plastic angle brackets

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

    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:

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:

http://www.ipscorp.com/ind_html/acrylics.html
(IPS 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

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

"Gordon McComb" wrote
<snipped>

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

Buy some aluminum and bend and drill.