View Full Version : Cutting foam core

12-18-2005, 10:34 AM
I have yet to build a foam core camera, but I'm starting to think I should. Making such a camera light tight would be greatly simplified by having nice, clean, straight edges on the cuts, but cutting with a utility knife doesn't seem to reliably produce such cuts; instead, I get cuts that waver, non-square angles, and other conditions that seem likely to produce wonky construction and hence light leaks.

I know the best way is to clamp a steel straight edge to the work on the cut line, and cut along it with the knife held vertically, as well as make multiple passes instead of trying to cut through on the first pass. However, a steel rule long enough to do this is expensive and I'd have little use for one other than this application. Same goes double for a sheet rock square, which is also difficult to use on thin material (the thinnest dry wall is 1/2 inch). To date, I've been guiding the knife with a piece of poplar stick gotten at the local building supply (don't recall if it was Lowe's or Home Depot; both carry these), but straightness becomes an issue with a longer length than the two feet I've got on hand, and it's hard to guide accurately on the knife blade because of the thickness of the stick and tendency for the blade to cut into the wood.

So -- foam core camera builders, how do you cut the stuff straight, square, and clean?

12-18-2005, 11:06 AM
the local place i buy foam core from has a variety of mat cutting gear available for public use ...

i'm sure you have incorporated or considered all the ideas i could come up with : mapping points out (with small map pins or something akin) using geometry rather than a rule and cutting shorter segments (from my long-past woodworking days), checking straightness with my old handheld laser pointer (proving even retired cat toys can be useful in a shop setting), multiple shallow cuts ... sorry i can't be of more help!

one might (if one were cynical enough) point out the fact that there are now opaque black RTV substances available in most automotive supply sources - not that anyone I know would resort to such nonsense.

12-18-2005, 11:56 AM

Always use a brand new exacto blade. Change it as soon as it starts making the foam ragged.

Then I cover all the seams of the camera with 3M black photographic tape after it's glued together. Not as pretty as Earl's cameras, but light tight on the first try.


12-18-2005, 01:55 PM
I agree with dvoracek, I was mounting photos onto foamcore and if I didn't use a new swan morton blade (or exacto being the same thing) it's just difficult to get that clean cut. I don't think you can get a clean straight cut without a metal rule with a nice edge IMO. Plus it's always best if you're trying to get those 45 degree angles. You could possibly get away with using a meter stick, a long spirit level ? Or you may have to use the poplar to cut it into more manageable pieces then a rule,

Another possibility for camera building is using empty paper sheet film boxes to construct a camera system (rigid, black and come in paper/film sizes).

This doesn't help with your question, but you can get cutters for trimming holes in foamcore i.e making a lensboard. Of course It depends on what you're using your camera for and how durable you wish to make it.

12-18-2005, 02:39 PM
I use an aluminum meter stick with radiused edges that cost me $6.99. I use a new blade in my #2 Xacto knife, and I hold the knife very straight and make multiple cuts. I do not need to tape my seams after glueing, and my cameras do not leak light.

12-18-2005, 03:10 PM
what kind of glue are you using?

the proof is in the pudding, and earl's camera post speaks volumes for his technique. but being the impatient, lazy type, i have been known to use my tablesaw when a sliding matte cutter is not available. just don't breathe the fumes- some deadly gases, no doubt.

this is admittedly like nuking houseflies, and a tablesaw maks a radiused straightedge look cheap.

12-18-2005, 03:35 PM
My current bottle of glue is Titebond II Premium Wood Glue. As you can see in my pictures, I try to clamp thing pretty tightly, and I make sure that the glue coverage is good. If the cut is straight, the glue covers the whole edge of the foamcore, and the joint is clamped well, a right angle glue joint is very tight and very strong. However, I know from experience that the same does not hold true for wood glue joints - I have had to fill the corners of my wooden 4X5 camera. The 8X10 camera was made of white foamcore, which is not opaque. In that case, it doesn't matter how good the glue joints are . . . ;D

Tom Persinger
12-18-2005, 06:06 PM
i have a nice 3' steel cutting edge (has anti-slip rubber on the back and a raised edge to guide the blade/protect your fingers) but all you really need is something long and straight that will guide the blade (and yes, a sharp blade is a necessity if only because you're less likely to cut yourself) a piece of thin wood would work, any random straight thin piece of metal, spare piece of matte board. If you go slowly and make multiple passes any of these things can be used in a pinch.... or like Josh suggested empty paper/film boxes work great (the commercial lab near me will give away extras) or if there's a cigar shop in your town, often they'll give away boxes if you ask nicely and explain what you're doing..... good luck!

12-18-2005, 08:35 PM
I have yet to build a foam core camera, but I'm starting to think I should. Making such a camera light tight would be greatly simplified by having nice, clean, straight edges on the cuts, but cutting with a utility knife doesn't seem to reliably produce such cuts; instead, I get cuts that waver, non-square angles, and other conditions that seem likely to produce wonky construction and hence light leaks.

I've never done that for cameras, but for normal household stuff the most simple way is to take a sharp knife and heat iy on a gas fire (if you have one)
In the shops it's just done with a wire under tension that also gets hot

12-19-2005, 02:18 AM
IM, I personally use single-edged razor blades, but any kind of razor knife will work, provided you're able to replace the blades when they start to get dull. I think the single edged blades are less expensive than X-Acto brand blades.

You can find strips of aluminum or steel in the hardware stores that are straight enough to use as cutting guides, yet cost < $10. I like to clamp the metal guide down on either end, with foam core underneath, and a protective surface like masonite under that. Then you can get a smooth, straight cut, and make accurate, multiple passes. With 1/4" thick foamcore, you don't want to cut it through in one pass with a razor knife, as the inner foam will flake off. Do even, multiple passes, keeping the blade firmly against the metal guide.

Wood glue works well for joining the panels together, but you'll want to seal the joints with an opaque substance. Black caulk is probably the cheapest, provided you already have a caulking gun. Or, use a regular wood glue fillet in the corners, then after its dry, brush paint it opaque with black hobby paint.

You'll probably want to waterproof the outside of the camera when you're done. You never know where you're gonna want to take a picture, and you don't want the paper to warp. You could use clear polyurethane varnish, or get really fancy and use wood-patterned, adhesive contact paper and give the camera a faux-wood grained appearance.

c.a. church
12-19-2005, 12:15 PM
After learning I simply couldn't cut a straight line with all of the clamps and rules in the world (I always cut into, or away from the rule, blegh) - I just got a mat cutter, which also works well for cutting mats, heh. Mine has a special setting on the straight-cutting blade for cutting foam-core board, and it cuts it cleanly and quickly in one movement.

12-19-2005, 02:42 PM
I use both a mat cutter and a rabbet cutter. Both work beautifully, but the key is still to keep a sharp blade. I haven't seen the rabbet cutter in stores for about 15 years, but did a search online just now and found it available at Dick Blick. http://www.dickblick.com/zz149/09/ Worth every little penny (10 bucks!) --I highly recommend it!

12-19-2005, 05:51 PM
http://www.dickblick.com/zz149/09/ Worth every little penny (10 bucks!) --I highly recommend it!

Oh, that's NICE. With one of those, every joint can be automatically light tight due to the geometry of the rabbet. Matt cutters, though, are a little pricey for my blood (I can buy and cut a lot of masonite or plywood for the price of a matt cutter). I'll take a look at the hardware store next time I'm over that way and see if they have some extruded aluminum or similar that I can use as a guide. Alternately, I should probably check if Harbor Freight has any steel rules at "Made in China" prices...

Tom Persinger
12-19-2005, 09:23 PM
speaking of masonite, you can use an old piece of floor tile as a straight edge too!

12-20-2005, 04:04 PM
Tom, straigth edges up to 12 inches long aren't a problem -- I have a couple nice combination squares with 12 inch steel rules included. It's cutting a strip the full length of a 42 inch board that's an issue; that requires a 4 foot rule, near enough, and those are just not cheap.