How to design and make soft plastic lure moulds.

I made these a while back but thought some of us might find it interesting during lockdown. I needed a large, cheap SP lure body for use on a 6oz jig head for vertical fishing but couldn't find anything off the shelf that was suitable, so I thought I'd try pouring my own. I'd never done this before so it was a bit of an experiment.

The first stage was to make a mould I can pour into, so I needed to make a master of the lure.

Using Fimo I made the rough shape of the lure body, then baked it. After baking I used a Dremel with a coarse sanding drum, plus 320 grit wet & dry to get the final shape. After shaping I mixed up some fine filler paste to smooth out a few low spots before sanding smooth again. The finished master below.

Now I had the master, I needed to make the mould. So first I bedded the master into a block of plasticine. This is started by hollowing out an imprint of the master so that it fits snugly half way into the plasticine.

I added the shape for the pouring funnel in plasticine too. I ended up opening it out once the mould was finished as it was too narrow to pour smoothly.

The next step was to build up the sides of the mould around the plasticine block. I used the kids' Duplo bricks as they were quick and easy to assemble. I also added some ball bearings from the kids' marble run toy to make locating lugs for the two halves of the mould.

See that ball of plasticine at the top of the pic below? We'll come back to that....

At this point I also sealed up all the edges with small beads of plasticine to give a good seal. I then gave everything a light coat of vaseline to ensure the mould releases well once cured. Now ready for the first pour.

I worked out the volume I'd need and used an online converter to work out the total weight I'd need, then worked out the respective weights of RTV and catalyst. This is quite a large mould so I ended up needing needing nearly 400gr of silicone for each half.

After weighing out and mixing for a good 5 minutes the first pour went in.

After curing for 24 hours the first half was ready to pull.

Not bad at all. Pleased with the way the first half came out - fully cured, released well and no bubbles.

Next step was to prep the first half for the second pour. So, while keeping the master in position I rebuilt the mould sides again, remade the second half of the pouring funnel and re-lubed everything with vaseline. The second pour went in - very few bubbles, which is good.



Mould fully cured and separated after curing.

Next step was a test pour. I found that with a large SP like this I had to warm the mould by doing a scratch pour, which let the next pour flow much better.

First batch of lures from the new mould...

They all have an imperfection or two but as a first attempt I was pleased with them.

PS: remember that ball of plasticine I mentioned earlier? It went missing overnight after I had poured the second half of the mould - I originally put it down to having a semi-senior moment - did I put it away somewhere and forgot? It turned up eventually..... out of the back end of the dog . She must have snaffled it during the night when the first part of the mould was curing. Who knew that dogs like plasticine...??