When I built 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 fuse solid. That not only makes them easier to work with and prevents getting pieces of thread all over the house, but it also ensures that they won’t come loose after years of use and abuse.
Rather than buy an expensive industrial hotknife, I made one easily from a cheap Harbor Freight soldering gun. I heated one of the tips until it turned red and then gently bent it into the shape of a hot knife blade and lightly hammered it flat. The tips are made of chrome plated copper, so they bend easily. The makeshift blade heats up fast and cuts quickly.
Unlike scissors, you can use a straightedge with a hotknife to make perfectly straight cuts. I have a leftover pane of glass that makes a perfect burnproof 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 hotknife is also handy for making clean cuts in any synthetic material like zippers, hook and loop fastener tape, sail cloth, webbing, and yacht braid.
Here’s a tip for cutting rope with a hotknife. First wrap the rope tightly with tape around the point where you want to cut it and then cut through both the tape and the rope. After the cut cools, remove what’s left of the tape. The tape will hold the rope strands together while the hotknife fuses the ends. This makes a smaller cut end that is easier to pass through blocks, deck organizers, fairleads, and so on.
Now, Harbor Freight tools have never been known for their high quality and their soldering guns are no exception. I found that the tips overheat easily when used continuously such as for cutting canvas and the case can begin to melt around the electrodes (see the picture above). For that reason, if you plan to buy one of these and cut a lot of canvas, this is one time that it might be worth buying the extended warranty. I minimized this problem by learning judicious use of the trigger. Only keep the gun as hot as you need to for as long as you need to make a cut, then let it cool a little while you prepare to make the next cut.
Also, the plating on the tips oxidizes and they quickly lose heat conductivity to the point that they won’t cut anymore. I solved this problem by applying a little heat sink grease that I already had on hand around the ends of the tips where they slide into the electrodes. It helps a lot. You can get heat sink grease at your local Radio Shack store.
Since making this hotknife, I’ve used it for numerous projects including: running rigging lines, cabin cushion covers, mainsail cover, foredeck sail bag, bimini cover, crib board storage bag, and lifeline cushions.
The Bottom Line
Suggested price: $139.95
$tingy Sailor cost: $14.95
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!
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