This is NOT a coffee cup!

[scruffy]

Harv, although my suggestions are not really welcome, I will make another one. Use MarkC's Marine Goop, and then add an acrylic pore into the recessed area and let it harden. Should provide a solid base, more adhesive 'power' that will not let go under any circumstances.

 

[Harv]

Scruffy -

I gladly accept suggestions from any tractor owner -- Hey! That doesn't include you! /w3tcompact/icons/wink.gif

Not sure how an acrylic pour would do anything to strengthen the bond. Unless I'm thinking of a totally different kind of stuff, I used to use containers made of plastic similar to the Chalkley Cup for molds, specifically 'cuz the acrylic would not stick to it.

I'm probably just being my ignorant self here, but maybe you could elaborate on the specific type of acrylic goo you're talking about?

 

[MChalkley]

Harv - Since the magnets are so strong, you might want to reconsider not allowing them to quite come in actual contact with the fender. This would place a lot less strain on the glue. Also, I'd take some coarse sandpaper and rough up the surface of the recess on the bottom of the cup a little. A little roughening tremendously increases the surface area the glue has to bond to.

MarkC

 

[Harv]

Mark -

Keeping the magnets from actually touching the fender would indeed reduce the strain on the glue, but it would also reduce the overall grip strength to the tractor. I'm greedy -- I want grip strength and a permanent bond between cup and magnet. /w3tcompact/icons/smile.gif

You're absolutely right about roughing up the surface of the plastic before gluing, and I have done so on my latest attempt.

As if I don't have any real work to do today, I talked to Aladdin Industries, who make the Extreme Gulp cup upon which the Chalkley Cup is based.

They tell me the cup is made of polypropylene, and they know of no adhesive that bonds with that material. They themselves use "spin welding" and "sonic welding" to attach the various cup parts, including the handle. Both of these processes essentially "melt" the plastic together in a true welding fashion. Of course that only works for joining pieces of polypropylene together, not to steel.

They laughed when I mentioned epoxy, and sure enough, my epoxy package has a disclaimer that it will not stick to polypropylene. They had no first-hand knowledge of Goop, and they conceded that it "might" work well enough for hobby use, but certainly would not be reliable enough for commercial use.

My web search so far has turned up one product which claims to bond polypropylene to itself and just about anything else. It's called Nbond, which, although it is a 2-part epoxy, is unlike all others in that it is specifically designed to adhere to polypropylene and polyethylene, claims the manufacturer.

Although it's not cheap ($11 for 50ml), it's not unreasonable, and I will probably give it a try. If I can't find it locally I will order it off their web page.

My wife says I "obsess" over trivial pursuits, such as sticking a magnet to a plastic cup. To me it's almost like a game -- the challenge ain't over 'til it's solved. /w3tcompact/icons/laugh.gif

 

[gordon]

Harv not only rough the bottom up but also soften it up with some M.E.K. or some type of solvent cleaner. Something else that works good to prep the surface and soften it up is 2+2 carb cleaner. Next best thing to spin welding I guess there are a couple of glues at work that we use with limited sucess. Sometimes they work and sometimes they don't. But surface prep is the key to getting the glue to bond to any plastic surface.

Or you could always spin weld using a router a tank flange on the bottom of the cup with the magnets inside of the flange. Or use a plastic welder and weld the magnets to the bottom of the cup using the flange of the magnets to run the bead on.
The ways to attach the magnets are endless it's just gettin them to stay. I used glue from work to attach mine and it's held up well so far. But I prepped the surface first and that is the key to getting any thing to even attempt to stick to a plastic.
Gordon

 

[Harv]

Gordon -

I used "glue from work", too -- but then, I work at home. /w3tcompact/icons/crazy.gif

What's the glue you used?

 

[gordon]

I believe what I used on the cup was KL-650 I'll double check tomorrow on the exact number and brand. You want to use a glue with a high solvent count so it will soften the plastic and help in the final bond. Just remember when glueing plastics your actually welding not just cementing. Did that make sense to you? I know what I'm tring to say hope you understood it.
Gordon

 

[Harv]

Gordon -

I follow you on the "welding" concept, but I think you're referring to acrylic-type plastics. Neither polypropylene nor polyethylene react with any solvents, which is why it's so difficult to bond to them. You may notice, for example, that some of your solvents come in plastic bottles -- that's polypropylene or polyethylene.

Interestingly, as difficult as it is to find something that will stick to these cups, that's one of the reasons they are a very good product. /w3tcompact/icons/crazy.gif

 

[PaulB]

OH FOR CRYING OUT LOUD I CAN NOT BELIEVE THIS COFFEE CUP THREAD IS STILL GOING STRONG!!!!! THE ONLY THING I CAN THINK OF THAT IS MORE BORING THAN MOUNTING A CUP TO A TRACTOR FENDER IS FISHING!!! /w3tcompact/icons/smile.gif

 

[gordon]

Yup you are exactly correct Harv, now that I think about it thats why I can get a gallon of M.E.K. out of the fiftyfive gallon drum at work and guess what---it does't melt abit--my fault. But any is a very strong word. There has to be something. AAAAAhhhhh the old K-L 650 works sometimes.

Now you got me thinking what about all the solvents and thinners that come in a metal cans---looks like I'll have to do some investagating. /w3tcompact/icons/smile.gif
Gordon

<P ID="edit"><FONT SIZE=-1>Edited by gordon on 11/6/00 09:25 PM.</FONT></P>