Cutting & splicing a Unicomp case?

[njbair]

I'm in the middle of heavily modding a Unicomp PC-122 into a sort of "unsaver" (but without nav cluster). I've got the barrel plate and membrane sheets all prepped and ready to go. Now I'm to the point where I need to cut out the nav/numpad clusters and reattach the end piece. I've never done anything like this before, but I'm thinking about trying my hand at welding it back together manually. I have a heat gun and a soldering gun, and plenty of matching plastic stock from the nav/numpad section, to use as "welding rod."

Has anyone ever done anything like this? Any tips or things to watch out for? Any help or advice would be huge.

Of course, once I get into this I hope to take a bunch of pics and do a nice write-up here in MST.

[VoteForDavid]

The larger plastic parts should be marked with what type of plastic they are.  If they're ABS, you might consider using acetone to melt them together.  Practice on scrap first!

[user 18]

Pretty sure I've seen this sort of undertaking before, but I can't remember where. If I do, I'll drop a link here.

Believe it was making a SSK case from a regular Model M case....

E: Take a look at this: https://geekhack.org/index.php?topic=37367.msg711892#msg711892
Images are broken at the other end of that link, but they appear to all be posted directly below the post I've linked.

Few other resources in that thread too.

[neverused]

I would make clean cuts and use abs glue. Then fill as needed

[njbair]

I like the idea of ABS glue. I hadn't thought of that. But I can't find any markings on the inside or outside of the case indicating the material. I'll have to buy some acetone to test and make sure it's ABS, unless someone can confirm that Unicomp cases are ABS.

[0100010]

https://geekhack.org/index.php?topic=29483.0

https://geekhack.org/index.php?topic=44875.0

[kurplop]

I've done a little plastic welding and the most important thing I found is getting the temperature right. Using filler rod made from similar stock is the best way to match the weld to the pieces being joined. It also removes the concern about what kind of plastic it is.

I used a Steinel heat gun with a special attachment that allows you to feed the rod through a tube at the nozzle, heating the rod and parts simultaneously . It worked great and I suspect it would be stronger than cements.

[njbair]

I've been working on this and have had some pretty good success. I'll have to take some pictures, but so far I've got each half of the case cut down to size, fitted, and spot-cemented together. I'm going to try to clean up some of the splotchy cement work and probably weld the rest of it for a more permanent hold.

There are other spots along the top of the board where the cord was wrapped around it for years and the plasticizers in the cord ate away at the case. I'd like to repair those spots as well.

I doubt I'll ever be able to match the pebbled texture finish on the plastic, so I may end up sanding the repaired areas smooth and using a textured spray paint meant for plastics. The nice thing about this is it gives me the chance to choose a custom color. The downside is you really need to wait a week or two after painting to allow the paint to properly cure.

I am still trying to figure out how I'm going to jam all the circuitry into this newly-shrunken case. My technique for fitting the membrane in there seems to be working alright, but until I get it all hooked up there's no way to know. I may end up replacing the original controller with a teensy.

As I said, I'll try and get some pics to share before the weekend.

[XMIT]

Are Unicomp cases made of PVC? Most Model M cases are. ABS tricks won't necessarily apply to PVC plastics.

[njbair]

Are Unicomp cases made of PVC? Most Model M cases are. ABS tricks won't necessarily apply to PVC plastics.

I'm no expert, but after having worked with this case quite a bit, I'm pretty positive this one's not vinyl. That, and the ABS cement seems to be working very well with it.

FWIW, I thoroughly scoured Unicomp's website for materials info, to no avail. I also couldn't find any material markings anywhere on the board, inside or out. The best I could do was the acetone test.

[Findecanor]

Ah.. I'm sorry I'm late to this thread.

I think that Unicomp's newer cases are ABS... but I'm not sure. I would use "Plastic cement" - the stuff for putting plastic model kits together. There are many brands. Humbrol is one of the more known ones.
ABS dissolved in acetone to make a sludge will also work - but do store it in a really air-tight container or you will be stuck with a plastic plug in the jar after a few days.

To match the pebbled texture: someone else once made a makeshift mould out of some silicone, cut the case, and used the mould at the seam-line.

[njbair]

Ah.. I'm sorry I'm late to this thread.

I think that Unicomp's newer cases are ABS... but I'm not sure. I would use "Plastic cement" - the stuff for putting plastic model kits together. There are many brands. Humbrol is one of the more known ones.
ABS dissolved in acetone to make a sludge will also work - but do store it in a really air-tight container or you will be stuck with a plastic plug in the jar after a few days.

To match the pebbled texture: someone else once made a makeshift mould out of some silicone, cut the case, and used the mould at the seam-line.

That sounds pretty involved. Right now the ABS cement seems to be doing the trick, and I'm honestly kind of excited about the notion of painting the case a unique color when I'm done. We'll see how obvious the difference in texture becomes.

I'm already planning on using an acetone "sludge," as you called it, to patch some smaller imperfections on the case.

[XMIT]

You might also try methyl ethyl ketone (MEK). I have not used it personally but I hear it dissolves ABS even better than acetone.