Templates with Extruded Polystyrene Foam

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Forum topic by KnickKnack posted 01-19-2012 04:34 PM 3973 views 1 time favorited 9 replies Add to Favorites Watch
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1088 posts in 3563 days

01-19-2012 04:34 PM

Topic tags/keywords: template router template polystyrene

For about 18 months now I’ve had a (I think) neat design for a tray. But it involves curves on non-concentric circles…

In the past I’d have done this with sanding but that never seems to be quite right, and, I figure, I ought to be beyond that now.
So I was stuck.

Then, last night, I had a brainwave. About 2 years ago I tried routing insulation.
Extruded Polystyrene Foam insulation.
About 1” thick.
Not only was it easy, but I actually ended up with a pretty clean cut.
And I wondered, so I tried…

Stage 1 – Cut your shape
Here, I think, is the potentially very cool bit…
  1. It’s incredibly easy to route, so you can do things you probably would not want to do on a piece of wood
  2. It’s pretty cheap
  3. It’s soft, but firm – you can cut it with a sharp knife – you can cut it with hot wire – you can sand it easily. So you can cut it into whatever shapes you want.

I experimented with the non-concentric circles (although I made them concentric – go figure!), of different radii…

This one I cut anti-clockwise – I get a very clean cut nearest the operator, and a slightly more ragged cut away from the operator.

Note that you do not want to go all the way through – enough that you’ll be able to use your flush-trim bit is enough. Leaving more not cut gives the thing more stability.

I then picked a new centre-point for the next cut. Drilling this hole didn’t work – way too big and fluffy. Pushing through a screwdriver worked way better. Hand tools – 1, Power Tools – 0!

I then made the next cut clockwise, to give me the cleanest cut away from the operator…

(This picture shows the end of the cut)

Now I have this…

which I can just hack off with a knife. A very small amount of cleanup with very gentle use of 400 grit and I have a template…

Stage 2 – Use it as a template
I was just interested to see if this was going to work, so I just put a bit of thin crappy pine on. I used bolts, but I guess you could glue etc etc.
Cut it to rough size, put in the flush trim bit, and trim…

the thing you need to be careful with here is heat on the bearing roller. This is polystyrene, after all and, whilst it’s pretty firm, it will melt if the roller gets hot and then, well, you don’t have a template any more.


I wish now I’d taken more care and actually made something I’d want to use, since this is a jolly fine template!

The blue template itself could be used again, but I think it’s going to be better to make a copy onto a more permanent template – MDF, pine etc etc

I think artistic types could have a lot of fun with this, so I thought I’d share.

Anyone who has done this before, or anyone who has ideas for how this might be improved – please chime in.

-- "Do not speak – unless it improves on silence." --- "Following the rules and protecting the regulations is binding oneself without rope."

9 replies so far

View KnotCurser's profile


2025 posts in 3065 days

#1 posted 01-19-2012 05:04 PM

Very cool idea – I can’t believe the foam holds up to the roller on the router bit. I don’t even see an indent after use.

Must remember this.


-- Robert Rhoades WoodWorks / Email: /

View kaschimer's profile


89 posts in 2386 days

#2 posted 01-19-2012 05:08 PM

This seems incredibly useful. Cost comparison to some other template material like MDF?

-- Steve, Michigan - "Every piece of work is a self portrait of the person who accomplished it - autograph your work with excellence!" - Author unknown

View DIYaholic's profile


19620 posts in 2672 days

#3 posted 01-19-2012 05:09 PM

Some may not see this as an improvement; Install the router into a CNC machine! Lol.
Ok, no Lol I want a CNC Router!

-- Randy-- I may not be good...but I am slow! If good things come to those who wait.... Why is procrastination a bad thing?

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Steven Davis

118 posts in 2911 days

#4 posted 01-19-2012 09:04 PM

Great idea!

-- Steven Davis - see me at

View dannelson's profile


193 posts in 2368 days

#5 posted 01-20-2012 12:17 AM

we machine this stuff all the time on our cnc it makes great indoor signs and the detail stays really well . we dial our spindle down to 3500 rps and no melting . we can cut it at 300 in/min

-- nelson woodcrafters

View rance's profile


4258 posts in 3157 days

#6 posted 08-30-2012 06:28 AM

Interesting process and use of material.

Once you have it cut out of foam, smearing the edges of the foam with joint compound might make them more durable until you can use the foam template to make a sturdier one. Not enough compound to change the shape or size, just enough to stiffen the surface.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View OggieOglethorpe's profile


1276 posts in 2107 days

#7 posted 08-30-2012 05:23 PM

I used to make model airplane forms with this stuff using a hot wire bow or hot knife. The bow was simply a nichrome wire across an insulated frame, attached to a cheap variable power supply. Here’s a commercial version demonstration of the process. You could also use a soldering iron that accepts a blade where the soldering tip normally goes.

The foam is handy stuff, though. I’ve built reusable door plugs for my spray fan, spray booth wings, taped together full scale mockups of built-ins to demonstrate scale, used it to cut sheet goods on, used it to pad the floor of the truck when carrying prefinished both sides plywood… I’ve cut it on the table and band saw, too.

Another way to toughen up the shape is to apply fiberglass cloth and epoxy to the foam. Brush on a thin coat of epoxy, lay the cloth in the epoxy, brush a little more epoxy on the cloth, and squeegee the excess out with a credit card. You can then leave the foam in place for structure, or add layers of cloth and epoxy, then melt out the foam to leave a hollow form.

View BentheViking's profile


1782 posts in 2561 days

#8 posted 08-31-2012 03:12 AM

how will the router handle the insulation dust…id be hesistant to use a good router

-- It's made of wood. Real sturdy.--Chubbs Peterson

View Michigander's profile


220 posts in 2416 days

#9 posted 09-01-2012 01:38 PM

I used to work for a company that makes this type of foam. It is regularly routed for application in garage doors and walk in freezers. If you live near a distributor, you might ask for higher density foams. The stuff you routed is probably 25 psi. You can buy higher densities to 100 psi , which is very rigid. Make sure you get either Owens Corning (pink) or Dow (blue) XPS foam (extruded polystyrene)
Good Luck,

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