[tobyak]

Finishing the mould, had a good bit of time to work today so ive finished the blank and set up the mould walls to retain the Silicone RTV

My two best friends polycement and a scalpel


Blank finished with all the reinforcing in place, and poly is set


Lets break out the sander.... MORE POWER!!!!

After some brief but interesting sanding where my pet Staffordshire Bull terier tried to eat the mouse sander i finialy got the edges nice and crisp and the bottom level all ready to glue to the sheet that will form the base of my mould

Crisp, clean.... and erm.... dusty



Brushed off the dust and debris and glued the blank to the mould floor


Lots of spare plasticard cut in to strips to form the mould wall


Mould all done all ready for the RTV to go in

Time to mould

Everything you need to make the mould

Pictured above, all the things you need to finish one single part mould

• Spatula
• Silicone RTV
• Catalyst
• Blank
• Mould box
• Mixing vessel.... (my wife's fave cake tin)
• Rice

As this is not a regular shape mould it is hard to work out the volume do you dont over or under mix a quantity of silicone

Fill your mould with rice until you have the blank covered to a depth that you feel you want for mould


Pour off the spare rice and empty the mould in to your mixing vessel, then mark the level the rice comes to as your "max fill" level

Although you may think that another approach would be to weight the rice for maximum accuracy but DONT, Silicone RTV is far more dense that rice and you will not get the same volume

Place your mixing vessel on some weighing scales and make sure you zero the reading... pour in the Silicone to the fill line.... make a note of the weight



As this is a 1-10 mix catalyst you need 1/10 (BY WEIGHT) so from the note you made on the scales work out a tenth and pour in the catalyst until you reach that weight


NOTE - The catalyst that comes with this brand of RTV is clear, i have tinted it with silicone dye for photographic use and to better illustrate a good mixture




And now we are ready to pour, do it slowly and try to avoid moving the pour stream around to much in the early stage as you will trap air bubbles



Pouring done, let it settle and check after an hour to see if the surface if free of bubbles, if it is not pop them, remember this will become the bottom of the finished mould and must be perfectly flat




Time to demould

One of the good ways to see if your silicone is ready to remove from the mould is to look at the surface it will lok tight and will have lost most of the shine it had as a liquid

Another popular but less scientific method would be "prod it a bit"

As with most materials set with a catalyst the thicker areas set first so to be 100% sure that it has set pull away one side of the mould to release the seal if its to soft push the side back and wait another 3 hours


Start taking the sides off our mold, NEVER try to take it out like a jelly mould, the suction from the material will more then likely destroy your blank and mould block before it becomes free


Starting at one edge peel the mould off the blank, this way you break the suction as you go


TADAAAAAA!!!!!!!!!!!!!!


Little bit of flashing around the mould edges, very easy to trim off