I have metal box to which I want to bolt something.

(numperrets to a bumper).

I cannot get access to the inside of the box.

How can I do this?

1. drill hole all the way though to insert socket head bolt from the back?
2. use internally spreading bolts, heavy duty versions of rivnuts but these are £ 3 a pop (I need 12) plus I don't think are flush.

other?

PU or welding is not an option.

I'd have gone for the rivnuts tbh or large rivets. Why can't you weld it on?

oh, and there is another problem, see if you can spot it!
Rescued attachment aabb.JPG

Rivnuts?

d'oh didnt read your post proper sorry

[Edited on 13/2/09 by chris_smith]

quote:

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Originally posted by Mr Whippy
I'd have gone for the rivnuts tbh or large rivets. Why can't you weld it on?

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hmmm, just htought, maybe make a secret panel on the rear?

drill some holes in the bumper, then weld bolts over the holes on the outside. Then simply bolt the box on.

Or drill holes large enough for the nuts to fit through, hold them in place with a bolt while you weld them to the bumper, welding round the edge of the nut. Like this (yellow is weld around the holes edge)

I know I'm a genius...

[Edited on 13/2/09 by Mr Whippy]
Rescued attachment 01bumper.JPG

Normal way is to use a crush tube

Drill a hole through both sides.
Increase the size of the hole on one side so you can insert a crush tube cut to the correct length in and use large diameter thick washers on both sides.

^^^ yep - that is what I have on the tow points - I don't want them coming off!!

but bumper needs to allow some bending.

what you cannot see that there are 2 botls that go from the top - correct bumper is square C shape - and the holes align hence the crush tube will get in the way.

Assuming the bumper is 3mm box or greater can you not drill and tap ?

Or use chunky hex-head self tappers, like they use for steel roofing panels.