Description
*The forms are now made from MDF, not softwood lumber.
Heat sealing curved seams (such as the tube-to-tube seams in a packraft) presents a challenge because the curves prevent the fabric from lying flat on your table. The solution is to drape the fabric over a rounded surface.
Several years ago Bruce Campbell, of Fairbanks, Alaska, sent me a curved wooden form and I’ve been using it ever since – you’ll see it in many of the instructional videos on this site.
The seam sealing form invented by Bruce Campbell. Note the centerline drawn on the outer edge over the masking tape. The sticky side of the tape faces out so it holds the fabric in place while you work.
Here I am heat sealing two Ultralight DIY Packraft tubes together. The curved edges of the fabric are aligned with each other along the wooden form’s centerline, which is faintly visible through the fabric.
The heat sealing instructional video explains what the heat sealing forms are for and demonstrates how to use them:
The larger form is useful when welding the tube-to-tube seams on most of the packraft, and the smaller form is useful when welding the tighter radius areas of the packraft’s pointy bow and stern.
These forms are not essential tools for making a packraft – an overturned bowl works too. In fact, as long as the diameter is the same as the diameter of the packraft’s tubes (or less), then anything sturdy, round, and heat resistant will work (though a purpose-built form will be easier to work with). Other things customers have used as heat sealing forms are:
- a disc of flower arrangement foam shaped with a bread knife and sandpaper and then covered with a strip of silicone (cut from a cheap silicone place mat) to insulate the foam from the heat of the iron – these things are available at Wal-Mart, Amazon, etc.
- a lacrosse ball
- a colander
- a tightly balled-up bathroom towel
I encourage you to make heat sealing forms yourself. The dimensions aren’t critical, but here are some guidelines to get you started:
The large form (with an optional tapered corner). The dimensions aren’t critical, but the packraft’s seam strips are 30 mm wide, so having a form at least 30 mm thick is best, and the tubes have a radius of about 275 mm, so the radius of the form should be no bigger than that.
Small form. The dimensions are even less important for this form. It’s mainly used for sealing the seams around the packraft’s pointy stern and bow.
Note: The forms pictured above are made out of dimensional lumber, but the forms I make for you may be made from MDF (medium density fiber board) and the shapes may be slightly different.
