grit edged rod saw

[darryl]

I'm cutting some rigid polyurethane foam about 10 inches wide- taking out a half circle shape with about a 3 inch diameter. The waste piece is 10 inches long- if you put two waste pieces together, they would form a solid rod 10 inches long and 3 inches diameter. The end result is an 8 ft long rigid foam piece that's 10 inches wide, 2-1/2 inches thick, with dozens of half-circular shapes cut out of it. So far I'm in the experimental stage, and I find that a grit-edged rod saw does a beautiful job on this stuff.

Only problem is that I can only find these blades in 12 inch length, designed for hacksaws. That leaves a pretty short stroke for cutting through 10 inch wide material. Anybody know where I can get these in longer lengths?

I plan to motorize this, so it will be guided- and it leaves a nicely sanded surface behind, so no further prep is required. That's a bonus I guess, but will save a lot of time. Hot wire is not an option for this material, as it has too many drawbacks. Hot wire is great for styrofoam, but not for polyurethane rigid foam.

My present method involves a hole saw on a guide rod, so it can go the length, but only two inches at a time, and I have to break out the cut piece five times to go the full 10 inch length of the cut. That isn't going to fly with this project- it was ok to make the prototypes, but not for production. And it leaves a surface that needs further smoothing, which I can avoid using the rod saw.

So- what I need is a rod coated with carbide, and perhaps 20 odd inches long- a 16 inch length would do I think. Even a 14 inch length would work, but it's better if the stroke can be long enough to clear the swarf out of the cut.

My other option is to figure out a laser cutter or a water jet- both probably out of my budget.

[J Tiers]

If motorized, you could have something like a powered jig saw. Because it cuts with relatively fine grit, the minimum stroke length is not set by the size of teeth. A 12" saw can then be moved plus and minus almost an inch in 10" material. For grit, that's pretty good, a lot of edges past any particular spot, and better if you move it back and forth rapidly, like a jig saw. I don't think you need anything like 20 inches.

There is not much bulk of removed material, since you are cutting foam. The swarf should not obstruct the cut. And, grit saws cut in any direction, so cutting would not require turning the foam piece to align it, just move it in the shape of the cut.

[Noitoen]

You can adapt the hole saw with a piece of tubing to make it long. 2 slits on each side can aid the removal of the core.

or you can get this: https://a.co/d/4Ot29nn

[darryl]

Well that becomes the start of a project to use these blades I've got. I think I'm gonna look at some cordless recips, maybe one of those would lend well to this adaptation. Or a pair, push-pull. Ha ha, that's kind of funny- trying to synchronize a pair of cordless recip saws with a common blade mounted between them. If it was perfect, it would be pretty cool. You could use any hacksaw blade, or rod.

Anyway, now I'm off on a tangent. Back to reality- tomorrow I'm on the hunt for a cordless hacksaw. Or the makings of one.

[Glug]

A few years back I was occasionally doing intricate cutting of foam poster board. I'd mostly use an x-acto blade. As I toiled, I thought about how slick it would be to have a simple band saw with a cutting wire that would allow me to cut in any direction. I assume those wires can be obtained without an obvious splice, in a loop. My application wouldn't need much power or even an abrasive - just a toothed wire. I didn't quite do it often enough to bother.

In hindsight, I might have used my drill press as a temporary frame, possibly on a "C" of plywood. Could probably use cheap bearings as wheels, doing something to form pulleys.

[Fasttrack]

Can you share any information about the application? I don't have much to offer as far as advice, but I'm very curious! We do a lot of complex foam geometries at work but we use EPP and generally have a company out in California cut it for us. They build, among other things, movie props and sets and are used to cutting complex geometries (think castles from foam, etc.)

[boslab]

Somthing like

https://www.sawsuk.com/blades/carbide-grit-bandsaw-blades/?gclid=CjwKCAiA3pugBhAwEiwAWFzwdZyg0b4NKet7tgLgJFVSRd0xr_VqNtIYQFvBv__ArZ2vaKIPDQJSTxoCwCUQAvD_BwE

mark

[reggie_obe]

Would a hot-wire saw work better? Longer, "infinite" length?

[gellfex]

I think one direction is making a taut saw frame for 'wire saw' material, and then have it in a jig that follows your radius and reciprocates it. Not easy but seems doable. Another is just make a belt driven 3" diameter by 12" long course sanding drum on an arm that lowers on the foam. Real messy!

https://www.amazon.com/NduR-ProForce-Commando-Wire-Saw/dp/B00ATCG3P0

[BCRider]

What about a wire bandsaw blade? I seemed to recall wire blades from years back and a quick search confirmed it.

Wire Cutting Blades | Precision Blades

This was one of the first hits on my search. And the blurb lists "expanded polyurethane foam" as one of the typical materials.
The neat thing about a bandsaw option is that it'll easily clear the dust out of the cut. The downside is that it'll need to be a pretty big machine or modified to gain the lift needed to clear your 10" height of the blocks.

[darryl]

Looks like I'm leaning towards a wire blade. I did not have a good experience today looking for anything powered that I could make use of. The last store I went into, the guy gave me about one minute, then simply said 'they don't make it' and walked away. As I think about this project, I realize that anything I come up with is going to take as long to make the cut as I can by hand- with an appropriate bow. So that's where I'm heading- a bow saw with a wire blade and a smooth portion over the blade in two spots so it can ride a template on both sides. Something I can put together quickly and get this project going.

I see that the biggest problem I would have with any blade is turning it to follow the cut line. With a wire blade things become much easier. I can't divulge what this project is, not now at least. But when it is ready for market I'll talk more about it.

[plunger]

That should also work pretty well if you are a plumber trying to cut pvc pipes that need repairing in chases and hard to get spots.

[no704]

I made a rig to cut bumper covers for rear access handicap vans using those survival saws. Couple of spring’s and Dc motors with eccentric cams.

[Baz]

Until about ten years ago there was an equivalent product called an Abrafile for coping saws that was intended for bathroom tile cutting but popular with modellers for cutting between drilled holes for cutting thick metal (before everyone had a bandsaw). Suddenly they stopped being available. The reason being that they were all made by one bloke in his garden shed and he decided to retire. So they must be easy to make.
I think a possible method is to run hot wire through a solder bath and while still hot in a furnace sprinkle crushed carbide over it.

[Joel]

How about taking off the hacksaw ends of the 12" blade, take a piece of rod about the diameter of the grit, drill the end for a slip fit and braze it on?
Maybe drill a small cross hole to feed in the braze at the bottom of the hole. I know the wall would be thin, but perhaps the rod could actually be a bit larger than the grit diameter (chamfer the end) without being a problem in foam. You could use the longer stroke you mentioned to clear the swarf. Tensioning one end with a spring like some scroll saws, might work OK (and would simplify things), maybe?