Loading on grubscrews.

[Owen_N]

I have a 15 N-m torque load on a 10mm shaft. torsional stress = 76.5 MPa.
Side load at the surface is 7.5 x 10**-2 N, which is easily borne by a 2mm pin.
1) Can I retain this by a normal grubscrew on a 316 stainless shaft?
2) Is this improved by a 1.5 mm deep flat on the shaft? This would help disassembly. I will use medium threadlocker on the grubscrew.
This is on a small engine running at 15,000 plus rpm, so there is a fair bit of vibration. I can add a roll pin if I have to. Up to a 2.5mm roll pin should be fine for a 10mm shaft.

 

[Rider40]

In this case I often use a pin of 2 - 3mm diameter "between leather and flesh", drilling parallel to the axis at the junction between shaft and pulley or gear. Easy to machine and good mechanical resistance, but both pieces must be made of steel.

 

[timo_gross]

Cut a keyway into the shaft? Then grind the grub screws thread off at the end to fit the keyway. If the grub screw is only ground to the thread depth you do not even loose a lot of strength.

or overengineer it with a nice complicated tapered clamp.

I think they are a useful option in a lot of cases.

Greetings Timo

 

[Owen_N]

I have been looking at multiple grubscrews. If I use grade 10.1 grubscrews, I think having a grubscrew section shear stress of under 200 MPa (29000psi) is a good indication that it will not drag through the shaft material or come loose.
You can go over the yield point of the shaft where the crown -tip of the grubscrew digs in, as it will take a lot more force to bodily drag the tip sideways through the shaft material.

The flats are good for disassembly, and to get a good grip on the surface. The shaft has to be a little softer than the grubscrew, though. Threadlock is still good. Extreme torsional vibration could still be a problem, like with a disc valve drive on an engine. A rubber coupling is not so bad, as it limits peak torque.