I've hit a bump in a project of mine. I need a simple assembly to house a small ball bearing that will support part of a robotic arm assembly. It plays a part in the wrist joint, as one side is directly servo driven but the other needs a bearing to hold in steady. The bearings I have are 8mm in diameter and have a 4mm diameter hole for a shaft or bolt. I have access to aluminium sheet, acryllic, and MDF wood, as well as M2, M3, M4 bolts and rivets for fasteners. Anything else I will have to source, but it shouldn't be too hard of a problem.
To put my setup simply, you have two pieces of sheet aluminium - one being part of the lower arm, another being part of the wrist servo mount. There is a 5-10mm gap between them in which I need to place my bearing. Obviously, the two need to be able to rotate freely. I've previously used M3 blots with ni-lock nuts as pivots, but I'd like something more robust.
Make a bearing holder out of mdf. Drill an 8mm hole in the center of a small mdf square, then saw a slot from the outside in to the circle. The bearing will fit inside, screw through the slot to pull it together it will hold the bearing secure.
It`s kind of hard to explain without a picture, but image a C shape of MDF and the bearing will fit in the center. Putting a bolt/screw through the C end points tightens it.
I get the idea. My main I get the idea. My main problem now is friction between the inner piece of aluminium and the ball bearing mount. I’m imagining that I’ll need a bush of some sort to act as a rotating spacer?
Fix the mdf solidly to 1 Fix the mdf solidly to 1 part of the wrist then an m4 bolt should fit through the bearing to fix into the other end of the wrist. Unless I`m missunderstanding the setup… which is quite possible
This was my original plan. The flaws are that the M4 bolt head is 8mm in diameter, and the MDF is exactly the same thickness as the bearing, so I have to drill a 8mm hole in the outer plate. This means the bearing can pop out, or at least become misaligned. Also, without some sort of spacer the second plate will be bolted directly against the MDF and the non-rotating part of the bearing. This will likely be problematic, especially as I’m likely to have some sore of fastener on that surface to mount the MDF (I hate glue, because the way I build stuff, I assemble, test, then often have to disassemble and try again).
After school I’ll try and come up with a diagram of what I think I can do.
Problem Solved I’ve come up with a working solution, It’s too dark for pictures though (aluminium + flash = bad photo) so I’ll post one tomorrow. It’s basically a MDF circle with a 8mm hole in it for the bearing, sandwiched between two pieces of aluminium with 6mm holes that hold the bearing in place, but allow a shaft to pass through. I’ve made a makeshift bush which allows a M3 Bolt to be passed through it and securely fastened in place.
