hot knife buying advice?

[Huzefa @ Blue Bolt Gear]

I want to buy a hot knife but I have no idea how to look for a good quality inexpensive product. Any brand recommendations? and where do I buy one? How do I find out how many watt I need or what kind of blade is suitable? Mostly I will be cutting LW synthetics like cuben, silnylon, primaloft, supplex, velcro etc.

Any advice will be greatly appreciated.

[Dave .]

I carry an A.G. Russell Featherlite. It's a great knife. It comes with an edge that is just super sharp. The locking mechanism on it is uniquely sturdy for a folder of that size and price. Weighs about 1 oz.

[Tim Marshall]

I got one from OWFINC.com and it was just a soldering iron. It was useless. It didn't get hot enough to melt clean and left a bumpy edge. I gave up on it right away.

I don't think you need to seal the edge on cuben and especially not primaloft.

If you keep all your raw edges inside your project or trapped under felled seams and use a seam allowance 1/2" or bigger you shouldn't have any troubles anyway.

-Tim

[Huzefa @ Blue Bolt Gear]

Dave, I am looking for electric "hot knife".

[Huzefa @ Blue Bolt Gear]

Tim, I want to make an insulated jacket without sewing. My plan is stack cut liner-insulation-shell with hot knife so that the pattern pieces are stabilized. Then tape the pieces using adhesive transfer tape.

I also plan to make a taped supplex pants and shell.

[Tim Marshall]

Just learn to sew, it isn't that hard.

To me trying to heat seal that stuff together is going to leave you with a piece of junk.

Don't try and cut corners on this, you'll end up with gear that you don't like. Gear you don't like is gear you won't use, and gear that is poorly made is gear you can't sell.

Learn to sew.

-Tim

[Huzefa @ Blue Bolt Gear]

>To me trying to heat seal that stuff together is going to leave you with a piece of junk.

If by "heat seal" you are referring to stack cutting the pattern pcs then can you pls explain why I will end up with piece of junk?

tape is not a heat seal tape.

[Matthew Roberts]

You will not have frayed edges cutting cuben.

Heating the edges of a pattern seems like a great way to cut down on holes created with sewing and cut weight now that sealing tape is out of the picture.

I had a friend who would use a large Heat Press to seal seams for his Inflatable Art pieces. These were huge art installations, made from melting the edges of plastic together with a bar Heat Press. I'm not refering to the square-shaped heat presses used in T-shirt heat transfers, but rather a length of two bars that would heat up – The top bar could be lowered using a lever similar to those on an upright drill press.

I would imagine you could do the same with some fabrics and eliminate the sewing and tape seal.

How cool would it be to make an inflatable shelter, no poles needed. Of course this opens up all kinds of new problems like, "I came back to my camp and found my shelter and all the gear in it blew away with the wind".

[Dave .]

Right, right…a hot knife.

I shouldn't post before having my coffee. Sorry.

Feel free to ignore me. ;)

[Greg Mihalik]

I use a "pencil style" always-on soldering iron.
I think it is a Weller. (I'm not at home.)

I use a piece of aluminum angle as a straightedge. When I cut a line I run the shoulder of the iron against the angle, not the point. That way the straightedge isn't sucking the heat out of the tip, and things cut clean and fast. If you do this on something like the smooth side of masonite, versus a wood work surface, the cut pieces come off cleanly, and you don't get "burn lines".

[Sean OLeary]

Sailrite has a Weller solder iron and a tip (sold separately) that they market as a hot knife, they also have a fancy (read expensive) hot knife. They even have a little video showing it in action. I'm about to order one myself. http://www.sailrite.com/

[Tim Marshall]

when you stack cut with a hot knife your are heat fusing the 3 layers together (melting all 3 into 1). If the layers don't melt together perfectly then there will be weak spots and the layers will pull apart at those places. Using a hot knife to seal the edge of fabric makes sense, relying on that seal to keep your entire project together doesn't. Every one of your seams will be flat, no loft, so cold. The heat melted edge will be hard and cause rubbing on your skin. The tape against your skin on the inside won't be that comfortable either. You will have to tape both sides of the seams as taping only the inside the tape will only be against the liner fabric and the shell can still pull away from the melt.

It just seems like a lot of work that most likely won't turn out great just to avoid sewing it.

I just think the gear will be shortlived as the seal will break eventually leaving you with pieces of a jacket.

Sewing is the way to go.

-Tim

P.S.
There are heat seal able fabrics out there for this purpose, but they won't be breathable.

[Chris Chastain]

Some options… I own the butane type but have -never- used it for anything remotely similar to what you are talking about, so no recommendations. Harbour Freight used to have one similar, but I can't find it listed anymore.

hot knife for foam type stuff

impulse sealer I want to try one of these on tyvek.

exacto/soldering iron type

another exacto/soldering iron type

butane soldering iron type this is the type I own

electric soldering iron type

[Tim Marshall]

If you must do this without sewing try doing it like this vs. a stack cut…

Cut out the shell and liner using pattern and including seam allowances.

heat seal and tape the shell pieces together and then the liner, keeping the melted edges and the tape all on the "wrong" side of the material.

You now have 2 wind shells with raw seams on the cuffs and bottom as well as the collar or hood.

cut out the insulation omitting the seam allowances. Then instead of melting it together baste the insulation pieces together with a needle and thread (yes it is sewing but barely)

now you can put the 3 layers together and close the cuffs, bottom and hood/collar.

I would close them by sewing elastic edging on or by sewing the hood pieces together while it is inside out so you can turn it right side out. You could heat seal the hood so you can turn it inside out and have a finished simple seam on the outside.

This way all 3 fabrics don't have to seal together and you won't have flat spots at each seam.

Not sure the best way to put a zipper in without sewing.

I still think sewing will result in a better product, but if you must skip sewing i guess i can try and help.

-Tim

[Huzefa @ Blue Bolt Gear]

Thanks Tim, for taking time to answer my question.

>If the layers don't melt together perfectly then there will be weak spots and the layers will pull apart at those places.

I am counting on a perfect cut. I can practice on scraps but if it doesnt work out sewing is always an option.

>Every one of your seams will be flat, no loft, so cold.

Yes, but when I join the seams the overlapping region will have loft.

>The heat melted edge will be hard and cause rubbing on your skin.

I am expecting a clean smooth cut. I think you are saying this based on your experience with OWF knife?

Tape I plan to use is 1/4" double sided adhesive transfer tape. There is no film or tissue. Basically it is a very strong adhesive applied in tape form.

In overlapping seam liner side of one piece will overlap shell side of another.

>I just think the gear will be shortlived as the seal will break eventually leaving you with pieces of a jacket.

I hope you are wrong.

ok seriously I think you have a point there. Only way it can work is if I have perfectly cut and fused layers. And for that my friend I need a good hot knife.

[Huzefa @ Blue Bolt Gear]

What you are describing will not work with Primaloft as it has to be stabilized with the liner. Could work with climashild may be thats what you had in mind?

[Huzefa @ Blue Bolt Gear]

I looked at all the link chris posted. thanks Chris.

Weller Soldering Iron
$24.00
# Power Consumption: 40W
# Tip Temperature: 900°F (482°C)
# Hotknife tip sold separately.

Hobbico Hot Knife w/Solder Tip 25 Watt
$5.99
# Power Consumption: 25W
# Tip Temperature: 750F
# Comes with #11 Exacto knife blade.

FiberToolsTM Electric Hot Knife
$24.95
# Power Consumption: 60W
# Includes a Flat Tip Blade & #11 Exacto Blade and Holder

I am not sure higher watt is useful without the ability to control temperature. Hobbico looks like a great deal.

[Tim Marshall]

From my experience with the hot knife but also from using a flame to melt the edges of fabric the fabric will become hard where it is melted. If the melted area is kept small it may not be to bad, but if it is small it has less chance of holding all the layers together, and being more prone to cracking. Once the fabric is melted don't think of it as fabric but as plastic, it will become hard and brittle.

I forgot all about primaloft needing stabilization. You're right on, i always use climashield.

-Tim

[Bill Fornshell]

Hi,

When I cut material that might or will fray I have a "hot knife" that I bought with a 50% off coupon from my local Micheals Store.

Woodburning Pen

It has a replaceable #11 Xacto knife blade that screws into what they call a Woodburning Pen. Total cost with the discount was about $7 or $8. It works fine but I only use it on Pertex Quantum.

For cutting Cuben I just use an Xacto knife with a #11 blade.

[christian gagas]

About a year or so ago I experimented with hot cutting materials. The best knife I found was in fact the cheapo "woodburing kit", probably the same one you found, Bill, about 12 bucks at Walmart. I even went so far as to begin making luan patterns for pieces that I wanted to be able to make regularly, say a pair of mitten shells, no sweat to pull out a pattern and cut out pieces. But…the issue was that the exacto style blade made a nice cut but lost it's heat very quickly so you had to cut very slowly. The coarser tips cuold cut fast but left a more ragged edge that was often a pain to sew, snagging on itself, and being wobbly enough that it was harder to get a consistent seam allowance. I also needed a surface to cut on, like Masonite, which even at 4×8 gets small fast when working with tarp sized pieces. In the end it has proven to be far faster to just lay it out and cut it out, small pieces with a rotary cutter, big panels with good old sharp scissors. Cut carefully to the line, if you used a pattern and work carefully there is no reason that your pieces shouldn't be really close in size (within a 1/16", plenty good enough for fabrics IMO). Sew it up and then heat seal if you must/need to. I agree with Tim though, as long as the raw edge isn't exposed I have never had any issues with just leaving them alone as long as there is proper seam allowance in the first place(fabric dependent).

The other issue I had with hot knives was the risk involved. Distracted by what I was doing in a limited space, I burned several holes in project material during the cutout. Never had a problem with scissors though.

Christian

[Huzefa @ Blue Bolt Gear]

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.

[Huzefa @ Blue Bolt Gear]

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.

[christian gagas]

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.

[Nicholas Miller]

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.

[Joe Kuster]

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.

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