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Nov 03, 2018, 10:59 PM
Registered User
Question

Steel wire (0.55 mm) for foam cutter


Hi
I am looking into making a handheld foam cutter. I have seen on YouTube many are using nichrome wire, guitar wire and even stainless steel.
Would this steel wire work for a foam cutter?
Thanks

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Nov 04, 2018, 01:38 AM
Registered User
SSteel lock wire even works decently.. I've used it... No reason that shouldn't... try and see??
I found 0.008" SSteel Braided 1/2A Control line flying wire Brodaks'
/Sig, or a CL combat contest for free, as best choice over all else .
Thin , Minimal heat stretch, cuts v cleanly and doesn't need much amperage also seemingly lives forever
Nov 04, 2018, 06:36 AM
gpw
gpw
“There’s no place like Foam”
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We’ve had great Luck with SS solid Fishing leader wire ...
Latest blog entry: Lost plans
Nov 04, 2018, 07:41 AM
Registered User
no reason why ot won't. it may take longer to heat up to good cutting temp, because of it's size, but really any wire will work. stainless and guitar string is used because of the higher nickle content, which handles the heat/cool down cycles better than plain steel wire.
Nov 04, 2018, 01:20 PM
Registered User
Ok - I was planning on using 7.2v NIMH battery to test it out first. Would this work?


I have a 3s lipo but afraid of shorting it out completely and ruining the battery. I also have 250watt computer power supply but not sure how to hook that up yet.
Nov 04, 2018, 08:21 PM
Foamy and Glider fanatic
Blacky's Boy's Avatar
Quote:
Originally Posted by dropout
Ok - I was planning on using 7.2v NIMH battery to test it out first. Would this work?


I have a 3s lipo but afraid of shorting it out completely and ruining the battery. I also have 250watt computer power supply but not sure how to hook that up yet.
It's SUPER easy. Check out my thread here

RCGroups member psychedvike has a YouTube channel called "Eyeball Aeronautics" where he walks you through the entire process. It took me next to no time to make it. It took longer for me to "pretty it up" by mounting it on a piece of plywood than it to to make it.
Nov 07, 2018, 12:04 PM
Registered User
psychedvike's Avatar
Quote:
Originally Posted by Blacky's Boy
It's SUPER easy. Check out my thread here

RCGroups member psychedvike has a YouTube channel called "Eyeball Aeronautics" where he walks you through the entire process. It took me next to no time to make it. It took longer for me to "pretty it up" by mounting it on a piece of plywood than it to to make it.
Thank B B for remembering me. It is pretty easy to put together a power supply that way. I checked out your post on your power supply. You did a nice job.
here is a link to the video that B B mentioned.
PowerSupplyPart2 (13 min 3 sec)


Quote:
Originally Posted by dropout
Hi
I am looking into making a handheld foam cutter. I have seen on YouTube many are using nichrome wire, guitar wire and even stainless steel.
Would this steel wire work for a foam cutter?
Thanks

Attachment 11317989
Hi dropout, the wire you have will work just fine. That is about the same diameter I use on my bows. I use mig welding wire. If you are also looking for an easy way to make a hot wire bow here is a link to a video I made on make one.
Easy to make hot wire bow with a DIY drill jig (13 min 40 sec)

Hope it helps.
Nov 08, 2018, 09:04 PM
Registered User
Thanks all for the pointers. It's very helpful getting started.

I have my mind set of using the following 2 types of foam from Home Depot
1) Cellofoam - 3/4 in. x 14-1/2 in. x 48 in. R-3 Polystyrene Insulating Sheathing
2) FOAMULAR 150 1 in. x 4 ft. x 8 ft.

First question... is it safe to use the foam cutter on either type of foam? I would be cutting in the garage with the doors opened but I'm concerned about gases released.
Secondly which foam would you suggest for cutting sail plane type airfoils?

Thanks!
Nov 09, 2018, 04:47 AM
Danish? Don't U eat that??
DKChris's Avatar
Ordinary steel has a fairly low resistance, compared materials like nichrome, inconel, kanthal and such, which means your wire need higher current to cut properly.
Now, I don't know the exact material properties of the wire you got, but if we make a guess the resistance is somewhere like piano wire, you should probably need somewhere in the range of 8-10 amps to cut. For a yard of wire, this corrosponds to a voltage drop across the wire piece of about 5-6 volts. So there could be 2 fairly easy ways to go with the power sources you have:

1) go with the 7.2V battery and try with about 1 yard of wire, adjusting the current through the wire with an old +20A brush motor ESC. Alternatively you can try with maybe 3 yards of wire (starting with an extra long piece just to be on the safe side; note that you don't have to cut the piece off the roll just yet.) connecting the battery directly to it, and gradually shortening the piece under power until it will just barely cut your foam. Then the remaining length is your "standard length"; If I'm not completely off you should end with something like 1˝ yards, maybe a little more or less, depending on the wire resistance and the power capability of the battery. You can then make shorter bows(should be at least 25-30% shorter), and by inserting the remaining bit of the standard length in series with the bow and connecting to it with an alligator clip, you have the possibility to adjust the current by moving the alligator clip forth and back. Nice and simple.

or

2) Make your PC supply go, and do basically the same as above, using the 12V output (do check that it is capable of sourcing at least 15-20A). If you go with the gator-clip adjustment method, I would just suggest starting with something like 4-5 yards of wire. Here, I'd guess the "standard length" to be around 2-2˝ yards or so, but the experiment will give you the exact right length automatically, so don't take my guess too seriously.

In both cases, if the remainder of the "standard length" ends up being more than a foot or so, you can make your adjustment wire piece easier to handle by winding it in a not too tight spiral on a squared off piece of wood and adding something at the ends to keep the hot wire off the table. If its not, just suspend it between 2 nails on a board.

In both cases, strongly consider adding a 20A fuse in series, just to avoid starting a fire. The PC power supply has some built in over current protection, so if it is a 15-20A output you probably won't need that. If it's a big supply capable of far more, i'd still consider the fuse. And take care that your loose wire lenght aren't flying around and can't start a fire when doing the experiments.

Now, I could be a bit off with regard to the resistance of your wire, but with the above approach you should still have a fair chance of getting the setup to work, as there is a limit to how off my guess can be, if that wire really is standard steel.
Last edited by DKChris; Nov 09, 2018 at 10:13 AM.
Nov 09, 2018, 09:29 AM
low tech high tech
vtdiy's Avatar
Looks reasonable with the Nimhs @ 7V. You'll probably either need about 4' of wire, or a means to vary for shorter -- either the brushed ESC and servo tester route, or get yourself a LED dimmer.

Both foams you list are styrofoam, so they are the usual types.

Avoid polyisocyanurate and urethane foams -- those will release toxic fumes.

But also, it's not ideal to breathe styrofoam mist either -- working outside is best, if possible.
Nov 09, 2018, 09:42 PM
Registered User

Steel wire (0.55 mm) for foam cutter


Sorry about the lighting..
But here is my set up... it’s not pretty.


I tried it with a 7.2v nimh and a 3s lipo. The wire heats up very quickly on 3s and cuts real quickly.

I’ll probably move to the computer power supply set up as the cutter drains the batteries very quickly.


And here is my first pass at cutting the 3/4” cello foam. (Not pretty either)
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I realize I need to have the foam on a flat surface while cutting the foam.
Last edited by dropout; Nov 09, 2018 at 09:51 PM.
Nov 09, 2018, 10:24 PM
low tech high tech
vtdiy's Avatar
Congrats!

Tips:
Too hot a wire can cause the problems you have. The hotter the wire, the faster and more consistent your cutting speed needs to be.

CNC wire cutters cut most accurately when running quite slowly, and cutting by radiation, rather than contact with the foam.

In manual cutting, template smoothness is important also to avoid the kinds of uneveness you are getting. Tension should be fairly high, especially with the thick wire you are using -- the wire looks quite slack and uneven in the photo.

Your bow isn't acting like a bow, unless you have a spring somewhere not in view in the photo. Instead of those solid arms, replace them with some heavy music wire, flexed in to add tension to the bow. The hot wire changes length when heated up and a springy bow setup is necessary to maintain tension.

If you use a computer supply, take care not to touch the live parts of the bow -- though nominally 12 volts, a circuit problem could put 120V on the working parts. They aren't isolated. If you use tho old style transformer and rectifier type 12V auto battery charger (not the newer digital "smart" type) for a power supply, it's safer because it has an isolation transformer. It can also use a router speed controller or AC dimmer on the power cord. Computer supplies can NOT do this, since they are regulated output. A DC LED dimmer on their output will work however.

I'd get an LED (DC) dimmer if you are going to a 12V computer supply -- otherwise, personally, I think that's going to be too much heat for the wire thickness (and probable length) you are using. It will cut fast, but be relatively inaccurate and rougher.

Sometimes working without a helper on small panels it's easier to get consistent results (I find) if you clamp the bow vertically, and lay the foam blank down onto it about mid chord, and pull the foam piece towards you with light even pressure, rather than trying to move the bow over the blank.

That does take 4 cuts to complete, but they may be easier for you to do well. The weight of the panel is enough to keep the templates tight to the wire without excess pressure, which can happen when trying to move a bow over the foam by yourself.

When cutting a tapered wing panel, use a pivot wire instead of a bow. Look up pivot wire here if you don't know what that is.

You'll work it all out, but there is a learning curve.
Last edited by vtdiy; Nov 09, 2018 at 10:59 PM.
Nov 10, 2018, 11:55 AM
Registered User

Steel wire (0.55 mm) for foam cutter


Thank you so much for the tips. They’re very helpful and informative.

Here is my second attempt with a much more simpler setup. I basically used a couple of hooks on the work bench edge and wrapped the wire around the hook snug fit. I was able to add tension on the wire by turning the hook.

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This set up come apart much easier too. I would be able to accommodate a foam piece 48” wide with the work bench underneath to support the foam.

So here is how a small piece came out. Much better than last time but still room for improvement.

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I used the 7.2 volt nimh which started out with slightly more than 8 volts.
12 volts was way too much... the wire gets to hot and snaps when I try to add tension.

I think 8 to 8.5 volts would be perfect for a set up like this. This range gives the right amount of heat without melting the foam and cut at a slow pace. I’m going to look into a cheap variac or brushed esc /servo tester. That should make it much easier to find a suitable operating point.

Yeah there is quite a learning curve. I want to get this set up going better before moving on to a pivot cutter.
Last edited by dropout; Nov 10, 2018 at 12:06 PM.
Nov 10, 2018, 12:14 PM
Registered User
Instead of using hooks are there threaded bolts with a hole in the shaft that I can use to thread the wire through and add tension by turning bolt?
I’m thinking that I would need a t-nut secured on the surface first.
Nov 10, 2018, 12:26 PM
low tech high tech
vtdiy's Avatar
Variac's are not line isolated, can put out 130V if accidentally set wrong and are very expensive. One little kid twiddling a knob and anyone touching your bow wire can have a big problem. Even a computer supply with 12V output is safer, though also not isolated.

Iif you're going to get a variable supply over 7 volts, why not just use a transformer type simple automobile charger, and connect it to a router speed controller. Everything is wired to plug together, cost is reasonable, and you can also charge your car battery, and control your router or other brushed AC motor with them separately. It is isolated by the internal transformer. Some current Ebay examples:

https://www.ebay.com/itm/For-Router-...QLN:rk:11:pf:0

https://www.ebay.com/itm/Ultra-Perfo...UAAOSwn1FbpFnq


NOTE: do not buy an "automatic" or "smart" or "digital" battery charger for use with a router speed controller.

You want the old fashioned "manual" type charger -- they always have a real analog meter on the front and switch(es) to change voltage from 12V to 6V and for full or partial amperage.

Ideally you have one already, or can find one at a tag sale. They were made by the millions before smart chargers took over a few years ago, unfortunately.


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