Bridge City Tool Works - Kerfmaker (Rating: 5)

I broke down and bought one of these gadgets despite the high price since I planned to give it a lot of use. It works as advertised but I had a different application in mind than cutting half laps or kerfs. I wanted to use it for its opposite function, one not advertised, making tenons. I understand that Bridge City plans to introduce a new tool for this purpose, but I think they don't understand that the Kerfmaker can already do this. The key is to invert your thinking and instead of using it to subtract the width of tool kerf, use it to add it.

First cut a piece of scrap wood (or metal) equal to the length of the main Kerfmaker body. This will be used to set a stop on the saw table. Next loosen both adjustment screws and while resting the unit on a flat surface lock the gray sliding unit. As described in the Kerfmaker instructions, make a gage to determine tool kerf by cutting a short kerf in a wood scrap, then cutting off one segment. When this is stacked as shown in the picture it creates a step which is the exact width of the kerf. Now rest the main body of the Kerfmaker on the higher portion of the stacked wood and extend the orange Kerfmaker segment to rest on the lower wood segment. This creates a gap between the sliding pieces equal to the tool kerf.

The next trick is to make a gage to measure the tenon thickness. Do this by taking a short piece of wood, about 3/4×1 x 3 and cutting it diagonally lengthwise to make 2 wedges. The size of the wood depends on the width of the mortise to be gaged. When these 2 wedges are placed in the mortise they can be slid relative to one another to expand the overall width to the width of the mortise. While holding them in their expanded position, use them to set the gap in the Kerfmaker between the main body and the sliding gray piece. The result now gives an overall length of the Kerfmaker equal to the length of the main body plus the width of the mortise plus the kerf of the the saw kerf.

I use a homemade version of the Delta or Grizzly tenon jig as shown in the picture attached. I first set the tenon jig to cut the outer tenon surface and then set a stop by spacing the rip fence the distance of the main Kerfmaker body away from the tenon jig using the previously cut piece of wood as shown in the attached picture. Cut the first face. Now move the tenon jig away from the rip fence by using the preset Kerfmaker as a spacer. The result of this is that the second tenon face is now spaced away from the first surface by the width of the saw kerf plus the tenon thickness. Cut the second tenon face. The result is a tenon the exact width of the mortise.

An advantage of this method of cutting the tenon is that its width is set from one face of the wood so even if the wood faces are not parallel you still get a perfect tenon. This works well on tapered pieces as well.

I hope you can follow the above description. I don't have video equipment which would have made the process easier to follow.