I have one of those much unloved Delta Tenoning jigs. It's an older model: 34-182, but the features seem to be the same as the more recent versions except for the location of the handles and and type of knobs on the adjustment screws. This link http://www.woodgears.ca/tenon/review.html lists some of the faults of this jig, as well as its' many clones. I remember trying to figure out how the various adjustments worked when I first got it. I used it for various projects, but found that some of the adjustments remained obscure. Recently, while reading the web site referenced above, I regained an interest in trying to get it to work better, especially after learning that author of the site had made a tenon jig capable of cutting both faces of a tenon without unclamping the work. This obviously improved the accuracy of the tenon since both cuts are referenced to the same side of the workpiece. Disassembly of the jig allowed me to clean up some burrs that I had created in the past, but allowed me to understand the functioning of the jig enough to modify it to allow cutting the two faces of the tenon without unclamping the workpiece in between cuts. I also substituted a Rockler cam lever for the difficult to use knob of the original jig.
The modification entails substituting a long 6 mm screw for the jig travel stop screw. It's the threaded rod with the brass handle and wingnut in the photo. The original set screw was used keep the face of the clamping plate from crossing the cutting plane of the saw blade. By lengthening the screw, I can limit the travel of the jig face even earlier, so that the closest saw cut is displaced from the clamping plate. The procedure is to advance the screw until the red indicator shows the position of the closest face (minus the width of the saw blade). (The smaller clamp on the jig surface, that locks the sleeve of the fine adjustment knob, is left loose). The fine adjuster is turned so that the shoulder of the fine adjuster sleeve will limit the travel of the jig for the second cut. With the jig cam clamp (blue) unlocked, the jig will travel between the stop screw and the shoulder of the fine adjuster sleeve. This defines the thickness of the tenon. The blue clamp locks the jig at either position. Since the jig top rests on the heavy steel rod and is clamped to the bottom by the large 10 mm bolt, it will hold its position relative to the saw blade once it is clamped.
The new cam lever uses existing bolt locations and threaded holes to implement its' actions. There is a small washer under the black plastic push handle to raise it just enough for the lever arm to to move freely. The pivot on the longer lever is a 6 mm bolt replacing the set screw holding the existing connector. This new lever enables moving the jig between the two positions without risking exposure to the blade during cutting, as well as doing it smoothly, since the mass of the jig makes it otherwise awkward.
The total cost of this modification is less than $10. Even less if you have enough scrap lying around.
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