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Proper Glue for Monitor Case

Tincanalley

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I know this is the tool forum, but glue to fix a broken monitor case seems like a tool to me.

I have an IBM 5151 monitor and during shipping a piece of the front top corner broke. I got lucky and it is a clean break, so the piece fits in perfectly with little visual. However, while the edges are clean, I know I only get one shot at doing it right the first time. If not, the glue will make it next to impossible to reglue and have it sit flush. So I need to know what type of glue works best on the type of plastic used in that monitor case and what doesn't expand as it dries?

Thanks 5151 Replaced Chip.jpg 5151 Missing chip.jpg
 

Hugo Holden

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In gluing the plastic on similar cases like the 5153 monitor I found it was better to use high strength 24r epoxy resin such JB weld (called Araldite here, this version is clear).

While it is tempting to want to find a solvent that will re-bond the plastic with a molecular weld, in practice with old plastic it creates a very weak bond. Also as the solvent melts the edges, there can be some volume loss and the small mating crevices in the cracked edges are destroyed and this can hamper perfect alignment.

If the fractured edges are left as they are, being rough, it increases the surface area of the bond, so when the edges are approximated, there is only a very thin film of epoxy resin between them and the bond becomes very strong after it has cured. So my advice is avoid any glue that is chemically reactive towards the plastic and use 24hr epoxy two pack resin.

Also these IBM monitors do very well with a re-spray with Dupli-color spray, which chemically bonds to the surface an doesn't flake off and doesn't obscure the original texture either. I have talked about this very special paint on other threads.

But, now you have been given conflicting advice as whether to attempt to use a solvent or a glue, what to do ? Often it will be a learning experience if you have never done it, so if you wanted to try both methods, it would have to be the solvent first and the glue second, but as noted the effect of the solvent previously applied to the fractured edges will degrade the effectivity of glue, if attempted after that.
 
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Tincanalley

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:shock: Maybe I should duct tape it. Seriously, though. I was also told by someone to use acetone. I am going to research all three suggestions and make a decision and hope it produces something I can live with. Thanks for all the great input.
 

Chuck(G)

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Solvent cement is tricky stuff; it's water-thin, so if you're not careful with it, you can create a real mess. That's why a needle bottle is supplied. You press the pieces together and carefully add the solvent bit by bit, so it's sucked into the crack by capillary action. Kept under clamping, the joint is nearly invisible.

Professional model shops use gallons of the stuff.

I've used solvent cement on old ABS that's so old it shattered. It all went together (the solvent cement is thin as water, so it takes a bit of practice). Missing pieces were formed of Bondo resin filler, sanded smooth and painted. Said gear is in use today after several years.

That being said, there has been some absolutely shoddy ABS molding done over the years. I've had experience with two Horrible Examples. One was an Apple color monitor used on early Performas. The thing would spontaneously shed bits of itself. while no one was in the room. The other was an Overland Data 9 track streamer drive whose faceplate simply disintegated. Stuck together several times with industrial epoxy (3M Scotchweld) and fiberglass mesh, didn't matter. It would crack regardless all by itself. Still thinking about fab-ing up a new acrylic faceplate, but may end up junking the thing instead. It depends on my level of boredom.

Sometimes, nothing will save bad plastic.
 
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Hugo Holden

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:shock: Maybe I should duct tape it. Seriously, though. I was also told by someone to use acetone. I am going to research all three suggestions and make a decision and hope it produces something I can live with. Thanks for all the great input.

Acetone melts most plastics well (except Nylon). Whether any particular solvent, that for Acrylic, or ABS (often MEK is used for that) or Acetone, it depends on the particular plastic which is the better solvent. It is not just a matter of dissolving it for a strong bond, it must form chemical links to the plastic surface, so the chemistry is all important when a solvent is attempted to create a bond. Acrylic solvents are specific for that, PCV solvents (like for pipe joiners) are specific for PVC, and specific solvents say for ABS. Are you familiar with the chemistry of the IBM monitor case plastic ?

In the case of IBM monitors of this vintage, I have experimented with this plastic with many solvents, I cannot advise any solvent I know of that will give a bond anywhere near as strong as the 24hr epoxy.

If you fail with some solvent, which is on the cards (only saying that because I was unable to succeed with it on this particular plastic ) it will ruin the opportunity for a perfect bond with the epoxy resin. So you will not be able to judge the effectivity of it for this particular plastic and repair job and you might conclude it is no better than the solvent. You will then have to wait until you have another cracked IBM VDU cabinet to repair where the epoxy is used initially on the fracture, without prior solvent melting the microscopic fractured surface topography.

One 5153 cabinet I had was smashed to pieces in transit and I got to repair multiple fractures, in some cases on the inside I also used small brass plates threaded for 2mm metric screws, as well as the glue and it looked like an Orthopedic surgeon had repaired it. This sort of thing works internally on the CRT mounts and they can be painted over later and do not look too bad.

PS: I have done some pretty tricky plastic repairs in my time. One was to replace the disintegrated binding around the perimeter and along the neck of a my vintage red Gretsch Jetfirebird guitar. It is three layers, white, then black then white around the body. I was advised by a number of professional Luthiers that is was not possible to replace this without repainting the guitar. But I was able to do it, replacing the binding with ABS, a photo here, I have a closeup photo somewhere. Of note, it was not done with ABS glues or solvents either, so a recommended product is not always the better product:

https://www.worldphaco.com/uploads/Gretschdoc.pdf
 
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Chuck(G)

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Most professional plastic solvent cements are methylene chloride-based. Weld-on No. 3 SDS. I don't know if they can be had in Oz, as dichloromethane is tightly controlled in some countries, not to mention the Trike that Weld-on uses. But it's considerably more powerful than acetone, MEK, xylol, toluene, etc. Plastics houses use it because it creates a stong clean join in acrylic. If properly used to join two sheets of clear acrylic, the join becomes invisible.

But you don't go sloshing it around. It will pretty much peel the paint off anything, including epoxy lacquers and paints. It's death on rubber (you use vinyl gloves, not latex or neoprene) That's why you apply it with what amounts to a blunt hypodermic--and it's somewhat toxic

You're not going to find this stuff in your local Home Depot. But when properly used, it's the cat's whiskers.
 

Hugo Holden

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Most professional plastic solvent cements are methylene chloride-based. Weld-on No. 3 SDS. I don't know if they can be had in Oz, as dichloromethane is tightly controlled in some countries, not to mention the Trike that Weld-on uses. But it's considerably more powerful than acetone, MEK, xylol, toluene, etc. Plastics houses use it because it creates a stong clean join in acrylic. If properly used to join two sheets of clear acrylic, the join becomes invisible.

But you don't go sloshing it around. It will pretty much peel the paint off anything, including epoxy lacquers and paints. It's death on rubber (you use vinyl gloves, not latex or neoprene) That's why you apply it with what amounts to a blunt hypodermic--and it's somewhat toxic

You're not going to find this stuff in your local Home Depot. But when properly used, it's the cat's whiskers.

I found that the local plastics company would sell me this acrylic solvent, I have a tin of it. And it does work wonderfully well to bond two acrylic pieces together to create a strong and near invisible bond. But the brittle plastic cases on aged VDU's do not behave like acrylic plates or interact with this solvent in the same manner. Do you know what plastic IBM used ?

When they glue up structures at the company, one trick is they leave the protective sticky paper on the surfaces until after it is done, it avoids small spill marking the surfaces.
 

Chuck(G)

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I found that the local plastics company would sell me this acrylic solvent, I have a tin of it. And it does work wonderfully well to bond two acrylic pieces together to create a strong and near invisible bond. But the brittle plastic cases on aged VDU's do not behave like acrylic plates or interact with this solvent in the same manner. Do you know what plastic IBM used ?

My guess from having dealt with some IBM monitors is ABS; i.e. pretty much standard practice. ABS is not really a simple plastic, as you probably are aware, but rather a polymerized emulsion of three components that can occur in varying proportions. Add the dimension of fillers and strength and durability can vary all over the place. My opinion is that the solvent cements act on the styrene component moreso than the acrylonitrile or polybutadiene. Depending on the proportions, ABS can be remarkably durable (as in sewer pipe) or terrible (my Horrible Examples, as well as the ABS used in my now-deceased Volvo turbobrick).

There is such a thing as ABS cement used in the plumbing trades. It's black and quite thick. I've used it to repair ABS water tanks always in conjunction with reinforcing fiberglass mesh. It's held up quite well. The trick behind this is to not depend on the cement for strength. I don't know if it would be suitable for repairing the monitor case, however.
 

DeltaDon

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Some monitor cases were made with a foaming agent added to the plastic to reduce the weight of the final product. The plastic forms a skin when pressed against the mold during processing, but the center will be filled with tiny bubbles. If the case is seemingly thicker than expected (1/4"?) you might have a case with foamed ABS.
 

Tincanalley

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Does anyone know what kind of plastic was using in the IBM cases from the 80s? They really are fragile now, but I remember installing and handling many new ones and never had an issue. Now they seem to break from the slightest bump.
 

Chuck(G)

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Problem is that IBM contracted out manufacture of a lot of things. I think the early monitors were done in Korea; external floppy drives in Japan, etc.
As I mentioned ABS is used because it can be molded easily and is relatively strong. But it's a witches brew of three polymers in variable proportions, so one ABS case can be very different from another.
 

Hugo Holden

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All of this, about the foaming to decrease the weight, making tiny bubbles, probably explains why I have had very good success with using 24hr expoxy resin. Likely at the bond/join area the material is a little porous and the resin adheres to it very well. But in cases where I had tried the solvent first, the surface got melted and after that the adherence of the glue was nowhere near as good, making a much weaker repair.
 

Chuck(G)

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The curious thing is that cases made of polyurethane high-density foam have survived very well to this day. No problem with discoloration, as they were always painted. Pretty rigid, especially for large cases (lightweight and tooling can be done in aluminum, rather than steel). I don't know why they aren't more popular.
 

Tincanalley

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This monitor has to be painted as it hasn't discolored at all. The only pieces to discolor are the top screw covers that are just color matching plastic. They are pretty yellow, but should be easy to retrobrite.
 

Tincanalley

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Okay, I found some solvent glue from a couple years ago when I had to fix a broken Lucite owl. Will this work, pic attached. Or how about the link to J-B clearweld. Will that one work?

20211112_164707.jpg
 

Chuck(G)

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Well, that glue says "medium bodied", which means that it does have dissolved plastics in it. Try a small bit in an inconspicuous place--it would be easier to handle that the pure solvent if it works.
 

Tincanalley

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Well, that glue says "medium bodied", which means that it does have dissolved plastics in it. Try a small bit in an inconspicuous place--it would be easier to handle that the pure solvent if it works.

Since I only have the one piece to glue back, how would I test it before gluing the piece? My guess is I'd have to try it on the same exact plastic as the broken piece, right?
 
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