On occasion, the question comes up about fixing or joining plastic, so I thought I'd show the technique. A couple weeks ago, some $%^^%$#@ hit one of my bikes and I ended up with a bunch of cracked fairings and broken mounts. The common responses are buy new ones (about $2000 for this bike... not gonna happen), glue them up, screw/pop rivet them up with backers, or fiberglass them. The fairings are ABS, one of the most common structural plastics on vehicles,but the techniques work for a variety of other thermoplastics as well.
There are advantages and disadvantages to the various repair methods, but all have drawbacks. Glue up can be real messy and can leach out the plasticizers, making the material brittle, needs good fitup, and getting the parts clean enough can be tough. It is also not suitable if parts don't fit well or small pieces are missing (large pieces need to be made up from new material anyway). Also, the glues make a mess out of paint and can damage other plastics (like lenses on lights). Screws/pop rivets are suitable for an emergency, but look like crap and don't hold up. I use clear packing tape and stitch with stainless wire in cases where This would be appropriate. And fiberglass? I HATE working with it, and have moral reservations against using it to repair anything but fiberglass.
The best option is welding. This can be done by spending a couple hundred dollars on a hot air unit (even the harbor freight kit is about $150 with a coupon), using a soldering iron (results look like crap, and it is real easy to burn the material, which requires cutting it out and filling the void), or friction welding.
Friction welding is easiest and cheapest.
I use a Dremel tool to spin the filler. The filler is 1/8 ABS rod (from McMaster Carr, but the packages from Harbor Freight have are probably fine) held in the collet of the tool. Speed is low, and the extension is about 3/4" max.
The first set of pictures shows the setup: This is a sample since I didn't take good pics of the repair work
Prep of the samples: bevel about 30 degrees. Note the chuck key. That is used later as a follower for the weld material
Filler rod in the collet
First tack from the front
tack from the root side. Note that the penetration is not quite all the way through. This will be dealt with later (the tack is on the right end)
(several more posts to follow)
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