pic: Gold VexPro sprocket

Apparently when you weld to a black anodized VexPro sprocket the black turns gold.

This reminds me of 2013. We used a press fit dead axle wheel assembly. To make assembly easier I put the shaft in a freezer and the sprockets on a hot plate, the sprockets would either get slightly lighter or turn a quite off putting green color.

It’s worth noting that for aluminum to turn the color your sprocket did it needs to be heated to almost 2000F. Annealing aluminum on the other hand is done below 1000F. Just something to be aware of.


edited: nevermind, noticed grinding marks.

“Easier” is one way to put it. I seem to remember you quickly putting two sprockets, a wheel, and the shaft in alignment, pouring on some green loctite, and hanging off a 5 ton arbor press in order to press the assembly together. With about a 50% success rate… :stuck_out_tongue:

Good times!


Is this because the chemical structure of the dye used in the ano changes at high temperatures, or because some kind of thin film interference varies due to head expansion between two layers?

At 2000 F your aluminum has turned into a puddle & no longer looks like a sprocket. Maybe even so at 1000F depending on the alloy. Anyway 1000 will have killed any age hardening. :]

I’m curious how you got the sprocket to hold its shape as the weld cooled - or was it a non-issue?

I was not personally around for the welding but I don’t believe they did anything special, nor did we instruct them to, and there is no warpage.

Good catch, thanks! I got my metals mixed up, aluminum melts at ~1200F so disregard my previous comment.


Let us know how it holds up now that you’ve removed most, if not all, of the heat treatment!

Was this a 6061 or 7075 sprocket?

It is a #25 plate sprocket, VexPro specifies that they are originally 6061-T6 AL

I doubt we will see any wear as it is a prototype in an extremely low rpm application, but if something interesting happens I’ll post it.