The Eleven Grooved Box – Tools Update

I have an improved fixture for making Eleven Grooved Box splines.  Roy Underhill’s video shows the spline blank placed in a grooved block. Then the blank is planed to size with a block plane.  The problem is, this eventually cuts some off the top surface of the grooved block causing the splines to come out too small. Then the splines won’t do their job well and look terrible.

My improved method has three secret weapons:

  1. A Kerfing Plane to make the blanks
  2. A modified Dado plane with skewed blade
  3. A sizing block with a channel to guide the modified plane

Secret Weapon #1

Tom Fidgen, in his book “Unplugged Woodshop” describes a kerfing plane. You can get parts to build one from Bad Axe Tool Works. Toms kerfing plane looks a lot like a stair saw with a fence, you can see it on his web site.  My version is made from a vintage plow plane and a blade cut from an old rip saw. It’s easy to cut  a tempered saw blade. Just score it on both sides with a Dremel grinder and cutoff wheel. Put the blade in a vise and flex it, it will break along the score line.  The next problem is drilling holes in the hardened blade. It will wreck a conventional twist bit, but I had good luck with carbide tipped masonry bits.  First, center punch the hole positions well, drill a pilot hole with a 1/8″ masonry bit, then finish with another masonry bit sized to fit your screws.  Use plenty of oil while drilling.


Kerfing Plane

Kerfing Plane


This old plow plane has an inch or so of the adjusting threads stripped so I added a spacer block to the fence to skip over the bad spot. The next photo shows the kerfing plane making 5/16 inch deep slots in the end grain of a Walnut scrap. The modified plane is accurate enough that I can easily slice four spline blanks from this 7/8″ thick bit of wood.

Kerfing plane in use

Kerfing plane in use

Now that three kerfs are cut, use a backsaw to cut the four spline blanks free. I kerfed both ends of the Walnut scrap while I was at it.

Cutting the spline blanks free

Cutting the spline blanks free

The end result after a bit of block planing to remove saw fuzz. Eight spline blanks ready to be trimmed to size.

Walnut splines

Batch of eight Walnut splines

Secret Weapon #2

I always had trouble using a block plane to trim the blanks. The plane would sometimes catch the blank and break it. Since these are planed across grain, then on end grain, the plane has to be held at a skewed angle. That makes it awkward and even easier to damage the sizing block.  I have a “vintage” 3/4 inch wide dado plane with a good skewed blade. That would do a nice job on the cross grain blank but would certainly tear up the sizing block. I thought about how a shooting board constrains the blade with the small bit of iron sole below the blade. A dado plane has a full width blade so that won’t work, but the solution I’m using adds outboard hardwood skates to the plane. These will stop the cut at the appropriate depth if I make a runway on the sizing block. The skates are made from a strip of Maple hardwood flooring sliced in half down the middle, then clamped onto the dado plane.


Modified Dado plane

Modified Dado plane

This photo is an end view of the modified plane. You can see at the bottom where the Maple has been thinned to 1/8″ on each side to form skates. Skate may not be the best term as these are used as guides and as a depth stop. They are adjusted to be even with the sole of the plane.

This outrigger skate technique would also work with a shoulder plane. Or you could make a wider sizing block and just use a block or smoothing plane, in which case you wouldn’t need the skates. The iron on either side of the blade would serve the purpose.

Modified Dado plane

Modified Dado plane

 Secret Weapon #3

For the modified plow plane to work, we need a sizing block that has a channel to guide and stop the skates. I made this on the table saw using a stacked dado blade set. The wood is from a backyard Apple tree, very hard. In this photo you can see the profile, wide channel for the plane on top and bottom, a groove for trimming thickness on the top, two grooves (with slightly different depths) for trimming width on the bottom. I cut the thickness groove a little too deep so it is shimmed with Post It note paper.

Spline sizing block

Spline sizing block

The other end of the sizing block has a stop screwed on. It’s removeable to make it easier to recut the grooves if necessary. Both ends are drilled to accept the stop. The sizing grooves are not centered so moving the stop to the other end from time to time will help even out wear on the dado plane blade.

Sizing block removable stop.

Sizing block removable stop.

Using the jig is a simple matter of clamping the block in the vise, inserting a blank in the groove and go to it.  Always plane the blank to proper 1/8″ thickness first and turn the blank over a couple of times so both sides are dressed. Here you can see how the channel in the sizing block is guiding the plane. The cut stops when the skates hit the bottom of the channel.

Thickness planing a spline blank

Thickness planing a spline blank

Coming out of the first step we have a blank evenly thicknessed to an eighth of an inch.  Also in this photo you can see the port sawn into the side of one maple skate to allow shavings to exit.

Spline planed to 1/8" width

Spline blank planed to 1/8″ width

The sizing block is now rotated in the vise so the quarter inch deep grooves are up. The thicknessed blank seats in one of the grooves where it can be trimmed to exactly a quarter inch width.

Width planing a spline blank

Width planing a spline blank

This final photo shows the completed cross grain spline accurately sized to 1/8″ thick and 1/4″ wide.

Finished splin

Finished spline

These three Secret Weapons work really well and make spline production easy.

    • tomfidgen
    • September 2nd, 2014

    Nice to see some shop made tools being put to good use!
    all the best~

    • Thank you Tom. Coming from someone who actually makes money using hand tools, that’s a great compliment. And thanks again for the kerfing saw idea. Thought I could use it to saw open the boxes but haven’t tried that yet.

  1. these are really ingenious solutions
    Good work!

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