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Best glue for repairing a TRS-80 Model I case?

Eudimorphodon

Eudimorphodon

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A quick one: What is the best type of glue for repairing a broken off screw post in a TRS-80 Model I? Google fu is failing me what kind of plastic it is, so is there a solvent-type glue that’s the best plan or should I try epoxy?

I have some of that purple stuff for welding PVC pipes lying around but I assume that’s definitely the wrong thing.
 
No, you don't glue, but a specialized acrylic solvent cement, such as this stuff. Note that it's water-thin, so apply a couple of drops to each surface, press together and clamp until set. You get a "weld" that's as strong as the base material, because it is the base material.
 
For my Model I (Level I with no upgrades), the problem is that the plastic is getting REALLY brittle. So being as strong as the base material won't help much.
 
Heck Im going to give that stuff a try. Once the can is opened how long does it last before going off or drying out?
 
It doesn't dry or go off, but it does evaporate quickly, so keep the can tightly sealed. (Usually the stuff is mostly methylene chloride with a few other goodies). Use in a well-ventilated space.
 
Thanks Chuck. So, next time I have the machine open I'll give that specific stuff a try because apparently the stuff I did just try failed, and... jeeze, Model I's are a PITA to put back together, especially if they have a lot of hack wires running to switches that need to go to randomly positioned holes drilled in the case. I'm going to live with the one edge of the case being a little squishy until I *have* to go back in there.

Long and short of it, I double-checked the chemical shelf in the garage and I found a tin of "Oatey All Purpose Cement" which looked like it might do the job; it's not a pure solvent, it has some polymerizing-stuff in it too, but it said it supported several different plastic types and since I had it I thought it could be worth a shot. And it *looked* like it worked great, the post felt like it was on there to stay after setting for a couple hours and it wasn't obviously turning the case into go, but, no, it let go when the screw was mostly back in, . (Torque is harder than wiggling, apparently.) So, yeah, that's *not* the right answer. I guess if it messed up the mating surfaces a blob of epoxy will probably be the way to go.
 
I've got a couple of large cans of the Oatey stuff--it's not water-thin. It's really meant for PVC pipe--but I've also used it successfully to cement together pieces of the Azek PVC plastic decking. It works well for that purpose, but is not a general-purpose solvent cement.
 
I've glued several of the Commodore C-64 Posts with JB-Weld and they held just fine over the years. I've seen a few come back
for different problems.

Larry
 
ldkraemer said:
I've glued several of the Commodore C-64 Posts with JB-Weld and they held just fine over the years. I've seen a few come back
for different problems.

Larry
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I've found JB Weld to be very good down through the years. Never had anything come apart using JB.
 
Acetone is best IMO, for ABS and styrene based plastic. It's more of a solvent than a glue and welds the surfaces together.
 
One reason I thought the pipe cement might be apropos is I discovered when I fit the pieces tightly together before gluing it looks like there is a thin flake/sliver missing that might pose a problem. The can for the cement said it contained polymerizing agents that would let it fill small gaps... but, yeah, that didn't work out. The gap is thin enough that a solvent might just handle it with clamping at the cost of making the post a little shorter, maybe.
 
Chuck(G) said:
MEK works better than acetone in those situations, but the specialized solvent cement is best.
Click to expand...

MEK can be dangerous and somewhat expensive for a small can. I use it mainly to clean parts like a carburetor which it will make look like band new.
 
I've never found MEK to be much more expensive than a can of, say, heptane. There are carburetor cleaners that work better for the purpose (I use Berryman B-12). A gallon of MEK is about $25 at my local Lowe's. In some cities, it's simply unobtainium because of local regulations (e.g. "precursor" chemicals used in the illicit drug trade).
 
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Chuck(G) said:
I've never found MEK to be much more expensive than a can of, say, heptane. There are carburetor cleaners that work better for the purpose (I use Berryman B-12). A gallon of MEK is about $25 at my local Lowe's. In some cities, it's simply unobtainium because of local regulations (e.g. "precursor" chemicals used in the illicit drug trade).
Click to expand...

I don't want to sound argumentative, but I've been using MEK since the 60's on automotive parts and such and have never needed to search out anything else. Since Berryman B-12 is in a spray type can, probably much easier to store and apply. Also, what can a part looking brand new lack when being doused with MEK? Great grease and grime eater.
 
Our industrial chemist when I was training, always claimed he could turn MEK into some seriously illegal pharmaceuticals, we just liked its smell (used it in ABS pipework fitting)
 
Agent Orange said:
I don't want to sound argumentative, but I've been using MEK since the 60's on automotive parts and such and have never needed to search out anything else. Since Berryman B-12 is in a spray type can, probably much easier to store and apply. Also, what can a part looking brand new lack when being doused with MEK? Great grease and grime eater.
Click to expand...

I'm not disputing your use of MEK for parts cleaner, just that sometimes there are cheaper (you did cite the expense of MEK) solutions that work as well or better. Take the B-12 stuff, for example--it's got not only MEK, but also toluene, methanol and acetone. The SDS for B-12 doesn't call out MEK, but the label on the can does. So much for accurate EPA reporting...
 
I've used MEK as a solvent to weld plastic laptop case cracks for decades. Read the warning label on the can as this stuff is not the most healthy stuff to breathe. For screw posts and other supports that need some strength I often use glass fiber to reinforce the break when coated with epoxy. But even a leftover small piece of window screen mesh will work to add reinforcement. Bondo and Tamiya model spray paint cans will repair appearance of the outer side of a plastic case. Quite a few laptops were resprayed by me since normal wear of the palm rest area often wore through the OEM paint. Hinges broke free from the lids or case backs and needed to be reinforced. Tamiya has lots of colors that match many if not most silvers and grays. Or changed Clevo gray parts into Alienware bright green or other colors used on their versions of the Clevo laptops. Often replacement plastics were not available or cost more than the value of the laptop. Goop (RTV) held in quite a few LCD's that were missing original LCD mounting points too.
 
For a very long time, the preferred cement for plastic model builders were Ambroid or Tenax--both solvent cements based on methylene chloride. Great stuff, but the vapors are hazardous. Neither is currently produced. There are, however, some modelers that still use methylene chloride (dichloromethane)--it can be very difficult to find; now mostly present in some paint strippers. MC will pretty much dissolve just about any plastic, including polycarbonate.

There's a comparison between Weldon cement and methylene chloride here
 
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