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Making a fixture to cut dovetail slots – Making the do-nothing machine manually

The Do-nothing machine base with hand cut slots.

I have read many many places that you can cut dovetail slots in a board by hand. They say use a saw to cut the outer edges and then use a chisel to remove the material in the center.  That all sounds good,  except I was never able to hold the saw accurate enough to cut those saw cuts.  Finally the brain kicked into gear and I figured out a method.

When I started this blog one of my goals is to not push the tools.  There are many do-it-yourself sites that show work being done, but often it is done with a whole workshop of high priced special purpose tools.   Work was done before all those tools were available using simple hand tools and skilled craftsmen.   I am no skilled craftsman but I can usually reason my way though a job.

When I decided to build the do-nothing machine the first time,  I used a special bit and a router to make the slots in the base plate.  Although a router is not one of the special purpose floor mounted large machines, I still wanted to figure out a way to do it using simple hand tools.  The problem is it was very hard to keep the saw from moving while I was starting the saw cut.  Holding the saw consistently at the same angle while starting the saw cut was impossible for me. I needed some sort of fixture to help me out and of course I started with complicated ideas.  Then one day while making a simple mitre cut using an inexpensive mitre box the idea hit me.

Marking the inside of the mitre box.

A mitre box is a wooden or plastic box with groves cut in it to align a saw while material is held to the back of the box.  These can be found for less than five dollars. My problem was that these have several 45 deg angles (mitre angles) and one 90 deg angle, but nothing that would work to produce the angle needed for the slots.  also the box is not wide enough to hold the  7 1/4″ board I was cutting to make the base plate.

14 deg sine and tangent calculations.

The solution was to cut guides out of scrap material. Since a 14 degree angle worked well on the router cut grooves I decided to use the same angle.  The chart to the left was a spreadsheet I used to calculate the sine and tangent of a 14 degree angle.  I used another even smaller scrap of wood to hold the end of the wood I was cutting up off the base of the mitre box.  This piece of wood was 1 1/2″ thick so all I had to do was measure a little over 6″ from the edge of the block and make a mark in the miter box.  This is where I placed the end of the piece being cut.   The piece would be at a 14 degree angle so vertical cuts would make my 14 degree groove when it was laid flat on the work piece.

Cutting one of the guides.

At that point the cutting the guide was straight-forward.  In all of these cuts I used a back saw.  A back saw is one with a stiff edge along the back side of the blade to prevent the blade from warping while being pushed.  I used a 1X2 pine board to make the guide.  If I was purchasing the material I would have chose something smaller, but this was the wood I had on hand.  A 1/2 square dowel rod would work well for this purpose.

Gluing the guides to the work piece.

Placing the first two of the guides was easy.  Simply place them on the lines drawn on the board.  Clamps could have been used to hold the guides to the base board but this would cause problems trying to hold the whole thing while sawing.  Instead I chose to glue the guides using hold melt glue.  Because this glue is quick setting and not absorbed into the wood it did no damage to the work piece.  It was easily removed with a wide sharp wood chisel being used as a scraper.  The first of the second piece was a little challenge.  I placed the saw next to the glued pieces before gluing the second piece.  This ensured I had just the right amount of clearance between the pieces.  The challenge was holding the saw while doing the gluing.

sawing the grooves

One everything was in place making the saw cuts was the easy part.   I clamped the workpiece to the work bench and just sawed away.  The only thing to be aware of doing this is it is easy to put too much pressure on the handle end of the saw and end up with the handle end of the cut deeper than the other end.

crosscut grooves cut


I chose to cut the cuts along with grain first and chisel out the center of it before doing the cross grain cuts.   I am not sure if the order of doing the work makes any difference.   There is a big difference in chiseling with the grain and cross grain.   It is easy to try to take off too much material too quickly while going with the grain and gouging the wood.   This would especially be a problem if working with some course grained material such as pine.   I was working with poplar which is fine grained and worked very well for this purpose.

chiseling out the cross grain wood

The last picture shows the chips as I was chiseling out the cross grain slot.   I used the handle of another chisel as a “hammer” so I did not cut very deep with each cut.  The work went quickly and easily.  I used my knees as the vice to hold the wood while I worked.   Make sure your chisel is sharp and for the final cuts sharpen it again.  For the final smoothing you will want to remove very little material and simply pushing the chisel by hand will work very well.

I did not make the shuttles for this one, but if I do I will probably use the same method to guide the saw.  It will be necessary to place another piece of wood next to the one I am cutting to have something to use to attach the guides.

I will have one more post about the do-nothing machine.  That one will be dedicated to power tools and how I would make fixtures if I were wanting to produce the machine in quantity for sales.  That would be for small scale manufacturing.

As always, thank you for your time.  I hope I have helped put it to good use.

If you find this blog interesting and entertaining, please consider subscribing using one of the methods available, RSS feed, facebook or twitter.  I also have an e-mail subscription method that sends a short e-mail each time I post something new.



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