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plastic angle brackets

My robot base has an octagonal shape. It means that it has no 90 degree angles. Instead, the angles are 45 degrees as expected.

I need to create a protection shell on top of the base, and I'm going to use

6mm polycarbonate to create the walls and roof of the protection shell.

For 90 degree things, I'm using some plastic angle brackets that I bought from budget robotics, but to join the 45 degree walls I'm having difficulties finding brackets at those angles. Don't they exist?

I could use cement, but as I expect the robot to flip and take hits eventually, I don't trust the bonding of cement. I could use brass or any other metal straight brackets and bend them at 45 degrees, but plastic would be perfect as it provides good shock resistance and very light weight.

Any pointers will be appreciated.

Padu

Reply to
Padu
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Ops, the brackets should have the complementary angle of 45 degrees, 135 degrees.

Reply to
Padu

You can bend polycarbonate in a sheet metal brake, or in a vise. Use a heat gun on it at the bend point.

John Nagle

Padu wrote:

Reply to
John Nagle

Buy some aluminum and bend and drill.

Reply to
mlw

I've tried that last night. Not so difficult to do on a 8x2 inches strip. I believe I got the precise angle I wanted (135 deg), but my robot base is kind of octagonal in shape, and total perimeter is almost 5 feet (1.62m). One think I can foresee is that I will have to build (probably out of wood blocks) my own tool to bend all the corners (8 corners) to the correct angle. Also I'd have to buy additional polycarbonate on strips of 5 feet.

Another test that I did yesterday was using a miter saw to make the corner cuts at 22.5 degrees and then glue the pieces with this glue:

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Weld-on #4)

It is a very thin liquid, but it is pretty strong. On the glue can, they say total cure time is 36 hours, but from yesterday to today, the connection is very strong. I cannot break it using moderate force. Neither it breaks if I smash it against the table or let drop from 5 feet height. I will wait the

36 hours and then try to really break it and see how strong it really is. At the local plastic shop, where I bought this glue, the salesman was showing me a 6ft high acrylic bookcase that was made using this glue. The shelfs had no other support to the walls other than this glue.

One caveat though is that for this try I've used 6mm polycarbonate, and the walls of my robot will be 4mm thick. Probably glue + aluminum brackets as mlw suggested would be the best bet. The biggest advantage on cutting individual straight pieces is precision. I can make very precise cuts using the miter saw and no special tool needed. Well, let's see.

Cheers

Padu

Reply to
Padu

Setting time and curing time are vastly different. Solvent-based cements attack (basically remelt) the plastic to form a weld bond. The adhesive manufacturers don't know under what conditions you're using their product, so they state worse-case times for full curing. This is the amount of time a fabricator would want to wait before delivery of the product, for liability issues, though it doesn't mean the bond won't handle the kinds of modest (relatively speaking) stresses you're putting on the pieces.

I definitely wouldn't trust butt-joints (go ahead and laugh) for plastics under 6mm, and even with these, not for the size I imagine your robot to be, and especially not for an outdoor robot. Out in the field, over time, even polycarbonate will start to crack from impact shocks. Some type of gusset piece or angle bracket would be a good idea for any outdoor robot.

-- Gordon

Reply to
Gordon McComb

"Gordon McComb" wrote

That's what I'm going to do. Use the weld-on adhesive plus aluminum brackets. I'll post up the design as soon as I finish it.

Padu

Reply to
Padu

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