Warren (22/06/2012)

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From the picture there is a lot that appears to have gone wrong.

1) if you use cardboard then it must be covered in flash tape or similar so it doesnt stick to the resin. Parcel tape or selotape you have knocking round the house will be fine, but dont forget to release coat it with wax and pva.

2) The fileting wax/plasticine you have used is applied incorrectly.  You need to create a smooth sealed curve between edge of the part and the flange. The wax is there to prevent mechanical lock by 2 methods: a) resin bleeding under the wax and b) smoothing sharp edges and overhangs that can cause physical mechanical lock.  An easy way to create the suitable curve is to make a 5-10mm sausage of wax/plasticine, press it into the edge then use the end of your finger to make a smooth curve. You can buy fancy ball shaped filleting tools for just such a purpose, but your finger is free.

3) Not sure about how you release coated the part, but follow the instructions to the letter and you will be fine.

4) your gel coat was way too thin. Supposed to be approx 1mm thick.  You can do 2 thin coats or one thick coat.

5) if youre worried about it breaking again, you could embed some thin wooden sticks into the putty, but in reality you shouldnt need to for most cases. Remember you need 10-15mm thick of putty.

6) remove your flange and part gently once cured. 

Its a learning process and you will get there in the end. The part you are making should be possible in carbon so its just the technique you need to refine.