Mark J

Best adhesive for plastic & magnets?

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Does anyone have any suggestions?  I buy those Ikea LED lights with the spring clamp base, then glue rare earth magnets to the bottom.  These work very well for me at the lathe and bandsaw, etc. 

The problem is the the adhesive keeps failing.  I have tried CA and DAP Rapid Fuse as well as hardware store squirt tube epoxy.  Rapid Fuse did the best, but all have failed, and it appears the failure is at the glue metal interface.

Any suggestions on another adhesive to try?  The metal casing of the magnets is smooth and shiny.  I need something that wiil stick to that.

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I expect the failure is from heat.  No epoxy, that I have ever worked with, is good for any amount of heat, long term.   There should be some especially for warm environments.  The first place I'd look would be at the 3M DP line.  There are a bunch of different specialized ones.  They come in fairly small "duotubes", and you can meter out a tiny bit with the mixing tips, and special gun, but the components can also just be pushed out of the tubes, and mixed with a little stick.  I bought my gun, and get the tips from Golfworks, but none of the golf adhesives are good for heat.

edited to add:   I just did a Google search, and this new one, on me, turned up:   https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Scotch-Weld-Epoxy-Adhesive-2214-Hi-Temp-New-Formula/?N=5002385+3291797505&rt=rud

edited to add again:  That's the most expensive glue I've ever seen: https://www.amazon.com/3M-Scotch-Weld-20833-Adhesive-Hi-Temp/dp/B072X3NP4Z

but I expect there are others that would work fine

Once more, this was listed on that same Amazon page for a more down to Earth price: https://www.amazon.com/J-B-Weld-37901-Temperature-Resistant/dp/B01IBOBY74/ref=pd_cp_328_2/137-8129970-5464712?_encoding=UTF8&pd_rd_i=B01IBOBY74&pd_rd_r=78b06b8f-7944-411d-bcad-64b385a852ea&pd_rd_w=2be5h&pd_rd_wg=u0YA1&pf_rd_p=ef4dc990-a9ca-4945-ae0b-f8d549198ed6&pf_rd_r=EKYH79VGVNDV2AESEHB2&psc=1&refRID=EKYH79VGVNDV2AESEHB2

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Have you tried contact cement?  Take some sandpaper and rough the surface of the lamp and give that a try.  No promises!

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Mark, did they not come with any form of adhesive such as double back tape, not that’s what I’m recommending. Are these under the counter type lights that a screw would hold? 

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Not many adhesive glues bond well to both metal and plastic. Any chance you can switch to a mechanical fastening? Maybe go to the washer-shaped magnets that a screw can hold?

Is the lamp base shaped in such a way that you can use Plasti-Dip to encapsulate the magent into place?

https://www.homedepot.com/p/Plasti-Dip-14-5-oz-Black-Plasti-Dip-11603-6/202196703

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Thanks for the responses.  Here's a picture of the problem.

20191001_220129.thumb.jpg.b9b2ca673b79ab767d7cc075a3196092.jpg

That's an impressive price on that tube of glue!  Tom, I'm not thinking this is heat related, the magnets are well away from the lamps, but it could be vibration.  In any case the JB Weld is a good suggestion.  And I'll definitely scuff the plastic.  Maybe I'll try scuffing the magnet, too.

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I’d imagine that 3M VHB tape would work well. I’ve used it on plastic and metal in high vibration and high impact applications and it always amazed me. 

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I've never seen a rare earth magnet shaped like a washer.  

Suppose I interpose a piece of wood between the metal and plastic?  Is there a good wood to metal glue?

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Recessing the magnet into a pocket filled with epoxy should do well if you go the route of interposing a wooden block. I'd still consider screwing the plastic clamp base to the wood.

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7 hours ago, Mark J said:

I've never seen a rare earth magnet shaped like a washer.  

Suppose I interpose a piece of wood between the metal and plastic?  Is there a good wood to metal glue?

Lee Valley sells them. Their other option, which I've used, are cup washers specifically meant to hold regular magnets that take a screw. They won't come out under load.

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If you use a piece of wood just slightly thicker than the magnets, and make the pocket just slightly less than the thickness of the wood, you might be able to glue (or screw) the pocket-side of the wood to the plastic clamp, trapping the magnets behind a thin layer of wood, and not have to use any glue on the magnets themselves.

Another option would be to buy magnets with a countersunk hole in the middle and attach to the plastic clamp with a short machine screw and nut.  https://www.magcraft.com/cup-magnets 

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Wow, lot of great ideas.  I'm glad I asked.  

Mechanical fastening with the cup magnets seems like it would be the easiest.  

That Milliput stuff seems like it would be great just to have around.  

Trapping the magnet underneath a thin layer of wood is a good idea to have in my back pocket.  Trapping the magnet behind a very thin sheet of steel would also work and probably reduces the pull of the magnet even less.

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Another option is the cup magnets screwed to a bit of thin plywood and then glue the plywood to the plastic.  So I'll ask, what glue do you recommend for the wood plastic bond?

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1 hour ago, Mark J said:

 So I'll ask, what glue do you recommend for the wood plastic bond?

For something small like this, I've had good luck with Loctite's gel-type super glue.  Rough up the plastic a bit, and apply a little gel to both the plastic and the wood.

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2 hours ago, G Ragatz said:

For something small like this, I've had good luck with Loctite's gel-type super glue.  Rough up the plastic a bit, and apply a little gel to both the plastic and the wood.

x2

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If you use the magnets with a screw hole, a plastic cement would hold them.  Just let a key form inside the tapered hole in the magnet. I know 3M DP100 would hold like that, but you need the applicators, and it's not a cheap glue like JB Weld, which should work fine, the same way.   Those magnets are very fragile, so if you do go machine screws, don't tighten them at all.  

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They're pretty brittle, and cheap.   Check ebay for size, and type you want, usually with free shipping.  You can buy different diameters for a given screw size, in different thicknesses.  The thickness determines the strength.  There are Many variations.

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1 hour ago, Immortan D said:

Is it possible to just drill and countersink a hole in those rare earth magnets?

K&J Magnetics for ring magnets.  ring magnets

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Well here's where I'm at so far.  I didn't find the JB Weld product that Tom was suggesting at the hardware store, but I did find JB Weld brand Plastic Bonder (different product from their Plastic Weld).  JB Weld recommends Plastic Bonder for bonding plastic and metal.  So I picked up some and I am giving it a try as it is right here and available.  I expect the magnets will come off one or the other of these lights soon enough, so in the meantime I am going to order some of the ring type magnets.  I absolutely love neodymium magnets so these won't go to waste no matter if Plastic Bonder works or not.   There's a Michael's on the way to Woodcraft, so next run I'll stop and check out the Milliput, too.   I'm beginning to think that adhesives are like clamps.  By the way does anyone have experience with Duco Cement?  I seem to have acquired a tube from somewhere, but I've never heard of it.  

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Ordered cup magnets,  and I learned something about these rare earth magnets.  Of course that's not saying much, what I knew about magnets wouldn't have filled a brief conversation.

There are different kinds of rare earth magnets, so they are not all neodymium.  The magnets themselves are not encased in anything; the shiny outer surface is electroplated nickel.  The material is brittle and easily broken, so no drilling.   

I found that there are ring magnets and cup magnets, which both look like a washer and are available with a countersunk hole.  The cup magnets sit inside a steel cup which is slightly deeper than the magnet is thick.  This gives some protection to the magnet, particularly if it is used in a closure where it may be repeatedly smacked.  Ring magnets are intended to be mortised into the mounting surface, like a wooden cabinet door.  

Cup magnets have an added benefit in that the steel cup redirects the magnetic field from the back of the magnet around to the front essentially doubling the field strength on that side.  

I almost hope the glue fails so I can try these magnets when they arrive.  In fact, if I can get over to Ikea I'll get some more lamps.  

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It seems like someone should sell that lamp with just a small, magnetic base.  I bought some just like, except the clamp base is slightly different, off of ebay.

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I tried a few other adhesives including ones marketed for plastic with no luck bonding the magnets and limited luck attaching a block of wood for the magnets to be screwed into.  

But mechanical attachement works.  Trick was to replace the rubber pad on the lower jaw of the clamp with a bit of ply and screw through the jaw attaching cup magnets.

15732407841791339394394.thumb.jpg.7c901d155d01e3314669d40c07de36af.jpg

 

 

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