Shop Made Rack for Toyota

I tested the Rhino bar today:

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It is dramatically quieter than the Thule bar. It is a smaller profile and a more aerodynamic shape.

I also made a mount as proof of concept:
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I would like to put something between the mount and the roof rail. For the test, I just put some tape on the back of the mount. That would work, but is there a better material? I could get a thin sheet of plastic? Rubber? Any recommendations? Keep in mind water and UV.

I plan to use M8 pin in torx head screws. All the hardware will be SS except for the load bar. Inside the rail will be a threaded SS plate. Toyota made no allowance to get something inside the rail so it will have to slip in the slot that you see.
 
have or have a friend with a 3d printer? Print a saddle mount shaped like the bar on top and flat on bottom with a stiff TPU filament
 
Bicycle tube is readily available. I looked at McMaster since I already need to order screws. They have EPDM rubber in sheets as thin as 1/32 and it's cheap. That might be the ticket.
That is an interesting idea to 3D print a saddle. My fear is how that would hold up after years of rain and sun.
By the way, that mount above is going to get scrapped. Some idiot drilled the holes in the wrong place.
Also, I did not realize these load bars have a slight curve to them. I don't think it is enough to cause an issue.
 
Working on some hardware:

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NOT looking forward to tapping 12 holes M8 in 304 and 316 SS! I need to order a new tap just for this. The small rectangles will slide into the load rail track and will accept screws from below.
I got kind of lucky on one thing. The angle iron I selected has and angle slightly greater than 90 deg. It should perfectly fit the curve in the load bar!
 
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Well is looks like the engineering department may have screwed up here. I really need some outside opinions.

This shot depicts how the brackets will attach to the factory rails:
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The question is about the long "T-nut" that goes inside the rail. This will result in metal to metal contact inside the rail and damage the finish. I believe the rails are powder coated steel, hence this may promote rust. After some thought I realized the engineer maybe should have used plastic?
Delrin or glass filled nylon are the first things that come to mind. Nylon absorbs water so maybe not a good idea? Is Delrin strong enough to hold the M8 threads? Is there a better plastic? I have already cut and drilled the SS but I want to get it right. Should I scrap the SS in favor of plastic? Another option would be to face the SS with rubber sheet? I would love to go with a bar of Delrin if it could handle the load? I could also easily machine it into a true T-nut
 
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I decided to try do a quick and dirty test on threads in Delrin. I cut a piece 3/8" long and threaded a 75% hole M8 x 1.25. I then tested it to failure in my shop press:

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It failed at about 1000 lbs. Interestingly, it failed rather catastrophically and I was able to recover the sheared thread intact.
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So what does this mean for use in my application? I have no idea but I hope you find this entertaining.
 
I have received some invited commentary from other forum members and formulated a new design.
One astute member pointed out that this is a "safety critical" item and I do not want to have any concerns about this rack coming off on the highway when my dumb friends overload it with gear. Plastics can cold flow over time and this part has to last for years. I also do not like the way the Delrin threads failed suddenly. I felt it was important to keep some steel threads in the mix. Pics to follow.

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Not sure 200 feet is enough?
 
So looking at the T-nut... I would think a thin layer of rubber/bicycle tube would be perfect for that to avoid rusting. I wouldn't do plastics, having a kayak/etc provide 1000lbs of lift is not unreasonable.

My other thought was some sort of heat-shrink tubing over it, but I see they are mostly either NOT UV stable, or subject to cold-flow.
 
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Rubber is a good idea. I have some 1/32" sheet coming. I will ponder that further.
One thing that occurs to me, is there will be very little axial (tensile) force on the screws/threads. Most of the force will be vertical (shear direction) as you indicated. This may force the screws against the inside edge of the slot in the rail. With that in mind, a true T-nut that fits in the rail slot may be optimal?
At this juncture, I should note that the Toyota rails are only rated to 150 lbs. Fake news...
 
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