Complementary Template Routing

I recently made this:

http://lumberjocks.com/projects/21049

The sides are mirror images of each other. I made a jig to do the routing. I used a piece of plywood with center lines marked on it. The blank had center lines marked on it. I centered the blank on top of the plywood jig by lining up the center lines. Then I screwed down some scrap wood around the blank to keep the blank from moving.I made stops on the outside perimeter of the plywood jig to limit how far the router could travel. I also made a 12” square router base to keep it flat at all times.

I centered the part of the blank that I wanted routed out, which is different from centering the blank on the jig. I did not use a bearing to follow a pattern, I restricted the travel of the router. In my case I needed a 4” square routed. The travel of the router was 2” out from the center.

I hope this helps. Good luck!

-- I'm a lumberjock and I'm ok, I sleep all night and I work all day!

I am not familiar with your project per se. I do have some thoughts on pattern routing that I would like to share with you though. First, If you get overly agressive with the solid carbide up cut spiral bet, it will snap and possibly cause an injury. Second, If it doesn’t snap, it may have some serious run out.

That aside, I prefer to use 1/2 inbch shanked patternmaker’s bits (bearing ont the top) or flush cut trim bits (bearing on the bottom. They can be resharpened and they won’t snap if you dont bandsaw close enough to your line (1/8” is about the norm).

Good luck,
Kimball

Based on a recommendation in another posting, I just this week bought a double bearing bit from MLCS. It is 1/2” shank and 1/2” diameter. I screw a template / pattern to one side and use the bearings to guide the bit. Great thing about the double bearing is that you can flip the work and be routing in the right direction of grain so you don’t get tear out on rounded corners. (you have to raise and lower the bit to align with the pattern)

I know this is different from what you are trying, but the tear out at the corners by only having one direction to go in drove me crazy and I had to give up on it until I heard about the double bearing. I guess you could switch bits (upper bearing one and then lower bearing one) for each direction, but that really breaks the work flow.

Steve.

Question. Is the cutting surface flush with the outer edge of the bearings? If the bearings are bigger than the cutting surface then I think that the wood that you are cutting has a different radius that the pattern.

That might be causing some of your problems.

-- What happens in the workshop stays in the workshop. No wait that doesn't sound right. Karson Southern Delaware karson_morrison@bigfoot.com †

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

Been there bro! All that offsetting and “magic” washer crap is your prob. When I tried this process I found that simplifying is best. Use just a flush trim or a pattern bit to go from you master template to your working template then to your work piece. I’m glad it worked for the router lady but some poeple just over complicate you know.

-- Rogue

Thanks, Rogue! Kimball made a similar suggestion earlier. I was a bit concerned that it would be asking a bit too much of a pattern bit (I have a nice 1/2” shank pattern bit) to chomp out a cut between the two templates since it’s usually used as a “clean up” bit. However, based on your experience, and Kimball’s, I think I’ll give that a whirl.

I agree on the “over complication” item as well. I mentioned that I had already chopped off one of “the router lady’s” other steps, which just seemed to me to be a waste of the original pattern. Always have liked the KISS principle, even though it seems I rarely follow it!

Again, thanks to all who have shared their experience and wisdom on this topic. I really appreciate everyone’s willingness to help.

-- Kevin, Vancouver, WA