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Frag plugs

I've designed and 3d printed molds for people who make their own frag plugs and I'm thinking about making some myself.

I've designed a few new molds this morning and I'll probably be ordering an emarco 400 kit this week.

I have worked in decorative concrete for years and have used emarco a few times so I'm familiar enough to get quality pieces but any tips are welcome.

Once I get some decent plugs/discs/tiles from the molds, I will share the stl files for the hexagonal molds. I already published several of the square ones I designed last year

I'm choosing to use emarco because it doesn't need to be cured like Portland cement or hydrolic cement does and thin discs (4mm) are still very strong but still easy to cut.
Something this thin is solid enough to be removed pretty quickly. It will take some trial. And error to find the perfect time and will depend on temp and humidity but I'll be sharing everything I learn.

I'll be sharing everything I find so people can make their own. Anyone with a printer will be able to make and sell the molds as they please, no restrictions on the publishing license.

I will eventually sell the molds but they take so much machine time that the demand won't be worth the price.
First few sets of molds are done. I am trying a few different materials to find which is best. I know emarco curing is an exothermic reaction, like most concrete is, so temperature resistance is something to consider.

PLA is super easy to print and prints at really high speed. However, it will warp at around 150°F and gets soft with prolonged moisture exposure.

PETG has some flex to it and that would make removing parts easier. It also has a higher temperature resistance and isn't affected by moisture. It is brittle though and I expect this might get worse with repeated exposures.
Its also more expensive and prints slowly.

ABS has high temperature resistance, isn't affected by moisture much and is also about the same price as PLA. It's very durable. It is more difficult to print and I only have one machine that I set up for abs printing. It requires more maintenance of the print surface and its very very stiff so part removal may be a pain in the ass.

TPU is very very very flexible. I made my daughter a pair of sandles with it and they do well. I know this works great as a mold material but it is very expensive and has to print rediculously slow. A full set of molds would take almost 2 weeks to print and I have to add a glass panel to the print bed to print the parts on. It can also be difficult to print with if the printer isn't modified for flexible filament.

My emarco order will be here on Friday. I have a frag swap on Saturday and the family wants to go to one of the public aquariums on Sunday so I may not get a test batch done until some time next week.


Supporting Member
I'm wondering if these would be easier to produce with traditional mold-making processes (vacuum forming, silicone mold making) once you have enough positives?
I'll be making silicone molds for the t-plugs (round and square) as soon as I have some spare $ to order silicone kits.

Im sure that anyone with access to vaccum forming equipment can do this a lot more cost effective than I can. 20 of each mold will probably be about 2 lbs of filament, $20-$60 depending on type and quality.
I did a batch yesterday and it was a failure for multiple reasons.

1st, I didn't mix the cement mixture properly. It was too wet and I diluted the acrylic polymer too much. The disc's I removed from molds were too brittle and weakly bonded. They crumbled in my hands.

2nd, the molds I made with PLA, ABS & PETG were too rigid. The flexible TPU is really the only choice. Sadly it's about $30/lb and takes a really long time to print.

I'm leaving tomorrow to spend a week in the hospital with my daughter while she has some tests done so I won't make any progress on this for a while.
Used a print to make a silicone mold for frag plugs. Mold came out great.

Mixed up another batch of emarco, thicker this time. I'll pull everything out this afternoon and see how it goes.

My best friend own a custom concrete company and he can get the raw materials in bulk so this may work out.
The frag plugs came out good but still really weak though. You can easily break the stem off with tour hands.

I'm done trying with emarco 400. Just dumped $40 worth in the trash.

I'll do it with Portland cement and cure them.


Supporting Member
I wonder what the deal is. The emarco that is holding my rock work together isn’t brittle.
I ran the numbers...

The 5# kit of E-marco 400 is $42
5 frag plugs is just over an ounce, raw material cost of roughly $1

Im going to get some fine grain (hopefully used) aragonite sand as filler. If I buy the raw materials in 50lb bags and 1gal jugs, the cost per ounce drops significantly but I don't plan on selling these and I don't need 5000 plugs.


Supporting Member
I think frag plugs are always going to be too small to use any type of concrete. There just isn't enough material where it would be strong enough to hold together.

Most frag plugs are made of ceramic and you might want to look into that as an alternative. It will require being cured and fired, but there are many places where you can get the clay and have it fired inexpensively.
The plugs themselves are actually really good after curing for a few days. I can still break the stems off by hand but they take a lot of force.

The discs and tiles are what I want to make the most. I know this material works, I have a dozen discs from someone I made molds from and only the large ones (3"+) can be broken by hand.
I want discs and tiles too if you figure it out.
Are we sure we wouldn’t Be better off just buying a ton in bulk though?
I want discs and tiles too if you figure it out.
Are we sure we wouldn’t Be better off just buying a ton in bulk though?
Buying a ton of E-marco or plugs / discs / tiles?

I only know one person who makes the low profile (4mm)thick discs, tiles and plugs and that's only because I designed his molds.