Telescoping mechanism with driveshaft

[hank1090]

Hello everyone,

I'm designing a telescoping mechanism with 3 cylindrical tubes, and a square driveshaft running through the middle. See the attached pic.

It's about 6 feet long fully extended, and I have custom plastic adapters holding and securing the tubes, with holes in the tubes for adjusting length. The driveshaft begins with a 7.7 mm square shaft, which again telescopes into two square tubes. I have two molded bearings at the ends of the cylindrical tubes, but I also need bearings in between. I thought of incorporating them with the plastic adapters, but I haven't found a proper way to secure them.

The other issue is, the square driveshaft is too small for me to design an adapter, and I need some feature so when you expand the tubes, the smaller shaft will lock on and drag the larger tube with it, or it will just get pulled out of the tube and get separated.

I'll appreciate any suggestions to solve this.

Thanks.

 

[Dana]

You don't say what the rpm or load on the shaft is; that will affect what kind of bearings are suitable. Is grease OK, or does it need to run clean?

As for the inner telescoping shaft, increase the clearance between the pieces. Then add a flange to the inner shaft and an internal collar on the larger, so that they can't pull past each other.

Perhaps the inner bearings can be plastic rings that are attached to and rotate with the inner tubes, rather than being fixed to the outer tubes. In this case they may be able to extend a bit ineard and serve as the collar that prevents the innermost tube from pulling out.