Thanks everyone for the advice.

I will be using hot knife only for cutting patterns where materials can fray or I want multiple layers welded. ie. supplex and the case I described earlier.

For everything else I will get xacto knife. Best thing is I can share the blade. And cost of blade is so much cheaper then rotary cutter blade.

I have decided to buy solder iron locally as I found some very high quality solder irons at comparable prices.





It seems that xacto "no. 1" knife" which has full metal body can be dismantled and the holder can be used in a hot knife. I am not sure this can be done with other xacto models.

Edited by huzefa on 03/25/2009 10:33:34 MDT.

The other issue I found with using exacto blades in a hot knife (other than losing heat too quickly), is that the steel seemed to lose it's temper, and the blade quickly became quite dull. I'd be curious to see if anyone else has seen this happen or if I just interpreted the events incorrectly.

I use a similar hot knife to the picture two posts up, purchased at a hardware store for ~$10. I have found that they do lose heat quickly, giving a very noticeable heat gradient from the base of the blade to the tip. The base will be hot but the tip won't even cut the thinnest fabrics. This caused me a few problems where I would be "hot" cutting part of the fabric, but occasionally it would move toward the tip, which was not hot enough and would just plain "cut" it. I noticed that areas of the fabric edge were fraying. To solve this, I just use the back (unsharpened) edge of the x-acto blade. That way it either cuts due to the heat or not at all. I guess what I'm saying is that I haven't noticed the blade getting dull, but that I've found the dull edge more practical anyway.

If you want some advice from someone who does professional sewing:

Look at the units sold by industrial sewing supply shops. They have radically different designs than the typical modified soldering iron, and for good reason. They perform well, but are often designed to cut through dozens of layers of fabrics in one movement. They offer a smooth rolling cut that will heat seal the ends at just the right temp. They of course are not in the $20 range, but it should point out the features you would be looking for. A quality hot knife costs more than a consumer sewing machine.

In reality, you're looking for an overkill solution that doesn't work the way you think it does. Heat sealed ends are not fray free in most materials after a little bit of use are are still designed to be hemmed in for most applications.

For those who are talking about heat sealing fabrics together - it doesn't work well with most of our ultralight fabrics. It melts the stuctural fibers together, yes, but it easily tears out unless you are using fabrics designed to be hot sealed. You can use the hot sealer on a vacuum sealer to experiment for yourself. Silnylon will make very promising looking forms with a hot sealer, but it rips the fabric next to the melt with around 2 lbs of pull.

When I first started hot sealing edges I found a good cheap solution though:
Use a roller cutter blade for patterns (a new blade is required for thin fabrics) for the cutting
Before handling the material much, take the material in hand and use a micro torch (often $5-15) and run it around the outside edge blowing 90 degrees from the fabric aiming about 1/4"-1/2" from the fabric as though you are aiming into the air. You'll see it begin to bead the end fibers rather quickly. You'll need practice to keep an even control but it does the job quite nicely.

Edited by slacklinejoe on 03/25/2009 12:50:21 MDT.

By accident I recently discovered that a simple snap-blade box knife works better than a roller cutter on silnylon. Surprise. Searing is rarely very useful and there is always the danger of melting lightweight fabric too far.

I think the issue of blade losing heat quickly can be addressed by using a hotter (watt++) knife. Heat loss is proportional to area of contact. When using a knife edge vs knife tip, you either need a MUCH hotter knife or you cut slowly. Hot knife like the ones used by professionals for cutting synthetics are hotter and also much more expensive.

>That way it either cuts due to the heat or not at all.

Thats a good trick.

Joe, thanks for sharing this interesting info.

Chris, I have used an impulse sealer similar to the one you link to at Harbor Frieght to seal tyvek. It does work. Tyvek is a PE and heat seals easily.