A hot cutting knife with fast response heating trigger and fully adjustable power setting. "A joy to use!"
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Hot knife cutting & welding

The benefits of hot knife cutting and welding as preparation for easy seam sewing for DIY backpacking tents and gear are discussed.

Background

In another post on making modular tent patterns for pyramid tents, I described the great benefits of hot cutting as opposed to the use of scissors. I started this evolution of hot cutting with a soldering iron as shown below.

A soldering iron was my first hot cutter. I could tell that it was not going to stay serviceable for very long when used as a cutter. However, it was so good that it inspired me to try proper hot knife cutting.

During the above post, I introduced the use of hot knife cutting. It was a great improvement on using a soldering iron which in itself was a big improvement on scissors. The benefits of hot knife cutting for DIY cutting and welding are so great that I thought that it deserved the prominence of a post of its own.

This simple tool provides hot knife cutting and welding with a fast response time, heating trigger and fully adjustable power setting. “A joy to use!” I also made a scabbard for the blade from thin stainless steel foil.

There are so many similar hot knife cutters available online. Many are designed for use with 110V so my choice was more limited because I needed a 240V model with an Australian standard plug. There are so many blades to choose from. I chose the KS Eagle Hot Cutter with the ‘arc-style’ blade. The blade shown has proven to be very versatile and as is my usual wont, I have modified it a little to suit my particular tasks better (described later).

I was delighted with the performance of the knife. As an example, for 58 gsm polyester fabric, it requires 5-15 seconds to heat to a magically smooth cutting temperature. The 15 seconds is for a cold start and 5 or more seconds for a restart of an already hot cutter. During extra-long cuts, the trigger can easily be pulsed on and off to prevent overheating (excessive smoking) while maintaining a smooth cutting temperature (dull red cutter blade).

“I often muck around with a sewing machine making things using technical fabrics. These are mainly (but not exclusivel) for selfish but noble pursuits like sailing, fishing, backpacking and skiing. Often in delightful combination. The hot knife cutter is one of those tools that I should have had long ago. At about $80 it has paid for itself in just a few moths.

I should also share with you that my new ‘sewing-high’ is somewhat boosted by other factors including Covid lockdowns and other little sewing breakthoughs. I think I can say that for a ‘crap sewer’ I have achieved a unique mastery of a very efficient lay flat seam that was taught to me by my mum. Silicone rubber as a sewable glue (instead of pins) to tack complex and long seams together was another breakthrough. Now hot cutting/melting/welding is another innovative step forward for this DIY tinkerer. I hope the ideas may advance your tinkering.”

Mothy The Elder

The benefits of hot knife cutting for sewn seam preparation

  • The blade glides smoothly through the fabric without disturbing the lay of the fabric.
  • When guided by a straight edge it can easily make perfectly straight cuts with minimal marking out.
  • The edges of the cut fabric do not fray to make a mess and tangle in the sewing machine and in the new Dyson.
  • Seams can be narrower because of the lack of fraying and the new strength of the fused fabric edge.
  • Seams can be simpler if fabric rolling is not required to hide and protect the fabric edges that would otherwise fray if cut with scissors.
  • Lastly, the hot cutting can also weld multiple fabric laminates together while cutting and this can make the subsequent sewing much easier or in some applications make sewing unnecessary.

Other benefits of hot knife cutting

  • Cuts seat-belt webbings and ‘tugboat ropes’ like butter.
  • Easily cuts PET and other plastic bottles and thick plastic drums.
  • Can soften and round cut plastic edges.
  • Does edge to edge welding of PET bottle plastic.
  • Acts as a hot scraper to remove synthetic fabric that is stuck to silicone rubber or other heat resistant surfaces.

Using the hot knife cutting/welding as preparation for easy seam sewing

Hot knife cutting/welding. When preparing to sew two layers of fabric together to form a sewn seam, crap sewers like me, need to pin the two layers of fabric together to make the seam easier to sew. This is particularly important when a bias grain edge must be sewn to a straight grain edge. The unwanted creep of the bias grain edge is often difficult to manage, particularly with fine and slippery synthetic technical fabrics.

The hot knife cutting (or trimming) of two pieces of fabric can weld them together. Then with the edges welded together the subsequent seam sewing is made very easy with no risk of fabric creep for the crap sewer. Because of the precision and lack of fraying the seams can be simpler or narrower than they may otherwise be.

Two layers of fabric have been placed together back-face to back-face with a bias cut edge on top and a straight-cut edge on the bottom where they have been hot cut/welded together with a hot knife cutter. This leaves the two edges conveniently welded together so that the subsequent seam sewing will be easy. This preparation eliminates the tendency of stretch creep of the edges (the bias cut edge in particular)during sewing. If there is a bias cut edge, then it should be arranged to be on the top so that when the fabric is rolled to form the seam the stretchy bias edge will be wrapped in straight grain fabric and will have no contact with the feed dogs or the pressure foot.
Two layers of fabric have been placed together back-face to back-face with a bias cut edge on top and a straight-cut edge on the bottom in preparation for hot cutting/welding. This cutting leaves the two edges conveniently welded together so that the subsequent seam sewing will be easy. This preparation eliminates the tendency of stretch creep of the edges (the bias cut edge in particular)during sewing. If there is a bias cut edge, then it should be arranged to be on the top so that when the fabric is rolled to form the seam the stretchy bias edge will be wrapped in straight grain fabric and will have no contact with the sewing machine feed dogs or the pressure foot. “The sewing is made so easy that it is like sewing a single sheet of straight-grain fabric.”

Single stitch simple seams. For medium strength seams, a single row of stitches without seam rolling will suffice as there will be no ugly fraying edge to protect or hide for aesthetic reasons.

As an example, simple storage bags with drawcord hems are so simple to make this way. A simply sewn drawcord seam can be sewn on a width of fabric (after hot cutting) and then it can be folded over to form multiple suitable sized bags before hot cutting/welding a side and bottom seams. Once welded together the sewing can be very easy and simple.

Single stitch rolled seams. Alternatively, the above seam can first be easily rolled and stitched through the four layers. This makes a plumper and stronger seam that is more resistant to tensile stretch/breakage (in use) and greatly improves the longitudinal seam strength.

Single stitch double rolled seams. The seam as described above can be rolled a second time before stitching. “Just like the traditional seam that we would do if we were protecting/hiding a fraying scissor cut edge.” This gives the seam six layers of thickness, more plumpness and greater stretch strength. “With edge welding, the seam is almost as easy to make as the single rolled seam and managing a bias-cut edge is made trouble-free because the two layers behave like one.”

A piece of straight grain and bias grain fabric have been joined by single stitch double rolled seam after their respective edges have been cut/welded with a hot knife. The welding make the seam sewing easy and eliminates the creep for the stretchy bias grain fabric.
A piece of straight grain and bias grain fabric that have been joined by a single stitch line after double rolling the seam. Their respective edges have been cut/welded with a hot knife. The welding makes the seam rolling and sewing easy and eliminates the creep for the stretchy bias grain fabric.

Rolled and lay-flat/double-stitched seam with or without embedded tie-outs. This seam can easily be formed by hot cutting/welding then rolling and stitching. Tent tie-out tabs can also be included in the hot cutting/weld to hold all the fabric layers together.

Two layers of fabric have been placed together back-face to back-face with a bias cut edge on top and a straight-cut edge on the bottom where they have been hot cut/welded together with a hot knife cutter. This leaves the two edges conveniently welded together so that the subsequent seam sewing is easy. A tie out tab has also been welded to the edges in preparation for embedding or integrating it with the Mock Felled Seam. This preparation eliminates the tendency of stretch creep of the edges (the bias cut edge in particular).If there is a bias cut edge, then it should be arranged to be on the top so that when the fabric is rolled to form the seam the stretchy bias edge will be wrapped in straight grain fabric and will have no contact with the feed dogs or the pressure foot. "The process means that all the preparation for the seam and tabs can be done calmly away from the sewing machine and that portion of the tent is virtually complete once the two lines of stitching are done. Also, if each tent panel is successively added in this way, only a one tent panel width of fabric must be passed under the sewing machine bridge while sewing the second line of stitches."
Two layers of fabric have been placed together back-face to back-face with a bias cut edge on top and a straight-cut edge on the bottom where they have been hot cut/welded together with a hot knife cutter. This leaves the two edges conveniently welded together so that the subsequent seam sewing is easy. A tie-out tab has also been welded to the edges in preparation for embedding or integrating it with the Mock Felled Seam. This preparation eliminates the tendency of stretch creep of the edges (the bias cut edge in particular). If there is a bias cut edge, then it should be arranged to be on the top so that when the fabric is rolled to form the seam the stretchy bias edge will be wrapped in straight grain fabric and will have no contact with the sewing machine feed dogs or the pressure foot. “The process means that all the preparation for the seam and tabs can be done calmly away from the sewing machine and that portion of the tent is virtually complete once the two lines of stitching are done. Also, if each tent panel is successively added in this way, only one tent panel width of fabric must be passed under the sewing machine bridge while sewing the second line of stitches.”

The sewing of the first row of stitches is at a distance from the rolled edge that equals the desired width of the finished flat seam.

The hot cut/welded fabric edges(and tab) have been easily rolled and sewn down with the first line of stitches that will form the Mock Felled Seam. "The process means that a 'crap sewer like' me can just focus on the simple rolling and straight sewing, . No pins, no forgetting tabs or putting them in the wrong place, or accidentally sewing into some other part of the tent. It is so easy that extra tabs can be added if I am unsure about their optimum location. Also, I leave the back stitching for extra strength for the tabs to be done during the second line of stitches. This means that the seam and the tabs can be sewn without needing to remove the work from under the sewing machine pressure foot!
The hot cut/welded fabric edges (and tab) have been easily rolled and sewn down with the first line of stitches that will form the Mock Felled Seam. “The process means that a ‘crap sewer like’ me can just focus on the simple rolling and straight sewing. “No pins, no forgetting tabs or putting them in the wrong place, or accidentally sewing into some other part of the tent. It is so easy that extra tabs can be added if I am unsure about their optimum location. Also, I leave the backstitching for the tabs, for extra strength, to be done during the second line of stitches. This means that the seam and the tabs can be sewn without needing to remove the work from under the sewing machine pressure foot!

The seam can then be laid flat to sew the second line of stitches and the back-stitching of the tent tie-out tabs can be done without removal from under the sewing machine pressure foot.

Completing the Mock Felled Seam after hot hot knife cutting/welding of the components together prior to sewing the seam. "The sewing of the seam and tab back-stitching can be completed with the work staying under the sewing machine pressure foot."
Completing the Mock Felled Seam after hot knife cutting/welding of the components together prior to sewing the seam. “The sewing of the seam and tab back-stitching can be completed with the work staying under the sewing machine pressure foot.”

To achieve the best lateral strength the flattened seam should be pulled tightly against the first line of stitches as the second line of stitches is made. This ensures that both lines of stitches bear the load equally. This is very appropriate for high-load and water-resistant tent seams.

Note: This seam that is formed this way is very similar to what people (including me) commonly call ‘lay-flat seam’. It should more correctly be called a Flat Felled Seam. It even has an ISO 4916 2.04.06 number. This number comes from this wonderful link that describes in detail most seams that seemingly one could dream up or have nightmares about. The seam that I describe with a welded start has one extra layer of fabric rolled within it (caused by the welded starting point). It just makes the seam a little stronger and plumper. The next seam that I describe does not have that extra layer and is a true Flat Felled Seam.

I find it somewhat ironic that most descriptions of making the Mock Felled Seam on YouTube start by sewing together the two layers with the edges flush (much like my welded start). They then faff around, cutting off an ‘unwanted’ strip of fabric and then roll and iron it before sewing the second line of stitches. This cut off strip could simply be left in place and rolled into the seam (as described above) making the seam stronger and simpler to sew.

Mock Felled Seam/Lay-flat seam (sic) with glue tacking instead of welding. This is straying away from hot cutting/welding. However, it was the forerunner to the cut/weld seam and it provides a context for the above seam sewing development. It is a near-equivalent seam when hot cut/welding is not available or suitable for a project.

My Mock Felled Seam is normally started in an unusual way. “This was taught to me by my dear and patient Mum who crafted magic at speed with a sewing machine. She also repaired many dead sewing machines wherever she visited. Having a professional sewing background she made every stitch count and did nothing that was not an improvement to strength, speed, economy or appearance. She was happy to share her skill and tricks with anyone who was interested.”

The seam starts by wrapping one edge tightly around the other and running the first line of stitches through the three layers of fabric at a distance from the rolled edge that will determine the subsequent seam width. This different approach immediately tames the stretch/creep problems if the wrapped edge happens to be bias cut fabric because (“Yes you guessed it!”) the bias cut fabric never touches the sewing machine feed dogs or pressure foot.

In other posts, Lay flat seams for pyramid tents, Glueing instead of pinning and Tie out tabs for pyramid tents I describe my evolution of tent seam forming that can easily integrated tie out tabs that start with glueing (instead of welding). They may also be of interest to you. l will let the following collage of photos tell the rest and possibly trigger your interest.

A long tent seam that has been prepared for sewing by glueing instead of pinning. DIY low profile spring clamps and plastic pads are used to hold the lay flat seam glueing points together at ~300 to 150mm intervals, depending upon the expected complexity of the sewing. I used two adjacent clamps at the bend in the seam where the ‘easing’ of the fabric layers around this bend would otherwise be difficult without glueing (or become very ugly sewing). “I had a feeling that this was going to make the sewing very easy.”
Low profile spring clamps holding a pressure pad made from a folded rectangle of a thick plastic sheet from an ice cream container lid. The rectangle has been folded in two and squeezed flat with pliers. This is a simple preparation for the start of a stress-free and perfect lay-flat seam without the hassles of pinning. The photo was taken before I discovered hot cutting, hence the ragged edge to the fabric. (Pre hot cutting photo.)
The guy out V-tab and web being glued with silicone rubber into the prepared lay flat seam on the bias cut side. “The glueing process is similar to my normal glue tacking that I use for preparing seams without pinning. So it does not take any more effort to locate a tab in this way. It is very much easier than sewing the straight tabs onto a fully formed tent!” Note all the neat hot cut edges in this sample of the Mock Felled Seam preparation.
The guy out tabs on its web has been glued into the first roll of the mock Felled Seam during glue tacking. It is ready for the easy sewing of the first critical line of stitches “The glueing process is similar to my normal glue tacking that I use for preparing seams without pinning, so it does not add any great extra effort if the tab point can be marked at the time of marking out the tent panel.” For more details please see Tie out tabs for ultralight tents.
The completed lay flat seam with extra lines of oversewn stitches holding the guy out V-tab securely in the folds of the seam. “When these seams are completed the tent is almost finished, so easy!”

Back to the hot knife cutting

Welded bias grain stabilization tape. Selvedge offcuts abound when you make a tent with the use of a hot knife cutter. Many meters of it mound up. In my case, it had cosmetic defects (one hairy edge, little manufacturing pinholes and missing some silver coating. It otherwise makes a very strong and effective straight grain stabilization tape that has no fraying fibres.

It can be sewn onto the back of bias-cut edges to stop their stretching while sewing. It also plumps up the seam to four layers of fabric when the edge is rolled once. “Such seams are usually rolled to protect and hide cut edges. However, the rolling also seems to make the seam more resilient, but I can’t explain why.”

Selvedge trimmings that have been removed with a hot knife cutter/welder while preparing tent panels for sewing together. They make wonderful lightweight tensile tape that can easily be hot cut/welded to bias cut fabric edges to control and manage stretch and creep while sewing.
Selvedge trimmings that have been removed with a hot knife cutter/welder while preparing tent panels for sewing together. They make a wonderful lightweight tensile tape that can easily be hot cut/welded to bias-cut fabric edges to control and manage stretch and creep while sewing. They are best left as long as possible for future use.
A tensile tape made from hot cut selvedge trimmings has been hot cut/welded to the bias cut edge of the same fabric to eliminate stretching when the edge is sewn to an other piece of fabric or a zipper.
A tensile tape made from hot cut selvedge trimmings has been hot cut/welded to the bias cut edge of the same fabric to eliminate stretching when the edge is to be sewn to another piece of fabric or a zipper.

An example could be where a bias cut edge of the tent panel is to be sewn onto a long doorway zipper. The bias cut fabric can be laid flat in its unstretched state under or over the straight grain tape. With both nearly covered by a metal straight edge, a new edge can be cut/welded so that both are bonded together. “It wastes negligible fabric and eliminates the bias stretch and makes the next step of sewing to the zipper as easy as using a straight-grain edge.

Here is a little video of the hot knife cutter/welder.

Is hot cutting/welding a possible substitute for stitching?

Above I have described the simplest seam that can be prepared by hot cutting/welding, followed by simple sewing. The weld can be so strong that sewing may not be needed for some applications such as bags for backpacking cutlery, food, toiletries, backpacking fishing gear and rod covers etc (ie durable reusable substitutes for plastic bags).

I load tested some of my polyester that had been cut/welded. For the silly vain reason of having blue contrasting with silver in the photo, I placed the fabric so that a blue side faced a silver one. Partway through the welding, which took less than half a second, I thought; “Is that silver going to make the seal weaker?”

But it was too late to stop. So I tested the weld strength by hanging ~2,000g of water on it. I caught a couple of photos of it and was adjusting for the sun glare while thinking; “how much can it hold?” Then the weld failed.

Testing of polyester tent fabric edge weld strength when welded blue to silver face. The weld supported 2,000g of water for about 15 seconds then failed.
Testing of polyester tent fabric edge weld strength when welded blue face to silver face. The weld supported 2,000g of water for about 15 seconds then failed.

Really quite strong, but I thought that putting the silver on the outside may leave a better weld.

Testing of polyester tent fabric edge weld strength when welded blue to blue face. The weld supperted 2,000g then 3,000g for hours and then when loaded with 4,000g it held for about 15 seconds before failing.h water for several seconds then failed.
Testing of polyester tent fabric edge cut/weld strength when welded blue to blue face. The weld supported 2,000g then 3,000g for hours and then when loaded with 4,000g it held for about 15 seconds before failing.

The weld supported 2,000g and then 3,000g over some hours. “However, if you know me by now, I always like to find the breaking point and not be left wondering.” I loaded the weld up with 4,000g and just like the first test it held for `15 seconds then failed.

The bottom line to all this is that custom bags and covers could be made using this technique, particularly if backstitching was used to strengthen vulnerable points. However, sewing a simple seam is very easy after the welding so it may as well be done.

A simple bag to hold a backpacking solar charger. It has been formed by sewing a draw cord seam then cut welding the folded fabric to form the bag. The welded edges have been rolled and sewn with a simple single rolled seam.
A simple bag to hold a backpacking solar charger. It has been formed by sewing a draw cord seam then cut welding the folded fabric to form the bag. The welded edges have been rolled and sewn with a simple single rolled seam.

What fabrics can be welded together with a hot knife cutting?

I expect this list to grow as I go on tinkering, however, the photo below should show that there are endless possibilities.

A sample of various fabrics that have be tacked together during hot knife cutting.
A sample of various fabrics that have been tacked together during hot knife cutting. From left to right; Top row, fleece (PET), polyethylene, polyester tent fabric (blue side), silnylon (ripstop nylon with silicone rubber impregnation), polyester tent fabric (blue-side), fleece (PET), fleece (PET), polyester tent fabric (silver-side), nylon (ripstop without silicone rubber treatment), Noseeum netting (polyester), polyester tent fabric (silver-side), polyester (blue-side). Second row; Tyvek (polyethylene), Plastic bag fabric (polyethylene), Tyvek (polyethylene), Tyvek (polyethylene). Next; Polyester tent fabric, space blanket (metallized PET), space blanket (metallized PET), fleece (PET). Third row; Plastic bag fabric (polyethylene), Plastic bag fabric (polyethylene). Next: Cotton shirt cloth/interface of plastic bag (polyester)/Cotton shirt cloth.

Hot knife cutting/welding of dissimilar fabrics. With a background in thermoplastic heat sealing, I expected the hot knife cutter to work with all synthetic polymers when welded to themselves. I was less sure that the welding would work effectively when welding different polymers to each other.

My preliminary test strip shown above indicates that this is a viable option for popular technical fabrics and should be great assistance with DIY innovations. The Tyvek (polyethylene) was only able to be tack welded to itself and the polyethylene sheet, but not the woven polyethylene. The space blanket only tack welded to itself and PET and an uncoated polyester tent fabric. Just for fun, I put some 100 micron polyethylene sheet between two layers of shirt cotton fabric and the hot cutting formed a heat weld. All such welding should be viewed as a temporary tacking to prepare for easy sewing for long term strength.

Hot knife cutting/welding of silnylon fabric. I was unsure of what would happen to silnylon because of the properties of the silicone rubber component of the fabric. By my estimation and a more authoritative source, it will withstand a temperature of 205-300C. Anyway, it cuts and tack welds just fine. I just don’t know where the silicone rubber goes when the nylon melts and why the residual silicone rubber does not detrimentally contaminate and spoil the bonding of the melted nylon?

Hot knife cutting/welding of Noseeum netting. If you have used Noseeum netting in your DIY projects for adding windows/vents to tents, you would know how difficult it is to cut and sew precisely. It is so easily distorted and horrid to sew.

Imagine how easy such windows could be if the netting was first laid out flat under straight edges and was cut/welded to a strip of stable straight grain tent fabric to form a stable ‘frame’ around the window before sewing it to the tent?

After initial welding, the frame fabric can easily be rolled and sewn to the netting with a row of stitching. Then the frame can be sewn to the tent. “This is much easier than my previous glue/sew method, but will involve a bit of inside out thinking. Making and framing the window before cutting the hole in the tent always seems to be prudent!”

Sewing a 'frame' of straight grain polyester tent fabric to Noseeum netting. The rolled frame is easily formed after hot cut welding both fabrics together.
Sewing a ‘frame’ of straight grain polyester tent fabric to Noseeum netting. The rolled frame is easily formed after hot cut welding both fabrics together.
A 'frame' of straight grain polyester tent fabric has been rolled and sewn to the edge of Noseeum netting. The sewing was made easy hot cut welding both fabrics together.
A ‘frame’ of straight grain polyester tent fabric has been rolled and sewn to the edge of Noseeum netting to form a window for a tent. The sewing was made easy by hot cut welding both fabrics together. The newly formed edge will make it stable for easy sewing to the tent.

Other welding possibilities

Welding plastic bottles with a hot knife cutter. PET soft drink bottles and other plastic containers are a wonderful tinkering resource for us to make all sorts of things out of. “Cutting them with a hot knife cutter is like cutting butter with a warm knife that has just stabbed a hot scone. ” Reassembling the bottle into a useful thing can also be made easy with the same knife as a plastic welder, using the flat face of the blade. The example of a DIY tape storage jar in the photo below may help to explain the idea.

Roll-up device for storing unruly lengths of feisty steel tape. It is a prototype and was made from a plastic peanut-butter jar. The container was shortened by cutting off the bottom and heat welding the bottom onto the shortened jar. For the welding, I used the above hot knife cutter, using the sharp blade edge to quickly form three tack-welds, just like you do with steel welding. Then I used the flat face to quickly weld the full circumference. “Now there is another use for this wonderful hot knife that I should have had for my tinkering years ago! Can you guess the topic of yet another tent-making post that will feature the use of a hot knife?” Using the jar with a lid was a good trick, as I found that with the lid removed I could easily assist the winding of the tape/s with my fingers,

Hot scraping of adhering polymers from heat resistant surfaces

With my tinkering with hot tent stoves, I usually make my DIY protective stove jacks with various laminates of material to exploit their multiple virtuous properties such as heat resistance, water resistance, sewability, permanent glueability, and even temporary glueability that will allow peel off when needed.

When making these laminates it is simpler and less error-prone to put all the laminates together as a unit before cutting the precise elliptical hole for the stove pipe.

The core laminate of silicone rubber is the most heat resistant and can safely rest against the hot stove pipe. Other laminates such as silnylon or polyester need a little more clearance to ensure that they do not melt/burn during use.

The blade of the hot knife cutter can easily be used to hot scrape away some of the silnylon (or other synthetic fabric) from the silicone rubber to set the appropriate safe clearance. Peeling and cutting with scissors was almost impossible and left a horrible fraying mess. The hot scraping by contrast was easy, precise and left a neat sealed edge.

A DIY stove jack that is made with multiple laminates. It is designed to accommodate various stove pipe diameter by having supplementary glue-on/peel-off silicone rubber covers that can be made to fit any smaller pipe. The most heat resistant laminate is pure silicone rubber Limit ~300C. It is surrounded by a sheet of common shirt cotton that has been DIY impregnated with RTV silicone rubber to make it waterproof and heat resistant to ~200C. The outer laminate is silnylon that bonds well to silicone rubber, but it has a defect that allows the bond to be broken an peel off when required.
A DIY stove jack that is made with multiple laminates. It is designed to accommodate various stove pipe diameters by having supplementary glue-on/peel-off silicone rubber covers that can be made to fit any smaller stove pipe diameters. The most heat resistant laminate is pure silicone rubber that is molded with a thick edge for stiffness and it has a temperature limit of ~300C (The ring of white material around the hole has been revealed by hot scraping the silnylon off the silicone rubber with a hot knife cutter.). It is surrounded by a sheet of common shirt cotton that has been DIY impregnated with RTV silicone rubber to make it sewable, glueable, waterproof and heat resistant to ~200+C (hidden behind the next silnylon layer). The outer laminate (showing) is silnylon that bonds well to silicone rubber, but it has a defect that allows the bond to be broken and peeled off when required. The stove jack assembly is pre-fabricated and sewn onto the pointy end of the tent panel and is then sewn normally as part of the Mock Felled tent seams.

Hot knife cutting of thick-stuff

The above use of the knife has focused on delicate and thin materials, but the hot knife can easily handle really thick materials such as seatbelt webbing and tugboat lines and it leaves a neat finish. I just will let the video do the talking.

[Add a link to the tugboat rope and webbing cutting video.]

Hot knife cutting blade modification

The hot knife cutting tool arrived with the ‘arc-style’ blade. It performed really well but it was very sharp and it scored the sheet of metal that I used as backing support for the cutting. Consequently, I rounded the blade profile with the use of an aluminium oxide abrasive. This minimized the scoring, allowed the blade to move more freely and made it safer. Expect a post on an alternative customised blade some time.

Conclusion

Hot knife cutting is great for a DIY tinkerer. The cutting is fast and convenient and its fabric welding function can make difficult seam sewing easy.

Tim

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