Tips for Designing Mold Masters

A new round of objective markers is on the workbench for Adepticon 08.  This year all of the event organizers are interested in markers for their tournaments.  In addition to 40K, I’ll be casting for WFB, LotR and WAB this year.  Several people have offered to help, and the first question always is:  how do I make something like this for casting purposes?

A one sided mold works just like an ice cube tray – everything needs to slope down (up) to a genital point.  The RTV generally use is flexible enough to allow for a few undercuts – but avoid any cuts that curve back on themselves.  And a big no-no is any sort of loop – if the RTV makes contact with it’s self the master will be locked into the mold.   The second item to avoid is any small, upright points such as a sword or gun barrel. 

crate with bubblesTo demonstrate this sort of problem, take a look at the Ammo Crate marker.  The circle to the left shows a shell laying flat on the base.  The circle to the right shows two upright shells.  The 3/16 wire used to create the shells was too small & the cavities created failed to release the trapped air.  No amount of poking and prodding would allow for a clean gravity cast. 

The second question asked is:  How much detail will the resin/RTV pick up?  The answer is:  damn near everything.  Very detail little is lost in the molding process.  I would not be surprised at all to find fingerprints trapped in green stuff transferring to the finished product.

The last question is:  What materials can I use?  Nearly any sort of material can be used to construct the master.  The RTV uses no pressure or excessive heat in the curing process and most times the master will survive the process.  Only the most delicate items like paper or sand/plaster attached with white glue will suffer from the demold.

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