GRP Sectional Rigid Tool
GRP Rigid Mould - Sectional or Split
Making a rigid tool in GRP with an integral split line to deal with undercuts. Simple step by step instructions.So you have a piece to mould with an undercut? The key to this is selecting the right place to split the mould. Every application is different and so we can only look at the basics here, but apply these basics to your own project. To create a two piece mould you must decide on the split point. A flange must be constructed to allow the two halves to be separated and rejoined to allow removal of the cast. These must be bolted together before casting or lamination begins but the halves can be prepared before joining.
To produce the flange a line of clay or plasticine is laid along the split point. Using fillet balls or marbles or clay balls, make small half circle pips along the clay to act as keyways. The clay and keyways are then painted with PVA. The same process as a single piece mould is use on that half, except that you continue up the side of the flange. Allow to fully cure.
Now remove the clay strip and fillet balls. You will notice that there are small round dips in the flange to act as keyways to ensure correct mating of the mould halves. Paint with PVA and wax heavily and repeat the whole process for the second half.
At this stage consider the points at which you will bolt the halves together. Select some large washers with small holes and encapsulate these under a small piece of glass mat. Make sure these match on opposite sides as these will be drilled to accept bolts and wing nuts. The reason for these washers is to prevent wear to the mould from frequent bolting actions.
Clamp the two halves together and drill through the centre of the washers using an HSS drill bit. Once complete you can remove the clamps. Allow the whole mould to cure fully before un-bolting and gently separating one half at a time in a similar way to single piece moulds.
Clean up the surface, wax and polish, paint with PVA and bolt back together. Along the seam line use some slurry wax to help mask the join. The mould is now ready for use!