9 tooth pinion Cracked - Any suggestions?

[Sh1ine]

We are trying to Press Vex 9 tooth pinions onto Neo Motors - were were able to remove the casing (with the tool that Rev recommended) and that went fine. However when we go to press the pinion on they crack. We have tried 4 pinions on 4 different neos all with the same results. We have even put the motors in the freezer overnight and heated the pinion to 400 degrees to come to the same conclusion.

Is anyone else having this issue? Does anyone know what we can do short of redesigning our Gearboxes? I am worried that the pinions were heat treated even though they shouldn’t have been.

[xnated]

Not sure if this is the best answer, but did you try to sand down the shaft with sand paper?

[Paul_Copioli]

Which 9 tooth pinion are you trying to press on the Neo? Falcon pinion or CIM pinion?

[Sh1ine]

CIM Pinion

[KrazyCarl92]

Would be interested in the following measurements:

-ID of 9 tooth pinion (if you have any remaining untracked ones), probably measured by the back end of calipers assuming a set of pin gauges is unavailable
-OD of NEO output shafts, micrometer would generally be most accurate, but could also use same calipers from gear ID
-OD of a normal CIM output shaft, keeping consistent with measurement technique for NEO motor

-If you (or anyone) happen to have the Thrifty Bot falcon CIM shaft replacement, it would certainly be interesting to compare OD measurements as well, though might not be quite as relevant to these particular gears cracking

With press fits like this, thousandths and even ten thousandths of an inch will impact how the parts interact. The various suppliers of different “CIM style” standard shafts may ride on different sides of the tolerances (e.g. supplier A is a few ten-thou too big, supplier B is a few ten-thou too small, and the difference stacks up to half a thou, and cracked pinions!.. just a possible explanation, unsure whether it would hold true).

May be worth reaching out to suppliers and discussing with them, but having these types of measurements handy may lead to more productive/fruitful discussions. Also worth providing possibly, the method for pressing them on? Arbor press?

I also noticed from the image on the VexPro website that the wall thickness near between the teeth of the 9 tooth pinions looks rather thin. I’m sure a true designed dimension could be measured in CAD though.

If it were me, I’d need a pretty darn satisfactory answer and solution to endorse risking implementation of that particular gear plus motor combo on my team’s bot. I had been hopeful for the possibilities offered by these smaller pinions, and more powerful motors, but maybe it’s not a readily obtainable reality quite yet.

Spring boarding off of @xnated’s sanding the shaft idea, reaming or drilling larger the gears themselves could work…but that might also make the part that’s cracking even thinner.
So I’d probably lean toward the sanding idea.

[ShIfTiNgBoT]

Are you using an arbor press?

If so, tighten the bolts used to align the slide. The rack and pinion setup causes the press to misalign when force is applied if the slide is not securely indexed. When you start pressing, the pressing face of the slide moves towards you, tweaking whatever you’re pressing onto a shaft.

When we do pinions, I make sure the slide is so tight that it’s physically hard to operate the press.

The reason I jump to this conclusion is that logically it’s much more likely to be user error over a material or product failure.

[GeeTwo]

NEO pinions are slightly larger than CIM pinions. Not enough to measure with a vernier, but enough to make installing a keyed pinion for a toughbox more difficult.