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Author Topic: Shoulder straps and seat back
Rob Gendreau
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I’m wondering if it’s OK to modify the holes where the shoulder straps enter a Kirkey aluminum seat. The attachment at the cage is sufficiently high, but the strap holes are a bit low to my shoulders, meaning the straps have to bend to go back up over the shoulders.

Adding more hole obviously leaves less strength in the back of the seat, but I’ve got a seat brace and the new holes would be just at the shoulder line, so that the only weight they’d have to take is the head snapping back. I suppose I could attach a piece of ⅛” steel or something to reinforce the old hole.

Ideas?

Rob

Rob Burgoon Verified Driver
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I made my holes a little taller to accommodate my hans. Can't speak to how safe it is though.

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It really makes my week when nobody crashes into me.

Keith in WA Verified Driver Made Donation to Website
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I don't know the Kirkey's seats that well but I know a few other alumiminum seats and I've designed a lot of sheet metal aluminum parts.

Two things to watch out for...

1) If there was a rolled edge on the hole, you just weakened the hole significantly. The rolled edge adds a whole lot of strength. With thin aluminum, most of the strength comes from the geometry. (Think of how hard it is to crush a pop can until it has a little dent in the side.)

2) Round off the sharp edges. It can cut your belts and easily cause cracks starting at the edge of the hole. Aluminum is prone to fatigue. Cracks love to start at sharp edges.

Personally I'd reinforce the hole if I were you.

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Keith Novak
(Will work for tires)

Casey Z Verified Driver Made Donation to Website
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quote:
Originally posted by Keith in WA:
I don't know the Kirkey's seats that well but I know a few other alumiminum seats and I've designed a lot of sheet metal aluminum parts.

Two things to watch out for...

1) If there was a rolled edge on the hole, you just weakened the hole significantly. The rolled edge adds a whole lot of strength. With thin aluminum, most of the strength comes from the geometry. (Think of how hard it is to crush a pop can until it has a little dent in the side.)

2) Round off the sharp edges. It can cut your belts and easily cause cracks starting at the edge of the hole. Aluminum is prone to fatigue. Cracks love to start at sharp edges.

Personally I'd reinforce the hole if I were you.

Agree 100% with the above.

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Z Brothers Racing / East Street Auto

Casey Z - 1.6 Kettle
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Connie 62 Verified Driver Made Donation to Website
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If the shoulder straps touch the top of the holes through the seat, then have to go up and over the shoulder, the straps will compress the shoulders downward in a frontal impact, raising the possibility of injury. The straps should go through the seat and slightly downward to the shoulder.

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Jim Thill
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Thrillz Racing

Rob Gendreau
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Sounds like I’ll open up new holes and fabricate a plate that I can bolt on that’ll cover the old hole and surround the new hole. I'll just bolt or rivet it on.

I agree about the need to avoid cutting the roll; I thought I’d avoid it entirely and do new holes just big enough for the straps. Smoothing out aluminum is a bit of a pain; I’ll just go at it with some flapper wheels and then see if I can get a smooth enough edge to avoid the fraying. I may have to apply something to give it a smooth edge.

Thanks,
Rob

Keith in WA Verified Driver Made Donation to Website
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When you bolt or rivet on a doubler to reinforce the new hole for the harness, the rule of thumb with aluminum sheet metal is leave more than twice the diameter of the fastener holes between the edge of the rivet holes and the next closest edge. At least 2D + .05" That's the bare minimum so I'd be conservative and leave more. It will help prevent the rivet holes themselves from starting cracks.

Aluminum is a pain to smooth out. It wouldn't hurt to bond some rubber or plastic tubing to the inside perimeter of the harness holes to prevent fraying the harness when you're done.

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Keith Novak
(Will work for tires)

Greg Bush Verified Driver
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If its like my seat there is some aluminum edging around the hole. Remove it first in one piece, "move" the hole as listed above, then reinstall the edging. Easy cheesy.

   

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