epoxy shinking

[Daren]

What effects can have curing of epoxy on 10inch DD coil nulled to 2mV. Is it worth doing two pours? First 90% then adjusting null and doing final 10%?
Right now I have it hot glued to the shell, with some styrofoam fillers. I will use glass microbaloon filler.
If the coil does go out of null can it be corrected by gluing small ferrite on the coil shell?

[dfbowers]

When I use MG chemicals 832B I noticed a little shrinkage but not too bad. Just don't use regular epoxies and you should be OK. You may want to try a few small pours but don't let the compound cure totally in between. That way, the layers will still bond.
Don

[Daren]

When I use MG chemicals 832B I noticed a little shrinkage but not too bad. Just don't use regular epoxies and you should be OK. You may want to try a few small pours but don't let the compound cure totally in between. That way, the layers will still bond.
Don

Thanks. I'm using the same epoxy. Adding inert filler (micobaloons) should further minimized shrinkage.

[punagold]

I'm not familiar with your epoxy, but most epoxies that I have used will generate a lot of heat if poured in thick layers. I have some stuff by "greenroom epoxy" that I can mix in fast or slow batches and anything in between. Just be aware of the heat factor. I've seen styrofoam smoke and melt before. Usually you have around 24 hours before you need to sand to get a mechanical bond between layers. 8 hours is a good workable time and you still get a good chemical bond without sanding. Often you need to let the layer set for at least 3-4 hours before adding another layer. The microballons will help to reduce the heat.

[SVEN1]

I use the same epoxy dfbowers uses when making my mono coils.
I do two pours. The first one to lock everything in place. Let it semi-cure 10 hours.
Then do the second pour.

[Koala]

epoxy resin does not cause any heat but requires over 20C degrees to set I have had no problems with this

Polyester resin has an exothermic reaction and the null changes whiles setting. Also dissolves polystyrene foam. Fiber glass matting uses this to go clear when using polyester resin and does not wet out as well with epoxy resin.

Epoxy sets harder and is more stable after building using both I will not be going back to the cheaper polyester.

I have a coil half built here but is too cold at the moment to set the null. I have done most of it using an oven set a 50C

[SVEN1]

Epoxy does produce heat when curing. The longer the cure time, the less heat is produced.
There are room temperature 68-70 degree F, cure epoxies as well as oven cure.
Room temperature epoxies work really well when temps are at least 72-75F.

[Daren]

My unused half of MG chemicals 832 epoxy dried up. I don't think I can stomach paying another 45$ for 10oz (maybe enough for 2 coils). I'll try "EpoxAcast 650"; for 35$ you get 3 lbs. Application notes say its can be used for electronic potting, and there is 24 h hardener for it. There is some tricky hardener ratio 100/14 so i many have to get a kitchen scale.. other than that looks good... There is a "mineral" filler used in the "EpoxAcast 650", I can't identify what exactly...
I searched older posts but there seem to be no good alternative to 832.. anyone with good results using other epoxies?

[SVEN1]

Yup, MG 832 has a shelf life as you found out once opened. Think shelf life is about 3 months.
First off you must stir the black pigment that settles to the bottom until its fully mixed after opening.
Let it sit so the bubbles work them self out. I buy the 3 liter pack, cheaper. A day before use I also tip the black bottle upside down, then rightside up, lay it on its side every 3 to 4 hours. You want that pigment mixed in with the resin, you also do not want to induce air bubbles.

Once you mix resin and hardener for 4-5 minutes slowly, pour it the mix into a shallow flat container, so it doesn't heat up and shorten the working time. Let it sit for 30 minutes. This allows air bubbles to come to the surface. Every 5 minutes, rake thru the epoxy once with a mixing stick this will break up surface bubbles. After 30 minutes, pour the mix into a pouring cup etc. But, pour it slowly from a height of about 8 or 9" from above the pour cup. This free fall helps break up any more air bubbles that remain within the resin. You will find you get a better final finish with less air bubble if any in your cured epoxy.

I have worked with epoxies for about 20 years or so and you pick up some good working techniques to get that perfect job....................

Smooth-On has some good epoxies that should work , they sell pigmenst as well. http://www.smooth-on.com/Tarbender%3...395/index.html take a look and see what they have to offer.
I use their laminating epoxy for many jobs. Excellent and easy to work with, no fumes to knock you over.

[Daren]

Yup, MG 832 has a shelf life as you found out once opened. Think shelf life is about 3 months.
First off you must stir the black pigment that settles to the bottom until its fully mixed after opening.
Let it sit so the bubbles work them self out. I buy the 3 liter pack, cheaper. A day before use I also tip the black bottle upside down, then rightside up, lay it on its side every 3 to 4 hours. You want that pigment mixed in with the resin, you also do not want to induce air bubbles.

Once you mix resin and hardener for 4-5 minutes slowly, pour it the mix into a shallow flat container, so it doesn't heat up and shorten the working time. Let it sit for 30 minutes. This allows air bubbles to come to the surface. Every 5 minutes, rake thru the epoxy once with a mixing stick this will break up surface bubbles. After 30 minutes, pour the mix into a pouring cup etc. But, pour it slowly from a height of about 8 or 9" from above the pour cup. This free fall helps break up any more air bubbles that remain within the resin. You will find you get a better final finish with less air bubble if any in your cured epoxy.

I have worked with epoxies for about 20 years or so and you pick up some good working techniques to get that perfect job....................

Smooth-On has some good epoxies that should work , they sell pigmenst as well. http://www.smooth-on.com/Tarbender%3...395/index.html take a look and see what they have to offer.
I use their laminating epoxy for many jobs. Excellent and easy to work with, no fumes to knock you over.

Excellent epoxy work advices.. thanks

[Koala]

Epoxy I use never gets warm to touch.

Last almost indefinitely as long as you keep it cold and out of the sun. Store mine in the fridge.


At 20C it will set after about 8 hours but will still quite flexible and takes days to harden. In the oven set at 50 takes about 1 hour to harden


This is what I use £15.34 for 750g including hardener not the cheapest but local to me

Does not wet out cchopped strand mat CSM properly

[dfbowers]

Yea, the self life thing got me too with 832b. I bought a liter and after a month of being opened it was a solid mass. Maybe it happens in larger masses as I have not had that issue with the smaller containers. Anyone try acrylic?

[Daren]

Epoxy I use never gets warm to touch.

Last almost indefinitely as long as you keep it cold and out of the sun. Store mine in the fridge.


At 20C it will set after about 8 hours but will still quite flexible and takes days to harden. In the oven set at 50 takes about 1 hour to harden


This is what I use £15.34 for 750g including hardener not the cheapest but local to me

Does not wet out cchopped strand mat CSM properly

The price is reasonable, looks like a solid stuff.

[sinclairuser]

hi all, have any of you tried this stuff,http://www.toolstation.com/shop/Elec...c+Gel+2/p47003
i got a £15 tool station voucher and got some of this, it works i filled an 8" mono loop with it, its not heavy could be of use to someone.
i've made an IB dd for the MPP, i'm going to try whats left of this stuff, its one of dons shells that andy gave me ages ago, so it wont need much, i will hold it with some epoxy and pot it with the gel, it should be light and waterproof.

[punagold]

I just got done mixing Fiberglass Hawaii's own brand of epoxy. This was the fast hardener. It is mixed 50/50 by volume, but it mixed 60/40 by weight. So read your direction carefully for epoxy must be mixed correctly. I mixed mine in a small plastic yogurt container. After a 2 minute mix it gets more viscous (runny) and after about 4 minutes you can feel the container getting hot. Most mixes stress a "pot life". That's how long you can leave it in the mixing container. If in warmer weather, beware, it will go off real quick if you don't spread it out. Do a search locally for surfboard building supplies or try your local marina/boat harbor.