Two-Part Mould - Part Two

Well? Did it work?...Yes and no. 

I think I just need more practise to work out the 'tricks' to doing this, but I think I am probably stretching the practical uses of Instant Mold by attempting two-part casting. Don't get me wrong, it is possible - with care - but I think the whole idea of Instant Mold is quick and easy press moulding really.

Two-part moulding is a slightly more complicated and precise type of moulding and - to be honest - if you are going as far as taking the time to make a properly aligned two-piece mould you will probably want to make something you can keep and use a lot of times.

So, what went right?
Well the quality of the cast was good it captured the general shape of my original object very nicely. And using Milliput mean I had a really hard duplicate that I can sand or otherwise modify further.

So, what didn't go right?
Registration. I did try to make registration dimples in the Instant Mould so the two halves of the mould would come together precisely, but I just didn't do a good enough job. The two halves slipped when I tried to put them back together again with the Milliput inside and so the cast was mis-aligned...

Now, I could rescue this casting by cutting it down the middle and realigning the two pieces again. But that kinds makes the whole process of trying a two-part mould a but of a waste of time. I might as well have just moulded the two pieces separately and then stuck them together at the end...

Alternative way of doing this (or how to rescue a failed two-part mould) is
to simply revert to doing the casting as two single part moulds and then to
glue the resultant pieces together. Perhaps? :(

The result of 'one piece' moulding the helmet parts. Now I don't have the
alignment problem BUT I now have to clean up and glue the two halves
together. Not so cool!

But the good thing about Instant Mold is you can just melt it down again in boiling water and start again. And this time I would make better registration marks (dimples) in the mould so that the whole thing aligns better (hopefully).

...And then again, I'm starting to think that I might as well invest in a proper resin casting set if I am going to start to do more complex casting from a much more detailed original. The resin mould would also have a longer life and allow me to use cheaper resin as a casting medium rather than expensive Milliput...

The Sylmasta Resin Casting Kit (£38). Perhaps the next
step in my casting experimentation?

Conclusion
Well, I feel I learned a lot about what Instant Mold is good and not so good for. It's ideal for one-piece press moulding but not so ideal for larger more detailed 3D two-piece casting. You can do it at a pinch, but the whole idea of Instant Mold is that it's 'instant' and you use it to copy something quickly and then re-melt it to use it again for something else.

My failed two-piece mould, melted back down to use again
for another mould. Best attribute about Instant Mold.

It's definitely a great tool to have on your workbench and I will be experimenting with it again to see what else I can copy (and I will be trying out different casting mediums, like Green Stuff and even PollyFilla plaster). But I think I will invest in a resin casting kit as well.

Anyway, to end off this post, here's my fudged two-piece (two separate single castings) pith helmet. I glued the two pieces together to make the complete helmet with super glue. It's a passable rescue of my failed (proper) two-piece mould attempt, but it will do for my prototype figure I'm making!

Two-Part Mould - Pith Helmet

So far I have made a very simple 'press mould' using Instant Mold (excuse the spelling but it's a Japanese product) to copy some basic shapes for my peg soldiers. Now it's time to get a bit more adventurous with a more complex shape and multi-part mould.

I'd like to make duplicates of a 'pith helmet' (think 'Zulu'), a prototype master I have made from - you guessed it - Milliput...

OK, my sculpting isn't great, but these helmets are for my peg 'toy soldiers' so absolute accuracy isn't quite as crucial. It's more of a caricature.

Now, how much Instant Mold will I need for this? Considering that this is quite a big hat and it will be a two-piece mould I'm thinking it will need two whole sticks...

Better to err on the side of caution an make too much rather than too little, especially as I intent to cast the peg's 'head' as well (I'll explain why later). Also, I drew a pencil line down the centre of the piece to give me an idea of where to make the mould halves.

First Attempt...
So...Turns out I needed substantially more Instant Mold than I thought! In fact, to get the space around the object I wanted to cast - so I could include reference points - I needed double what I originally estimated (two sticks)...

I think I'm probably stretching the envelope with Instant Mold regarding the size of the object I can cast accurately. It's quite a deep object and Instant Mold seems to handle shallower object better.

The bigger the object to cast (and the more complicated the shape of that object) the longer time you have to spend pushing the Instant Mold tightly into all the nooks and crannies of that object...And time is crucial element in this process, as the Instant Mold is cooling and hardening while you are doing this. So...You may end up having a few attempts in order to get it right!

SO, TIP 1: WORK FAST!

This is where things get tricky...Adding the second half of the two-part mould. It's definitely more art than science and you'll have to keep your fingers crossed. Unfortunately, you won't really know how successful you are in your mould-making until you actually make your first casting.

This isn't precision fitting, the jelly-like consistency of soft Instant Mold means that there is some movement when you press it into the object. Press the sides and the top and bottom move a little, sometimes opening a small gap between the object and the Instant Mold. It can be a little frustrating.

TIP 2: TRY, TRY, AND TRY AGAIN (If your mould isn't good enough, melt the Instant Mold down and start again.)

Still, as I alluded to earlier, the proof is in the pudding and you will only know how good your mould is when you make your casting.

I'm using Milliput again as the casting medium. I fill each half of the mould with the Milliput and then press the two halves together (so that the Milliput sticks together)...

And now the long wait while the Milliput dries. This will be a bit nerve wracking.

Next: I open the mould - will it be a good casting? Hope so!