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gluing plastic under tension
Posted by: mrbigstuff
Date: February 15, 2019 12:10PM
any good epoxies or glues that I can get away with, in this case a plastic housing for a conical burr coffee grinder. I can clamp it to cure, but I need something strong enough to hold it together when it under the tension.

FWIW, they sell the part with the metal cone, but I don't need all that, just the plastic part.
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Re: gluing plastic under tension
Posted by: Forrest
Date: February 15, 2019 12:17PM
My experience is SuperGlue does NOT work on most plastics - it just melts the plastic
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Re: gluing plastic under tension
Posted by: Acer
Date: February 15, 2019 12:20PM
A solvent-based cement that dissolves the plastic would be best, I would think, better than an adhesive that depends on itself to bond, like super glue.
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Re: gluing plastic under tension
Posted by: mrbigstuff
Date: February 15, 2019 12:21PM
yeah, not considering an acrylic type glue, i think something two-part with a hardener are called for in this case
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Re: gluing plastic under tension
Posted by: 3d
Date: February 15, 2019 12:28PM
Testors plastic model airplane glue?
No sniffing!

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Re: gluing plastic under tension
Posted by: cbelt3
Date: February 15, 2019 12:29PM
Plastic Welding
[www.harborfreight.com]
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Re: gluing plastic under tension
Posted by: neophyte
Date: February 15, 2019 12:36PM
If appearance is less of an issue than function, consider adding something to absorb the strain, like a metal staple spanning the break, inserted thru holes before glueing, or using silk thread wraps before gluing, etc.
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Re: gluing plastic under tension
Posted by: macphanatic
Date: February 15, 2019 01:09PM
Know anyone with a 3d printer that could print a new part for you?
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Re: gluing plastic under tension
Posted by: rgG
Date: February 15, 2019 03:57PM
The JB Weld brand two part epoxy is good.
There are several different kinds and they also have putty versions.
Your local HD should have a good variety, in the paint department.





Roswell, GA (Atlanta suburb)
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Re: gluing plastic under tension
Posted by: mrbigstuff
Date: February 15, 2019 04:14PM
Yes, thanks for the suggestion, rg. I think I'm going to try regular JB, as I've got some in hand and I've read that people have used it on plastic.
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Re: gluing plastic under tension
Posted by: Cary
Date: February 15, 2019 04:27PM
I recommend this stuff - works great on most plastics: Loctite Epoxy
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Re: gluing plastic under tension
Posted by: nwyaker
Date: February 15, 2019 06:31PM
If aesthetics not an issue, you could add a piece of fibreglass cloth to the epoxy to reinforce.
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Re: gluing plastic under tension
Posted by: mrbigstuff
Date: February 15, 2019 07:30PM
no, aesthetics are definitely not an issue, but it is possibly too tight. I have nothing to lose, however, so I guess I could try
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Re: gluing plastic under tension
Posted by: Sarcany
Date: February 15, 2019 08:14PM
Quote
Acer
A solvent-based cement that dissolves the plastic would be best, I would think, better than an adhesive that depends on itself to bond, like super glue.

This.

If you can identify the type of plastic (look for a number stamped on it on the bottom or back) then you can find the exact right solvent/cement with a quick Google search. Otherwise try Weld-On Acrylic adhesive #16 applied via toothpick. In my experience it works on most plastics.

Use it in a well-ventilated space, remember that it sets very very quickly so you need to be ready to bind the pieces as soon as you apply the stuff, and remember that the tiniest bit goes very far.

Might want to test it on a few scraps of plastic so you get the feel of it before you use it on your appliance.



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Re: gluing plastic under tension
Posted by: pdq
Date: February 15, 2019 09:22PM
My go-to cement in a variety of different situations is Goop. Adheres to pretty much anything, very tenacious and flexible - not brittle like epoxy. Never been very impressed with super glue, except when you're trying to glue fingers together.

Whether Goop is good for this job depends on the details.
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Re: gluing plastic under tension
Posted by: rexs
Date: February 16, 2019 01:55AM
How about this plastic welder
Bondic - Liquid Plastic Welder - LED UV Light Activated Bonding Tool - Waterproof and Heat Resistant Bond, Build, Fix, Fill Anything In Seconds. Starter Kit Includes Bonus Refill

Bondic
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Re: gluing plastic under tension
Posted by: pdq
Date: February 16, 2019 10:12AM
Quote
rexs
How about this plastic welder
Bondic - Liquid Plastic Welder - LED UV Light Activated Bonding Tool - Waterproof and Heat Resistant Bond, Build, Fix, Fill Anything In Seconds. Starter Kit Includes Bonus Refill

Bondic

Those UV-activated glues are amazing, and great for tacking something in place (within 5 seconds!), but I don’t know how strong they are.
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Re: gluing plastic under tension
Posted by: Forrest
Date: February 16, 2019 01:23PM
Huh?
Quote
Goop
is a hand cleaner http://goophandcleaner.com/
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Re: gluing plastic under tension
Posted by: Winston
Date: February 16, 2019 02:27PM
Quote
pdq
Those UV-activated glues are amazing, and great for tacking something in place (within 5 seconds!), but I don’t know how strong they are.

Some of them must be pretty strong. They are used commercially to attach glass pieces together (such as a stem to the bowl of a wine glass).

But you need either a UV light or sunlight. There are some that will cure under ordinary light. My issue with using one is holding whatever needs gluing together/in place while setting the glue with UV. For UV glue, you have to have the parts in exactly the right place as setting is almost instant. I was looking at it to repair a broken wine glass, and decided to go with clear epoxy.


Good luck.

- Winston



------------------------
Be seeing you.
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Re: gluing plastic under tension
Posted by: Winston
Date: February 16, 2019 02:43PM
Quote
mrbigstuff
Yes, thanks for the suggestion, rg. I think I'm going to try regular JB, as I've got some in hand and I've read that people have used it on plastic.

I've generally had good luck with JB Weld Plastic Bonder.


Comes in black or tan. It's a two-part epoxy that is designed to work with plastic. I've found it works well on plastic car panels (most likely ABS), and I recently used it on a plastic housing for a light fixture, which was a harder brittle plastic. But I've had it fail on things like glasses frames, which might be a form of acrylic.

Recently I've learned that epoxy takes longer to fully cure than the package instructions say. Suggest you give it a week after gluing before putting it back in service.


If it's a hard plastic, consider Duco cement. It's a bit "hot" (i.e. it tends to melt plastics), which might be what you need. Duco is less likely to be helpful the more flexible the plastic.


Also make sure to clean well the surfaces to be bonded. JB Weld customer support told me unequivocally not to use "alcohol" to clean surfaces to be epoxied, but the rep refused to distinguish between denatured alcohol and isopropyl alcohol. When I researched it, denatured alcohol tends to leave oily residues, but isopropyl alcohol is excellent at leaving a clean surface. They recommended acetone, but acetone melts most plastics. I've had very good luck using isopropyl alcohol to clean plastics before using glue on them, including epoxy.

I used to say "rubbing alcohol", but then my daughter showed me a bottle of "rubbing alcohol" that had acetone and ethanol in it (!).


Good luck.

- Winston



------------------------
Be seeing you.
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Re: gluing plastic under tension
Posted by: mrbigstuff
Date: February 16, 2019 09:42PM
Good insights, Winston. Yes, this happens to be a hard, brittle plastic, and it snapped like a hard, brittle plastic does. I'll check out the Duco stuff. I recall that I may have had some at one point.
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Re: gluing plastic under tension
Posted by: Sarcany
Date: February 17, 2019 09:56AM
Quote
mrbigstuff
Good insights, Winston. Yes, this happens to be a hard, brittle plastic, and it snapped like a hard, brittle plastic does. I'll check out the Duco stuff. I recall that I may have had some at one point.

Duco is best for repairing surfaces with a lot of texture that it can grab onto, like broken porcelain. It does have solvents in it, so will work with soft plastics (about as well as model-cement), but I wouldn't recommend it for hard plastics where it's more likely to mar the surface than to adhere well.



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Re: gluing plastic under tension
Posted by: MrNoBody
Date: February 18, 2019 04:36AM
aesthetics are definitely not an issue
In combination with a 'glue', I've made small patch plates from aluminum
sheet attached with 1/8" pop rivets or #4 sheet metal screws.
Fixed a variety of plastic items that way.



39°36'17"N 75°44'43"W

The search engine that doesn't track you.

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Re: gluing plastic under tension
Posted by: Winston
Date: February 18, 2019 02:14PM
Quote
MrNoBody
aesthetics are definitely not an issue
In combination with a 'glue', I've made small patch plates from aluminum
sheet attached with 1/8" pop rivets or #4 sheet metal screws.
Fixed a variety of plastic items that way.


I've used aluminum plate or aluminum rods for the same purpose, but glued them in place with plastic bonder epoxy.


One other note on epoxy: unlike most glues, epoxy can fill voids and be used to make an item thicker. So, in the case of the part for the conical burr grinder, you can add a bead of epoxy along the break to make it stronger, assuming space allows for that. Epoxy can also be carved with a razor blade after setting up, or sanded or filed once hard.


Good luck.

- Winston



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Be seeing you.
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