Bolts through hex shaft?

Technical Technical Discussion
1

For our climber we had planned on putting a bolt through a tube to grab a loop in the rope, however we don’t have a way to put the bolts through the pipe without drilling through the hex shaft or have two pieces of shaft that don’t go all the way through. We are using 1/2in hex shaft from vex and a 1.25 od roller tube from wcp.

Would drilling a hole through the shaft ruin its structural strength and if so is there another way of doing this?

Thanks for your help

2

I don’t have any real data to back this up, but I wouldn’t drill into the shafts. I tend to be conservative when it comes to mechanical design, but the idea of all of the robot’s weight on a single .5" hex shaft scares me a bit. This even more so with two partial hex shafts or a shaft with a hole drilled in it. Even if you do decide to drill into the shaft, I wouldn’t drill for any more than a #8 screw (mayyyyybe a #10) and I definitely wouldn’t hang my robot on a single #8 screw.

My suggestion would be this:

  1. Drill a hole in the tube
  2. Thread a nut a little bit of the way onto the bolt
  3. Put the bolt into the hole up to the nut
  4. Put another nut on the bolt on the inside of the tube (this is the hard part)
  5. Tighten the nuts together to keep the bolt from moving
3

A hole crosswise in a shaft does weaken it. A small bolt might be OK. What diameter bolt were you thinking? I wouldn’t go bigger than #10, or even #8

4

We’re thinking about using 8-32 bolts

5

We are using a 20in steel hex shaft with multiple #10 bolts in it and It works well.

6

How about drilling and tapping a hole in the side of a clamping hex shaft collar, and putting your bolt(s) in that? No strength lost whatsoever.

OBTW, Not worried about “carrying the whole weight of the robot on the #8 bolt” as long as you get a couple of wraps before the weight load gets serious. Wraps around a drum, especially if it has a decent CoF with the rope, will do 99+% of the holding after a few wraps.

7

Look on McMaster for hex tubing, the 1/2 inch inner diameter/ 3/4 outer diameter slips right onto vexpro hex shafts

8

Alternatively but along the same lines, some item that fits within the tube and slips over the hex shaft, into which you can drill and tap for whatever bolt you like. This could be round shaft, drilled to accept the hex shaft (not a hex hole - round!) and then fastened to the hex shaft with setscrews. Now you ahve as much ‘meat’ as you want to thread a bolt into. It can even be made of steel…