This instructable is going to go through the process of designing a simple mould in 2D Design, to be laser cut into either card or acrylic, and then cast with pewter. The picture shows a selection of the castings completed by one of my year 10 (14/15 year old) classes.
You're going to need:
For the mould you will need:
Access to 2D Design (or similar software - whatever your choice of CAD programme is)
Access to a laser cutter (or, a really really sharp scalpel/craft knife and a cutting mat)
Material for your mould - either a heavyweight fibre/pulp board, or 3mm acrylic
For the casting you need:
A metal ladle
Access to a brazing hearth, gas cooker ring, or small blow torch
2 x frame plates (either metal or MDF)
Vice (either bench mounted or a hand vice)
It's also really important to point out that, although pewter and most low-melt alloys become liquid around the point of 180o, you still need to be wearing protective clothing. Before any of my students cast anything, I insist on them wearing safety goggles, an apron (preferably leather, but a heavyweight cotton will do), and heat gloves. I also make sure that there is always a bucket of water nearby, in case of burns, as well as the standard first aid kit and burns box.
Step 1: Preparing the Mould
I'm going to show a really simple shape, with initials on it, cast as a two layered piece - specifically, a heart with my initials (LS) on it.
To begin with, I drew a 100mm x 100mm box on my page. I'll be using this to outline my template, for when it cuts. Using this size means that I can allow a reasonable sized edge and make sure that my casting isn't too large - think pendant/keyring sized.
I found the outline of the shape I wanted to use on google. Even though there were nicer versions of the heart on the search results, I selected a nice simple one to use.
You need to copy and paste the image into 2D Design, and vectorise it. In 2D, you need to click on Bitmaps, then Vectorise Bitmap, then click on the image you are changing. For the purposes of this, all you need to do is change it a straight forward monochrome image and then click on ok. The standard default settings are fine for this, as we are only using it for an outline.
To cut down on the amount of time it takes to make the moulds, I'm going to delete the fill out of the newly vectorised image, so that it only cuts the outline. I've also changed it to red, as that is the colour that our machine is set to cut on. After making sure that the image is centered in the box that was drawn first, we now need to add a pouring gap. I tend to use a gap that is 1.5cm wide, from the top of the box to the start of the image. As a general hint, try to connect these lines to a flat edge of your casting - so, with my heart, I've moved the pouring spout to about a third of the way along that line, so that it connects with the diagonal, rather than the point in the middle. You'll notice that I've left the heart outline complete - when it cuts out, I'll be left with the frame, as well as a solid heart. I'll add a small circle to the cutting file, so that the cut out makes a keyring, as a "freebie".
Step 2: Preparing the Mould (2)
To do this, start by duplicating the mould you've made so far. This will make it easier to line everything up.
I've used the text tool on 2D Design to put the initials on, and once again, I've taken the fill out and changed the lines to red.
Once everything is in place, you can then delete anything that shouldn't be on the top layer - in this case, the heart shape. I've left the pouring lines in place, to allow the pewter to pour more easily.
Congratulations! Your moulds are now ready to cut!
You need to choose what you are going to output them to. There are a couple of options from this point:
If you have access to a laser cutter, you could produce them in either 3mm acrylic (this is good for using up scrap in school), or 2mm fibreboard (also known as greyboard or pulpboard). Use your settings manual to choose the cutting speeds, suiting the power of your laser and the material you have selected.
If you do not have access to a laser, you can print these out on a normal printer, and then use them as stencils - glue them to a piece of grey board or similar, and then with a sharp craft knife, cut them out. Remember it is the outer frame that you are wanting to keep, so don't worry about cutting up the inside parts!
Step 3: Casting
Start by putting your moulds in between flat pieces of MDF or metal. The material you use for this should be around 1cm thick. Sandwich all of this together in the vice, making sure that the gap you left for pouring faces upwards.
Once that part is ready, put your pewter into the metal ladle, and put it over your heat source - I find it helps to have a tripod or similar to balance the ladle on while I'm sorting out the heat. Heat the ladle, rather than directly heating the pewter, and keep heating it gently until the pewter is liquid. It should appear to have a mirror-like quality when it is ready to pour, and shouldn't take more than a few minutes.
Carefully pour the metal into your mould, trying to pour in a steady stream - breaks in the pour can create weak spots in your casting. Once the metal reaches the top of the mould, stop pouring. It should create a small raised mound over the pouring spout. You need to leave the mould alone to cool, until that raised mound collapses and curves inwards. Give it at least 5 minutes.
There's a really simple casting sheet attached as an image - it can help as a quick quide.
Step 4: Finishing Off
Depending on the finish you got from casting, you may also want to polish it up a little - you can either do this by hand, with wet & dry papers, and a polishing cloth, or using a small dremel or similar.
To turn it into a keyring or pendant, you'll need to drill a hole. Because pewter is soft, this is a little easier than drilling into most metals, but you'll need to be careful as it can be quite "sticky", so can take a little patience. A hand drill will go through pewter, and shouldn't take too much effort - be sure to clamp it down before trying though, and, if possible, put a sheet of thin MDF or similar between the clamp and your pewter. Because pewter is soft, it will mark quite easily, and the pressure of the clamp could easily dent or damage the surface of your newly cast piece. I generally recommend a 3mm or 4mm drill bit for most castings, although smaller and larger can both work depending on what you're doing at the end. A 4mm will accomodate most keyrings/split rings with ease, and for jewellery, a 3mm is pretty large for a jump ring.
Enjoy, and show it off!