Epoxy casting resin

[9fingers]

Any expertise in the house.
I've got a possible application needing metal components potting into a disc about 75mm diameter and say 20mm thick.
It seems that polyester resin cure is exothermic and best in thin layers whereas true epoxies are best for thicker layers. I really want to pour in one go.

Watching youtube river table videos they seem to just wave a hot air gun over the surface and air bubbles disappear. Is this true.

My application does not have to look good but I need as much strength as possible so minimal air bubbles would be good.

Any particular brands/suppliers to goto or indeed avoid.

Each cast will be less than 100 grammes and I need a minimum yield of 2 plus a bit of experimenting so not a great quantity needed.

What does the team know?
Any useful "epoxy 101" websites?

Bob

 

[Malc2098]

Andy at Manor Wood uses GlassCast.

https://www.glasscastresin.com

Maybe this video of his might help at the beginning. The rest is about finishes.

[youtubessl]mJ7KaMmvzgI[/youtubessl]

 

[9fingers]

Thanks Malcolm.
Useful website!

Bob

 

[meccarroll]

Thanks Malcolm.
Useful website!

Bob

A chap who used to rent a unit on the site I upkeep used to use resin quite a lot and he recommended "GlassCast" ( https://www.glasscastresin.com/ ).

They have a lot of videos to help you choose the right resin.

The resin they and other sites sell is generally based on the thickness you require. The resin choice will depending upon the thickness of resin cast required and this is in part because of the way the resin sets. Heat is a factor.

Once you start the cast you will probably need to keep the resin in a room of constant temperature for best results.

Some people seem to use a vacuum chamber to eradicate air bubbles but most don't.

Regards Mark

 

[9fingers]

Thanks Mark!

I ended up ordering from Resin Pro as they do better priced starter kits to experiment with. I went for the slow cure/deep cast stuff. I possibly only need a finished thickness of 12 mm or so but might cast thicker and reduce to final size in the lathe.
I don't need it optically true so I hope the slow cure will allow the air bubbles to come out naturally without drawing a vacuum.

I hope this method will avoid the need for lots of precision machining in plastic or aluminium which whilst I do have the machinery to undertake this, my aim would be to use a method that others will be able to do at home.
Assuming casting works out and my design also works, I'll write it up here.
The project is to make a home brew magnetic switch to allow jigs and fixtures to be used on cast iron machine tables.

Bob

 

[meccarroll]

Thanks Mark!

I ended up ordering from Resin Pro as they do better priced starter kits to experiment with. I went for the slow cure/deep cast stuff. I possibly only need a finished thickness of 12 mm or so but might cast thicker and reduce to final size in the lathe.
I don't need it optically true so I hope the slow cure will allow the air bubbles to come out naturally without drawing a vacuum.

I hope this method will avoid the need for lots of precision machining in plastic or aluminium which whilst I do have the machinery to undertake this, my aim would be to use a method that others will be able to do at home.
Assuming casting works out and my design also works, I'll write it up here.
The project is to make a home brew magnetic switch to allow jigs and fixtures to be used on cast iron machine tables.

Bob

Bob it would be very informative if you did have the time to post your experience with epoxy resin with the forum. It's something I intend doing in the near future too! Regards Mark

 

[9fingers]

Whilst waiting for my resin and other materials to arrive, I thought I might have my first try of ChatGPT

Here is what it came up with in response to my query.

User
How do I start with epoxy resin casting
ChatGPT
Epoxy resin casting is a versatile and popular craft that allows you to create a wide range of items, from jewelry to decorative pieces. Here's a step-by-step guide to help you get started:

1. Gather Your Materials:

Epoxy Resin: Choose a high-quality epoxy resin suitable for casting. There are various brands available, so read reviews and follow recommendations.

Hardener: Epoxy resin typically comes with a separate hardener. Make sure to use the correct ratio of resin to hardener as specified in the product instructions.

Mixing Containers: Use disposable cups or containers for measuring and mixing the resin.

Stir Sticks: Choose stir sticks made of plastic or wood. Avoid metal, as it can introduce impurities.

Mold: Select a mold that suits your project. Silicone molds are commonly used for epoxy resin casting and are available in various shapes and sizes.

Release Agent: To help with demolding, use a release agent like mold release spray or petroleum jelly on the mold.

Safety Gear: Wear gloves to protect your hands and work in a well-ventilated area or use a respirator to avoid inhaling fumes.

2. Prepare Your Workspace:

Cover your work surface with a disposable tablecloth or plastic sheet to protect it from spills.

Ensure good ventilation to dissipate any fumes.

Keep your workspace organized and have all materials within reach.

3. Measure and Mix:

Measure the epoxy resin and hardener according to the manufacturer's instructions. The ratio is crucial for proper curing.

Pour the measured amounts into a mixing container and stir thoroughly. Scrape the sides and bottom of the container to ensure complete mixing.

Avoid mixing too quickly to minimize the introduction of air bubbles.

4. Add Color and Additives:

If desired, add pigments, dyes, or other additives to the resin to achieve the desired color or effects. Mix well.

You can also embed objects like flowers, shells, or small decorations into the resin at this stage.

5. Pouring:

Pour the mixed resin into the mold slowly and evenly to avoid trapping air bubbles.

Use a heat gun or torch to remove any surface bubbles by passing it over the resin briefly.

6. Curing:

Follow the recommended curing time provided by the manufacturer. This can range from a few hours to a day or more, depending on the product.
7. Demolding:

Once the resin has cured, carefully demold your piece. If you encounter resistance, give it more time to cure.
8. Finishing:

Sand the edges or surfaces if needed.

Polish the resin to achieve a clear and glossy finish.

Remember to read and follow the specific instructions provided by the manufacturer of the epoxy resin you're using, as different products may have slightly different requirements.


Seems sensible and reminded me that I should use some mould release agent.

Bob

 

[Phil Pascoe]

Don't forget if you need to cast in layers to ensure the place is 100% dust free or you'll cast a layer of dust in without noticing. Don't forget that the resin will pick up any slight markings in the mould - we used to use dead 150w lightbulbs to make glass fibre moulds which we used for casts of flowers, insects, coins etc. and visible on the top of every one was the legend "Osram 150W" until we learned to polish it out of the moulds first.

 

[9fingers]

Thanks Phil.
I've ordered the slow cure stuff as I want to do a single pour. Final thickness is going to be 12-15mm.
Unusually in this application the finish is unimportant but minimal bubbles will be better for final strength.

There will be 7 pole pieces so I might sand the faces to make sure they are fully exposed. Magnetic strength will be compromised even with the smallest gap whether it be resin or air.

As previously mentioned, I'm looking for a method that can be used by members who dont have metalworking facilities.

Bob

 

[Cabinetman]

One bit of information I just thought of that wasn’t mentioned especially when casting discs that you don’t want to machine, is to ensure the surface beneath is completely level.
If I remember correctly don’t use polystyrene cups, ( it’s only 52 years since I did any but I do remember the mess and smell lol)

 

[9fingers]

I think there are two basic types of casting resins. One is polyester based with the resin needing a small amount of catalyst to cure and the resin will eat plastic cups and similar. Heavy fumes as it cures/dries
Often used with fibreglass mat and similar chemically to car body filler. It is relatively quick drying

The resin I'm using is classed as an epoxy often around 55% part A and 45% Part B with far less odour in use. This is chemically similar to Araldite and West Sytems products. Much slower drying than polyester.

Bob