Best place to drill into a tube?

[Crispin]

Folks,

As some of you know I dabble in quadcopters etc. On my latest build I need to drill mid-way into one of the arms (25mm round carbon fibre tube) to allow for some cables to exit and was wondering where would be best to drill? Top, side, bottom, off-centred?

The arms are 25mm carbon fibre, prop and motor at one end pulling up (max thrust is about 1.1KGs I believe) and load at the other end which will be 1/6th of 2-3KGs.

Personally I don't think that there will be a problem with small loads like this if I drill a 10mm hole into the side of the tube (I may be wrong?) But was curious about where the best place would be? I think the bottom as it is a tensile load around the hole then.


cheers,
CP

 

[Mblinko]

You are probably right about it coping with those loads, it really depends on the wall thickness as the hole will compromise integrity without some form of strenghtening. I would worry about non-standard loads, e.g. If you crash land it, it may fail at the weakest point.

as for where the load is, if the hole is underneath, then when thrust is applied the area under shear is reduced by virtue of the hole so strength is compromised. If on top, then it would be stronger under these conditions.

 

[Shayne]

My vote would be to drill the hole in the top because you can then fill it with something that will be compressed under load if there is any resulting flex .

 

[Crispin]

Thanks, I'll give it a try at some point. If managed to get away without the need for now.

The loads though are so small compared to what the tube can take I doubt it'll be a problem.

 

[Philip A]

If the loads are vertical, then drill horizontally. That's where beams are drilled or void, along the centerline...

 

[warrenpfo]

I guess you have been working on this http://www.engadget.com/2014/11/05/film-company-does-the-inevitable-shoots-porn-using-a-drone/

 

[Crispin]

ha ha, read that Warren. Quite funny. I like the line where it says "if a device has a camera it will be used for porn". Is that true?