Kerfmaker uses

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Review by tenonitis posted 06-15-2010 05:09 PM 9666 views 10 times favorited 10 comments Add to Favorites Watch
Kerfmaker uses Kerfmaker uses No-picture-s Click the pictures to enlarge them

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.

View tenonitis's profile


3 posts in 3681 days

10 comments so far

View a1Jim's profile


118066 posts in 4352 days

#1 posted 06-15-2010 05:16 PM

Super Review well done


View timber715's profile


59 posts in 3879 days

#2 posted 06-15-2010 07:05 PM

forgive my ignorance, can you do it in a picture by picture step?

-- timber715 - Manila, Philippines

View j_olsen's profile


155 posts in 3946 days

#3 posted 06-15-2010 07:54 PM

timber if you go to bridge city tools site they have video that shows use of the tool

edit—sorry misread the post

-- Jeff - Bell Buckle, TN

View timber715's profile


59 posts in 3879 days

#4 posted 06-15-2010 08:16 PM

thanks Jeff, but I was referring to what he used it for. not what bridge city sells it for, if you read closer he had a different application for it…

-- timber715 - Manila, Philippines

View TheDane's profile


5823 posts in 4438 days

#5 posted 06-15-2010 10:44 PM

Excellent, useful review … Thanks!

I knew there was a reason I needed one of these!

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View Kent Shepherd's profile

Kent Shepherd

2718 posts in 4061 days

#6 posted 06-16-2010 12:08 AM

I too would like pictures. I have the Kerfmaker, so this is something I will look at closely

Thanks for the review


View tenonitis's profile


3 posts in 3681 days

#7 posted 06-18-2010 07:58 AM

I’ve got a couple of pics that may make the tenon cutting process a bit clearer. The first step is to close the Kerfmaker completely and using its shortest lenght cut a scrap of wood to the collapsed length. This is used as a stop in cutting the first face of the tenon. I used the saw rip fence as a backstop for the the block to set the tenon jig for the cut of the first tenon face. Once the fence is set it’s never moved. Cut the first face.

The next picture shows the kerf setting gadget made by taking a short cut into a scrap piece, then cutting off a short section.
The offset here is equal to the kerf made by the saw blade. The kerfmaker is first set by resting the Kerfmaker on a flat surface with both slides resting on the surface, then locking the gray slider to the main body. The combination is now placed on the kerf blockand the orange slider extended and locked to the gray slider. There is now a gap between the two sliders equal to the saw kerf.

Next I make a mortise-measuring gadget from a small block of wood small enough to loosely fit into the mortise. The block is then cut diagonally lengthwise to form two wedges.

Insert the wedges into the mortise and slide them against one another to expand the combination to tightly fit the mortise.

Remove the wedges holding them together to prevent movement and use them as a gage to set a gap in the Kerfmaker equal to the mortise width.

The overall length of the Kerfmaker is now equal to the collapsed Kerfmakerl length plus the kerf width plus the mortise width. Now use the Kerfmaker to reposition the tenon jig to cut the second tenon face.

The same method can be used to cut the remaining 2 tenon faces. If all has been done carefully you’ll have a close fitting tenon.

View Ollie's profile


146 posts in 4050 days

#8 posted 06-25-2010 11:33 AM

This looks like a great plan. However it is interesting to note that cutting timber this way on a table saw is actually illegal in the uk. No table saws are available with vertical attachments in uk, also some other european countries.

-- Ollie, UK.

View cutmantom's profile


407 posts in 3810 days

#9 posted 06-27-2010 12:57 AM

good work

View Rick's profile


367 posts in 3985 days

#10 posted 07-07-2010 04:23 PM

Cool looking little tool. Nice review.
I’d have one by now if they kept these little things in stock. I’m more of an impulse buyer. The higher price and knowing that I won’t receive it for a few months is enough to keep me from buying.

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