Hot Knife

[BuffaloEngineer]

I heard about/googled something called a "hot knife" for working on ABS project boxes. Has anyone used these, or have any recommendations on one to buy? I'm mostly interested in using them on the ABS and HDPE project boxes they sell. Thanks!

 

[jpanhalt]

Use a soldering gun -- the type that looks like a real gun and has a trigger for on/off. You can get plastic cutting tips for them, or make your own with flattened , large gauge wire.

John

 

[alec_t]

A wooden bow frame with ~ 24 gauge resistance wire as the bow 'string' also works.

 

[dr pepper]

You can get portable gas powered solder irons with a hot knife tip.
I find them very smokey and messy.
If you use one use it outside, some plastics produce hf gases when melted which are really nasty.

 

[ronv]

I've used the resistance wire (nicrome). Works good, but smelly.

 

[Vizier87]

Usually I send them down to the CADCAM department so they can use their laser cutters. Man the smell gets to you real fast. Noxious. I gave up that and proceeded to just using cutter blades to make the ridges, then snap them in the direction I wanted.

 

[misterT]

I know that you can "weld" plastic using ultrasound, but has anyone used it to cut plastic? Is it any good? I found this video: https://www.youtube.com/watch?v=QvJJDwOocsU
Better video: https://www.youtube.com/watch?v=BcA2qQvGoF8

 

[Vizier87]

I know that you can "weld" plastic using ultrasound, but has anyone used it to cut plastic? Is it any good? I found this video: https://www.youtube.com/watch?v=QvJJDwOocsU
Better video: https://www.youtube.com/watch?v=BcA2qQvGoF8

Interesting... but it still uses heat to cut, doesn't it? If so, how is it better than using a soldering iron with a specific cutting tip? I'm also thinking of buying one actually. I've been cutting plastic my whole life using cutter blades.

Vizier87

 

[Mr RB]

Handheld nibbler can go through that stuff like butter, no small or fumes and leaves a nice clean edge.

I also use a drill to make some holes and a Dremel with a rotary file type bit to shape the hole to be square etc, also cuts it like butter but makes some melt and needs a bit of cleanup.

Even a thin hot knife is going to displace plastic out of the cut and leave hard edge swarf etc that needs to be cleaned up.

 

[Vizier87]

Handheld nibbler can go through that stuff like butter, no small or fumes and leaves a nice clean edge.

I also use a drill to make some holes and a Dremel with a rotary file type bit to shape the hole to be square etc, also cuts it like butter but makes some melt and needs a bit of cleanup.

Even a thin hot knife is going to displace plastic out of the cut and leave hard edge swarf etc that needs to be cleaned up.

I looked it up on youtube... https://www.youtube.com/watch?v=uNAz63vHYDg
Does it come with smaller widths?

 

[MrAl]

Hi,

Ultrasonics are used to 'weld' plastic but that's because the plastic vibrates and rubs on the joining piece and that creates heat which then melts the plastic in only the area that is touching.

Another way to cut plastic is with a Dremel. There are various cutting bits and disks you can buy, but you can make a much better one yourself quite easily. Take one of the 'saw blades' they sell for the Dremel and grind all the teeth off of it with a grinding wheel. These are the very thin metal saw blades that are used at the end of a mandrel (screwed on the end). The teeth are no good to keep on there as they keep grabbing the work. So without the teeth you essentially have a disk that rotates, rotates at high speed and when it touches the plastic it melts it, but melts only a tiny width of material, so even long cuts dont smell. The amount of material that is removed in order to make the cut is very very small too, almost negligible, less than 1/32 of an inch. The edges need cleaning up a little after the cut but it's not difficult only taking a minute or less.
I suppose you can make one out of a steel washer too, but that would be thicker than the Dremel saw blades they sell for the mandrel. They are extremely thin and make a nice cut when they have no teeth. The teeth might be ok for wood but not for plastic, and even in wood they keep grabbing the material and the Dremel tries to jerk out of your hand. Note that these are not the saw blades they sell for their special saw blade attachement whcih are bigger and bulky and quite thick (maybe 1/16 inch or thicker). The thin ones (with no teeth) that screw onto the end of a mandrel work best.

I've cut quite a bit of plastic with this kind of home made (partly home made anyway) saw blade. Plexiglass, ABS, etc., and i've done some long cuts this way too with a curvy cut pattern so curved cuts work too. Max thickness maybe 1/4 inch or less. 1/8 inch thick plastic goes fast, the thicker takes longer. If it is too thick then it requires cutting on both sides but that's not too easy to do.

 

[Mr RB]

I looked it up on youtube... https://www.youtube.com/watch?v=uNAz63vHYDg
Does it come with smaller widths?

Sorry my Flash is unflashed and i can't see youtubes. If you are talking about the handheld nibbler, I recommend you get one as they can also be used on aluminium front panels and are ideal for shaping PCBs too.

Mine are older style nibblers from the 70's, but google found a typical example for $14 from ToolKing.com;

**broken link removed**

I can't say for that new model, but my nibblers will just take PCB thickness so the max thickness is about 1.7mm, and the cut width is 3 vero tracks or 0.3". Also you need a hole about 10mm (3/8") to get the nibbler head through, if you want to nibble on the inside of a hole.