Quote:
Originally Posted by Richard Wallace
Yes. So if REV gets their 8mm hex shaft stock from MMC it will not fit in a hole made using a 5/16" broach.
However, MMC is not the only source for hex shaft stock -- for example, FRC teams generally have a much easier time fitting hex shafts into broached holes if they buy their shaft stock from VEXPro.
So again, what is the actual size of REV's 8mm hex shaft?
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Let me start out by saying that tolerance stackups are a challenging kind of fun, especially when you are dealing with different manufacturing methods, materials, and suppliers.
When we chose 8mm we were aware of how close 5/16 was to 8mm and did consider that teams might want to use that instead. From the cost of the broach perspective we actually have sourced 8mm broaches that are much lower cost and may start to sell them if it seems like there is a demand.
The answer to the question at hand is actually in 2 parts. The size of our standard holes and the size of our shafts (motor and axle).
Our basic aluminum axle (made by extrusion) is dimensioned as 7.95mm +0/-.15 (or in inches .307 - .313)
Our basic hex hole (which is mostly used in plastic) is dimentioned as 8mm +.25/-0 (or in inches .315 - .325
This means our minimum fit tolerance is .05mm (.002 in) and our max range is .45mm (.018 in). The max range is kind of deceiving, because of some of the tuning we will do in our plastic gears to get a good fit.
With these tolerances the 5/16 broach from mcmaster will be fine, along with the steel shafts at both 8mm and 5/16. The Aluminum 5/16 shaft from mcmaster will most likely work most of the time (but not guaranteed) and the aluminum 8mm shaft is to wide of a tolerance range to actually predict, but the ones that came when I bought some measured at 7.93mm
All of the gears and shafts are still about 6 weeks from launch (as we are going to launch them all at once) so there is still the possibility of some of this changing, although I doubt it.