We recently purchased 32DP 15 tooth gears for our MK 3 Swerve drive pods. We expected them to press on to the 8 mm shaft on a neo. Unfortunately they slide on easily. We understand that Rev considers the smaller .312 inch shafts to be within an acceptable tolerance to the .315 inch 8mm spec.
Can anyone recommend how to get the pinions to work with the small 8mm shaft?
Typically you don’t press pinions onto large (Neos / Falcons / CIM) motor shafts.
A key + an external retaining ring on the end of the 8mm shaft usually works to retain the pinions (if they are keyed, not sure if your 32DP 15T gear is).
Alternatively, if the gap is small enough, you can bond things on instead of press-fit using something like green Loctite.
The pinion is not keyed. Would you suggest the retaining clip and green loctite?
I believe that was REV’s recommendation when the NEO 550 shafts were undersized.
The retaining ring won’t be necessary if you bond it on.
If possible, try to leave at least an 1/8" between the bottom the gear and the motor boss (i.e. don’t push it on all the way). So if you need to get the gear off you can slip something behind the gear to press it off.
If that doesnt work, you can always slightly knurl or dimple the shaft with a punch.
You might want to try getting some of the 32DP 15 tooth pinions that Andymark has for use with the EVO shifter gearbox. These are spec’ed at 0.312 bore and are supposed to be a press fit on NEOs. They’re only $5 each, so you could easily order one and see if it will work for you.
That’s the pinion we have. I may have been wrong with the sizes I listed above but we did buy these pinions and they slip right on the neo shaft
Specifically, you might try Loctite 680. But beware, when properly applied, you probably won’t get it apart without destroying the motor.
Is there a reason you can’t broach the pinion?
This was my initial thought as well but upon further research of the pinion they’re referring to.
That doesn’t seem to be a viable option.
Personally I will always use a pinion with a keyway on rounded keyed shafts like the CIMs NEO and the replacement shafts for Falcons when designing things but this was a cots assembly so kinda stuck.
The newest addition to the SDS product line the MK4i only uses keyed pinions.
So yeah for anyone who wasn’t aware the smallest pinions in either 32dp or 24dp have no room for a keyway. If you can avoid using key less pinions, that certainly saves some hassle, but we usually do it anyway to minimize the size of our gearboxes. (We usually end up having to cut them off with a dremel causing minor damage to the shaft and face of the motor)
As far as the small shafts, I would try the AM pinions if you currently have the SDS ones. Then try green Loctite. If all else fails and you have a lathe, you might be able to fine a 15t 32dp gear with a smaller bore, and ream it to fit, but this is a royal pain unless you know some professional machinists.
In a pinch, you can also hold the pinion in place on the shaft and use a drill press to drill through both at the very edge of the shaft (perpendicular to the keyway), then tap in a roll pin to interlock the two, but:
You’ll probably want a dowel of the correct size to insert the roll pin, and save it so you can knock out the roll pin if you need to.
A problem with this method is the same as the problem with the Locktite–if your gear is off-center because it’s too big for the shaft, you can get some fun* frictional effects as the gears mesh more and less with every rotation.
An advantage this method has over Locktite 680 is that you can remove the pinion without ruining the motor, but to put on another one, you’re likely never going to get the holes you drilled to line up, so you have to do it again, which can weaken the shaft further. At some point you need to not trust that shaft anymore.
*read: not fun
Interesting. Andymark insists that you need a minimum 3-ton arbor press to get these things on a NEO shaft. They definitely should not be a slip fit if things are correctly manufactured (the pinions, the shafts, whichever is out of spec.) If I were you, I’d honestly check back with Andymark about these to make sure they haven’t gotten a bad batch of pinions. You might also want to put a micrometer to them and check to make sure that they’re really 0.312 bore like they’re supposed to be (and check the NEO shafts too, while you’re at it.)
We have unfortunately been dealing with this for a few years now. Every batch of motors and pinions have slightly different measurements, all well within reasonable manufacturing tolerances, so it’s like trying to hit a moving target to get the pinions to always be a press fit. To that end we developed a procedure to ensure that you will always be able to use these pinions with any “8mm” motor shaft. The procedure has been on the pinion product page for a while, but I updated it today to be more clear. This should also work when pinions of this size from other vendors end up being slip fits.
You will notice we recommend Loctite 271 (aka “Red” ) which is normally used on threaded fasteners. We found this to have a higher breaking torque than the green Loctite retaining compound we tried. This test was done 2 years ago and unfortunately I can’t locate the Loctite product number that was used, to confirm if it was 680 or a different one, but the red seems to be more than sufficient and more teams are likely to have this in their shop already.
Has anyone done the Locktight trick, and does it work?
Is that the pinion that calls for press fitting with a 2-ton arbor press? Seems like I recall one like that on one of the Evo gearboxes.
Yes, it is.
We did use the red loctite. It worked, but it’s not battle tested yet. I would assume this is the best solution though. I talked to folks at Rev and Andymark and they both recommended this approach. Andy Mark tested with different loctites to ensure this is a good fix. Red (680 I believe) was the best they tested.
Thank you. We are trying ours here soon.
