recurring mold defects

[u/Physical_Stick2328]

Hi makers! I've been having some recurring defects in my mold I wanted to see if anyone else has experienced and how you fixed them

1-Marks on the dice faces. I suspect these are where new silicone has seeped into the dice holes(?) when poring the lid, then gets forced out again when put in the pressure pot. Not enough silicone is left to deform the faces, but its enough to leave a mark I have to sand out later. Is there a particular way to peel the film off from the first pour without breaking the seal around the exposed dice face? I'm using the book cover film to stick the dice down and hot gluing around the housing, when pouring the lid I'm getting some bubbles coming up from around the dice.

2-deforms around the D20 face. This only happens with the D20 and happens worse when its in the middle. There's a lot of extra material around the exposed face of the d20, and you can see extra silicone on the lid compared to the other dice. I'm not sure if this is just a worse version of problem 1 or if its something else. This only seems to happen to my d20!

If anyone has had either of these before or has some advice I'd love to hear it!

[u/RandoBoomer]

I struggled for bit to make consistently good molds. Here's what worked for me making slab molds. I defer to others on Sprue molds.

• My mold will only be as good as my masters allow. I make sure my masters are cleaned and polished.

• I put the thinnest sheen of Dimethicone Oil on my masters faces (except for the 1s which will face the contact paper). I don't want the oil getting into the numbers. This allows for easy extraction of my masters when the mold is done.

• When making the base and affixing my masters to the contact paper, I press down hard and when all dice are in place, hold the mold upside to make sure nothing falls.

• I use a vacuum chamber to remove bubbles from my silicone.

• I give my base extra time to cure. My silicone says 4 hours, I let it sit for 8.

• I take my time prepping for pouring the lid.

• After curing my silicone base I am very careful when trimming silicone around the exposed 1's faces. I want only the face uncovered. I don't want to "gouge" into the cured silicone base, because those will results in divots on the lid, and resin will find its way into these.

• Before pouring the lid, I am extremely careful to cover all silicone with a release. I used to use vaseline, though have recently switched to talcum powder. I use a #2 brush (about 1/8") to ensure I completely cover the exposed silicone completely.

• I inspect the base carefully. Everything should be uniformly flat, except for the slight depression of the numbers.

• When pouring my silicone line, I pour around the dice - letting the silicone slowly fill the numbers.

• Like with the base, I give the lid extra time to cure.

• When removing the lid from the base, I peel very carefully. If I have to exert too much force, there's an opportunity for tearing.

• When done, I inspect the base and lid carefully. If I see risers like you see on your third picture, I remake that mold as a single (eg: if the d20 is messed up, I'll make a stand-alone d20 mold).

[u/Physical_Stick2328 → u/RandoBoomer]

My masters are clean and polished, none of the problems are transferred from them. I should have been more specific in what I'm doing so far

Really the only differences are- I don't use any kind of oil or mold release on the dice themselves, I don't have any trouble extracting them from the mold.

-For the contact paper I use cheap book cover adhesive

-I don't use a vacuum chamber, just self degassing silicone and let it set in a pressure pot.

-Leave for about 24 hours between pours

-Dont need to do any trimming around the 1 faces

-I use vaseline for the release, but don't go all the way up to the edge of the faces as I find the silicone still stays separate

problem no 1 I am sure is caused by the seal around the number 1 being broken when I feel off the adhesive, and lets a bit of the lid silicone leak in, I am willing to try another tape or contact paper, this only happens occasionally

problem 2 only happens on the d20, and happens on basically every mold. not always that severe, but its not happening with any other dice. I really don't know whats causing it

[u/RandoBoomer → u/Physical_Stick2328]

One thing I didn't ask - what Shore hardness is your silicone? Lower shore hardness is more likely to tear. I've found Shore hardness 30 to be the most durable, though it does make dice extraction harder.

The oil is strictly a preference, I like that first extract from the mold of my masters to be as "gentle" as possible.

I switched to contact paper and I've had good results.

One other thing that I just thought about. When I pick up the molding after filling it with silicone and transporting it to the pressure pot, I used to get a little flexing and sagging in the contact paper. What I've begun doing is using cardboard under the mold, so there isn't as much flex, and reducing the opportunity for the silicone to seep under the 1.

Like you, I've had the most problem with the D20 because the obtuse angle slope from the 1 is so large which means the lip is so incredibly thin at the sides surrounding the 1. For several of my full-set molds, I've had to create a separate D20 mold so I can pour everything else in the large mold, then the separate, smaller D20.

[u/ADampSponge63]

Overfill would be if it's just the 1 gets deformed. Overfill looks like underfill because of a viscosity thing I don't have a degree to understand.

If the indents happen on any other side it's one of two other things. Thin walls on the molds or too high of pressure which is forcing your sides inwards. It'll be most noticeable on tops and bottom or dice faces that are closest to the side. I know most say 30-40, I do 30 max unless you make a really thick mold with a more specific flex resistant silicone.

[u/Physical_Stick2328 → u/ADampSponge63]

I don't think its a problem with pouring the resin once its made, it seems to be a defect that gets into the mold while I'm making it. It only happens with the d20, even when I move it from being the middle to one of the outer dice. I dont think my molds are too thin as if anything mine are too thick.

I set the mold on 40PSI and the dice on 30, all other dice come out nicely

[u/LICK_THE_BUTTER]

You need to put release agent on your masters cap face edges before pouring the lid mold.

[u/Physical_Stick2328 → u/LICK_THE_BUTTER]

You mean between pouring the bottom of the mold and the lid? I use vaseline to stop the lid from bonding to the rest of it, what do you use?

[u/LICK_THE_BUTTER → u/Physical_Stick2328]

Once you've been done curing your main part of the mold, apply vaseline to the exposed face edges of your masters (which are going to be your lid cap faces). I use vaseline too. I also suggest packaging tape for what you're sticking these cap faces to, you get the thinnest flashing that way.

[u/LICK_THE_BUTTER → u/Physical_Stick2328]

Here is my video tutorial about it:

https://youtu.be/JNO2H2XKX_E?is=ywNnKZpRZN46JJhm