Hybrid Roof Rack (sorry 4x4mike)

[Seanz0rz]

Tie a red flag to the end of it and you're fine.

[Kryptoroxx]

Tie a red flag to the end of it and you're fine.

That's what I was going to do as a guess but I would rather not have to deal with the chp.

[Seanz0rz]

I will be starting a new roof rack design soon. Not sure what direction I will go, but I think more of a flat rack than a basket. I'd like to be able to toss the RTT up there on occasion

[Kryptoroxx]

I have been meaning to upload the results of my solidworks efforts on the roof rack and here it is. For now I am going to leave it without expanded metal as it's 40lbs as is and most of the stuff I will be carrying is going to span the braces anyway. I'm picking up some .5 sq for closing up the big gaps but since the stuff is so cheap I can afford to get plenty. Right now I'm just picking up 24ft because it's about that much a foot.

Another tiny project I wanted to do is shackle hangers since a plate bumper is a long ways off for me. I am thinking of doing some really lightweight minimalist ideas to keep the front end from diving around though. This week I am going to be pricing out some laser cutting on this. I imagine it won't be cheap but I guess I could see on the price. This particular one is designed for the rear rather than the front. I am starting to really enjoy the SolidWorks experience (is there such a thing?) and it's getting much easier to design according to how that program works.



I am not the one that originally came up with the idea however spent some time tweaking the design this weekend with plywood and came up with something satisfactory for my own twist.

[Robinhood4x4]

Are you going to laser cut the outline and then weld in the gusset? Since it's going to be cut with a computer you might as well have it all done in one step. I'd recommend a nice round fillet instead of the hard angles of the gusset to minimize stress risers.

[Kryptoroxx]

Are you going to laser cut the outline and then weld in the gusset? Since it's going to be cut with a computer you might as well have it all done in one step. I'd recommend a nice round fillet instead of the hard angles of the gusset to minimize stress risers.

I was just trying to eliminate hard edges but you bring up a good point. Haven't messed with arch much yet but I have to learn sometime. Thanks!

[Kryptoroxx]

Are you going to laser cut the outline and then weld in the gusset? Since it's going to be cut with a computer you might as well have it all done in one step. I'd recommend a nice round fillet instead of the hard angles of the gusset to minimize stress risers.

Hate to double post but I have to ask the question. What is a stress riser? I'm guessing that it's the stress introduced into the piece by the heat of welding.

I am not an engineer and not even a professional welder but I design and build off my idea of function so any and all tips anyone has are always considered and appreciated.

[Seanz0rz]

I think the best way to explain it would be to show you this:
https://www.youtube.com/watch?v=ndSR_S0JmdU
https://www.youtube.com/watch?v=_BZnn5OYcBc

If you have ~hour, watch this: https://www.youtube.com/watch?v=MdCh5W8mP-U

Here is a more scientific explanation:
http://www.engineersedge.com/materia...ntals_9902.htm

When I was in school, we would use test coupons to find material properties. They were tested to failure. The failure point was always at the end of the necked down section where the tool was allowed to rest at the start or end of the cut. This area was probably .001 or less deeper than the rest of the section. Since it was the thinnest section, the stress was higher in that section and failed first.

[Robinhood4x4]

Yup, what sean said. Basically, any inside corner increases stress.

Weld stress is something a little different. That's the HAZ or Heat Affected Zone.

[Kryptoroxx]

I think the best way to explain it would be to show you this:
https://www.youtube.com/watch?v=ndSR_S0JmdU
https://www.youtube.com/watch?v=_BZnn5OYcBc

If you have ~hour, watch this: https://www.youtube.com/watch?v=MdCh5W8mP-U


Here is a more scientific explanation:
http://www.engineersedge.com/materia...ntals_9902.htm

When I was in school, we would use test coupons to find material properties. They were tested to failure. The failure point was always at the end of the necked down section where the tool was allowed to rest at the start or end of the cut. This area was probably .001 or less deeper than the rest of the section. Since it was the thinnest section, the stress was higher in that section and failed first.

Very interesting! Definitely appreciate the explanation guys. I will keep that in mind for future ideas I might try to design. There are a lot of times I wish I could just leave the military and go finish my education now instead of later but I've got a good thing going right now and a retirement check will do a lot more good when trying to finish my education than a separation payment.