It seems I am forever needing to cut a board into equal halves. I always have a tape measure handy, but sometimes it's just quicker and more accurate to use a center finding jig to find the center of a board, especially when they are strange widths ... like 13-9/16. Oh sure I can stop and figure this out in my head ... of use the metric scale, or just grab my center finder jig and have it done in a few seconds ... and anyway, it's fun to make these jigs and see if there are ways we can make them better and more useful.
Watch it on Youtube: https://youtu.be/54IMIBnKEnw
This version of the center finding jig has been around for many, many years but I have never seen an adjustable version ... not that there aren't some out there somewhere, just that I have never seen one.
This jig requires a a few bits and pieces, like some 1/4" bolts about 4 inches long and 1 square nut for each and a wing-nut and washer as well. I also requires a a piece of hardwood, in my case I used a left over piece of Oak.
Cutting Rabbets
The first order of business is to cut the rabbers that that square nuts will slide along. The best thing to do is to cut these in your stock piece of wood first because it's easier and safer to handle as a larger piece of wood. When I measure the recess I needed to cut it turns out about 1/8 inch square was about perfect to hold the square nuts in place.
Cutting the Strips
After the rabbets are cut, is's simple matter of cutting each side of your stock wood to width. I chose 3/8 as this seemed to be the most stable size for the hardware I was using. and I want this jig to be sturdy and accurate.
Gluing the Center Pieces
Next it's time to glue the center piece, which in my case is 1/4" the same distance as the diameter of the hardware I am using. I also cut a couple of small extra pieces that I would use on each end of the jig to keep the ends aligned. I also added a top piece to the center section and drilled a 9/16" hole that would snugly hold one of the pencils that use.
Assembly
After the glue was dry, I drilled holes in each of the ends, including the small square dividers that would hold the ends apart so the center bolts would slide back and forth with ease. I trimmed the bolts down and assembled them in the jig making sure that the square nuts sat inside the rabbets I cut earlier, then laid the flat washers on top and fastened everything down with the wing-nuts.
Testing
If you take your time, you can align this jig so that it will make perfect center lines for you. If you are adjusting the size frequently, setting the 2 bolts in a "close enough" settings will not give you a perfect center, but if you mark a line, then flip the jig end for end, and mark another line you will find that you have 2 parallel lines in very close proximity to one another. At this point it's often very easy to eye-ball the center mark and work from there.
As you begin using the jig, you will find that for most of the work you do, you will be leaving the jig a one convenient setting on only making adjustment from time to time as needed. Most of my wood is about 7 inches wide so I can leave my jig in a setting that will work best on that width.
Copyright Colin Knecht
woodworkweb.com
