I have a product where we transmit quite a lot of shear force through a small bolted join. On our current design the contact area is about 10mm², the bolt is M2, and the force is 45N, and it works quite well. But now we want more, the requirements are:
- We want to go up to 300N, in either direction along one axis.
- No sliding between the parts, even at the micron level. Elastic deformation of a few microns is OK though.
- Both parts are grade 4 (pure) titanium.
- The top of the lower part must be flat, nothing sticking up when the second part is removed. Shallow holes are OK.
- Ideally, the position of the top part in the direction of the force should be adjustable. Preferably continuously, but failing that then in about 0.5mm steps.
- The join can be made and un-made about 100-1000 times over the life of the product. By a competent and careful operator.
As is, at 300N the joint as is slides around all over the place. I could go up to a M2.5 machine screw, or maybe M3 at a pinch, but some back-of-the-envelope scribbling suggests that won't be enough. I could specify a removable epoxy, but can't find one strong enough. So I thought about mechanically keying the two parts so that they cannot slide.
I could cut both surfaces with a zig-zag profile, like a screw thread. In fact I guess it might be possible for a machine shop to do that with an M3 thread cutting mill (if I pick the right profile) or the corner of an end mill (for a 45 degree profile).
I've not seen such a thing before, at least not at this scale. Does it sound like a good plan? What should I watch out for? Is there an easier option I have missed?