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Tonneau cover


Kpcseven

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Simple little question here.  I'm going to have my tonneau modifed to add pockets for tillet seats.  With the addition of the harnesses and the hardware for the shoulder straps, how are people attaching the back edge over the boot cover?  I was thinking of having heavy velcro sewn onto the edge of the boot cover and the back edge of the tonneau with holes and grommets to go over the harness bolts.  I'm in the US so just sending to Softbits is out.  Am I better off just getting a showercap from Softbits?

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For my tonneau, I drilled into the tops of the bolts securing the harnesses and riveted popper bases to the bolt heads.

I guess it could be argued that weakening a safety-critical component such as a harness fixing bolt isn't wise, but I reasoned that what I was doing was largely similar to using a caphead bolt - and that you'd be looking at an almighty impact to come anywhere near to shearing the harness bolts, drilled or not.

FWIW ... Adam

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... that what I was doing was largely similar to using a caphead bolt...

The crack propagation might be very different between the two even if they end up with the same dimensions. And if it is the limiting failure condition might also be.

I wouldn't do this.

Jonathan

 

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Agree, I'm no engineer but drilling into the bolts very near to where they would be most stressed when in need doesn't sound like a good idea. If poppers onto the bolt heads is the best place, perhaps they might stick well enough with epoxy, doubtful, but worth an experiment.  Adam, I'd replace your bolt heads if I were you.  Thanks for the comments though.

 

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Following the comments above, I haven't been able to resist pondering the effect of a hole into which to rivet a popper in the head of a harness bolt - I must get out more!

If one considers the bolt to be a (very short) cantilever beam, built in to the chassis and with a point load where the harness attachment sits (and this seams reasonable to me), then the first point to note is that the only stresses present in the bolt above the harness attachment are those due to the pretension of the bolt - no stresses would be induced in that region by load from the harness.  Unless one gets very heavy handed with the torque wrench, I wouldn't have thought those pretension stresses would be that great - certainly not compared with those caused by the impact of an accident (heaven forbid).  The pretension stresses are also constant (or near constant) so there's no fatigue crack growth.

So as long as the hole doesn't extend below the top of the harness attachment (pretty much the bottom of the bolt head), I don't see how any harm can be done.

Getting carried away, I had a look at the effect of a 3 mm hole down the entire length of the 10 mm bolt.  With a 100 kg driver in a 50g impact, my back-of-the-envelope sums (and it was a static rather than dynamic analysis (especially with the rate at which my brain works!)) give reserve factors of 2.6 in shear and 3.5 in tension compared with 2.9 and 3.6 resp. for a bolt with no hole. 

Anyway, forgive my ramblings - as I say, I need to get out more ...

Adam

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Adam, in a head-on impact the 1” tube into which the harnesses are mounted can bend forwards with only the mass of one occupant ... there’s a massive difference between static and dynamic loading.

Stu.

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KPC, I think those are very wise words - something similar is definitely at the forefront of my mind every time I go out in my Seven.  Similar to a biker mentality I guess.

Stu, I acknowledge what you say completely - my exercise was really more intended to show the relatively minor effect of the hole rather than to suggest anything absolute - the RELATIVE effect wouldn't change much in going from static to dynamic.  And the deformation of the tube would absorb energy and relieve stress on the harness bolt.  As I say though, it was very much a back-of-the-envelope calculation ...

Adam

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