Making a Mold for Resin Casting

You can use other material. I have used plaster of paris to make simple molds. But, you must be good at designing rigid molds.  You must provide relief angles on all vertical surfaces. If you have vertical parallel surfaces the casting will not come out of the mold.  Google "casting mold relief angle."  In a flexible mold, you do not need relief angle, you can even have slight undercuts in the side.  Best is two piece flexible mold.  Even then, you do not need silicone.  You can use latex rubber, for instance.  But rubber molds are not easy to make!  I have used clay successfully for small, simple parts.

you could try blue stuff , not messy and cheap .

www.youtube.com/watch?v=mVZLXLaidjQ&list=PLEkvE7dt72tTY2RslQJtrTCo1p1ISY0GC

David from PA

Hi.

How do you make a mold in order to make a resin casting? Does the mold material need to be silicone or can I use a silicone spray once the mold is made? I have not seen an article about this. BTW, the part I want to duplicate is made of aluminum.

You can use a variety of material in which to imbed a part to be cast.   Remember that the original part needs to be able to be removed in order that the resin can be cast.  Plaster or clay can work but may yeild less than satisfactory results.  Plaster may be porous and show in the final part.   Some sulfur-rich clays may affect the two-part epoxy resin's hardening properties.  

Resin & RTV supplier Smooth-On has a number of resources on their website for both the beginner & more advanced resin caster.  

https://www.smooth-on.com/howto/basics-mold-making/

This page is their basics of mold-making which includes several how-to videos.   They also have a link to download a PDF copy of the instruction booklet which they include in many of their sets.  

https://www.smooth-on.com/tutorials/download-booklet/

I see that you are out of Pennsylvania.   Smooth-On is based in Easton, PA  (they also have distributorships nationwide and worldwide).   I have found the countermen at my local Smooth-On distributor to be very knowledgeable and helpful with product & technique suggestions.  I'm also able to purchase my RTV & resin needs over the counter rather than relying on online suppliers & potential hazardous material shipping hassles.

My preferred product is their OOMOO-30 RTV and their 5-minute set Smooth Cast resin.  Both are available in a beginner product pack along with mold release spray.