I began work in my shop this morning by squaring up the corners or ends of these router bit made mortises. As you can see I have an Irwin Marples 3/8” or 10 mm hand chisel as well as a Robert Sorby mortising chisel in the same size 3/8” or 10 mm.
For this blog entry I am writing what I plan to do next instead of writing briefly what I did in my shop. Maybe this way I will be more thorough and clear of what my steps will be.
I subscribe to Woodcraft Magazine. I love their articles.
Paul Anthony wrote a Woodcraft article on Twin Blade Joinery in the Feb/Mar 2016 magazine. In the article he instructs how he cuts his tenons on his table saw. He uses two rip table saw blades that leaves him flat tenon shoulders. He knows exactly what shims to place on his arbor to get the tenons widths that he needs for his mortise and tenon joinery. I decided to use this same method after analyzing many methods used by experienced woodworkers.
Since I recently purchased a Saw Stop table saw, I also needed to make a new tenon cutting jig. I wanted a tenon JIG that would ride and track on top of my Saw Stop’s T-Glide fence. I liked Bob Van Dyke's multi-use tablesaw Rip Fence JIG. His instructions were the magazine cover article for Fine Woodworking Magazine , issue #231. I am already enjoy using this rip fence JIG system.
To cut tenons using twin rip blades on my table saw I went as far as following Paul’s instructions to order a 1/4 inch aluminum plate. I even cut the shims out at my bandsaw like his article instructed. That was two much work. Messy. I was sweeping pieces up for days, or maybe even weeks afterwards. Plus my disks did not turn out as pretty as Paul’s, but they are functional. They will do the job.
It was after these disks were formed that I discovered in my local Woodcraft store that I could have bought a set of extra DADO shims that would have worked for cutting tenons. If I had done that I could have given my Diablo DADO set to my son when I gave him my Porter Cable contractor table saw. Maybe he will still end up with a free DADO set, but he better get using that saw. Right?
As can be seen in the photo below I use two Freud RIP table saw blades with shims I cut from the aluminum plate plus the shims I own in a Freud Diablo DADO set. I have labeled every shim with a unique letter from our alphabet. I also wrote the thickness I measured with my digital calipers. Those measure are close, or in the ballpark since every attempt measuring their thickness can vary a bit when getting precise to the 1,000ths or 10,000ths.
With a scrap block of construction Douglas Fir, I punched test mortises for the different size of hollow mortising chisels I own for use with my Powermatic bench top mortiser. I recorded in my shop journal on page 40 the combination of shims I used inside the twin Freud rip blades that gave me a good tenon fit in this test mortise block.
Today, with the 3/8” mortises I cut in this test board, I will check if my combination of shims will be a good fit to these plunge router bit made mortises. Either way I will record the combination of shims that give me the best friction fit. I suspect each mortise I cut will be unique, but the best shim combinations I record will give me a good starting point. I would rather have the tenon a bit thick instead of too shinny. I can always use a shoulder planer or a rasp file to thin a tenon in order to get my preferred fitting.
That is my plan for today or tomorrow. I will not only perform a test in this scrap Douglas Fir, but I will also test mortises in a cherry scrap piece of hardwood.
After all of these test I will begin cutting the mortises and tenons for my trestle table leg assemblies. I am hoping after all these test that I will have a reliable procedure to follow on my trestle table build.
-- --- Happy Howie