Working With Foam: Tips and Tricks - Convexed Layering

As we catch up with the weekly posts, this instructable looks at the techniques used to add layers in foam to achieve definition or added thickness to our props and armour or other foam projects. The difference here is that this technique looks at layering over a convexed shape.

This takes generally known techniques, but adds a twist so that you DON'T have to take into account foam thicknesses when making your templates for your builds.

These instructables are designed to be simple and informative, and the skills can be transfered easily across to other mediums. If you have any questions about the tips or any suggestions or comments on tips you'd like to see, I'd be very interested in hearing them.

- Your Base shape/ prop/ armour that you want to layer on to

- Masking Tape and Paper to make your template from your base layer

- Dressmaker Pins

- Foam to make your layer

- Contact Cement

- Boxcutter

- Pen

First thing you need to do is get your base shape, and using the methods showcased in the previous Tips and Tricks post, work out your detail design and put this onto a template to transfer onto foam. This is explained briefly in Tips and Tricks: Detail Templating but there are some slight changes we need to make, as this is a 3d shape we are trying to make into a 2d pattern.

• So first off layer over the area you are adding details in masking tape, and then over the ridge lines of the shape mark out some cutting lines. We try to use as few as possible, to keep a smooth finish, but sometimes you need to cut more to make the pattern lie flat when we take it off.

• Secondly, and REALLY importantly, we mark on registration marks. This helps us put the foam back into the original shape accurately without any overlaps. These are the 'stitches' on the lines in the images.

• Then using the box cutter we cut through the masking tape along the lines and carefully peel it off our base shape before transferring this onto our paper to make a sturdy template.

You now have your 3d convexed shape in a 2d template format ready to transfer to foam

When transferring your template to foam, it can be helpful to make sure that it doesnt move about when tracing around it.
Take your dressmaker pins and secure the template to the foam in the corners and at the end of the darts.

Don't forget to mark off where your registration marks are, as you need these when gluing your foam together to get a 3d shape.

Remove the pins and the template and write on the foam 'inside face'. This is important so you know which way we are gluing this together, as explained in the next step

Now this is where things get a little head-spinny.

What you need to know for this, is that with most shapes and tubes there is an outer and inner diameter, (the measurement of the surface on the exterior or interior side of a shape). In order to make sure our new layer fits the base shape properly we need the INNER diameter of the layer to match the OUTER diameter of the base shape. So in order to do this we are going to invert our foam pattern when sticking it together.

What this will do will mean that the dimensions traced from our template ,(the OUTER diameter of the base shape), are now the INNER diameter of the foam layer.

If we stuck this together the traditional method it would mean that the OUTER diameter of the foam layer would be the same as the OUTER diameter of the base shape, and because of the foam thickness, the INNER diameter of the foam layer would now be smaller than the OUTER layer of the base shape, meaning it wont fit properly, and you will end up with gaps in your work.

This is why we marked our foam with 'inside face' so we know which way to curve and glue our foam layer.

So, with this in mind, we need to re-connect our foam template.

First apply your contact cement in a thin layer to each edge of the darts, and leave a few minutes to cure and go tacky. (this may vary depending on the brand you are using)

Then slowly and carefully match up the registration marks, trying to keep the foam edges level with each other press them together. You will notice that the foam naturally begins to take the shape of base shape

Your 2d pattern is now a 3d shape again. And ready to be applied to your base layer.

Now our layer is complete and stuck together and should simply slot over the base shape, we can glue it on using our contact cement.

To reassure you as to why we bothered inverting the layer and talked about INNER and OUTER Diameters, the second image here shows you the template pinned to the OUTER diameter of the foam layer. This is where the foam layer would have finished if we used the conventional technique. For a prop or armour, that is quite a large gap to try to fix.

Hopefully this serves as some help in your foamsmithing.