Thanks to one of my subscribers Fred, who sent me a picture of what this jig looks like, I thought it was a neat idea so decided to make one for myself. Like many things in woodworking there are often many ways to accomplish the same thing and I have made designs in doors like this in the past and there are pros and cons to each method but this looked like a fun little project ... so here goes ...
Watch it on Youtube: https://youtu.be/_PdtkqFz5X0
The first thing I decided to do was to make it out of clear plastic. This base needs to be very accurate in order to go around the whole inside of the frame and still end up in the same place for the cuts and that is another reason I preferred plastic. Hardboard would work fine and be easier to work with but plastic is a bit sturdier for a job like this ...
To start off with I picked a size that I thought would work best for me, and for the Trim Router, I was using, which has a 4-bolt base attachment. So the new base I design needs to fit within this 4-bolt pattern. I wanted to make a version that would cut lines as close to the edge as possible because it is easy to move the cut edges out by adding wood blanks around the frame of any width as I did in the dual cut version.
I started off by making an even-sided paper triangle that I could use only as a guideline so I could see where I needed to position the 4-bolt pattern on the blank piece of plastic.
Once I knew that my plastic blank was big enough and where it needed to be positioned on the sheet, I measured up the 4-bolt pattern the first drilled the countersink holes, then the through holes for the bolts and finally tested them to see if they all fit. With a tiny bit of round file work, all the bolts went in and the base was snug to the trim router.
Next, I needed to find the very center of the base and used a tiny router bit to make a small indentation that I could use as the center point. I didn't make the indentation all the way through the base, only used it to mark it.
Next, I needed to draw a circle, in my case an 8-inch circle on the plastic which I scribed with a sharpened awl that I have. The 3 points of the triangle need to be 120 degrees apart (120 + 120 + 120 = 360 degrees) So I set my digital angle finder at exactly 120 degrees and marked the 3 points. This sounds easy but was, in fact, a challenge because the plastic was slippery and so was the metal digital angle finder and it was hard to get all three points marked and lined up but after a few tries and double checking, it appeared all the points were in alignment.
Next, I etched lines between the three points because of all the material above the line needed to be cut away. This was another challenge when working with plastic, it's very hard and does take time cut and sand. I rough cut with my bandsaw then used my oscillating sander to get very close to the lines and finally used a manual method of sanding to remove the excess plastic as close to the lines as I could.
The last chore was to bore a hole in the middle of the jig to allow for the bit in the trim router to come through the plastic base and finally ... attach the base to the trim router.
To test the jig I made a mock-up frame with some scrap wood and accurately measured and cut the sides so that it would work just like a cabinet door frame. To test the jig I started off with a carbide 1/4" router bit and cut the lower half of the mock-up door. What I realized quickly was there was lot of sawdust coming off the bit and collecting in the corners so it would be important to either have someone hold a vacuum in these areas so the build-up of sawdust does not affect the accuracy of the base, or, be prepared another way to ensure the sawdust was removed. In my case, blowing the dust out worked..
The second test I changed bits to the 1/16" bit because I wanted to try a parallel cut version. This bit didn't produce nearly as much sawdust, but it is still a concern, especially in the corners where the jig needs to rotate and sawdust in these areas could affect how accurate the jig is, so be aware of this.
All in all I liked the jig but could see that it has some limitations in terms of the distance it cuts from the inside frame and that in some cases it might be necessary to have a few version sizes of the jig in order to accommodate different door sizes ... and of course the dust issue is something that can't be ignored with this jig, but all in all it worked well ... was fun to make and did what I expected, now I wonder what other things it might be capable of ...
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Copyright Colin Knecht