CNC Scarf Joints
John C. Harris - 17 Years of CNC Machines: An (Unsentimental) Look Back
(This is an experimental 100k Garages web App…test thoroughly before using in Production!)
Create a “wavy” scarf file
Wavy scarf Traditional CNC-cut stepped scarfs work well but there are a couple of issues with scarfs in general. One is that no matter how many steps you cut (up to a point at least), the weakest point of any scarf is at the glue joint at the outermost steps. If you glue up a scarf and then stress it until it breaks, it will usually fail at the edge of the scarf because the continuous grain is broken there…basically the old “tear along dotted line” scenario. The second issue is a minor one, but it’s the straight glue line at the edge of the scarf. No matter how well it’s cut, clamped, and glued, that line always draws your eye, especially in a hull that’s varnished.
One solution for both of these issues is, for want of a better name, a “wavy” scarf that is cut in a series of curves. This breaks up the glue line so that there isn’t a “dotted line” to break along, and the waves look a little more “organic” when glued together than the straight lines of traditional scarfs. This Wavy scarf requires more work to lay out on the sheet so that you’re sure that panels will fit together correctly, but I think the benefits are worth the extra one-time effort of laying out the parts.
To make it easier for others to try this scarf I’ve created a web interface to let designer set up scarf files, that they can then get Fabbers in 100kGarages to cut. Fill out the values below and when you click the “Create my scarf file” button a custom ShopBot file will be sent to you, with your values filled in and Inputs for the Fabber for values that are tool and material specific. Email the zip file to the Fabber you’ve selected so that they can use it when cutting your parts.
youtube like this Ed Vickery - Super easy scarfing jig
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