Reply by Vulture

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Posted on Complementary Template Routing

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23 posts in 2267 days

#1 posted 10-02-2009 05:27 PM

Thanks to everyone for their suggestions, but based on the responses so far I don’t think I explained very well what it is that I’m trying to do. The process, as outlined by Carol Reed is this:
1. Draw the master pattern on MDF stock, band saw the outline and smooth curves by sanding, filing, etc., until you have the shape you want. This part is sort of a no-brainer and I’ve got that one down.
2. Using hot glue, attach the master pattern to another piece of MDF. Using a 1/4” “magic washer” (her term to indicate a washer whose difference between outer diameter an inner diameter is 1/4”), trace the pattern onto the new piece of MDF that’s as wide as the master pattern and at least 6” wide at the narrowest point of the design; the washer acts as a “bearing” against the master pattern. Cut out the pattern on the new chunk of MDF and sand/file to the line as was done in step 1. Mark this as the master template. (Note: I determined that if you use a piece of MDF in step 1 that is at least 6” wide at the narrowest point of the design, step 1 actually produces the master template, thus saving the waste of another piece of MDF!)
3. Make the “working”, or complementary, left and right templates that will allow routing of the actual workpieces. Attach the master template on top of another piece of MDF with hot glue, ensuring that this new piece of MDF is at least twice as wide as the template (so that your left and right templates will both be at least 6” wide at the narrowest part of each complementary template). Secure a 3/4” bearing and a stop collar on the shank of a 1/4” spiral bit. Attach an offset baseplate to the router (to provide stability over the template) and then set the bit depth so that the bearing will ride against the edge of the master template. The bit will cut the bottom piece of MDF in two. Keeping the bearing firmly against the master template, rout the target piece of MDF completely in two.

It is this last step that is giving me fits! I’m not attempting to produce the production workpieces yet; only create the two complementary master templates. I am well aware that any drift of the bearing away from the master template during this routing operation will lead to a “new” and unintended design. However, as I’ve already said, I’ve taken extra care to ensure that the bearing is maintaining contact with the master template. If I wasn’t actually doing this, then the left complementary template would not match the master template, but I find them to be a perfect match. For some reason, though, the right complementary template does not match either the left complementary template or the master template.

The creation of the actual complementary workpieces is done from the complementary templates by tracing the pattern of each template on the target workpieces, band sawing the workpieces about 1/8” oversize from the line traced on them, gluing the appropriate complementary template to each workpiece and, finally, using a pattern matching bit or flush trim bit to rout the workpieces smooth to the contours of the complementary template. I can’t even get to this step, though, as the templates don’t mate perfectly!

-- Kevin, Vancouver, WA

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