Polycarbonate head/camera shield

A project log for Droidbot 07 - Wheeled-Quadruped

An ambitious mobile robot for testing my skills and learning new ones.

Paul CrouchPaul Crouch 08/04/2018 at 19:340 Comments
I'd read that polycarbonate can be welded with methylene chloride so I bought some (1 litre for less than £10 including the £5 shipping). I tested it on some scraps of polycarb and ABS and can say it solvent-welds polycarbonate and ABS extremely well. In the photo below, the top two pieces are well-and-truly fused and will not peel apart and the bottom piece, that was bonded to a failed ABS print, still has the skin of the print on it after some not-inconsiderable force was used to separate them.
Solvent-weld polycarbonate and ABS with methylene chloride.
Just to check; acetone barely touches polycarbonate and though it does fog it slightly it then fades. The polycarbonate strip in the photo below was dipped for a few seconds in each chemical. I would say methylene chloride is better than acetone for ABS too, certainly faster, though harder to spell :-) 
Acetone dip on top, methylene chloride on bottom.


I did a dry-fit of the parts and checked for any show-stoppers. I didn't want to ruin the material. It's not hugely expensive but it's not zero cost either and would take another week to come through.


The image below shows my intended plan. The main reasons for the overly complicated layering are because I didn't want the LED strip to sit proud of the main skin and I'd had an internal dimension to match for mounting.

The plan.

I just had to hope I'd not ruined the plastic after attempting to solvent-weld the camera shield and cap with a less-than-steady hand. Annoyingly I managed to scuff the polycarb too. As advised, I left it  overnight to fully set.
Letting it go off over night.
It's far from flawless, but it fits and I'm making progress! In my eagerness, I didn't take any photos of the spacer strip being bonded. I used four clamps (in the photo above) to clamp the spacer strip after I'd applied the methylene chloride with a small paint brush, then I brought the "oldest" clamp to the newest position, working my way around. If you don't look too closely it looks fine. It's a first for me so shouldn't beat myself up over it.
Test fit for size.
Before I mounted the RGB LED strip I again did a test-fit. The wire termination end has heat-shrink tubing on it that I cut off so it wouldn't restrict the wire routing. I'll have to re-insulate it somehow. To my surprise there was another LED under the heatshrink. I hadn't given it much thought, how else would they do it? They're not going to remove one, that's not cost effective. Just struck me as odd.
First LED is covered up. Common practice?
With the LEDs stuck on, I clamped the strip of polycarb (that will become the sensor collar) in place to get a feel for how it will look. The white protective film is a close match for the white that it will eventually be painted. I'll need to mask and paint the dodgy-looking welded areas too.
Mock-up of sensor collar.

Now I need to work out exactly what sensors I'm placing and where. Back to the CAD...