@Paolo B
I greatly appreciate your time to offer some thoughts.
Those ribs are tiny. Drilling top-down into them for the sake of inserting a metal rib (the source of which is currently unknown) is scary to me, personally because the size of the drill but would need to be super tiny. The required drill bit would be so tiny in fact that I wonder if the insert of even titanium metal rods would hold. Again, this is me assuming that the advice give was to drill
inside the plastic ribs from the
top-down. But I could have misread you on that.
Last night, prior to posting this thread, I had a
multi-hour session with ChatGPT, primarily because I have a hard time getting feedback from the brilliant folk who are most informed about the Portable (well, folks other than you, Paolo). ChatGPT is the best I can do without human advice.
I discussed with ChatGPT all the details of the matter, which require the AI to have an understanding of how the Portable is constructed and the plastics being Polycarbonate, and the fact the machine is quite old. I also mentioned that I have the original 24-hour-cure JB Weld which is a very strong material when fully hardened.
ChatGPT claimed to understand the forces applied to the hinge and then told me that neither SuperGlue nor any kind of Epoxy would really fit the bill. It suggested a glue that basically dissolves plastic in order to "weld" the broken pieces together.
Specifically, ChatGPT told this:
If you want a structural, lasting repair, Methyl Methacrylate Adhesive (MMA) or a solvent-welding polycarbonate adhesive is far superior. MMA chemically fuses the plastic; epoxy only grips the surface.
Why JB Weld Is Not Ideal for Polycarbonate
Original JB Weld (the 24-hour steel-reinforced epoxy) does NOT bond well to polycarbonate.
- Polycarbonate is smooth, low-porosity, and chemically resistant.
- Epoxy forms only a surface bond, not a chemical one.
- Under hinge stress (opening/closing the LCD), epoxy repairs almost always fail over time, typically by peeling off the plastic rather than the plastic cracking again.
It may hold for a short while if perfectly clamped, but it is not a structural PC hinge fix.
What Actually Works: MMA (Methyl Methacrylate Adhesive)
MMA chemically melts/fuses polycarbonate, creating a repair close to the strength of the original plastic. This is why it's used in motorcycle fairings, PC machine guards, and certain automotive plastics.
Benefits:
- Creates a chemical weld rather than a glue layer
- Very strong shear and peel strength
- Fills small gaps
- Bonds even aged polycarbonate
This is the best repair chemistry for your case.
Oh sure, but where can I find that in product form! So I did a long back-and-forth because I didn't believe its suggestions were accurate. I asked for things I could buy in Japan, and it then turns around and suggests these 2-part Epoxy products of all things:
- Cemedine Metal Lock AY-123
- 3M Scotch Weld DP8805NS (expensive)
I then did more back-and-forth with ChatGPT because I didn't trust its suggestion above. Am I about to pay big bucks for Scotch Weld, having no idea if it's really best or even contains the very "MMA" ChatGPT earlier said is needed to weld/bond/metal the broken pieces together?
I then Googled up a Reddit thread where some "random guy from the internet" said to fix broken polycarbonate at a high stress area, one must use SCIGRIP 16. So that set me on another discussion journey with ChatGPT, resulting in a product named...
The stuff is toxic, causes cancer, and even has shipping restrictions on it, which is why I was surprised a tube made its way to be found on Amazon Japan at any price.
ChatGPT then reviewed our previous dialog and give me this summary if its conclusions...
What That Means for Polycarbonate Repair
Polycarbonate (PC) reacts differently to these chemicals:
MEK
- Softens PC surface
- Provides some weld action
- Can cause stress cracking if overapplied
Methylene Chloride
- Attacks PC more aggressively
- Makes surface tacky very quickly
- Creates a brittle layer if the material is old
- Risk of “crazing”
MMA Monomer
- Useful — but in Weld-On 16 it’s a minor component, not a full-strength MMA adhesive
- Adds gap-filling ability
- Adds strength, but not structural strength like a 2-part MMA cartridge
Methyl Acetate
- Just a fast solvent to thin and help capillary penetration
So, Does Weld-On 16 Work on Polycarbonate?
Yes — it will bond polycarbonate.
Better than JB Weld, better than super glue.
It does:
- Surface melting
- Solvent welding
- Filling the crack with cured acrylic resin
BUT…
Is it strong enough for a Macintosh Portable hinge?
Not reliably.
Your hinge sees:
- high torque
- high shear
- repeated cycles
- stress on old, brittle PC
Weld-On 16 is:
- stronger than JB Weld on PC
- stronger than pure solvent
- but weaker and more brittle than true 2-part MMA adhesives
Under hinge loads, the crack may:
- re-crack along the edge of the weld
- propagate next to the solvent-affected area
- fail after repeated opening/closing
If you simply apply Weld-On 16 to the crack and reassemble the hinge:
It will look good; it may hold for a while;
but long-term durability is questionable.
Best-case scenario with Weld-On 16
If you reinforce the hinge internally (thin steel/aluminum strip epoxied or screwed inside), AND use Weld-On 16:
✔ Will likely last long-term
✔ Good fusion + added mechanical strength
✔ Much better than epoxy alone
If you use Weld-On 16 alone:
⚠ Might fail within months or even weeks
If you want an adhesive that definitely survives hinge loads:
You want a true 2-part structural MMA, not a solvent cement.
Examples (all bond PC extremely well and remain flexible enough under stress):
- 3M DP8005
- 3M DP8010 Blue
- 3M DP8805NS
- Konishi メタルロック AY-123 (Japan)
These are chemically different:
They do not rely on solvents — they polymerize into a tough, shock-resistant structural material.
Final Recommendation (Very Direct)
If your choice is between:
- JB Weld →
terrible for polycarbonate
- Methylene chloride alone → too brittle
- Weld-On 16 → ✔ decent, workable
- 2-part MMA →
best, longest-lasting, hinge-safe
So:
✔ Weld-On 16 is acceptable,
but not optimal,
unless combined with mechanical reinforcement.
I then told ChatGPT to compare the
ingredients of its recommended Cemedine and 3M Scotch Guard Epoxies with the SCIGRIP Weld-ON 16 to confirm Absolutely what is best and what I can actually buy here in Japan. ChatGPT responded:
Practical recommendation for a cracked polycarbonate hinge (your situation)
- If the goal is a single-product chemical repair that actually fuses polycarbonate, the solvent-type (Weld-On/SCIGRIP 16 or similar MMA/DCM formulas) is usually the best single-product result because it chemically melts the polymer and merges the crack surfaces. That gives very strong, low-gap bonds — but methylene chloride is toxic and may cause stress-cracking or surface whitening (crazing) if mis-applied. If you go this route, do it outdoors or in a fume hood, use nitrile gloves + respirator (organic vapor) and mask nearby surfaces.
- If you want a safer / more robust structural repair with better long-term fatigue performance, use a two-part structural adhesive plus mechanical reinforcement: e.g. 3M DP-460 (epoxy) or 3M DP-8005/DP-8805 (structural acrylate) and add a small internal reinforcement (stainless pin/dowel, a tiny metal or carbon fiber strap bonded along the hinge, or a glued-in sleeve). Epoxy + mechanical reinforcement will tolerate repeated opening/closing better than a brittle glue line alone. Epoxy is less likely to chemically attack or craze the polycarbonate, but you must prepare (clean, roughen) the surfaces.
- Cemedine AY-123: it’s an acrylic two-part product aimed at metal/CFRP. Manufacturer notes: “may be difficult to bond some plastics or painted metal” — so I would not pick AY-123 as the first choice for polycarbonate hinge repair unless you can confirm adhesion to your specific polycarbonate. (SDS confirms it’s a methacrylate-type chemistry, not a polycarbonate solvent weld.)
Safety & technique notes (do these or the repair will fail)
- If using Weld-On/SCIGRIP 16: extreme ventilation, nitrile gloves, goggles, and preferably an organic-vapor respirator. Apply in very small amounts (needle applicator) at the crack, clamp until cured. Expect some surface finish change — practice on scrap if possible. (SDS warnings: methylene chloride = serious hazard.)
- If using 3M epoxy (DP-460/DP-420): roughen both sides with very fine sandpaper, clean with isopropyl alcohol, clamp, and consider embedding a small stainless pin or backing plate for load transfer. Epoxy cures stronger when mixed precisely and can be accelerated by gentle heating per manufacturer instructions.
Final, direct answer to your original (and follow-up) questions
- Was I wrong to mention AY-123 earlier? Not “wrong” — AY-123 is a high-strength two-part acrylic and can be strong — but it is not a solvent MMA weld and the manufacturer specifically warns about plastics being sometimes difficult to bond. For polycarbonate hinge work, AY-123 is not the first choice. The SDS proves AY-123 is methacrylate-based (see above).
- Is SCIGRIP / Weld-On 16 really methylene-chloride / MEK / MMA? Yes — older/current SDS/TDS show methylene chloride + MEK + methyl acetate + small MMA monomer; many product pages state the formula and that it dissolves acrylic and can bond polycarbonate. That’s why it’s commonly recommended for plastic “welds.” Strongest single-product fix but hazardous.
- Are 3M Scotch-Weld epoxies “better” than Weld-On 16? They are different: epoxies give strong structural bonds and are safer to handle in normal environments; they do not solvent-weld the plastic, so success depends on surface prep and reinforcement. For a hinge under repeated mechanical stress, epoxy + reinforcement is the most robust long-term solution if you cannot or will not use solvent welds.
Would love to hear thoughts regarding the above. Yes, I know it's a lot to dig through, but again, it's actually only a small part of the larger dialog I had with ChatGPT.
