Technique: Building Foam Molds

Background:

For constructing decks with the vacuum bag technique you will need a mold to press veneer sheets onto if you want to build up your own plywood...or you could also press 4 layers of 3mm plywood...These molds can be made from different materials...foam is easy to use... Here's some general info on how to construct a foam mold that I received from Grega from Slovenia...Dough Kumph, who got inspired by the complete DIY vacuum deck building kit from Roarockit, also has the right stuff about sanding them on his website The size of the mold and hot-wire totally depends on your needs...

This is what Grega mailed:

"So, I start with hard foam (Stirodur, Armgate,...) which is used for insulation. Expanded stuff. I am cutting it with a hot wire. Simple to make and you get a nearly finished cut, with almost no sanding required."

1: Hot Wire...what is it:

He starts by cutting this hard foam into shape using a "hot wire"...I used this technique also to cut wings for my RC model airplanes...it works perfect but you'll need the right gear for it... Remember that this technique is ideal if you want to build many types of molds... What you do is actually heating up a steel wire by letting a (!) LOW VOLTAGE (!) current flow through it...the wire is tensioned by hand (you'll have to be with 2 persons) or you can tension it by using a bow... Here's a picture:

It looks a bit like an old wood saw...the 2 vertical beams can pivot around the center beam... This keeps up the tension of the steel wire, it will expand a bit because of heating up. Next you'll need some low voltage power supply with different voltage settings that can handle currents up to 10 Amp. I used a car battery charger that has voltage settings from 6 to 24 volt and current ratings up to 10 Amp. The leads are connected to ends of the steel wire...the steel wire is of the "Chrome-Nickel" type...used for electric heaters...piano string will do also I think :-) Build something that will be long enough to shape a good sized piece of foam...90 cm to 110 cm or something...very long wires will drag too much in the middle and the cut might be erratic and distorted

2: some templates:

You'll need templates to guide the steel wire when cutting foam...I used cardboard for them and rubbed a piece of lead on the edges to get a smooth sliding surface...remember that the hot wire can burn into the cardboard when it is not moved for some seconds...

This is a concave template

You'll need 2 of these...holes are made into the template to stick the template in place with some fairly big nails... You can drive those through the holes, into the foam...

3: cutting the foam: concave

Always put some wooden panel and some weights on-top of the foam when cutting...this is ommited here to have a clear view of things...

You can see that the templates are wider than the piece of foam...this is to be able to get some starting point for the hot wire...it can rest there before dragging it along the edge of the template when hot... This setup would give us a concave deck with no curve...

This is what you get after cutting that concave...don't throw that top piece away...you'll need it for the next step... This is where Grega comes back in with info...

"Just some tip. If you like to have concave and curve, there is no problem. First you cut the concave, then put the foam together and turn it over. Place a piece of something underneath the foam block and put some weights on tips. Another cut and you have the mould.

I had to think a while about what Grega mentioned here...but it's simple...After cutting the concave for the deck, the foam is already a bit thinner...and will bend more easily... Grega mentions placing the top piece back and turning the lot upside down...adding something underneath and bending the foam on the tips...this is a straight forward way to get the mold... A few mails later Grega mentioned using another set of templates to add the curve to the mold...

4: cutting the foam: curve

This is a curve template

Placing that first cut piece of foam back and turning it all upside down will look a bit like this...add the curve templates on the sides and cut from front to back or otherwise...

Off comes the second piece of foam...you won't need this any more...

In the end you will have cut something like this...we only need the middle part of the 3...

Now, when you turn that middle part upside down again, bend and stick it to some sturdy wooden panel, the same size of the mold, you end up with a fairly ready mold to work with... Some minor sanding will get rid of un-even patches that could have occurred while cutting with the hot-wire... This mold will do for good longboards without tails...

5: cutting the foam: something else

Imagine you want to build a 1,40 meter deck...then you'll have to build your mold with 2 pieces of foam...because that hot-wire will really drag when cutting concave... Just build 2 curve templates long enough for the complete template...and cut 2 pieces of 80 cm long foam...after cutting you can glue them both on a sturdy panel...when you don't do concave then there's no trouble at all... Not finding foam that is long enough can be solved this way too ;-)

6: Foam molds: Grega's pictures

Grega suplied us all with a set off pictures that show his work using the info on this page...If anyone else of you all out there wants to join me in turning this site into a construction library, please feel free to contact me :-)

First Grega did cut foam into the right useable size with this little handy aid. Two guides are attached on his workbench to give a perfect clean cut... The foam is placed between the guides and some weight on-top keeps it in place... This is a good way to cut foam at a straight angle...

Here his hot wire bow is in action... While cutting foam this way, you have to put some weight on-top of it...it won't disturb the flow of the wire through the foam...

The end result of his labour looks exactly like the stuff mentioned up above...a clean, smooth shaped foam mold is the result...All is ready to start a vacuum process to laminate a deck...