Tek-Tip: Tools & Techniques for Cutting Rubber Molds
Some rubber molds require one or multiple cuts in order to remove the original model and subsequent castings.
![Poured Blanket Mold with Mold Shell](/content/images/Cutting-Molds_1.jpg)
![Cutting_RubberMold](/content/images/Cutting-Molds_2.jpg)
Here are some tips regarding the tools and cutting techniques that we use here at
Polytek:
Tools that we use:
A tool like your kitchen paring knife will not work well for cutting rubber molds. At Polytek, we most often use the following:
- Mold Key Knife
- Scalpel
- Razor Blade (one-sided for safety)
- X-Acto Knife
![Cutting Rubber Molds - Tools](/content/images/Cutting-Molds_3.jpg)
General notes about these tools:
- Mold Key Knives automatically create a tongue-and-groove pattern.
- Scalpels, razor blades and X-Acto knives can fit into tighter spaces/corners than mold key knives. Often, a mold key knife is used to create the first cut (this cut should not reach the model) and then a scalpel/razor blade/X-Acto knife is used to make the final cut.
- Depending on the rubber being cut, blades can degrade rather quickly (i.e., after cutting 2-3 molds), so it’s a good idea to keep multiple on-hand.
General notes on cutting rubber molds:
- It is very difficult to cut mold rubbers that are harder than Shore A45.
- Silicones are generally easier to cut than polyurethanes.
- To avoid damaging the model, the first cut should not go completely through to the model. As mentioned in the previous section, the final cut should be made with a scalpel or X-acto knife as these tools are more precise.
- Avoid making a straight cut in the mold; make a zig-zag/tongue-and-groove pattern for better alignment when casting.
![ZigZag_CutinMold](/content/images/Cutting-Molds_4.jpg)
Planning ahead:
- If you are planning on cutting a mold, it is a good idea to create a thicker section of rubber in the area that you intend to cut (~0.75″). An example is shown on the far right below. You can also see this technique in a video tutorial on our YouTube Channel.
![Rubber Flange for Cutting-01](/content/images/Cutting-Molds_5.jpg)
For brush-on blanket molds (like the mold pictured above), we make these thick pieces of rubber by casting the rubber in strips (we have a silicone mold that we made specifically for this purpose) and then applying them to the mold:
![Casting Rubber Strips-01](/content/images/Cutting-Molds_6.jpg)
- When selecting a location for the cut, choose an area where seam lines will not be as noticeable if they appear on the casting (e.g., avoid the face).
- Repetitive opening and closing of the mold can cause tears over time. Embedding Tietex® Fabric in the area where the cut ends can improve strength. The red arrow below indicates an area where TieTex would be beneficial.
![TieTex next to cut-01](/content/images/Cutting-Molds_7.jpg)
![TieTex Fabric for Cut Molds](/content/images/Cutting-Molds_8.jpg)
Are you working on a mold making project and have a question about technique?
Call us at 800.858.5990.
Email us at sales@polytek.com.
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