A Hotknife for the Rest of Us

When I made my first canvas project, a mainsail cover, I cut out the pieces using scissors as usual. Later, when I made the cabin cushion covers, I discovered how much better a hotknife works for cutting synthetic marine canvas like Sunbrella. Instead of the edges unravelling, they fused solid. That not only makes them easier to work with and prevents getting pieces of thread everywhere, but it also helps to ensure that the seams won’t come loose after years of use and abuse.

Before I get any further, a bit of legal housekeeping. This post contains affiliate links. That means I receive a small commission if you make a purchase using these links. You can buy these products anywhere you like, of course. For a complete explanation of why I’m telling you this and how you can support this blog without paying more, please read my full disclosure.

Sunbrella marine canvas cut with a soldering gun (left) and scissors (right)

Rather than buy an expensive industrial hotknife, you can get similar results using a tool that you might already own, an ordinary soldering gun with a blade shaped or rope cutting tip. If you don’t already have one, I do not recommend trying a cheap Harbor Freight soldering gun. They aren’t built to withstand the long periods of use that it takes to cut canvas. Instead, get a high quality soldering gun like a Weller D650.

Unlike scissors, you can use a straightedge with a soldering gun to make perfectly straight cuts. I have a leftover pane of glass that makes a good burn-proof cutting surface. Cutting this way produces a little smoke from the melted acrylic that can be irritating, so do it in a well ventilated area.

A soldering gun is also handy for making clean cuts in other synthetic materials like zippers, hook and loop fastener tape, sail cloth, webbing, and yacht braid.

Here’s a tip for cutting rope with a soldering gun. First wrap the rope tightly with tape over the point where you want to cut it and then cut through both the tape and the rope. After the cut ends cool, remove what’s left of the tape. The tape will hold the rope strands together while the soldering gun fuses the ends. This makes a smaller cut end that is easier to pass through blocks, deck organizers, fairleads, and so on.

A soldering gun works so well as a hotknife that I’ve used it for numerous projects including: running rigging linescabin cushion covers, mainsail cover, foredeck sail bag, bimini covercrib board storage bag, and lifeline cushions.


If you like this project, then you’ll really like my ebook Do-It-Yourself Small Sailboat Canvaswork. It contains this tip and nine full canvaswork projects with dimensioned drawings, all for only $20 USD. Click the picture at right to order your copy for immediate download and get started today!



Would you like to be notified when I publish more posts like this? Enter your email address below to subscribe to this blog and receive notifications of new posts by email. You will also receive occasional newsletters with exclusive info and deals only for subscribers and the password to the Downloads page. It’s free and you can unsubscribe at any time but almost nobody does!

Enter your email address to subscribe to this blog and receive notifications of new posts by email.


14 Comments Add yours

  1. captnmike says:

    Seattle Fabrics have a hot knife that is based on a soldering iron – cost under $ 40.- http://www.seattlefabrics.com/scissors.html – not as low cost as yours, but a bit less work – if you have the proper base soldering iron, you might be able to buy a replacement tip – I think Sailrite has a tip with a 1/4 inch shank that will fit into some soldering irons

    Not as low cost as your solution – the hot knife from Seattle Fabric is I think the same one I bought years ago and it worked fine – eventually I got the fancy Englow (sp?) with a foot for the knife so I did not need to worry about burning up the surface I was cutting on

    1. Thanks for the tip, Mike! A pen style hotknife would indeed be more convenient for some folks or projects than a gun style one. And I had forgot about Seattle Fabrics. I came across them while I was shopping for some sail cloth awhile ago. It’s good to have alternatives to Sailrite for marine fabrics.

      1. captnmike says:

        Perfect Fit (http://www.perfectfit.com/) – in Tuckwilla / Southcenter is another good place – good prices – the site says wholesale but they have sold to me when I just walked in. Do some homework before going down as they don’t have a “store” area as such – they are a large warehouse operation – bit of a drive for me – but you on Mercer Island are closer – I always save up and get as much stuff as I can on one trip to make the trip worthwhile – the folks were helpful when I went in

      2. I’ll make a note of them for the next time I’m over there. I bought Summer Dance on Mercer Island but I live in eastern Washington and make an occasional trip over to the wet side.

      3. captnmike says:

        What part of Eastern Washington? I used to live in Walla Walla and still have relatives in the area & in Pullman

      4. About 10 miles NW of Spokane near Colbert. I did some work in Walla Walla years ago. It looked like a nice community. Been thinking of taking Mrs, $tingy down there for a wine tasting tour. I’ve heard it’s good.

  2. Tomas Kruska says:

    Hehe… nice idea. I had the completely same a few months ago when I was “cutting” the canvas for the window shades.

    BTW. I’m glad you fixed the the boat after the storm and saved her from scrap 🙂

    1. Hi, Tomas

      I just visited your blog and left a comment. It looks like your family really enjoys vacationing on Sole Mio. Have fun working on her!

  3. Desirer says:

    What a cool idea! Heading to home depot now…!

  4. Flick says:

    Harbor Freight Tools offers an 80-watt “Plastic Welding Kit” (item #60660). It has the happy feature that its screw-in soldering tip holder will accept the copper wire-feed welder tips I found at Lowe’s.
    The combination support serious DIY experimentation and customization for soldering and hot-knife applications. HF’s iron with a hammered-flat copper tip works quite well for my hot knife — though I expect the author’s soldering gun would provide more power.

    1. The HF plastic welding kit might work well for some plastic repairs and cutting small cord but at only 80 watts, it doubt that it generates enough heat to cut canvas at a fast enough rate to make it practical for sewing projects. The Weller D650 has two heat ranges, 200 or 300 watts and in my experience, the 300 watt range works best.

  5. Jim says:

    I made one of these from a garage sale Weller and a piece of solid copper ground wire hammered flat. Works great on rope and fabric. I got the idea from you some time ago. Thanks.

  6. bigsnit says:

    It’s more expensive, but I love this hotknife from Sailrite – there are similar ones around – all look to be about the same manufacturer, just labelled differently. https://www.sailrite.com/Sailrite-Edge-Hotknife-Package-110-Volt

  7. Roland Demers says:

    This is an outstanding tip on using the soldering iron. Many thanks.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.