Cracked Hinge on Mac Portable

[JDW]

I wonder if the mentioned dental scaler would work for removing this metallic covering?

If you look closely, the tips are all sharp hooks...

Amazon.com

For my plan to work using DCM solvent, my flat PC rectangular piece (shown in red in my previous post) would need to lay flat across the ribs with virtually no grit or scratches on the backs of those ribs because DCM doesn't fill gaps. So my concern about using a spinning-hook dental cleaning instrument is that it would basically remove the chrome paint and roughen up the surface of the plastic too, making less surface area for the DCM to do its job. That's my guess anyway.

With that said, I still haven't figured out how to get that chrome paint off cleanly though.

 

[JDW]

And so it begins…

 

[JDW]

Cutting out only this tiny 27 x 10 mm piece for reinforcing the back of the 5 ribs was tough, even though the polycarbonate is only 2mm thick. It was cold in my room before, but now sweat is pouring off my brow! But I can’t use that until I have tried to close the crack with the solvent, and after that finely sand off the backs or the ribs somehow to they are perfectly fat and level to be solvent-welded to this 27x10 piece I just cut out.



I have no good ventilation inside my home and it’s now dark outside, so the solvent-weld of the crack must wait until tomorrow.

I also cut out another piece for testing…

 

[Paolo B]

Cutting out only this tiny 27 x 10 mm piece for reinforcing the back of the 5 ribs was tough, even though the polycarbonate is only 2mm thick. It was cold in my room before, but now sweat is pouring off my brow! But I can’t use that until I have tried to close the crack with the solvent, and after that finely sand off the backs or the ribs somehow to they are perfectly fat and level to be solvent-welded to this 27x10 piece I just cut out.

View attachment 24887

I have no good ventilation inside my home and it’s now dark outside, so the solvent-weld of the crack must wait until tomorrow.

Was just about suggesting using some metal reinforcement…

 

[JDW]

Cutting 2.0mm thick polycarbonate zapped all my energy, so I can only imagine how precisely cutting METAL would be!

ChatGPT suggested I use fiberglass mesh tape that has adhesive backing and then put JB weld on top of that. Why mesh? Because the JB Weld would be able to go through the gaps in the mesh and make contact with the polycarbonate surface underneath, making a better bond overall, rather than just trying to pack it on top of something.

But for that JB Weld to stick, I would need to scrape off all of the metallic paint, which is probably going to be the most painful job of all. How in THE world can I get that off? I really have no idea. The gaps between the ribs don’t really make it that practical to sand out. Using a box cutter with a fine tip is the only thing I can think of.

The only thing is, photos on Amazon are not very detailed, so I couldn’t tell how wide the fiberglass mesh was until it actually arrived, and the mesh gaps are fairly wide.

 

[JDW]

The order of steps would be as follows:

1. Weld cracked together with DCM liquid solvent.
   
   
2. Scrape off as much metallic paint as possible with a small box cutter in between the ribs. Then apply the fiberglass mesh and JB weld.
   
   
3. Somehow, perfectly sand off the metallic paint on the backs of the five ribs and ensure they are completely level. Then use DCM solvent to weld the 27 x 10 mm polycarbonate piece to the backs of those ribs.

There is barely enough clearance for my 2.0mm thick polycarbonate piece. It won’t touch the metal drive bracket but just barely.

 

[Paolo B]

The mesh is definitely wide, but I think you are going in the right direction!

 

[phunguss]

I couldn’t tell how wide the fiberglass mesh was until it actually arrived, and the mesh gaps are fairly wide.

Just double layer it with offset halfway (bad Photoshop example).

 

[Oelmuvun]

But for that JB Weld to stick, I would need to scrape off all of the metallic paint, which is probably going to be the most painful job of all. How in THE world can I get that off? I really have no idea. The gaps between the ribs don’t really make it that practical to sand out.

Use the technology of the sanding block.
You want to mate these two surfaces into each other, so use them together. Either use the sandpaper between them or use an abrasive lapping compound between them.. or both. In this case I would imagine the sandpaper to be enough, but if you really want to get fancy you could go extreme.

For between the ribs there are probably dremel attachments that would work. flap-discs, wire brushes, etc. Or wrap the sandpaper around the end of a strip of your polycarbonate and stuff that in there?

 

[JDW]

Well everything is now only hold due to my compete lack of knowledge about chemical solvents and the SHEER STUPIDITY of ChatGPT.

AI is such an idiot most of the time that I have to call into question the entire process!

While reading through the instructions that came with the DCM liquid solvent, it says very clearly that the protective gloves need to be PE…



And when I chastised ChatGPT for having told me to buy Nitrile gloves, even though it knew I was buying DCM liquid solvent, it merely had this to say…

I gave you nitrile-glove recommendations earlier because nitrile is the right general choice for many lab/repair tasks and for many solvents — it’s a common default for handling adhesives and general chemicals. That was an oversight: I should have checked DCM compatibility specifically before recommending. DCM (dichloromethane / methylene chloride) permeates nitrile and PVC rapidly; the DCM instructions specifying PE are correct. I should have caught that sooner. I’m sorry for the mistake and for the wasted time.

What a complete moron! And we’re supposed to fear this kind of stuff taking over the world? Replacing workers? And where are all those self driving fully autonomous cars? Oh yeah…

We live in a world of lies.

This is why I was hoping I could find a firsthand experience from someone who’s actually done this kind of stuff before, but I seem to be forging new ground.

For now, I need to place an order for PE gloves, but since today is a national holiday and I have to start work tomorrow, I probably need to put it on hold until the next weekend. What a mess!

 

[JDW]

Ah yes... Now ChatGPT says that even the DCM manufacturer-recommended PE is not enough...

Naturally, all those EVOH and specialist gloves are outrageously priced or so thick it's impossible to do precision work.

Maybe I should just use the Nitrile and turn a blind eye to it all? Maybe use bare hands? It's all a huge shot in the dark anyway because none of us are chemical engineers, and my attempt to gain the attention of engineers on Reddit has been a complete failure.

WHY CARE?

Because, sadly, you have to POUR OUT the DCM from its glass bottle into its smaller plastic bottle so you can add the syringe attachment in order to properly dispense it to weld plastic joints together.

There's a secondary reason too. The DCM printed instructions say that heat from your hand alone can inadvertently cause the DCM laid to shoot out or flow out unexpectedly, prompting the need for some kind of gloved hand protection.

​

 

[phunguss]

can inadvertently cause the DCM laid to shoot out or flow out unexpectedly

Better go with the full face shield as well?

 

[JDW]

I'm not buying a face shield. And I may not even glove at all. At the end of the day, of protection prevents me from properly dispensing the liquid in a very precise manner, what good is the DCM solvent in the first place?


I decided to go to the chemistry sub-reddit and found interesting advice from chemsts about handling:

DISCUSSION #1

DISCUSSION #2

As you can see in those discussions, some say double-glove with Nitrile gloves, while others say use bare naked hands because any DCM will penetrate gloves quickly and once penetrated, the DCM would stay on the skin longer than if no gloves at all were used.

So what I did was join that group and posted the following (still waiting for moderator approval):

LINK to the above.

I will do whatever the forthcoming recommendations suggest. That will probably be to do it without gloves. But I wonder if I'll get good advice about how to properly DISPENSE the DCM, with the crack tightly closed (like ChatGPT suggests), or apply it while the crack is open, then quickly close the crack. THAT is the bigger question!

---

UPDATE: When checking in a web browser, it shows still awaiting moderation, but when checking in the Reddit app, it says my post was deleted...



So I retitled and eliminated some references to ChatGPT, and posted in the r/OrganicChemistry subreddit here. No silly "awaiting moderation" and has 27 views as of this writing. Fingers crossed.