Epoxy encapsultation for the busy working mum.

[David Schwab]

It may require a mechanical mixer for a complete mix. One can do this by hand with a spatula knife, but it's tedious. People use centrifugal mixers for such things.

I used a flat wood mixing stick and mixed the heck out of it! I also poured it to a second cup and continued mixing, before pouring it to a squeeze bottle. And it wasn't like it didn't cure... some from the same pour would and some wouldn't. Some times a section on one pickup would stay soft while the rest cured.

I have no issues with the MG Chemicals epoxy, so I'm going to stick to that.

[David Schwab]

Most of the epoxies made for potting electronics, at least the ones that I've tried, are too thick for getting good castings.

The MG Chemicals epoxy flows like water. Or maybe warm maple syrup. After you mix it you let it sit for 30 minutes so the bubbles rise to the top, and then give it a stir and then you can pour.

I've used it in moulds where the master was made from wood, and you can see all the grain, and even the curly stuff from maple.

[Peter Naglitsch]

I've used it in moulds where the master was made from wood, and you can see all the grain, and even the curly stuff from maple.

And thar is IMHO the beauty of casting pickups, when the grain of the wooden master is visible. Almost like black wooden covers but with a fraction of the work when the master is finally done.

Whoa, that is one big pickup David. Care to share details?

[Joe Gwinn]

I used a flat wood mixing stick and mixed the heck out of it! I also poured it to a second cup and continued mixing, before pouring it to a squeeze bottle. And it wasn't like it didn't cure... some from the same pour would and some wouldn't. Some times a section on one pickup would stay soft while the rest cured.

This nonuniformity of cure is the classic diagnostic symptom of incomplete mixing.

I have no issues with the MG Chemicals epoxy, so I'm going to stick to that.

I don't think that the problem is with the supplier. In another posting, you say that the viscosity is like warm maple syrup. One should be able to get a complete mix by hand, and yet we are getting nonuniform cure. If one waits for a week, do the sticky parts eventually cure? I bet not.


War story: In the late 1960s, I worked in the Plastics Lab at RCA in Burlington, MA, as a summer-hire technician. What we did was mix and apply all manner of plastics, including epoxies, for use on the US Space Program, NASA being the customer.

Bad batches were a real problem, so whenever we mixed a batch of goop, a sample was given to Inspection, who put the sample in a little oven running at 180 F. After a suitable delay, the sample was pulled out and tested: if the sample was still tacky or soft (for what was supposed to be hard epoxy), the entire batch was rejected. We were religious about using only fresh material, and still we had bad batches, usually due to a bad mix (proportions wrong, not properly mixed, or a contaminant crept in).

Many materials could not be mixed by stirring, instead needing to be folded time and time again with a spatula, and smeared out against the container wall many times.

[David Schwab]

And thar is IMHO the beauty of casting pickups, when the grain of the wooden master is visible. Almost like black wooden covers but with a fraction of the work when the master is finally done.

Whoa, that is one big pickup David. Care to share details?

It's a ramp, which some bass players like. It has two pickups in it. The idea of the ramp is it limits how hard you can pluck the strings because it sits right under them.

[David Schwab]

This nonuniformity of cure is the classic diagnostic symptom of incomplete mixing.

I don't think that the problem is with the supplier. In another posting, you say that the viscosity is like warm maple syrup. One should be able to get a complete mix by hand, and yet we are getting nonuniform cure. If one waits for a week, do the sticky parts eventually cure? I bet not.

Both epoxies have a thin viscosity. It in the winter months, I warm them up on the radiator before mixing to make sure they flow well. The way I mix epoxy is to measure out the amounts into plastic dixie cups on which I have marked how much of each part to pour in. So I fill part A up to the line, and then part B up to the next line. This way I don't have to worry about scraping the sides of two cups and not getting the same amount mixed together.

I stir for about 3 minutes. I don't mix big batches at a time, only a cup full.

I have never had an issue with the MG Chemicals epoxy, but have had inconstant results with the AeroMarine stuff. The AreoMarine epoxy also tends to cure tacky feeling, which I know is from poor mixing, but I'm not sure how much more I have to do to get it mixed well. I'd rather pay twice as much for better quality epoxy at this point since it gives me zero problems.

The MG chemicals Epoxy also cures faster. The AM stuff often took longer than 24 hours. The MG is kicked over in about 12 (at room temperatures).

Also, as I mentioned the AE epoxy ruined a brand new mold made from Silicones Inc., tin cured rubber. The epoxy didn't cure and left a wavy pattern in the mold. On a few other molds it started to break them down and then started sticking, eventually not being able to be removed from the molds.

My buddy helped with the molds and he's a professional industrial designer and model maker. He never heard of such a problem and neither did Silicones Inc.

[Bruce Johnson]

My guess is that you got a batch of the AeroMarine epoxy with weak hardener. If you have some non-critical epoxy job and want to use up what you have, try mixing it "hot" with about an extra 10% more hardener than you should. That will probably cure it just fine. I've played around a bit with mix ratios of the West Systems, going with slightly more or less hardener to adjust the cure time. When you get down into the slow range of 12 hours or more, the mix starts getting critical. Just a little bit too light on the hardener, and you'll get that incomplete curing/soft cure thing. Since you went by the book and got incomplete curing, I'd say that you got some bad hardener. Not spoiled, but just weak in its original mix.

I may have to try that MG epoxy. I've got a good thing going with the West Systems, but there are a few parts I make where it's a little touchy.

The potting epoxies that I used when I was working in an electronics lab were 3M, and they were too thick most casting work.

[Joe Gwinn]

I have never had an issue with the MG Chemicals epoxy, but have had inconstant results with the AeroMarine stuff. The AreoMarine epoxy also tends to cure tacky feeling, which I know is from poor mixing, but I'm not sure how much more I have to do to get it mixed well. I'd rather pay twice as much for better quality epoxy at this point since it gives me zero problems.

The MG chemicals Epoxy also cures faster. The AM stuff often took longer than 24 hours. The MG is kicked over in about 12 (at room temperatures).

This sounds like there was too little hardener for the resin, or the provided hardener was weak and/or incorrect for the resin.

Some kinds of epoxy are critical about the mix ratio. The only reliable method is by weight, and that's how we did it for NASA.

Also, as I mentioned the AE epoxy ruined a brand new mold made from Silicones Inc., tin cured rubber. The epoxy didn't cure and left a wavy pattern in the mold. On a few other molds it started to break them down and then started sticking, eventually not being able to be removed from the molds.

I never heard of this either. Perhaps a chemical incompatibility? (If I recall from my RCA days, some kinds of silicon rubber prevent some kinds of urethane rubber from curing.) What did Aero Marine say?

[David Schwab]

My guess is that you got a batch of the AeroMarine epoxy with weak hardener.

Try three batches. The first batch was mostly good, but I had someone report oozing epoxy some months after he bought the pickups. The next two times I bought it I had really inconsistent results, even though I hadn't changed anything.

From what I understand he repackages his epoxy. I have no idea where he gets it from.

[David Schwab]

This sounds like there was too little hardener for the resin, or the provided hardener was weak and/or incorrect for the resin.

Some kinds of epoxy are critical about the mix ratio. The only reliable method is by weight, and that's how we did it for NASA.

I was very careful with the ratio (which was 1:1). I have a digital scale, so I can do it by weight, but the instructions say "by volume", so that's what I have been doing.

I never heard of this either. Perhaps a chemical incompatibility? (If I recall from my RCA days, some kinds of silicon rubber prevent some kinds of urethane rubber from curing.) What did Aero Marine say?

I didn't talk to him about the mold. I did talk to him about thew curing problem, and he said measure the two parts in cups, and then pour them into a third cup, and don't scape the sides. That gave better results, but I still had issues. So I just went back to the MG Chemicals epoxy. That uses a 2:1 ratio and doesn't seem fussy at all about mixing, etc. It's also just nicer to work with.

[rdrr]

I was very careful with the ratio (which was 1:1). I have a digital scale, so I can do it by weight, but the instructions say "by volume", so that's what I have been doing.

I'm just getting started in this (winding that is) and have some of the AM stuff. I've just been making some small test castings before I actually commit any pickups and have had some inconsistent results too. This very well could be do to attempting to make small batches, but as David points out the instructions state that it's a "non critical 1 to 1 ratio", I did still measure it out 1 to 1 pretty carefully. I had one 1/8in casting take well over the 24hr period to fully cure. I took it out after about 30hr and it was still very flexible, took another couple of days to become fully rigid. Another attempt I tied to up the hardener a bit and it did help it cure quicker but it left the piece feeling tacky. It was quite hard but felt like a tack cloth. I would attempt to do it by weight but I didn't see anything that told me what the weight by volume of each of the parts is, guess I'll have to give them a call and see if they can get that info to me.

[Joe Gwinn]

I was very careful with the ratio (which was 1:1). I have a digital scale, so I can do it by weight, but the instructions say "by volume", so that's what I have been doing.

If you have a digital scale, it's best to use it. Even if the standard instructions are by volume, the vendor will know the by-weight ratio. Use the scale's tare function and weigh what's in the mixing cup. Then one need not worry about scraping the measuring cups or not (as mentioned below).

I didn't talk to him [at AeroMarine] about the mold. I did talk to him about the curing problem, and he said measure the two parts in cups, and then pour them into a third cup, and don't scape the sides. That gave better results, but I still had issues.

If he wants you to worry about scraping the measuring cups, the mix ratio is real critical. I would ask them about the effect of 10% under or over correct ratio, as a way to quantify the importance of getting the ratio exactly right.

But I suspect you also got a bad batch.

So I just went back to the MG Chemicals epoxy. That uses a 2:1 ratio and doesn't seem fussy at all about mixing, etc. It's also just nicer to work with.

OK. But I would still mix by weight. NASA beat that into me.

And I would do an incoming inspection of new batches of material - mix some up and cure it in the same way as for the product. If it don't cure right, return nonconforming material to supplier.

[David Schwab]

I'm just getting started in this (winding that is) and have some of the AM stuff. I've just been making some small test castings before I actually commit any pickups and have had some inconsistent results too. This very well could be do to attempting to make small batches, but as David points out the instructions state that it's a "non critical 1 to 1 ratio", I did still measure it out 1 to 1 pretty carefully. I had one 1/8in casting take well over the 24hr period to fully cure. I took it out after about 30hr and it was still very flexible, took another couple of days to become fully rigid. Another attempt I tied to up the hardener a bit and it did help it cure quicker but it left the piece feeling tacky. It was quite hard but felt like a tack cloth. I would attempt to do it by weight but I didn't see anything that told me what the weight by volume of each of the parts is, guess I'll have to give them a call and see if they can get that info to me.

I've had the same experiences with the stuff. Some stayed very flexible and other times it hardens and stays tacky feeling. This was often from the same mixed batch. Something's not right, and it's not worth the trouble to figure out what it is.

The MG Chemicals epoxy works flawlessly every time. It dries hard and is never tacky. It's nylon filled so it doesn't shrink. It's not cheap though.

[Joe Gwinn]

My instinct is that the AeroMarine stuff is OK, and there is some other problem. Epoxies are widely used, and are formulated to optimize many things, but always at the expense of something else, and most failures are due to a mismatch of application and formulation. So I have been looking for the mismatch.

It also occurs to me that many industrial epoxies really require heat for best cure, even if they permit room temperature cures in the datasheets. And there are epoxy systems that require 180F min to even start curing. Many of the best epoxies are like this, in particular those "structural adhesives" used to glue commercial airplanes together.

3M

The question for pickups is how much of this is necessary, but it's good to know the larger story.


As for using a digital scale, I should say exactly how best to do this:

Put mixing cup on scale. You will see the weight of the empty cup.

Press the "Tare" button on the scale; the indicated weight will become zero.

Add Part A until the desired weight is indicated.

Press Tare again; the reading will again become zero.

Add Part B until the desired weight is indicated.

Remove mixing cup from scale and mix contents thoroughly.

[RedHouse]

On this episode of Ice Road Pickup Makers, poster-1 makes multiple posts about how he "tried it, doesn't work consistantly, moved on to a product that works consistantly", but poster-2 in several posts insists poster-1 is just doing it wrong.

Try this, try that, NASA, yadda, blah, a non-issue needs to be solved right here, right now.

Hold onto your bobbins folks, on the next episode of Ice Road Pickup Makers the perenial favorite (cue ominous Jaws music in background) ...eddy currents!.

(sorry, I must'a got up too early and had too much coffee)