Force req'd for connection to fail

[craigclick]

Hi - I'm a woodworker, and not an engineer, and would be much obliged if someone could tell me how may lbs/lg would it take for this connection to fail. The force is static. Thanks.

 

[Jboggs]

Thanks for the question, but... you aren't going to get an answer without answering more questions. I'll go first:
1. What is PTR? I found this on Google: "Fiberglass-reinforced plastic (Fiberglass PTR)"
2. I would not trust tapped holes in fiberglass or plastic. VERY weak. Find another way.
A suggestion: Find a way for the screws to engage in metal, not plastic. The screws could go all the way through the tube to engage in tapped holes in a steel plate on the far side of the tube.
Do some research on recommended fabrication and assembly methods for that material.
3. Where are the screw holes located in the angle? The closer to the top of the angle the better..

 

[dvd]

You may have some luck with something like a Lindapter Hollo-Bolt - contact Lindapter and speak with an applications engineer.

 

[Stick.]

More questions/thoughts:

1. Do you have a target for the force you want to hold? I find it's usually easier to approach the problem from that direction than just finding the maximum.
2. What is applying this force? The answer on capacity could change depending on what this thing is holding.
3. How far away from the tube is the force applied?
4. What is the wall thickness of the tube? Even if it's steel tube, just eyeballing it, the wall thickness looks a bit thin for 1/4" dia screws (assuming tapped holes in the tube). You may have to step up the wall thickness, use nuts or a backing plate inside the tube (like Jboggs said), or look at something like Rivnuts.
5. Do you need the countersunk flat head screw or could they be changed out for hex head or socket head screw? I don't love using flat head screws in highly loaded applications. Ease of manufacture is also worse with flat heads since mismatches in hole spacing between the tube and angle can cause issues due to the taper of the countersink.

 

[craigclick]

Thanks for the input. I'll clarify:
1. I thought the nomenclature PTR was universal, but I guess it only applies to Mexico. In this case, it is square tube, A36 steel, with a wall of 1/8". In this size, 2"x2". A thicker wall is not available.
2. The FLD HD screws, 28 TPI, are to keep a clean visual look. The wall is tapped.These are supports for shelves in a high-end residential installation.
3. I have placed the screws above center. Perhaps I should place them higher, closer to the angle.
4. A backing plate inside the square tube is not possible, nor is it possible to place nuts. If you thought it essential, I could place nut-serts to support more thread length, but then I would have to remove material from the aluminum angle, so that they would not stand/off (proud) from the post 1/16". In which case, I would probably consider usine 1/4" thick angle.
3. The shelves are 10' long, and have an internal structure of steel to keep them from sagging under the weight of books. Total weight of shelf, filled with books is apprximately 330 lbs.
4. I've attached another drawing that shows how the shelves are mounted. There will be two angle supports in front off the posts. There will be five anglem supports off the rear wall, each 4" long.
Thanks all for your comments; it's appreciated.

 

[craigclick]

Thanks for the input. I'll clarify:
1. I thought the nomenclature PTR was universal, but I guess it only applies to Mexico. In this case, it is square tube, A36 steel, with a wall of 1/8". In this size, 2"x2". A thicker wall is not available.
2. The FLD HD screws, 28 TPI, are to keep a clean visual look. The wall is tapped.These are supports for shelves in a high-end residential installation.
3. I have placed the screws above center. Perhaps I should place them higher, closer to the angle.
4. A backing plate inside the square tube is not possible, nor is it possible to place nuts. If you thought it essential, I could place nut-serts to support more thread length, but then I would have to remove material from the aluminum angle, so that they would not stand/off (proud) from the post 1/16". In which case, I would probably consider usine 1/4" thick angle.
3. The shelves are 10' long, and have an internal structure of steel to keep them from sagging under the weight of books. Total weight of shelf, filled with books is apprximately 330 lbs.
4. I've attached another drawing that shows how the shelves are mounted. There will be two angle supports in front off the posts. There will be five anglem supports off the rear wall, each 4" long.
Thanks all for your comments; it's appreciated.