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Forum topic by 4wood posted 07-21-2019 04:46 PM 316 views 0 times favorited 5 replies Add to Favorites Watch
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4wood

22 posts in 401 days


07-21-2019 04:46 PM

What is the best adhesive to use to re-attach the permanent magnets to the motor housing of a gear motor for a drum sander? They broke loose from the motor housing and now are magnetically attached to the armature.


5 replies so far

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4wood

22 posts in 401 days


#1 posted 07-21-2019 05:12 PM

The magnets look like they were attached with some kind of adhesive.

View LesB's profile

LesB

2151 posts in 3890 days


#2 posted 07-21-2019 07:24 PM

I’m not aware of any DIY type adhesive that would do the job SAFELY. Commercial applications have adhesives that are far stronger than anything we can easily get and often involve heat application to set them

You could try an epoxy but I would be seriously concerned about the centrifugal forces throwing the magnet off in such an application.

-- Les B, Oregon

View bilyo's profile

bilyo

774 posts in 1550 days


#3 posted 07-21-2019 11:03 PM

LesB. I really don’t know what the best adhesive would be, but aren’t these magnets glued to the motor frame and stationary. I can’t help but wonder if epoxy would be worth a try. If the epoxy fails, the magnets will again stick to the armature and the motor will stop. Before I tried this, I would try to clean off all the old adhesive first. I’m no expert, I could be wrong.
I also wonder about expansion and contraction from heating and cooling possibly cracking a rigid adhesive. Maybe a good quality silicone or other flexible adhesive would work.
Maybe getting some advice from the motor manufacturer or perhaps from a shop that repairs motors would be the way to go.

View CaptainKlutz's profile

CaptainKlutz

1613 posts in 1942 days


#4 posted 07-21-2019 11:39 PM

If magnets are glued to metal:
Use JB WELD (aluminum filled) or Devcon Plastic Steel Epoxy (steel filled).

If magnets are glued to plastic:
Use flexibilized cyanoacrylate (like Loctite 4902, MasterBond MB297FL), flexibilized epoxy (like SikaPower®-1200), or last but least – retail moisture curing polyurethane (gorilla glue),

Sorry, many of those are commercial materials, and will require sourcing from an online distributor like Ellsworth Adhesives, or similar.

They key to strong bond:
- Must have rough surfaces, and increased surface area for strongest bond.
No shinny surfaces. Use 40-80 grit sand paper and make both surfaces rough.

- Must be clean!
Mechanically remove any trace of old adhesive, dirt, oils, etc. Then clean with little soapy water for water soluble stuff. Next clean with lacquer thinner (mix of acetone, hydrocarbon, and ester solvents). Let dry thoroughly.

- Wet surface will reduce adhesion and bond strength – except polyurethane.
If humidity is over 50% RH, need to bake moisture off the surface. Pre-bake the parts in oven at 140F for 2 hours to remove all surface moisture. Must bond the surfaces in less than 20 minutes or when they reach room temp, else bake and start over. Some adhesives are more tolerant of moisture, but they work best with dry surface. Ignore this tip for Gorilla Glue

FWIW – Devcon Plastic Steel (thicker putty version) sticks like grime death to properly prepared steel surfaces. You can grind, machine, and even tap threads into it when fully cured. Great for repairing cast iron or other pot metal parts.

PS – not an expert, just sharing what has worked in past for me.
Maybe not entirely true? I have worked with adhesives and polymers for over 30yrs professionally. But, I am still an idiot klutz.

Best Luck!

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

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4wood

22 posts in 401 days


#5 posted 07-23-2019 02:40 AM

Thank you for all of the fantastic information. Since I live in South Florida I will definitly put it in the oven.

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