An Easier Kerfmaker




Introduction: An Easier Kerfmaker

I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making an...

Someone showed a group of us a simple kerfmaker he built from scrap. I was reminded of a nice aluminum kerfmaker Instructable posted by Steliart and I thought about building it. This Instructable describes an easier kerfmaker I built from some hardwood. It is not a disposable kerfmaker fitted for only one tool. The precision sliding parts are so easy to make well that it is almost foolproof.

A kerfmaker is initially set by you for the thickness of your cutting tool (saw blade, router bit, bandsaw blade). From that point, it allows you to set the kerfmaker for the thickness of a piece of work so you can make a precise dado for that piece without further measuring.


  • 3/4 inch oak
  • #8 screws, nuts, and a Tee-nut
  • Tempered fiberboard
  • Glue
  • Paraffin


  • Table saw
  • Plane or sanding drum and small table for smoothing and truing
  • Drill and bits, including countersink bits
  • Router and bits, router table
  • Clamps
  • Hammer
  • File
  • Pliers

Step 1: Rip Oak

I ripped some scrap oak to strips 1/2 x 3/4 inch. (I would use 1/2 x 1 or 1 1/4 inch next time, if possible.)

I smoothed and trued the pieces. (second photo) I have a 2 1/4 x 3 inch sanding drum on my radial arm saw. I often use it and a small table to push pieces under a sanding drum. The table acts like the bed of a plane. The pieces are smoothed and straightened at the same time. It is important to keep the work moving so it does not burn or get cupping. That means several light cuts and flipping the workpiece often.

Step 2: Cut and Rout

The length of the pieces is determined by the width of the largest dados you will ever cut. One pair of pieces are around seven inches long, each. The other pair are about an inch shorter. I could make a dado almost as wide as a 2 x 4.

The two longer pieces will be glued face to face, but also need a screw slot down the center. I used a router in a table to remove half of the #8 screw's thickness from each face. Remove about 3/32 inch from each inner face, but leave some of the face untouched near both ends as shown in the photo. (My router bit is old and leaves burn marks.)

Step 3: Remove More Material

I removed about 3/16 inch of material from what will be the top surface of the two longer pieces. I could have used the router, but decided to use my homebuilt table saw. I moved the miter gauge during the process and worked from both sides of the blade to keep my fingers farther away from the spinning blade.

Step 4: Make Bevelled Edges

I used a bevel or chamfer router bit to make an angled surface on one edge of each of the four pieces. When the pieces are glued together in their proper order, one set will make an external "V" and the other will make an internal "V." (See the second graphic.) This makes two parts of the kerfmaker that slide over one another in a very precise and smooth manner without the multiple operations involved in making and fitting a raised surface and a corresponding recessed surface and then making it all fit closely. I carefully marked the end of each piece on one end with a diagonal pencil line so I would not become confused and make a cut in the wrong direction. (I have another fence I made that encloses the bit while it is spinning, but my wife cleaned my workshop and I have not found it again.)

Step 5: Fiberboard End

You will need to trim a tiny amount from each glued up assembly to make certain the ends are square and smooth..

I cut a piece of tempered Masonite 1 x 1 1/4 inches for the end of the longer slotted piece. I glued and clamped it to dry.

See the second photo. The two main pieces are resting one on the other. I added a screw to add extra security to the glued joint. The head is countersunk, but I still needed to file and grind a little to make sure the end is smooth.

See the text box in the second photo. While the nascent kerfmaker was in this position, I drilled a hole for a #8 screw vertically near the closer end of the screw slot from step 2. I drilled a countersink for the head on the underside of the bottom piece.(My photo of this was very blurry. See one of the text boxes in the photo from the next step for a photo that includes the screw. When viewing that photo and text box remember that the screw appears to be at the far end because the piece has been turned end for end.)

For smooth operation, I rubbed a little paraffin on the mating surfaces.

The soft jaws on the vise are from another Instructable I posted.

Step 6: Bottom Piece

I cut the bottom piece so it is about an inch shorter than the upper piece. (See the very last step for dimensions.) I am using a Tee-nut for an 8-32 screw. I drilled a hole straight into the front end of the bottom piece for an 8-32 machine screw 1 1/2 inches long. I expanded the hole near the surface to 1/4 inch in diameter to accommodate the threaded portion of the Tee-nut. In order to make certain the screw aligned with the longer hole inside the bottom piece, I threaded a substantial amount of the screw into the Tee-nut. I tapped the screw enough to start the prongs on the Tee-nut. (Be careful, tapping too hard makes it is easy to damage threads on either the screw or the Tee-nut.)

I removed the screw and drove the Tee-nut home. This aspect of the kerfmaker allows very precise adjustment for the thickness of the cutter. The screw acts as an adjustable spacer. It can be extended or retracted a few thousandths of an inch and locked with a hex nut against the Tee-nut. Making it is much lower tech. than what usually goes into a homebuilt kerfmaker, but it is also very easy to do.

I used a file to grind the Tee-nut flush with the bottom surface of the kerfmaker.

Step 7: Set for Your Cutting Tool

I am setting the kerfmaker for the saw blade I normally use on my table saw. Kerfmakers can be used with dado blades, router bits, and saw blades.

Place a straight piece of wood against the saw blade. Use a square to align the kerfmaker with the straight piece of wood. Be sure the lower piece is slid tightly against the Masonite. Turn the adjusting screw so it just touches the near edge of a sawtooth. Tighten the locking nut without allowing the screw to turn out of adjustment. Check again to be sure the setting is accurate. (If the screw is adjusted too tightly against the sawtooth, it will be as if you erroneously made the setting for a thinner blade and your dado will fit more loosely. If the screw is adjusted too loosely against the sawtooth, it will be as if you erroneously made the setting for a thicker blade and your dado will fit too tightly.)

If you use only one cutting tool to make dados, you can leave this adjustment undisturbed forever. Otherwise, you will need to make this adjustment each time you use a different cutting tool.

Step 8: Fit the Kerfmaker to the Piece in the Dado

You are making a dado to fit closely around a shelf or a cleat. Fit the kerfmaker to the wood for the shelf or the cleat. Tighten the adjusting nut with your fingers. Without allowing anything to move out of adjustment, tighten the adjusting nut a little more with a pliers. (There really is not enough space for a wingnut.)

Step 9: Mark One Side of the Dado

I have made a pencil line where I want the left side (as viewed) of the dado to be, and I have aligned it with the saw blade so the blade cut will be inside the dado.

Step 10: Place the Kerfmaker

The dado I am cutting will open to the right of the pencil line in the photo from the previous step. Regardless the actual size of the two parts in the kerfmaker, look at it now as adjusted for the thickness of the wood that will fit into the dado. The half with the adjusting screw is longer than the side without the screw. I am setting a stop clamped to the saw table. The short side of the kerfmaker sets the space between the 2 x 4 into which the kerf is being cut and the stop. Make a saw cut.

Step 11: Second Kerfmaker Cut

Turn the kerfmaker end for end. The long side of the kerfmaker now sets the distance between the end of the 2 x 4 and the fixed stop.

See the second photo. The outside edges of the two saw cuts define the dado. Now all that is left is to cut out the waste between these two saw cuts.

Step 12: The Fit

Pictured is the result of sizing a dado using a kerfmaker. It fits acceptably well, but a little more loosely than I expected. I did discover the very tip of the sawtooth was able to dip into the recess for the screwdriver in the screwhead and that distorted the accuracy of the set up in step 7. I could have filled the screwhead with a bead from a welder, but not everyone who reads this has a welder.

See the second photo. I cut the head from the screw with a hacksaw. I laid the screw end on a piece of steel and flattened the threads a little at the end of the screw with a hammer. I turned on a nut from the other end and jammed it onto the slightly crushed threads. I ground the face of the nut and screw flat to be flush with one another. I went back to step 7 and set the screw for the thickness of the sawblade.

See the third photo. I set the kerfmaker for this piece. My dados were still a little looser than I expected, although acceptable, so I turned the screw a third of a turn into the kerfmaker (made the screw shorter) and locked the retaining nut. The dado in the third photo is nicely snug like I was expecting it to be. A third of a turn is a tiny amount of difference. I am finding it is easy to be a tiny bit inconsistent in how much pressure is applied when fitting the kerfmaker to the piece that will fit into the dado in step 8, or when adjusting for the cutter thickness in step 7, or even when pushing the kerfmaker against the stop or the work against the kerfmaker when making the cuts. Each of these changes the snugness of the fit in the dado. (If the dado fits too snugly, there is less room for glue on all sides of the dado. Much depends on your needs. I will probably make a test dado or two if I need a special fit.)

Step 13: Dimensions I Used

The photo shows superimposed dimensions taken from my kerfmaker for anyone who wants a starting point in building his or her own.

Here is a very complete video on using a commercial kerfmaker.



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    29 Discussions

    I wasn't understanding exactly what you were making... so I did a Google search and found a VIDEO showing it in use... actually another slightly different style.

    So now I get it.

    1 reply

    I did include a video on using a kerfmaker in the last step. I am glad you got it.

    Is "kerfmaker" a real word? I get the feeling someone is playing a joke and kidding around with fake words.

    2 replies

    It is the common term used to name these. Do a Google search and you may not find a Merriam-Webster entry for it, but you will find the word has wide use otherwise.

    My Grand Dad had missing fingers from working on a "home made" table saw.

    there are always reasons for not working safely

    the jig is clever!

    uncle frogy

    1 reply

    safety is always the key! making or using feathered boards or other jigs to hold items in place is the key to keeping your fingers from being sanded or rubbed.

    I'm glad you are learning and working on different projects but you need to make a throat plate before you destroy your saw or you. You are asking for trouble cutting wood that way, so please take the time to make one out of suitable material before you end up in the hospital. I wish you were a neighbor because I would help you fix that, but since I'm not find someone that can. I have an old tablesaw that would help someone like you because it has the basics but it needs some love. Good luck.

    10 replies

    I have looked at the throat opening on my saw and thought about closing it, but had not resolved some possible problems involved in adding a throat plate.

    Long ago I heard a couple of stories about early carbide tipped blades throwing teeth, and have always stood off to one side when sawing in case the saw did throw something, whether a carbide tooth or a piece of wood. (It never has thrown anything.) And, when I am cutting something that will result in a small piece falling off of the work into the opening, I cut it part of the way until I can pull the miter gauge toward myself and break off the waste piece by hand so it does not fall through the opening. Then I push the miter gauge forward and remove the burr left by breaking off the waste with my hand. I have added some precautions to circumvent the absence of a throat plate, and those precautions have served me very well over quite a few years.

    Thank you for your concern.

    Had a friend that hooked an DC series (constant power) motor to his table saw. His shop was in Colorado at such a high altitude, the air resistance was nill so the blade ran extra fast. So fast in fact it threw all the carbide teeth. They punctured the walls and roof and during the next big wind storm the building ripped in half along the dotted line. Luckily he was not standing directly behind the blade ;-).

    Thank you for the story. I recently saw a router bit on Harbor Freight's web site rated for 12,000 rpm, but routers often run at 30,000 rpm. The bit has a carbide tip. I am always cautious about carbide tipped cutting tools.

    A lot of Routers have variable speed. I can set mine to run at 10,000 or 30,000 RPM.

    I got my router in 1974, and routers did not have variable speed then. It still works too well to replace. You are fortunate to be able to enjoy variable speed when you need it. I have always believed a big part of what makes a router do a good job is its speed. How is the cut quality at 1/3 the speed?

    I absolutely love my router! I've fought with garage sale routers, cheap ryobi, I had finally got a good deal on the Bosch 16/17 router and like it, it works very well. But I just picked up the Porter cable 7518 and WOW! I'm blown away with its performance every time I run it. If your router is 1974, you really should splurge and pick up a newer model. The soft start, variable speed really are nice to have. Especially when you want to raise a panel!

    I got my router in 1974, and routers did not have variable speed then. It still works too well to replace. You are fortunate to be able to enjoy variable speed when you need it. I have always believed a big part of what makes a router do a good job is its speed. How is the cut quality at 1/3 the speed?

    you can pick up a cheap variable speed controller for your Router, I did that with my first one. it was an old Craftsman and all I had to do was plug the speed controller into the wall and plug the router into the controller... I added a foot switch and was good to go. Now I finally have a really good router that's got the internal speed controller so I use the external controller for my wood lathe... lol Oh but I LOVE the foot switch.. I use it on all my machines, its so convenient. BTW, My Table saw came with a metal throat plate that was worn so I made a new one out of oak, I used the saws blade to cut the opening in it so its a zero clearance plate it works great. was super easy to make and looks good too! lol

    I do hope that somewhere down the road you're able to make a throat plate along with a guard and riving knife. I've been fortunate because I've cut aluminum, magnesium and wood on my tablesaw and miter saw, and with my cutoff saw I've cut steel and copper and have never lost any carbide teeth, knock on wood, if I do that will be the last time I purchase a blade from that manufacturer. Like you I enjoy building or rebuilding vintage tools but safety is always at the forefront, except I could never justify the cost for a finger sensor. I'll get off my soap box because we both have other things to take care of. Keep building and inventing and be safe, I'll get off my soap box. Best wishes for the future.

    Thank you. I was quite young when I knew I wanted a table saw or a bench saw, a term that dates me. In those days no one had heard of blade guards or riving knives. We knew table saw are dangerous. Some sustained injuries, but I remember more people with stubby fingers from an encounter with a planer/joiner than with a table saw. One of the better safety tips I have seen is to keep the blade elevation as low as possible. If my fingers did tangle with the blade during use, it would be a shallow flesh wound, not the loss of fingers. From what I see, very few people pay any attention to how far above the work the blade rises.

    I did make a riving knife for a saw I sometimes use. I even made it adjustable side to side for careful alignment. For whatever reason it caused the wood to bind between the riving knife and the saw fence a couple of times. Life is too short for that. Once I was ripping a piece of 3/4 inch stock and it had some internal stresses released by my rip cut. The two sides of the cut began to bow into one another. After that, when I saw a hint of bowing to close the kerf, I have kept a screwdriver near and pushed it into the kerf far behind the blade to keep the kerf open, but, even that has been a very rare happening.

    I listened once to a very interesting feature on shortwave radio. Research in Germany showed people driving automobiles take more risks when there are more safety features, like ABS brakes, on a car. Safety features should be a supplement leading to added safety, not a reason to take more chances. For many additional safety features provide a false reason to be less cautious.

    My only visit to the ER was 50 years ago to get precautionary X-rays a few hours after a guy opened his car door in front of me without looking while he was parked and I was going nearly as fast as I could on a bicycle. I did once get a small scratch on my hand while changing a saw blade, but it did not even require a bandage. I grew up around open saws mounted on a tractor for cutting limbs for firewood. I learned early to assess where the dangers are and take precautions against them happening. That was long before many of the safety features many consider essential today. If you read the other comments, you know both Popular Mechanics and Popular Science published plans for circular saw to table saw conversions. Those did not have throat plates, but they were offered for the public in national DIY magazines.

    great job... I'll have to make one of these soon! Thanks!