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Did you know that feelers aren’t just for machinists or for checking and adjusting our steel and cast iron woodworking equipment? How do I know? Because I recently discovered that a set of feeler gauges can be very useful for setting the exact amount of play (tolerance) needed for a jig router I have built.
This week I built a jig to help me mill the two grooves on the head of my signature cutting boards. My cutting boards have two grooves that intersect with the large hole and allow the hanging rope to nest inside them.
To help me get rid of the grove I built a template that drives my Ryobi router. The plan was to mount two hardwood slats on the plywood board to flank and direct the router as it passed.
After screwing the first batten onto the plywood plate, I slipped the router base against it and introduced the second batten onto the other side of the plastic plate. I moved the router and felt the resistance or friction created by the two ribs. It seemed excessive, so I decided to leave a small gap between the router plate and the slats.
Many carpenters use paper bills or money when they need this type of shimming. However, I wanted to find the ideal amount of tolerance, so I decided to use a feeler gauge.
After making sure that the base of the router was well pushed against the first batten, I placed a steel shim against the other side of the base and pushed the second batten towards it. I held the splint down and removed the shim. So I tried sliding the router and rated the game. I repeated this process several times with thicknesses of different thicknesses until I found the right one. I brought back the thickness, slipped the batten firmly against the router, locked the batten and screwed it in. After removing the shim I tested the setup – The router glided perfectly and with just the right amount of play.
A few more points to remember
Wood is a working medium that swells or shrinks in relation to the amount of moisture in the air. So you need to incorporate shims in an informed way when setting tolerances for moving parts or parts that will swell or shrink. It may take trial and error (parts that were set up in the winter may jam or freeze in the summer), so try to find the right spot for the right amount of play. Another good idea is to incorporate some configuration flexibility into your design. For example, drill through holes wider for the hardware to allow for later adjustment. In my case, I used plywood and ash strips. I’m not expecting any jamming this summer, but if that happens I’ll loosen one of the laths, slide a thin shim between the router base and the loose lath, and re-tighten the lath screws. It is worth noting that pan head screws should be used instead of flat head screws designed to center in the hole.
One last point. The holes in these inexpensive power meters like the one I received are stamped and the circles may lift up and add unintended thickness to this area. So avoid using the thickness hole area or smooth it out before slipping it between the parts.
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