Wednesday, July 4, 2012

How to Cold Cast a plastic Part in Your Kitchen

Part 1 – Making the Wax Mold

Have you every cried over throwing away a functional device or toy just because you lost or broke one small plastic part? 

I recently visited my mechanic to find out what was wrong with my AC, and in the process, they broke one of the plastic slide for the air vent. The knob is  a one off part, not something one can order a replacement part for – there are only two possible ways to find another – 1) Visit the local junk yard and hope to God that you will find a matching part from an accidented vehicle.  2) Make one. Yes make another one in my kitchen.
I know any wise guy would have chosen the easy way out, but trust me, I rather stay indoors and engage myself in a small DIY project than to venture out doors – with planes falling out of the skies, and Boko Haram incessant bombings, I have made the tough choice of making it myself. I took the one weekend out to make a replacement part for the AC vent and the account below is how I went about it.
What do you need for this project?
  • Candles
  • Paper Box
  • Sticky Tape
  • Large syringe
  • Empty tin can
  • Epoxy

  • Depending on size of the item to be replaced, find an appropriate box that will hold the mold
  • Make sure the box is big enough to hold the item and still leave enough space on the edge. The space will ensure that the wax does not break off. The rule of thumb is making sure that the item will sit in about 50% of the space.
  • Decide the part of to cast. From experience, it is better to cast in two parts – top and bottom, is a way that allows you to remove both molds without breaking the molds as such. It is often easy to make this choice by looking at the lines on the original piece to be cast – most plastic objects bear the tell tail sign of how they were cast – often in two parts. – we will call that line the “Cast Line”.
  • Cut up the candles and put it in the tin can and set the can on low heat on the cooker.
  • The following process might be very messy, so make sure you are wearing gloves and mask off the working area to prevent greasy stains.

  • After the wax melts… pour the wax into the box and allow it to cool off.  From experience, I noticed that the very first time I poured wax into a box, the wax leaked out (of course, it is liquid). I found it quite handy to tape the entire corners of the box with cello tape (sticky tape) to prevent any leakages. 

  • Wait until it is cool enough to leave your finger prints on. Not too hot, not too cold. After a few experiments you will know when the time is right. 
  • With a steady hand push the part into the molten wax to get the first mold. Don’t be tempted to pull it out or jiggle it. Just let it sit deep, allow the wax to rise above the Cast Line where you would like the second mold to start from.
Post picture of the two replicas sitting in the molten wax
  • Wait for the wax to solidify – To speed things up, I placed the mold in the freezer, and then the fridge, but it always resulted in cracks, as the wax cooled too fast. It is best to allow the mold to cool at room temperature.
  • With the original piece still in place and using a sharp blade, carve out the Cast line – make the surface of the mold flat. Enough angle to ensure that the 1st and second molds will meet on a some worth flat surface. Drill out holes to ensure that there will be no air pockets when both molds meet.

  • Set the first mold aside and prepare the box for 2nd mold – follow steps 1 – 4 above.
  • When the second mold has reached the right temperature, slowly lower mold 1 into the second mold, press hard until wax is dripping out of the drilled holes in mold 1

  • Leave it to harden overnight. Don’t be afraid that they will bind together, Wax is actually has its own oils, as long as two drops are not the same temperature, chances are that they will come apart with a minimal effort.
  • Make sure to wait for the wax in the middle of the mold to set before continuing this procedure
  • Make guide marks across the two sides of the mold – this will help you align the two parts properly. From experience, I put a scratch mark on all sides of the mold. Magic marker lines will eventually rub off so avoid them, unless you have already secured a masking tape.
  • Pry the two parts apart, make sure you are gentle and avoid breaking the mold
  • Slowly bring out the original part from the two molds. If the mold breaks, it is just a temporary setback, just cutup the wax and smelt it down again. From experience, some waxy residue remain on the original part after each attempt. Washing it off or cleaning it off did not work – The best way to get rid of the extra wax was dipping the part in Hot water (you risk melting the part if you dip it into Very hot water).
  • Examine the two molds. You should notice every small detail; even part numbers will show up clearly in a good mold.
  • If you successfully get to this part without any problems, Shout Hurray! – you are half way there.