for fixing this issue Andy! The hex bearings have many applications for FRC teams so its nice to see an even more reliable one coming from you guys.


we just ordered 30 of the am-0439 a month ago.

Fantastic, thanks Andy and crew.


Is the flange thickness, etc. identical to a normal FR8?

the outside diameter is 1/4" larger

The outside diameter is the same of a Normal FR8 (1.125), The Flange thickness, Flange Diameter, and overall bearing thickness aren’t posted.

thought you meant relative to the replaced bearing
flange thickness is .062, overall thickness: 0.312 inch

I see that its posted now. The first time I clicked Andy’s link it took me to just a picture. Thanks!

Good to know it’s identical to an FR8 in size.

Don’t cut metal yet. I just went to the shelf, grabbed a few, and measured the overall thickness and flange thickness.

The overall thickness is correct on the website, at 0.312". However, the flange thickness is a tad thinner than what we designed. It is 0.055". I see a minimum dimension of 0.054" and a maximum of 0.056". The website has been updated.

So, the outside geometry is a bit different from a regular FR8ZZ, as the flange thickness on this new bearing is 0.007" thinner.

Andy Baker