Drilling Hole in Steel Tube for Go Kart Cables: Safe?

[AEC]

I want to drill a 3/8" hole in one side (not through) of a steel tube, 1-3/16" OD 1/16" wall tube in order to run cables through it. The tube is my son's go kart frame so I want to make sure it is safe to drill a hole into it. I'd appreciate any comments.

 

[GunnaSix]

Depending on the loading, it has the potential to weaken the tube fairly significantly. If failure of the tube would cause an unsafe situation, I would be hesitant.

 

[AlephZero]

I don't think we can give you any "definite" advice without knowing a lot more about the situation.

A small hole will increase the local stresses in the tube by a factor of about 3 times, but whether that matters is just guessing, on the (lack of) information we have.

If you do go ahead with this, make sure you file the edges of the hole smooth to get rid of any "sharp corners" where a crack might start to form.

 

[AEC]

Thank you very much for the feedback. The go kart fram is about 50" in length, the hole would need to be near the center of the two axles so that's probably the worse possible place. I won't take a chance since my son get the kart up to 80 klm/hr and we figure pulls 3G in the corners. Thanks again, this forum is an awesome resource!

 

[xxChrisxx]

Thank you very much for the feedback. The go kart fram is about 50" in length, the hole would need to be near the center of the two axles so that's probably the worse possible place.

Even though the hole is pretty big, the tube is colossal.The stress concentration factor is probably larger than 3, as the worst case is combined bending and torsion. It's really not much of a risk though, the tubes have a huge safety margin to the loads you are talking about.

Why not drill and feed the wires, either with a smaller hole, or just weld the hole back up again.

I won't take a chance since my son get the kart up to 80 klm/hr and we figure pulls 3G in the corners.

I can gaurantee you that's not the case. Superkarts with aero don't pull 3G.

 

[AlephZero]

I can gaurantee you that's not the case. Superkarts with aero don't pull 3G.

Any type of kart can pull more than 3G if it crashes. You have to design for the worst case!

 

[xxChrisxx]

Any type of kart can pull more than 3G if it crashes. You have to design for the worst case!

Sorry, I can't tell. Are you being serious?

 

[AlephZero]

Sorry, I can't tell. Are you being serious?

Absolutely. Impacts between hard objects can easily generate short-duration decelerations of hundreds or even thousands of g. Of course the loads that get to the place in the chassis where you drilled the hole may be less than that, but we don't really know how much less, in a scenario like side-impact collision after a spin for example.

You might be able to get some information about the max loads or acclerations assumed for kart design. I would hope there is some consensus in the "karting industry" about safety issues, but that's outside my field of knowledge.

 

[xxChrisxx]

If it crashes that badly, it's ******. It's a Kart, there's nothing you can do about it.

There are crash structures around the main chassis for general contact and knocks and bumps. So it's distributed and fed into the main chassis at multiple locations.

The three G as told was a sustained cornering force, not an impact load. And kiddie karts, just aren't loaded that badly.

It's made from 14 gauge, 1-3/16" tube. Considering that spaceframes designed to take real car bits, are made from 1" 16 gauge, and can easily be made to run wiring down the tube. It's fine.