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Best glue or method for attaching magnets to a plastic container?

#1 User is offline   JustFolks 

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Posted 11 August 2009 - 06:02 PM

Need some advice from those of you who have successfully glued magnets onto plastic containers.

I'm using a small lock-n-lock and small (quarter-size) disc magnets. Glued 4 to the top using "hot" glue....didn't last a day in the South Carolina heat....melted and oozed loose. :drama:

Tried again with Gorilla Glue....applied per directions, clamped and let set....tested this a bit more thoroughly and two of the magnets popped off quickly. :D

So....any advice out there for what I can do to get a reliable long-lasting attachment?

JustFolks
South Carolina

#2 User is offline   bittsen 

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Posted 11 August 2009 - 06:05 PM

 JustFolks, on Aug 11 2009, 07:02 PM, said:

Need some advice from those of you who have successfully glued magnets onto plastic containers.

I'm using a small lock-n-lock and small (quarter-size) disc magnets. Glued 4 to the top using "hot" glue....didn't last a day in the South Carolina heat....melted and oozed loose. :drama:

Tried again with Gorilla Glue....applied per directions, clamped and let set....tested this a bit more thoroughly and two of the magnets popped off quickly. :D

So....any advice out there for what I can do to get a reliable long-lasting attachment?

JustFolks
South Carolina


It really does depend on the plastic. Some plastics reject glue while others seem to enjoy it.
What I have done with tests is to glue the magnet with regular super glue and then place another magnet on the inside of the container to "help" hold the original magnet in place.
I use NdFeB-N45 magnets since they have the best holding power for the buck.

#3 User is offline   kunarion 

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  Posted 11 August 2009 - 07:10 PM

 JustFolks, on Aug 11 2009, 07:02 PM, said:

glue the magnet with regular super glue and then place another magnet on the inside of the container to "help" hold the original magnet in place.


I like that idea! Not only is some soft plastic tough to glue, so are those neodymium magnets.

If I need to use magnets, I'll go with a little over-kill. The magnet will be epoxied into a metal cup (just about the size of the magnet), which will be securely bolted to the container. Or I'll find magnets that are manufactured with threaded hardware. At least the magnet will be inset, so it's surrounded by glue. Because my hide is gonna be sinister, devious, evil, and if it ever falls off, it loses a lot of its sinisterly devious evilness.

This post has been edited by kunarion: 11 August 2009 - 07:14 PM


#4 User is offline   mrbrit 

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Posted 11 August 2009 - 07:16 PM

Greetings!

Well two part epoxy is the best i have found. But, the issue here is most likely a shiny surface which the glue is not bonding to. I would take some sand paper and rough up the surface then glue the magnets on. If you are looking for a little insurance i would then camo duct tape the box for good measure.

Have fun making your hide!

MrBrit

#5 User is offline   Team Bashspa 

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Posted 11 August 2009 - 08:27 PM

I have used JB weld it is really tough the only thing is it has iron in the mix so you will see it cover your magnet but it can be remove before it gets full strength. Rough up the plastic first . I tried the glue gun to are hot sun did melt it to.

#6 User is offline   Kabuthunk 

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Posted 11 August 2009 - 08:32 PM

GOOP brand glue is what I use to make all my geocaches. I have yet to have it fail due to regular wear-and-tear... however animals appear to have been able to rip the leaves glued to an ammo can off. That's about the extent of it.

#7 User is offline   Chrysalides 

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Posted 11 August 2009 - 08:51 PM

 bittsen, on Aug 11 2009, 07:05 PM, said:

What I have done with tests is to glue the magnet with regular super glue and then place another magnet on the inside of the container to "help" hold the original magnet in place.
I use NdFeB-N45 magnets since they have the best holding power for the buck.

N45 magnets are usually strong enough that having just one or two magnets inside is strong enough to hold a container to steel. Being inside, it won't rip loose when the container is removed.

#8 User is offline   bittsen 

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Posted 11 August 2009 - 09:11 PM

 Chrysalides, on Aug 11 2009, 09:51 PM, said:

 bittsen, on Aug 11 2009, 07:05 PM, said:

What I have done with tests is to glue the magnet with regular super glue and then place another magnet on the inside of the container to "help" hold the original magnet in place.
I use NdFeB-N45 magnets since they have the best holding power for the buck.

N45 magnets are usually strong enough that having just one or two magnets inside is strong enough to hold a container to steel. Being inside, it won't rip loose when the container is removed.


Good point depending on the size of the magnet and the weight of the container.
I would use mostly 3/8 X 3/8 X 1/8 for the caches. My 5/8 disk ones could be used for a heavier one.

#9 User is offline   Chrysalides 

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Posted 11 August 2009 - 09:22 PM

I've also used kneadable epoxy putty (similar to J-B Stik). I shape them so that they cover a bit of the magnet, and appears to work very well. The only problem with them is cleaning the residue from my hands after I'm done.

 bittsen, on Aug 11 2009, 10:11 PM, said:

I would use mostly 3/8 X 3/8 X 1/8 for the caches. My 5/8 disk ones could be used for a heavier one.

Slight off topic, where do you get your magnets from? It's been a while since I bought my last batch, the place appears to have gone out of business, and I'm running low.

I bought a batch of epoxy coated magnets before. The glue seems to stick on to the epoxy coating better than the nickel plating, but I did not do a scientific study, so just take that as "possibly better, but definitely no worse".

#10 User is offline   bittsen 

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Posted 11 August 2009 - 09:34 PM

 Chrysalides, on Aug 11 2009, 10:22 PM, said:

Slight off topic, where do you get your magnets from? It's been a while since I bought my last batch, the place appears to have gone out of business, and I'm running low.



I buy them from an Ebay seller named emovendo
He has minerals I like to play with as well as magnets.
A very reliable seller.

#11 User is offline   Chrysalides 

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Posted 11 August 2009 - 09:37 PM

 bittsen, on Aug 11 2009, 10:34 PM, said:

I buy them from an Ebay seller named emovendo
He has minerals I like to play with as well as magnets.
A very reliable seller.

Thanks for the info, I'll check his ebay listings.

Edit: yikes, some of the minerals are really exotic! (and priced to match :D)

This post has been edited by Chrysalides: 11 August 2009 - 09:41 PM


#12 User is offline   knowschad 

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Posted 11 August 2009 - 09:51 PM

If the magnets are INSIDE of the plastic, you won't need much. The magnetic attraction to what you are attaching it to will be enough except for to hold them in place when the container is off. I recently found one that tried to use ceramic magnets inside of a Lock 'n Lock to help hold rare-earth magnets to the outslde. Good idea, but it has had a Needs Maintenance log for weeks now because it didn't hold upl

I recently archived one that had four rare-earth magnets on the outside of a sheet of plexiglas. I had drilled holes through the plexiglas in hopes that the glue would be like rivets. I used JB weld, but that did't hold up for long either.

Bottom line... its tough!

#13 User is offline   sbell111 

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Posted 12 August 2009 - 04:56 AM

 Kabuthunk, on Aug 11 2009, 11:32 PM, said:

GOOP brand glue is what I use to make all my geocaches. I have yet to have it fail due to regular wear-and-tear... however animals appear to have been able to rip the leaves glued to an ammo can off. That's about the extent of it.
I second GOOP. Unlike most glues, Goop doesn't get really rigid when it sets up. This keeps the slight plastic flexing from popping it off like it does with glues that set up hard like gorilla glue.

Also, remember to hit the plastic with sandpaper to rough it up prior to gluing.

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Posted 12 August 2009 - 05:46 AM

 JustFolks, on Aug 11 2009, 08:02 PM, said:

Need some advice from those of you who have successfully glued magnets onto plastic containers.
Some plastics, nylon and polypropylene as examples, are really hard to deal with. If you're running into problems, I'd almost bet you've got a polypropylene container. The second thing that can hurt you is the surface texture of the magnet itself. Some are extremely well polished, making adhesion to those a bit of a bugger, too.

Your third problem will be outdoor use where the plastic and magnet will exhibit very different coefficients of expansion with temperature changes. This will very often cause the any brittle adhesive to crack at the junction. 2 part epoxy will often fail in outdoor use for that reason alone. As an example ... I can't tell you how many times I've come up to a "silver bullet" cache and found it on the ground with the magnet separated from the mini-bison to which it was attached. Brittle adhesive on a polished surface is a double whammy!

My suggestion would be to try a stronger than usual magnet on the inside as suggested by many above. Rough up the inside of the container surface where the magnet will rest, and use RTV (silicone seal) material liberally on TOP of the magnet and around its outside edges. Use very LITTLE of it under the magnet itself. The spacing of a magnet from the surface to which it is expected to "stick" has everything to do with the strength of the hold of the magnet, and it's already going to be holding through the thickness of the plastic container you are using. Trying to set your magnet on top of 1/8" of goo is going to space it quite far from the object you're parking your cache on, and the magnetic attraction will be substantially weakened.

Be sure to let the RTV cure for a least a full day with the container open, especially if it's a small container.

The RTV will remain flexible in temperature shifts, and flexible when the magnet and plastic change size with temperature.

#15 User is offline   texasgrillchef 

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Posted 12 August 2009 - 10:40 AM

 JustFolks, on Aug 11 2009, 06:02 PM, said:

Need some advice from those of you who have successfully glued magnets onto plastic containers.

I'm using a small lock-n-lock and small (quarter-size) disc magnets. Glued 4 to the top using "hot" glue....didn't last a day in the South Carolina heat....melted and oozed loose. :P

Tried again with Gorilla Glue....applied per directions, clamped and let set....tested this a bit more thoroughly and two of the magnets popped off quickly. :D

So....any advice out there for what I can do to get a reliable long-lasting attachment?

JustFolks
South Carolina


Get you some Neodymium magnets... 2 big ones... put one on the INSIDE of your plastic container, & one on the OUTSIDE.

These are super magnets... so you can get ALOT of magnetic power from a very SMALL physical size. The two magnets inside & outside will hold each other together, & the outside magnet will hold the container to the metal that you want to attache it too.

I use this setup in my kitchen to hold plastic SPICE bottles to my spice rack. a 1" diameter, 1/8" thick neodymium magnet (With a N45 rating) will easily hold up to about 5lbs when stuck to Steel. Less if the quality of metal is lower. If your attaching it to cast iron, it can hold as much as 10lbs.

The cost of 2 of those 1" round 1/8" thick Neodymium magnets? About $2 - $4

There are many places on the internet you can find them. Look for a neodymium magnets with at least a N45 rating.

TGC

#16 User is offline   Gitchee-Gummee 

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Posted 12 August 2009 - 10:41 AM

Good idea there............... rare earth magnets. That'll do the trick.

#17 User is offline   Gitchee-Gummee 

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Posted 12 August 2009 - 10:46 AM

By the way....... should've mentioned it earlier........... sorry......................

Glues and/or epoxies have a habit of letting go after a while outdoors, mostly because of expansion and contraction differences with the other materials they are trying to hold.

Sorry for the oversight.

#18 User is offline   StarBrand 

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Posted 12 August 2009 - 12:58 PM

Strong rare earth magnets glued INSIDE the container have always worked well for me.

#19 User is offline   emmanogoldfish 

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Posted 13 August 2009 - 06:05 AM

What about taping the magnets in place on the inside?

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Posted 13 August 2009 - 06:33 AM

Rare earth magnets. Because they're stronger.

Magnets on the inside. Keeps them dryer and keeps them from being pulled free when you disengage the container from the metal surface.

Use a flexible adhesive/glue. Silicone or GOOP works well. Hot glue often melts (as it's designed to.) Gorilla Glue and Super Glue dry stiff and will not flex with the container and will cause the whole thing to break free of the container.

Fill the bottom of the container with the glue/adhesive and cover it with a layer of Gorilla Tape. The tape is a "just in case" measure.

Some folks will say skip the glue and just use the tape, but I find that the magnets sometimes "drift" in hot weather if there's not a solid disk of flexible glue/caulk to keep them in place.

#21 User is offline   DragonsWest 

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Posted 13 August 2009 - 07:33 AM

I usually glue magnets inside, with gorilla glue, which seems to stick to everything. Watch out, it foams!

#22 User is offline   PhxChem 

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Posted 13 August 2009 - 04:23 PM

I must be the only one with this method but.....I usually drill some small holes into the plastic in the area the magnet will cover. Then I apply JB Weld to the surface allowing it to get into the holes (you can use tape on the other side of the plastic so the JB Weld will stop at the inside surface). Seems to work.....

#23 User is offline   JM Chicago 

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Posted 16 August 2009 - 01:15 PM

If the container is flexible ya need a flexible glue not a hard glue like epoxy/JB weld/ super glue. Surface prep can do wonders...ruff it up, check for solvent cleaning the glued face, that kinda thang.
If all else fails go find a magnet with a hole in it and attach with a screw or bolt...seal the thru hole with a bit of silicone sealant or caulk before assembly.
Look here for mags with holes (http://www.sciplus.c...11/category/117)
Jeff
The Chicagoan

#24 User is offline   AZcachemeister 

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Posted 16 August 2009 - 01:42 PM

Gluing a strong magnet to the inside of the container will probably work best. Even if it comes loose, it can still hold the container in place.

You can get one or two really strong magnets from a defunct computer hard-drive. You will need a set of small TORX screwdrivers and some determination to get them out.

In some areas you can get defunct Hard Drives from a technology recycling business...maybe for free, maybe for $1 each. Once you get the drive open, the magnet(s) will be glued to a Stainless Steel bracket.

To remove the magnets from the bracket with minimal damage, hold the assembly in boiling water for a minute or two, and then bend the bracket using a vise, or two pairs of pliers...the magnet will slide right off.

As an added benefit, the Hard Drive platters make cool swag, and work well as emergency signal mirrors.

#25 User is offline   JustFolks 

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Posted 16 August 2009 - 05:40 PM

Thanks to all who responded! I've got some great things to try, and will be attempting some more creative hides with the help of your ideas!

JustFolks

#26 User is offline   texasgrillchef 

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Posted 17 August 2009 - 12:39 AM

The easiest thing without messing with glue, or tape, inside or out... is simply TWO magnets. One on the inside & one on the outside.

However.... according to this one company. All you may need is ONE magnet on the INSIDE and it could hold almost anything you wanted!

Check out... http://www.unitednuc...com/magnets.htm

They have a couple of magnets that I bet could hold a HUNDRED pounds or more to most things & only be the size of a 3" x 1" disk!

I garuntee no glue or tape is needed then!

TGC

#27 User is offline   Curioddity 

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Posted 17 August 2009 - 06:15 AM

I'm yet another advocate for GOOP. That stuff will stick well to just about anything. Model aviators have been using GOOP for years on EPP foam and EPP foam is made from polypropylene which is almost as hard to stick stuff to as Teflon. Marine GOOP is the best because it has UV inhibitors in it.

In Europe and many other parts of the world GOOP isn't available because of it's Toluene base, but Eclectic Products, Inc. also makes the E6000 series of adhesives which are the same as GOOP except they uses PERC (Perchloroethylene) as a solvent instead of Toluene. I've used both and one seems as good as the other, although the E6000 takes longer to dry.

Pete

#28 User is offline   Knight2000 

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Posted 17 August 2009 - 06:27 AM

 emmanogoldfish, on Aug 13 2009, 10:05 AM, said:

What about taping the magnets in place on the inside?

I have used different glues on my mag caches. Always on the inside as my first cache was on the outside and it failed in a day or two. Neo mag on inside with adhesive and then put duct tape over it. I did replace the duct tape on one after two years.

#29 User is offline   AZWheeler 

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Posted 17 August 2009 - 11:08 AM

Have not tried gluing magnets to plastic, but I find a lot of uses for Liquid Nails construction glue (the regular, not the indoor type). It dries strong and a full-size caulk tube is under $2.

#30 User is offline   dragonflytotem 

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Posted 16 October 2009 - 02:00 AM

Nobody has mentioned this yet so thought that I"d ask -- what about a magnet that has been encased in plastic? I have looked at various sources for magnets and did check out emovendo's ebay store (he's got a 100% satisfaction rating out of some 38K transactions!) and see that he sells some that are encased in plastic - N48 grade, impact resistant hard plastic shell. Has anyone tried those?

I suppose you might have a problem with the plastic cracking under temperature extremes and he mentions a problem with strength drop off because of the plastic (but from the below I'm not sure how much of a problem that is, especially if you used more than one or they were stacked by having one inside and one outside). Here's what he says in the listing:

"The biggest drawback to Neodymium magnets is while magnetically very strong, they are very physically fragile. Tough coatings, such as nickel, go a long way toward protecting the magnets from cracks and breakage. However, after repeated impacts with each other or other surfaces, even the best metal coatings will fail. Plastic coatings offer an impact and corrosion protection for the fragile magnets inside. These magnets can sustain far more punishment than the standard metal coated magnets, making these a good play or experimention magnet. However, on the negative side, this relatively thick coating reduces the effective power of the magnet due to the logarithmic drop in magnet strength as the distance increases from the surface of magnet. How much of a difference? 2 standard nickel coated 3/4 x 1/8" N48 disc magnets will pull at each other with about 9 pounds of force. Two 3/4 x 1/8" N48 plastic coated will only pull with about 5 pounds of force. That is 45% less strength. So it is a tradeoff. If you require maximum power, go with metal coated: if you plan on playing with neodymium magnets A LOT these are the magnets for you!"

#31 User is offline   NYPaddleCacher 

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Posted 16 October 2009 - 02:55 AM

 JM Chicago, on Aug 16 2009, 01:15 PM, said:

If the container is flexible ya need a flexible glue not a hard glue like epoxy/JB weld/ super glue.



Another flexible adhesive that I don't think I've ever seen mentioned in the forums is 3M 5200. I haven't used it for a geocache but I've used it for gluing/sealing stuff on the inside of a couple of kayaks I've built. From the 3M web site:

"The seal is extremely strong, retains its strength above or below the water line. Stays flexible too - allows for structural movement. Has excellent resistance to weathering and salt water."

3m 4200 is similar but is less permanent.

#32 User is offline   Pajaholic 

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Posted 16 October 2009 - 06:09 AM

I've not tried this with caches yet. However, I have used a product called "FenderMender" to glue smooth, flexible plastic things to rigid surfaces with great success. The product was originally designed to repair Lexan (polycarbonate) bodies of radio-control model cars and, once cured, seems unaffected by vibration, fuel, water, and temperatures up to just under the melting point of Lexan and down to at least a few degrees below freezing.

You should be able to buy this product in most good R/C model shops in the USA. Unfortunately, it seems no longer available in UK - so I'll have to order my next tin from the States.

#33 User is offline   bittsen 

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Posted 16 October 2009 - 09:50 AM

 drdan01, on Oct 16 2009, 03:00 AM, said:

Nobody has mentioned this yet so thought that I"d ask -- what about a magnet that has been encased in plastic? I have looked at various sources for magnets and did check out emovendo's ebay store (he's got a 100% satisfaction rating out of some 38K transactions!) and see that he sells some that are encased in plastic - N48 grade, impact resistant hard plastic shell. Has anyone tried those?

I suppose you might have a problem with the plastic cracking under temperature extremes and he mentions a problem with strength drop off because of the plastic (but from the below I'm not sure how much of a problem that is, especially if you used more than one or they were stacked by having one inside and one outside). Here's what he says in the listing:

"The biggest drawback to Neodymium magnets is while magnetically very strong, they are very physically fragile. Tough coatings, such as nickel, go a long way toward protecting the magnets from cracks and breakage. However, after repeated impacts with each other or other surfaces, even the best metal coatings will fail. Plastic coatings offer an impact and corrosion protection for the fragile magnets inside. These magnets can sustain far more punishment than the standard metal coated magnets, making these a good play or experimention magnet. However, on the negative side, this relatively thick coating reduces the effective power of the magnet due to the logarithmic drop in magnet strength as the distance increases from the surface of magnet. How much of a difference? 2 standard nickel coated 3/4 x 1/8" N48 disc magnets will pull at each other with about 9 pounds of force. Two 3/4 x 1/8" N48 plastic coated will only pull with about 5 pounds of force. That is 45% less strength. So it is a tradeoff. If you require maximum power, go with metal coated: if you plan on playing with neodymium magnets A LOT these are the magnets for you!"


The plastic coating would help prevent the glue from suffering the heat/cold expansion failure issues but you will have a new problem. Many plastics reject many glues. The best scenario you could hope for is to find a glue that would bond to the magnet covering and your cache as well.

Best case scenario is to put the magnet on the inside of the cache container and hold it there with a good flexible adhesive.

#34 User is offline   6079smithw 

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Posted 17 October 2009 - 09:30 PM

I've had outstanding luck with Permatex Red RTV Silicone Gasket Maker. Couple of dots on the magnet, press together. Once it sets up its almost impossible to remove and totally unaffected by heat or moisture. Available at any auto parts store or Wally-World. Hope this helps...

#35 User is offline   meark 

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Posted 17 October 2009 - 10:17 PM

www.thistothat.com

for glue whatever, to well you know whatever.

#36 User is offline   Vater_Araignee 

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Posted 18 October 2009 - 12:17 PM

NdFeB-N45 or stronger magnets "inside" the container with a little JB weld or even a lot of super glue gel will keep them in place. Inside.
I tried to glue some magnets to the outside of an acrylic box.
Superglue failed.
But somebody took my failed attempt with the superglue and just stuck them in the box. It works and nobody has ganked them... yet.
I wanted a bigger box so..
Gorilla glue failed.
JB weld failed.
It took acetone and acrylic nail filler to keep it on there.
Now I wonder why I bothered testing because I'm making an acrylic box from scratch and can poor it so the magnets are in the wall.

#37 User is offline   bittsen 

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Posted 26 December 2009 - 09:38 PM

BUMP

I just had an epiphany while I was playing with magnets and trying to figure the best way to glue a magnet to a plastic container.

Put the magnet in some shrink tube and shrink it up first. Then the plastic of the shrink tube will adhere to the other plastic much easier, thus encasing the magnet in plastic.

I hope that makes sense. There's some pretty wicked plastic glue fumes going on in my place right now.

#38 User is offline   dragonflytotem 

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Posted 27 December 2009 - 12:41 AM

 bittsen, on Dec 26 2009, 09:38 PM, said:

BUMP

I just had an epiphany while I was playing with magnets and trying to figure the best way to glue a magnet to a plastic container.

Put the magnet in some shrink tube and shrink it up first. Then the plastic of the shrink tube will adhere to the other plastic much easier, thus encasing the magnet in plastic.

I hope that makes sense. There's some pretty wicked plastic glue fumes going on in my place right now.



I'd be interested in hearing more down the road as to how well it holds up for you. I've already thought of this one myself, but had rejected the idea without trying it because my past experience with shrink wrap tube is that it gets to be quite brittle when subjected to the cold and it will crack. I did a career in Navy electronics and we used that stuff all the time, but seldom if ever were able to use it outdoors for that reason. And by cold, I'm talking anything below freezing. So if you were in a warmer climate I think that it could be a workable idea, but I'd have my doubts anyplace else and so would love to hear back from you after you've given it a go. :-)

#39 User is offline   Migs 

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Posted 27 December 2009 - 03:00 AM

Sandpaper the plastic where you will apply the epoxy. That will certainly help. If your also degrease your magnet with a little alcohol swab and let it dry then the bond should be very good.
-Migs

#40 User is offline   Wooden Cyclist 

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Posted 27 December 2009 - 05:10 AM

I've been using Loctite Stick "n Seal Ultra. Two caches have benn out for two months with no failures. One is a Lock & Lock and the other is a film can. Both have ceramic magnets adhered to the outside of the containers.

I also used this glue to make some micro containers out of plastic pop bottle caps and necks. Some have been out in the elements for 6 months and the adhesive has yet to fail.

This post has been edited by Wooden Cyclist: 27 December 2009 - 05:13 AM


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