paper: 3008 Custom AM Super Shifter Plates Pocketed

[Tristan Lall]

Originally Posted by GRT808

Yes we have gotten it waterjetted thanks.

As for it bending we are using aircraft grade aluminum (not sure what alloy) but in our past competitions we have used the same grade and have never seen it break in any of our applications. I'm a bit more concerned about the effort it is going to take to make everything fit (such as the bearings) since the jet is so precise.

We are using 0.187" aluminum plate.

Any suggestions or concerns I should be aware about before season starts?

Alloys of aluminum tend to have very similar elastic moduli, no matter their strength—in other words, if it's just bending you're worried about (and not stresses due to bending, which are tiny in this application), the alloy and temper don't matter very much. (That's why Cory is telling you to save your money.)

Strength (not stiffness) matters when you're worried about yielding or breakage of the material. For most gearboxes, this isn't an issue. Instead, you need some degree of stiffness to maintain alignment (e.g. when chains or wheels put loads on shafts, or when the frame of the robot flexes during use). While much of that stiffness depends mostly on the connections (tolerances, fastener types, preload, friction, etc.), the plates could play a role in it if you lighten them aggressively like that.

By the way, the kerf from waterjet cutting isn't perpendicular to the plane of the workpiece (except on the fanciest tilting-head machines). Also, the surface finish depends on how quickly the machine is travelling—slower is better, but time is money. While it is possible to cut many gearbox plates directly on some waterjets with no secondary machining, very precise cuts probably will not be possible or feasible at the shop you're working with.

You should experiment with bearing fits if you're going to pursue this, and consider flanged bearings and gap filling retaining compound (see Loctite's 600-series documentation). Also, by introducing error into bearing positions, you introduce error into your gear meshes. You may need to add a couple thousandths of an inch of extra clearance between nominal centres, to account for potential misalignment. (A little backlash is less worrisome than binding gears.)