Make a Hot Knife Using a Soldering Iron





Introduction: Make a Hot Knife Using a Soldering Iron

About: ––––––––––––––––––––––– "Energy cannot be created nor destroy...

Are you having trouble cutting plastics with an ordinary x-acto knife? Then here is a simple tool mod you can do, turn an old soldering iron and a x-acto blade into a Hot Knife!

This hot knife idea isn't really mine, I found this idea made by somebody from MAKE:, I can't remember who made it. And so I decide to make one for my self to make my life of cutting hard plastic easier.

Disclaimer: This is a fairly dangerous work tool, it can burn and/or cut you if you misuse it. And I am not responsible what ever happens to you with this tool mod.

Step 1: What You Will Need...

You will need:
  • Any soldering iron will do - the higher the wattage, the better
  • A nasty old soldering iron bit you don't want to use.
  • A spare x-acto blade

Because I don't have a welder which is most recommended for this mod, I will have to use a different technique to attach the blade to the soldering iron bit...

My idea is to cut a groove into the soldering iron bit with my dremel with a cutting head. Then put the blade into the groove and squeeze the soldering iron bit onto the blade using the vice.

Step 2: Cut Out a Groove

Cut out a groove onto the bit!
You will need something to hold the bit tightly while you cut out a groove with the dremel. I used my vice to hold the bit. I wrapped the thread part of the bit in cloth to prevent damage to it.

Step 3: Squeeze It!

After you cut out a groove, make sure the blade can fit okay into the groove. Cut a bit more if necessarily. Then squeeze the bit onto the blade tightly with the vice, but be careful not to squeeze it too much otherwise the bit or the blade might break.

Before you squeeze the bit onto the blade, it is a good idea to add a little bit of glue to hold the blade at the right angle,

Step 4: And You're Done!

Thats it!

I tried to cut some plastics with my hot knife, but it did not work out quite well, my soldering iron wattage is too low (15 watt)... Or it might be the cold weather. :-)

Be careful not to burn and cut your self with it!



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I'm not sure if 15W is enough. My Xacto 30W soldering iron came with a hotknife, and it cuts fairly well, although the blade loses heat quickly.

I wonder if you could add a hotknife to one of those huge 130W soldering guns...

This is a great idea! Have been looking for a more efficient way of trimming plastic parts. This idea will adapt nicely to my requirements. Thanks!

At least if you cut yourself with it, it'll cauterize itself.

1 reply

Yeah, a built-in "Safety device."

The flat blade might be causing to much heat loss (due to a larger surface area).

I am also worried about how much downward pressure you can put on this when cutting.

But great idea. Thanks for the insperation.

1 reply

pressure is reall ynot needed, just go slow and let the melt do the work.

I'll give this a try when my current soldering iron tip is rusty enough to be qualified as a "A nasty old soldering iron bit you don't want to use.".

8 replies

LOL! I am not trying to say use a soldering bit that you don't use that much anymore because you are going to destroy it. You can use a new one or an old one.

Yeah, I realised but for two things... *I'm the kind of guy that hates destroying things that you can still use, even if it is destroying it to make something awesome *The local electronics shop only sells Weller tips ($29.99!) and I hate buying online I'm not going to use a new one. PS: If you're wondering how I'm supposed to get a new tip when my current one is a knife then yes I will buy a new new iron ($10).

I just posted an instructable about this. about the one ive been using, for one out of the two irons i used i didnt have to modify the iron at all. I found the cheapo exacto knifes you can buy at places like ace hardware (with a plastic handle) fit where the tip was in an old iron. let me replace blades. and also if i need to solder with it pop out the tip and put in the non knife one. (the other iron i did have to tap out a little bit to get it to fit. works best on irons where there is jsut a screw on the side to hold the tip in.

If the new Iron is $10, why would anyone buy a $30 tip?

THat u pretty expensive for a tip. in maurititius a tip cost me Rs5 or $0.2 yeah the big one

i could just see someone a huge pile of old irons in ur workshop plasmana

wow i just realized that is the worst grammar ever!!
i mean to say i can just someone like plasmana having a huge pile of soldering irons laying around in ther work shop if you hook em all up a once u have a heater!

I've tried to make something like that with and old solerding iron, but this one is way easier. I can't wait to injure myself horribly with that!

4 replies

Quote from lordofthedonuts: I can't wait to injure myself horribly with that! Isn't that kinda emo?

Hi Awang8 - Please forgive me, I am not well versed in internet shorthand so, what does EMO stand for?

emo is not shorthand but is a term for people who like to be goth dress all black talk about death and most commonly cut themselves purposly