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Non-Gun DIY Projects and Customizations This section is for your DIY spearfishing projects and customization other then spearguns.

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Old 01-20-2019, 06:59 PM   #1
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hot knife?

From inflatable sport boats, to sailboats, and powerboats…speargun and dive equipment travel covers, bags and more. Customization projects seem to be needed everywhere. Sailing Dodgers, Bimini covers, sunshades and more all require fabrics such as sunbrella, dacron, nylon, webbing etc. Even with an industrial sewing machine, you need a good way to cut the materials.

This is what I want to be able to do:


These hot knives seem to sell across a wide range of price points. From $85 up to $300 across varying manufacturers. But they all run off all the same “R” shaped blade that seems to function just like the tips that go on every 100W soldering gun. And there lies the question. I purchased the “R” shaped blade off eBay for $12. Will it function like the video if I managed to fit it into a typical 100watt soldering gun.

If the soldering gun works off a transformer that utilizes the concept of electrical resistance, and if I understand this correctly, current forces the thicker materials to heat up, but the thinner materials will get substantially hotter when the electrical current passes through them. I’m not an electrical engineer so I’m posing the question to others who may have that skill set. Most of the fabric cutting knife’s advertised run at 100 Watts.

If I can fit that “R” shaped blade into a 100W-140W soldering gun, do you think it will glow hot just like in the video? And if that works, I could buy a regular soldering gun and save a lot of money. The more expensive hot knives run $2-$300, the Chinese knockoffs sell between $85-$130. Yet name brands such as “Weller” soldering guns are only $40-$50 brand-new.

Informed and educational comments and suggestions are welcome.

or just pay for the special tool?
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Old 01-20-2019, 09:19 PM   #2
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Re: hot knife?

It should work, try it, what do you have to loose?
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I have the actual cutter, it draws .6 amps at 125 volts, which is only 75 watts.
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Old 01-21-2019, 07:34 AM   #3
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Re: hot knife?

This is the brand knife I use, keep an eye on it..you might get lucky;

I have no experience with the off brands and knock offs, I'm sure some work better than others. That being said I just bought this for my knife, will see if it works as well;
https://www.ebay.com/itm/172557472695 $14.98 Free SH

You got me thinking, so I did do a little testing on my knife VS the Weller.
The Primary draws are almost identical, however My calculations show the transformer of the hot knife is a 150:1 ratio and By contrast the Weller is 268:1 ratio. ( calculated by measuring the output voltages )

So as you can see the Weller secondary is going to be putting out way more amps !
( Tho that was on the High switch, I didn't measure the Low switch)

Your right, mine should be drawing more like 100 watts instead of the 75 watts that it does, that's probably due to the bad/broken tip I have in it, thus the new tip being purchased)

Last edited by SEATUX; 01-21-2019 at 07:44 AM.
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Old 02-10-2019, 01:53 PM   #4
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Re: hot knife?

I have used a Rillfit hot knife for cutting tire treads, it was a pretty heavy duty item and they may make one for your purpose with a different shape blade in the clamps.
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