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This Instructable is an introduction to the basics of mold making for people interested in mold making with little to no knowledge on the subject.

It will walk you through some important vocabulary, break down the major mold types and help you select the correct mold for your project.

Here are some great mold making resources:

http://www.smooth-on.com/

Tap Plastics

http://www.aeromarineproducts.com/silicone-mold-making

Step 1: Types of Molds

There are a variety of mold types for different applications:

  • Pour mold - Mold made by pour silicone over an original inside of a containing box
  • 1-part pour mold (block mold) - a pour mold with only one side (simplest type of mold)
  • 2-part pour mold - a pour mold with two or more halves and registration keys to align the parts
  • Brush-on mold - a mold made by brushing on thin layers of silicone to build up a skin that is then encased in a rigid mother mold to give structure while casting
  • Glove mold - A brush-on mold that does not require a parting line (sometimes uses a small slit)
  • 2-part brush-on mold - A brush-on mold that is split into two or more parts
  • Lifecasting - Mold made of a living human

Diagrams of the cross section of several mold types

Here is more information on Mold types.

Step 2: Vocabulary (helpful Terms)

Some helpful mold making terms:

  • mold - Overall system of parts used to replicate parts
  • casting (cast) - replicated part made of final material
  • flashing (flash) - extra unwanted material left on casting as a result of casting process. Usually along part line
  • original (prototype/part) - What is being replicated
  • box - container for pour molds (mold walls)
  • mother mold (shell) - hard exterior covering to give brush-on molds structure while casting
  • runner (sprue) - hole that casting material is poured into
  • key - registration points for lining up sides of multiple part molds and holding them in place for registering mother mold to silicone and silicone to silicone
  • part (split) line - borders between two sides of multiple part molds
  • mold release - release agent applied to original and mold to facilitate release of original and casting from mold
  • undercut - area of original that overhangs and can create difficulties casting
  • lifecast - mold made with a living original. Usually a person.
  • air vent - passage for air to escape mold chamber during casting process helps avoid trapped air in casting
  • rotational casting - rotating mold while casting to create hollow final model

Diagram of a basic 2-part pour mold

Step 3: 1-part Pour Mold (block Mold)

This is a 1-part pour mold.

These type of molds require a box or mold container.

It is created by pouring silicone over an original leaving one side fused to the bottom of the box.

This fused area will later serve as an opening in the mold to pour casting material into.

Here's an Instructable for a 1-part pour mold

Step 4: 2-part Pour Mold

A 2-part pour mold is similar to a 1-part mold however instead of leaving one side open it is sealed off with another half of silicone. A runner is placed in one end to allow an opening in the mold for casting material to be poured into later.

The two halves of the mold are aligned using registration keys placed along the parting line.

2-Part pour mold instructable can be found here

Step 5: Glove Mold

A glove mold is a type of brush-on mold best for molding complex shapes where the silicone needs to be flexible to allow parts to be removed. (note: a glove mold does not necessarily need to be on a hand)

Several thin coats of silicone are applied to the original until a skin of silicone is built up (thickness depends on the type of mold usually 3/16" - 1/2" thick) a mother mold is then built around the silicone mold to give it structure while casting.

Occasionally a glove mold will require a partial parting line in order to get the part out. (this parting line does not cut the mold into two parts it's more like the buttons at the top of a polo shirt)

Lifecasting brush on glove mold Instructable can be found here

Step 6: 2-part Brush-on Mold

A 2-part brush-on mold is a type of brush-on mold similar to a glove mold but split into multiple parts. It is best for molding extremely complex shapes where the silicone needs to be flexible to allow parts to be removed or to account for undercuts.

Several thin coats of silicone are applied to the original until a skin of silicone is built up (thickness depends on the type of mold usually 1/2" thick) a rigid mother mold is then built around the silicone mold to give it structure while casting. A 2-part brush-on mold requires a partial parting line in order to get the original out. Sometimes these molds will require more than one parting line and will be split into more than 2 parts.

Here is a 2-part brush-on mold

Instructable can be found here

Step 7: How to Select a Mold Type

Now that you have a basic understanding of what mold making is all about you should put this knowledge to use by making your own mold!

How do you know you're picking the right type of mold for your part?

As we discussed earlier there is a family of mold types to choose from.

The type of mold you choose should be driven by the geometry of the part you're molding.

Start by examining your part from all angles. If this is your first time molding I would suggest picking something very simple until you get a hang of the process.


Is it flat or one sided with a shallow height? (like a medallion or coin)

A 1-part pour mold is probably best

Is there more than one side and it is more or less one main block of material? (like a head)

A 2-part pour mold might work


Is it really complicated with undercuts or no good place for a part line (a deer head with antlers)

A glove mold or 2-part brush-on mold is probably your best choice


The more molds you make, the better you will get better at picking mold types and placing your part line

Don't get discouraged if your first mold doesn't work exactly right. I've messed up countless molds and casts for every one I've gotten right.

Learn from your mistakes, keep practicing and remember to think through all the steps before you start mixing your silicone. It might help to draw out each step or write a list. There's nothing worse than forgetting to put mold release between the two halves of your 2-part silicone mold (speaking from experience)

Mold making materials are expensive and can be difficult to handle. Make sure everything is in place and your environment is prepared before you start. You don't want to run around looking for materials or move your mold once you've started. (remember molding and casting materials require a warm environment to cure properly if you're working in a garage or basement set up a space heater)

<p>cool</p>
Thank you so much for this ible! I have so many interests, and today I was looking for information about making soap molds. Then I came across this - the holy grail of mold making!!!!! This one ible answers all my questions about anything and everything I might want to make a mold of / for. I noticed that you haven't made any ibles in a while, please come back, we need you!!!!!!!!!!<br>Very Sincerely,<br>Rose
<p>Really helpful instructable and good questions to help one determine type of mold. I'm a soap maker who would like to replicate a silicone liner used in a wooden box soap mold (4 lb. capacity) that I purchased some years ago. The makers went out of business or I would just order from them. Notice in picture the mold has score lines for perfect bars of soap...Shall I just walk it to my local TAP Plastic store and ask them where to begin? Thank you!</p>
<p>Hi I'm trying to find the list and prices for PMC121-30. I was there once and lost it.It had qt.,gal.,5 gal. and black rubber dust extender. If I can get there again,I'm ready to order.PLEASE help me. thank you</p><p>bob111934@you.com</p>
<p>Hi I'm trying to find the list and prices for PMC121-30. I was there once and lost it.It had qt.,gal.,5 gal. and black rubber dust extender. If I can get there again,I'm ready to order.PLEASE help me. thank you</p><p>bob111934@you.com</p>
<p>Hi I'm trying to find the list and prices for PMC121-30. I was there once and lost it.It had qt.,gal.,5 gal. and black rubber dust extender. If I can get there again,I'm ready to order.PLEASE help me. thank you</p><p>bob111934@you.com</p>
May I have your mail so I could ask you things about molding?
<p>Post any questions about molding here incase someone else has the same question!</p>
<p>The part I want to reproduce is a hard nylon think I can make the mold. What material could I use to have a hardness like Black Nylon</p>
<p>Smooth-On's Onyx resin is a good choice. (And it's black too!)</p>
<p>Afaik, nylon is melted, not two part cast.</p>
<p>There are lots of options when it comes to selecting a material to cast in. I haven't come across any nylon casting materials (though I'm sure they exist). Smoothon.com has a lot of different options, plastics, foams, rubbers, etc. I usually use Smoothcast 300. It is a very strong plastic, however it's a bit brittle so I wouldn't use it for anything that will take impact. Maybe start by looking at the different polyurethane plastics at smoothon. Let me know if you find an interesting material!</p>
<p>In fact, a lifecast mold is not really a separate category; they can be simple, complex, poured, painted-on, etc. Big difference is there's a person in there!</p>
<p>New to molding/casting and was wondering if I could get your input. I want to replicate a picture frame I have. What type of mold would you suggest? Thanks!</p>
<p>Since there are only features on one side, and the other is flat I would use a one part pour mold as described in the instructable</p>
<p>Everything I saw was links to other instructables. Do you not show and tell how to make molds? I could have searched other instructables without reading this.</p>
<p>This instructable is a broad overview and introduction to the world of mold making. It teaches you the basic vocabulary and reasoning behind choosing a mold. It would be difficult to fit all the types of molds into one Instructable so instead I included links to each kind of mold. If you're interested in how to make a specific type of mold reference the links provided for each kind.</p>
<p>Thanks for the Instructable. I've been planning on doing a mold and cast of my friend Yorik. It looks like a two part brush on mold would be the best for him.<br></p>
<p>haha...from the thumbnail on the instructible email, i thought that was a urinal. i was thinking, &quot;oh wow, how handy!!&quot; :) (they cut off the top of the helmet)</p>
<p>here is the part photo</p>
wow! that's some detail. you've made it exciting enough for newbies to try their hand at some molding. thanks for this.
<p>No problem! give it a try it's a lot of fun!</p>
<p>Fantastic instructable thanks so much for posting!</p>

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Bio: Hey there! I'm recent graduate of Carnegie Mellon University's Industrial Design program and a former Instructables intern. When I'm not working in ... More »
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