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Nov 03, 2005, 11:31 AM
Registered User

Foam cutting wire

I need to order some cutting wire for my gravity feed type of foam cutter. In the past i have used stainless steel leadout wire sold for deep sea fishing in diameters between .014" and .018". I have looked at the McMaster-Carr catalog and have some questions about what type of wire to buy.

I have heard that inconel wire is good for foam cutting but I can't see why. Page 3458 of the catalog lists the tensile strength at 80,00-105,000psi for inconel wire. My .018" diameter stainless steel leadout wire is rated at 80lb which computes to 314,000psi. So why would inconel wire be better?

The stainless steel wire from McMaster-Carr is almost all "soft temper". I wonder if that is the correct temper or would that have too much tendency to get kinks. My stainless steel leadout wire is very stiff and a bit hard to tie to the bow but it certainly has no tendency to get kinks. Anybody have any advice on the exact type and temper of stainless steel wire for a cutting bow?
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Nov 03, 2005, 12:52 PM
Registered User

Check out - just type in the material you are interested in
and it will bring up bunch of properties and links to manufacturers.

I think people have used inconel since it has a higher electrical resistance and
has good performance and resistance to corosion at higher temperatures.
I don't think the temperatures we use to cut foam warrent the use of the inconel.
I think the high strength fishing leader you have been using is fine.

I took a quick look at McMaster and it doesn't look like they sell what you are looking for. I think what you want is something more like this:
Unfortunately they do not say what alloy they use, but perhaps with some more
searching, you may be able to find it.

Nov 03, 2005, 01:52 PM
Registered User
Thanks, Tom. that Malin brand wire is exactly what I have been using. Somebody picked it up for me from a store on the Eastern shore where they sell deep sea fishing supplies. My supply just ran out and I hoped to find an internet source. I searched all sorts of fishing supply places including the Malin web site and couldn't find that stuff. I just took one more shot at it and finally found a retail supplier for exactly what I have been using. It's the Malin Stealth wire.

By the way, I'd still like to hear opinions about the best type and diameter of wire for a hot wire bow.
Last edited by Phil Barnes; Nov 28, 2008 at 08:49 PM.
Nov 03, 2005, 02:20 PM
Flying IS the hobby
Inconel has higher temperature strength, which is required by CNCs since they cut by radiance, in order to maintain a desirable speed and still cut by radiance the wire requires a significant amount of heat, if you where to use the same heat on steel wire, it would turn bright red, bend in a “S” shape and snap.

You could probably block and skin foam almost twice as fast using Inconel, with out changing anything but the temperature dial in your heat source. I would anticipate a gravity cutter could also benefit from the increase in speed, for the average hobbies speed isn’t that much, but not for a manufacturer.

Regardless of the PSI, the alloy found in Inconel, Nickel/Chromium/Molybdenum, gives you the speed and small kerfs, if you can benefit from any of those two, it might be worth experimenting with.

Nov 03, 2005, 02:30 PM
Flying IS the hobby
BTW the diameter of Inconel I am talking about is .012" - and the steel I have used is .018"
Nov 03, 2005, 02:35 PM
Registered User

I did notice the higher temperature allowance for the inconel, something like 700 degrees for inconel vs. 350 degrees farenheit for the S.S. I wonder if you would get smaller kerfs with higher temperature in the inconel or would you get smaller kerfs with smaller diameter wire? The Stainless steel comes in smaller diameters. The smallest inconel is only .020", at least at Mcmaster-Carr.

I think I may try some inconel just for the speed. Maybe get some fine stainless steel for cutting really small cores.

Nov 03, 2005, 03:25 PM
Registered User

The inconel would be interesting to experiment with, but I'm not sure it is worth it
for you since you have a system that works.

I can see why it would be good for the CNC cutters using radiant heat to cut the foam. For the gravity fed machine, there is a balance between strength and temperature. Since the foam is cut through conductive heat transfer, there is a force on the wire other than gravity (the force from the foam). So good bow tension is important. I suspect that the strength of the stainless is better than the inconel at the temperatures used by the gravity cut system. I don't know this for sure, but based on the data available on Matweb for various stainless alloys (lower strength than the Malin fishing leaders), I'm pretty confident the tensile properties of the Malin fishing leader will be better than the inconel at 200 C.

I'm not sure how much effect the diameter has on the important part of the kerf (below the template). As long as the wire temperature and speed is set so the cutting is done by conduction and not radiant heating, I don't think the kerf below the template will change with wire size. I have not done any tests, but I don't see why this would not be the case. Setting up this condition may not be easy if you are trying to cut fast. I don't do production work, so I usually set the wire on the cool side and cut reasonably slow. So I would recommend getting the .018" wire and stay the course. . .

Nov 03, 2005, 04:59 PM
Dave Register
okiesoar's Avatar

Inconel/Leader Wire Source

Used Inconel for a number of years before switching to SS leader wire. By comparison, inconel was softer and did not seem take tension as well - tended to sag as compared to SS. Seemed to take a 'set' after a number of cuts and had to be re-tensioned. After several of those it would break under load.

A readily available source for SS leader wire is Cabelas. Salt water tackle is only available in coastal states so Cabelas has been a very useful web-source for most common diameters of SS wire (including push rod wire) in relatively small quantities (few hundred feet).

Go to the Cabelas site (below), In the sidebar: Fishing (Saltwater), In the main list: Line/leaders, then Cabela's single strand wire. Other SS leaders are either stranded or coated.

Alloy is not listed but test values are given for all diameters. Sold in 1/4 lb rolls for ~ $6.
1/4 lb roll of 0.016" is 362ft. 1/4lb roll of 0.020" is 232ft.
Nov 03, 2005, 05:05 PM
Flying IS the hobby
I think the properties of Inconel allow you to run very small diameter wire, thus achieving a smaller Kerf, while still maintaining a reasonable working speed where in order to keep that speed the power would have to be increase, making other wires of the same diameter fail under the same circumstances

I would be interested in finding out what kind of results you would get in a gravity system by using the smaller diameter SS vs. Inconel, especially with small wing cords.

There is a source for .012” Inconel:

Recently, I got lucky and found some 0.0078” Inconel, it was special ordered and a bunch of guys went in on the deal, with this diameter very tight tolerance can be achieved, especially the smaller cords with out burning or curling tips, but it requires a lot more power to heat up the wire where the cutting machine still runs at a decent pace

With the smaller diameter you can run faster, and melting less foam than if you where running a wire with a larger diameter, as long as the wire can withstand the heat.
Nov 03, 2005, 05:20 PM
Flying IS the hobby
I have only run Inconel on my CNC and blocking foam by gravity, I am not sure what kind of results you would get on a gravity system specially under the added tension from the foam.

I did a small tests, so I cut some .012” SS and .012” Inconel put them under a small amount of tension, and set my standard head source about ½ power, I took the temperature of both wires with a cheep heat sensor. (But as long as both wires are measure with the same cheap sensor all I am looking for is the difference.) and this is what I got.

.012” SS 180*F +/- 5*F
.012” Inconel 150*F +/- 5*F
Nov 03, 2005, 05:34 PM
Registered User
Thanks, Okiesoar.

I actually orderred some wire from cabellas but I got the trolling wire. This turns out to be soft temper stuff and I haven't tried it yet. Your link has directed me to the leader wire which is likely spring temper or some harder temper wire. I have already ordered some different sizes of the Malin brand leader wire just like I had before so I probably won't need to get any from Cabellas.


Perhaps the inconel is good for small cores. I have definitely seen trouble in the past with really small cores especially if they are highly tapered when I would try to cut them with .018 stainless. I may try some of that .012" inconel.....perhaps the .0078" would be better still???
Nov 03, 2005, 06:07 PM
Registered User

I can see where the high taper would be a problem. On the small chord side you will be getting the combination conduction/radiant cutting effect, so the kerf will be bigger than on the conduction only larger chord side. For these cases, the smaller diameter wire will be better. The view factor for the smaller wire will be lower and less radiant heat will be transferred. It might be interesting to know what the emissivity difference is between inconel and SS. I think you'll find that the smaller diameter SS still works better than the small diameter inconel for a gravity type system. It doesn't hurt to try though. . .

Nov 03, 2005, 07:41 PM
Registered User
Hi Phil

I use the trolling wire also for my gravity feed. Same manufacturer American, in the 25# .015 size and 15# .011 size. the .015 has 1.8 ohms /foot and the .011 has ~ 2.3 ohms /foot. I find it does bow a little bit compared to my earlier wire but only need to pause or slow down for a moment on hard edges for it to catch up. My power is a dimmer + 24V 2A transformer which is rarely turned up past 60%. This is for a 54 inch bow which has tension supplied by a turnbuckle and a heavy spring. The spring keeps the tension more consistant when the wire expands from heat.

Well have to go setup for a hobby show.

Last edited by The Tellurian; Nov 04, 2005 at 04:13 PM.
Nov 04, 2005, 10:01 AM
Registered User

Rene cutting wire

I've been using and selling a type of wire used by the foam industry on their cutting machines for years. The trade name is Rene and it is used in the medical industry but is also used for cutting foam. It can handle a lot of heat, to the point of being red hot and still maintain consistent tension. It is also very tough and does not break easily.

Their are two issues with this wire. One it is expensive. We sell it for $.50 a foot in minimums of 50 feet.

Two, this wire does not like sharp bends. It breaks easily when folded but since we don't subject cutting wire to bends like these it normally isn't an issue. Oh yes, a third one that comes to mind. It is springy like a Slinky so you have to carefully unspool it.

I've used this product for nearly twenty years and have tried many others just for comparison. I stock it in .014. It can be found on my web site:

I sell a lot of this stuff and have never had it returned by a disatisfied user.
Nov 04, 2005, 11:45 AM
Registered User

How does the Rene wire attach to the bow? Can it be wrapped around a 1/4" diameter rod and the twisted around itself a few times as is done with the Feather Cut bow? Or is it too stiff for that?

I guess I'll find out first hand anyway, I just sent you an order for a spool of Rene wire.

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