Making a Wooden Screw and Nut: Part 2

OK, this time I'm attempting to make a screw-box.  This device has two blocks and a cutter.  The two blocks are the same length and width, but different thicknesses.  In his book "The Woodwright's Workbook", Roy suggests making the rearmost block as thick as 6 threads of the screw.  With a pitch of 3/8", that's 2 1/4" thick.  The front block is about half as thick.

It's best to make them the same length and width for layout purposes.  I used the bottom edge as the reference and used a marking gauge to scribe a centerline around both blocks' long axes.  Then a square and a knife were used to mark a centerline across the grain.  These lines help with alignment of the two pieces later.  The blocks were screwed together and marked together for this.  The marks also give a center for laying out and drilling the holes.

The front block gets a 2 1/8" hole.  This was done with coping saw, incannel gouge, rasps and files due to not having the proper size drill.  The rear block gets a 1 3/4" hole (made similarly).  Once these holes were made, I used the tap from last week's post to cut the interior threads in the rear block.

Turning the tap into the rear block

Testing with the screw that I made last week

The next step was to shape a cutter.  The only steel I had on hand that might be big enough was some 1/4" square O-1 steel.  With thread pitch of 3/8" and a 90 degree angle between threads, the math works out that I need just over 1/4" (about 17/64") on each side of a cutter to cut these threads.  And it's better to have more than not enough.

Well, I started shaping the 1/4" stuff I had just to see if it might work, but I'm getting bogged down.  Here are some shots of the shaping.

Creating an angled flat on one corner

Going from corner to opposite corner and back to 1" from the end

Then marked a center line on the resulting flat

Used a hack saw, then square and triangular files to get final shape.
Sharpened the edge with slipstone and strop. 

There's another problem when shaping a square piece of steel as I've done.  When it is mounted in the rear block, there's a corner of the square rod sitting down into the recess that has been chiseled out.  That means I had to chisel the recess with a matching shape.  Not sure how well it shows up in the next pic, but the recess is pentagonal - like the roof of a house upside down in the bottom of the recess. 

The recess for the cutter

I can tell this isn't working out.  I was thinking about ordering some 3/8" square steel, but even then if I orient the steel so there is a flat face at the bottom of the recess, the "wings" of the cutter are just 17/64".  Damn!  After a quick calculation, it looks like I'll need some 1/2" x 1/4" steel.  And I can get it in a 6" length from McMaster-Carr.  Let's hope it goes better with that!