How to Glue Magnets on Acrylic (Dust Foot)?

[pkirby]

So I'm making a new dust foot out of 0.5" cast acrylic. I tried gluing the rare earth magnets to it with some Loctite 2 part epoxy from Home Depot (it said it glues metal to plastics). Well... that didn't work to well because they fell off. Any ideas on a glue that will work? Thanks.

[Ajcoholic]

if you scuff up the acrylic where you want the magnet to stick, a thick CA (cyanoacrylate) should work. Also, I use a polyurethane based hot melt adhesive marketed by Titebond, which incudes an adhesive which would also work very well for gluing metal to plastic (but of course if you dont have or have access to the system it is not worth it to buy it for one job). Silicone sealant should also work if you take the glossy finish off the acrylic where the magnets are to go.

AJC

[Brady Watson]

WeldOn #40 will work...If you can't find that, you can try polyurethane (Gorilla et al) or epoxy.

-B

[knight_toolworks]

it is a tough glue joint. not too much sticks to plastic well and rare earth magnets even when you sand them don't glue well because the coating is so hard. the silicone adhesive is a good choice because it has flex. but one of the keys is to put the magnet into a snug fitting pocket. if they fit nice and tight a little super glue will do the last bit of holding.
my last one I used a 1/2" wide 1/2" long magnet I cut sample holes in the acrylic till the hole was really tight. then I drove them in and they stay very well.
the vibration is the issue so with most glues and the two different materials it is tough.
not the best pic but I used 1/2" magnets on the bottom part and 1/2" threaded rod on the top as two of the 1/2" magnets were too strong. but with these the holes are snug enough I just pounded them in.
http://i154.photobucket.com/albums/s266/knighttoolworks/posting/F667C4A1.jpg

[steve_g]

Paul

I experienced the same issues you did, both with my dust foot and with refrigerator magnets. For me the solution for the Dust foot was to redesign the foot so that the magnets were in a pocket and the forces were pulling them into the pocket. With the fridge magnets, I cover the magnet and backside of the part with a self promoting sticker.

Steve

[gene]

instead of drilling a thru hole couldnt you fit a tight pocket with a very thin bottom so the magnetic properties will hold the magnet in its place? i hope this makes sense.:confused:

[knight_toolworks]

you need magnet touching magnet or metal. otherwise the hold is not enough. using a longer magnet lets you use the magnet as a pin to hold the foot in place both sideways and vertical.
a very snug fit is the best thing to shoot for and a magnet long enough to get a good grip. then just a drop of super glue and a hammer to pound it in will work well. I got 1/2" magnets and they were too strong. I would have a tug of war to get them off and pinch my fingers when I used them so I used threaded rod and that made life easy since it screwed into the plastic and the magnets fit by pressure.

[steve_g]

you need magnet touching magnet or metal. otherwise the hold is not enough


Not necessarily

It's actually very easy to design how much force will be necessary to separate items. The attached chart from K&J Magnetics is for the N52 .5 X .125 magnets I used. I pocketed them into 1/2" ply leaving .125" on both surfaces... As you can see from the chart, when these magnets are separated by .25" (.125 X 2) I have 1lb. of force attracting them together... Since I embedded 8 magnets into each surface, my brush assembly requires 8 lbs. of force to remove... Very adequate!

Steve

[Jerome]

They make rare earth magnet cups that are pre drilled. You attach the cup to the plastic with a small bolt then place the magnet in the cup. It also increases the holding power of the magnet. Rockler has them.

Jerome

[cr2]

ditto Gene and Steve G...I used some scrap HDPE for my dust boot, so gluing was out. My magnets are 1/2" X 1/8" and they do not need to be touching each other to create more than enough holding power. The receiving holes don't go all the way through (about .020 shy). The upper holes are drilled from the top, and the lower holes are drilled from the bottom, so the magnets, when pressed in, are sucked into their holes and held in place by the magnetic force. It has worked great for over a year now. It takes a couple of pounds of force to pull the brush part away from the top piece. It has never come off when I didn't want it to.

[michael_schwartz]

I have glued metal to acrylic with epoxy, and it worked. I sanded both surfaces with 80 grit, and cleaned them both with denatured alcohol to remove dust, and any contamination

I am not sure how this would hold up as far as long term use, especially with vibration as Steve mentioned.

[pkirby]

Thanks guys for all of the help! This forum reassures my decision in buying a ShopBot because of the wonderful support I get on here. So I don't make anybody mad ;) I'll try the suggestions in the order they were received (LOL). But seriously, I'm going to try Andrew's suggestion of the thick CA glue first because I have some lying around:D. I'll report back if this works or not. Thanks again.

[gene]

you could use a few for the allignment purpose and add extra for the holding force. Use the Tim Taylor approach more is better ALWAYS!

[knight_toolworks]

I have a prt and the brushes sometimes hit the front bar. so I need a lot of holding power. I have had the brushes fall off before because of it. There is so little room for the dust foot and hose in my setup.

[khaos]

has anyone mentioned 5200? I have attached plat glass to fiberglass on an offshore boat with it. The only complaint is its on for good. :cool:

[gerryv]

Lee Valley rare earth magnets with cup & screw sets with a silicon seal?

http://www.leevalley.com/en/wood/page.aspx?p=58750&cat=1,42363,42348&ap=1

[oddcoach]

I just put some clear packaging tape over the magnet

[Brady Watson]

has anyone mentioned 5200? I have attached plat glass to fiberglass on an offshore boat with it. The only complaint is its on for good. :cool:

5200 is awesome stuff! Problem is...once you open it, ya gotta use it. I'd be too Scotch to open up a fresh tube for a few little magnets.

-B

[knight_toolworks]

5200 is awesome stuff! Problem is...once you open it, ya gotta use it. I'd be too Scotch to open up a fresh tube for a few little magnets.

-B
you get about a month or so after opening. better then silicone. the problem with it is if it does nto get enough air it takes forever to dry.

[twelchPTM]

although much harder to find and much more delicate, uncoated rare earth magnets work great in applications that require glue, also if you scuff the acrylic a bit and use super glue the glue wil actually "melt" the acrylic a bit and create a stronger bond.

[ssflyer]

I agree with Thomas -the uncoated magnets bond pretty well. The coated ones can usually be effectively glued after cleaning/decreasing with a good solvent. I actually have some 2"x2"x1" rare earth magnets, and I think they would almost pick up my car...

The small round ones, ~1/4" or so, pocketed into the plastic, hold really well...

[mporter88]

3M VHB (Very High Bond) double sided tapes can be bought in short pieces on ebay. It is amazing stuff with incredible sheer strength and is used to hold the stainless sheets to the outside of Disney Hall in Los Angeles.
I have had great results using vhb tape to fix magnets to non ferrous surfaces.
Follow instructions as to surface prep and cure time.