deskthority

Anyone had any luck repairing hair-line cracks in 30 year old keyboard plastics? I'm guessing it is ABS since it is yellow.

I should be able to dissemble the chassis and not make the crack worse. The rest of the plastic seems fairly maleable; this crack is on an edge, that had the most UV exposure.

Any ideas are greatly appreciated!

Edit: Added some pics

Unless you intend to paint it afterwards, I would not try to glue the crack itself but primarily reinforce it from the inside.

Sand the inside surface to flatten it and roughen it up. Then glue a flat piece of ABS to the inside, preferably using a glue for plastics that contains solvent (or is mostly solvent). I prefer Humbrol Poly Cement in the yellow plastic bottle.

If you do use some solvent-based cement, you could first drop some on the inside surface and rub back and forth with an edge of a tool or a piece of plastic (that would itself dissolve partially) to get some dissolved plastic into the crack from the inside. When you lay your reinforcing shim on the inside with solvent-based adhesive in-between, also move that back and forth to make the surfaces mate properly.
Be very thorough so that you don't spill solvent where it isn't supposed to go - it would mar the surface.

I really do not want to paint, so I'll see if there is room for reinforcement next time I pull the lid. The crack starts at the edge where the top meets the bottom tray

Looking through older pics, its been there since I recovered the keyboard and hasn't spread. However, I will be pulling this guy apart a few times over the next few months, so its needs something to stop the spread. Thanks for your input!

twinrotor wrote: ↑I really do not want to paint, so I'll see if there is room for reinforcement next time I pull the lid. The crack starts at the edge where the top meets the bottom tray

Looking through older pics, its been there since I recovered the keyboard and hasn't spread. However, I will be pulling this guy apart a few times over the next few months, so its needs something to stop the spread. Thanks for your input!

It would really be difficult to seal it without painting it so my best guess is to just be careful when taking it apart.

Very careful. Hopefully more do not appear, or paint would be pointless venture as well.

twinrotor wrote: ↑Very careful. Hopefully more do not appear, or paint would be pointless venture as well.

A picture wouldnt hurt either

It wouldn't, huh?

{moved pics to first post}

Renforce it form the other side and leave it at that unless its getting painted just use some epoxy, dont get the cheap £ store stuff , its never worked well for me , the clear stuff from UHU is pritty good

You could try some wiking grade superglue but at your own risk.

andrewjoy wrote: ↑Renforce it form the other side and leave it at that unless its getting painted just use some epoxy, dont get the cheap £ store stuff , its never worked well for me , the clear stuff from UHU is pritty good

You could try some whiking grade superglue but at your own risk.

Wouldnt epoxy seep through though?

andrewjoy wrote: ↑Renforce it form the other side and leave it at that unless its getting painted just use some epoxy, dont get the cheap £ store stuff , its never worked well for me , the clear stuff from UHU is pritty good

You could try some wiking grade superglue but at your own risk.

Its all a pain for me, but I really have a love/hate relationship with cyanoacrylate....

Dingster wrote: ↑ Wouldnt epoxy seep through though?

I thought about that as well. I assume I could bind the crack to prevent as much seepage, but I would use a thicker, quick-set epoxy as well.

I'm really looking for the "right" epoxy, I guess. I've used a few, but mostly on broken pieces inside of notebooks, ect. Nothing on the outside. I've also used stuff in the automotive industry, which normally never works (most likely from endless contamination). Contamination of the adhesive in the form of the chemical leech also worries me, but no leeching inside the case, of course.

Just out of curiosity, is this a Chicony KB-5161?

Blaise170 wrote: ↑Just out of curiosity, is this a Chicony KB-5161?

Multitech KB-101A, predecessor of the Acer

Findecanor wrote: ↑ Sand the inside surface to flatten it and roughen it up. Then glue a flat piece of ABS to the inside, preferably using a glue for plastics that contains solvent (or is mostly solvent). I prefer Humbrol Poly Cement in the yellow plastic bottle.

Yeah organic solvent seems to be the best option here. Acetone + syringe with needle. Compress the crack and gently squeeze acetone into it (fron the inside of a case). It'll fill the gap and weld it together.

Problem here is, how to put pressure on the crack. Clamps maybe?

Something like this:
[youtube]https://www.youtube.com/watch?v=OqjWPdZe-wk[/youtube]

Pressure could be added by a band/strap. I can see how the plastic will react with acetone. I need to check the mold and see if it might be marked with exactly what plastic it is. They did use date inserts in the molds, so maybe there are others.

The usual way to test for ABS is to wet a Q-tip with acetone and rub it somewhere that is not visible. If there are streaks, it is ABS. On PBT, the acetone just evaporates. On some other plastics, there can be some discolouration but it will not rub. I find it very likely that it is ABS though.

Another way would be to cut a V-shaped groove on the inside of the crack (with dremel and/or needle file), fill that with glue (or whatever) and press together.
By using a V-groove you increase the surface area and the amount of glue you can use.
Before gluing, press together the outside and tape it with broad packing tape and smooth that out. That way, no glue should leak onto the surface.

Instead of glue, you could use "ABS slurry": cut/break small pieces of ABS (from a trash keyboard or whatever that has a similar colour) and place into a small airtight jar. Cover that with acetone, place the lid on and wait overnight. The next day you will have a slurry that can be used to join ABS parts.
It is difficult to work with though. While you work with it, the acetone evaporates and it can change consistency from toothpaste to chewing gum, and like with chewing gum there can be long threads... You need to lay thin layers, or it will never fully cure. It may also shrink a bit when it dries.

I am assuming it is ABS because of the UV degradation/bromine leech.

The slurry idea is a neat idea. I'll definitely practice before attempting anything. Never would have thought of putting tape on the outside. I'm really terrible at this type of stuff. My wife generally does all my cosmetic work; I am a mechanic by trade, but I couldn't prep/fill/paint a body panel to save my life. Everything looks straight until I put paint on it

No marks inside the case as far as manufacturing. However, I found an issue that is going to make things a bit difficult. The top and bottom "slot" together, leaving no room for inside reinforcement.

You can barely make out the crack here






So maybe seeping is my only choice here. The "lid" is pretty stiff and the crack still hasn't spread, although I was really ginger while disassembling this time. I'm also getting a bit worried about the self tapping fasteners. They're still tight, but you can see the state of the holes.

Ah. I guess that the case screw near the crack had been overtightened...

Findecanor wrote: ↑Ah. I guess that the case screw near the crack had been overtightened...

Looking back through my pics, the crack was there when I "found" the keyboard, so who knows. There is a stand-off right there as well that could have had debris/flashing in the way when originally assembled. Who knows.

I think I'll try the slurry/acetone. That way I can limit the amount of material and sand back any that interferes with the alignment channel.

I think the slurry should work well for you. Binds it while adding some extra plastic to it.