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Originally Posted by R.C.
But I can't see you having an issue with loading them as "spacers". As we've been using 6063 for all our spacers since its so darn cheap/easy. We also use a handful of plastic spacers on gearboxes as well. No issues with either or.
6063 can gum up pretty badly when machining but your taking off so little that it shouldn't be an issue. We sometimes drill out the current spacers for 1/4" bolts.
-RC
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We do everything mentioned in this thread in various spots; counterbored, the specific 3/8" tubing above, and plastic spacers.
We choose them in different spots depending on the alignment required. Very few of our gearboxes have their alignment and spacing entirely set by the standoffs. Those that do (like our drive boxes) we generally will counterbore, but not always (as it is a more time expensive process).
The aluminum tubing we use when we just need to attach two plates together for stiffness, but aren't counting on it for any alignment. I'm a big fan of clamping frame members with gearboxes, and the frame member handles all alignment. This specific tubing size is something 254/968 found on mcmaster a while ago and have shared with others as it's convenient. There is no concern of failing this tube, even w/ it being 6063. We use it in high loaded situations no problem. The time saved over drilling is really nice.
We use the plastic standoffs for the same reason as above, but when the load is lower. This is an example; 94639A134. This ENTIRE series on mcmaster/fastenal is just awesome. I'm proud that we introduced it into FRC as it has saved us so much time. They come in standard thickness from 1/8" to inches, in varying OD's per bolt size. We use them all over the robots and save massive time. They come as an ugly nylon, but we RIT dye them black and they're beautiful.
In summary, all the ideas posted about standoffs are valid so far, but they apply to different cases. It's not a good idea to assume that because you want things to work well at the system level, all parts MUST be super precise.
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The different sizes are necessary because of the shaft's shape: the back end is 0.375" and round, the front is 0.5" hex. The fitting bearings for each side are different in size. I could change the shaft to allow using the same bearing, but then it'll have to be manufactured instead of just buying it from andymark.
As to the standoffs, I didn't actually consider how to make them... I'll look into it.
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Using an off the shelf is a great idea if you have limited access to fabrication. It can even be a great idea when you do have access if the shaft meets all your needs. We've got a full, capable shop for FRC and we LOVE not having to make parts!