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Repairing an old Logitech TrackMan trackball: what is the best way to do this?


I would like to have a go at repairing a Logitech trackball.  The problem?  The trackball has a crack in the palm rest as seen here:

And, more alarmingly, here:

My tentative plan, at least, is to apply "J-B Weld" brand "Plastic Bonder" to the crack, then use the edge of a bit of cardboard to force the adhesive into the crack (and to remove most of the excess adhesive before it dries). 

I chose this particular product because a) it lists a strength of 3770 PSI; b) it dries the colour black (which, whilst not ideal, certainly beats adhesives that dry a revolting, mucous-coloured yellow); and c) it is supposedly safe to the skin once it dries (according to the manufacturer, anyway), which is a must for something that will constantly be in contact with my hand.

Here is the embarrassing bit: In case you can't already tell, I am a complete n00b at this sort of thing.  If anyone reading this has any suggestions regarding choice of adhesives and/or application techniques, I am all ears. 

Finally, as near as I have been able to discover, the palm rest is made of some variety of ABS plastic, but that's about all I can tell you.

Any ideas?

Something you may want to try, and I will totally admit it's just an idea but would allow max strength without additives or destroying the finish would be to find someone with an acetone vapor chamber for ABS 3d printers. With this they print a part in ABS and then place it in the chamber to soften and smooth out the part. In your case the chamber could cause the ABS crack to fuse. You would likely lose some of the outer texture but would do the most to fix the crack itself. It could also just completely destroy the part entirely by melting it or causing the crack to separate. High risk, high reward.  If you do try this, let me know how it goes.

You could just use Acetone from the underside and try to fuse it. Personally I would go this route and once dry add some 2 part epoxy of some sort. It can be JB or something else, in most cases, especially with plastic just ignore the strength claims. The epoxy is stronger than the plastic in almost all cases, where it fails is the bond where it meets the plastic or the plastic itself. This shouldn't be a high stress part anyhow so any 2 part should be good enough especially if you use as much as you can.

If you really want to go hardcore on this though, maybe check out some keyboard restorations on Youtube (Model M and Alps specifically). Those guys will probably have some ideas on how to restore this, including the finish.

You also may just want to see what these sell for on Ebay though, frankly it may be cheaper, easier and better to just buy one in better condition.

I'm not sure what J-B Weld Plastic Bonder actually is and the Safety Data Sheet does not make me any wiser ...

I have tried to fix cracks like that with a "plastic glue" / "plastic cement" in the joint a few times, and not got a very good result. Those contain solvent that dissolves the plastic in the joint and then evaporates so the parts would need to be pushed together more, and then you'd lose the perfect fit between the cracked parts.
When solvents are used to mend plastic, you'd need to add plastic: dissolve ABS plastic in acetone and carefully apply it.
One problem with solvents (such as acetone, and the stronger ones in plastic glues/cements) is that you must absolutely not spill anything on the part you are about to repair, or it will leave a mark.
Solvents can be very unforgiving, so I would recommend not to try that.

I think the safest method would be to use a two-part epoxy. Smear a tiny amount in the crack using a toothpick, being careful not to widen the crack when doing so.
Glue a reinforcing splint of some material (ABS plastic, metal or fibreglass weave or whatever) to the inside of the cracked part. If you can't use a wise or clamps, then tape the parts together: glue does not permanently stick to clear tape!
Spills and excess uncured epoxy coming out of the crack could be wiped off with water (if it's a nice epoxy) or with alcohol (isopropyl or denatured alcohol).


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