Thursday, May 20, 2021

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!

Saturday, May 15, 2021

Making a Wooden Screw and Nut: Part 1

A few years ago while rehabbing a wooden screw-arm plough plane, I looked into making wooden screws.  Let's just say it was not a stunning success.  I have Roy Underhill's "The Woodwright's Workbook", which has a section on making wooden screws and nuts.  But as many times as I've read it (several!), some parts still don't sink in.

After recently seeing something about it on YouTube, I thought I'd give it another try.  This time, I'm making a much larger screw and nut: the root diameter will be 1 3/4".  I'm just winging it with regards to the thread pitch.  It seemed that 3/8" peak to peak would be about right.  With a 90° angle between threads, the geometry works out that each gullet will be 3/16" deep. 

Mistake at bottom: should read 1 3/4 diam --> 5 1/2" circumference

There are two parts to the tap that is used to cut inside threads.  The first is a dowel that has a spiral kerf sawn into it and a cutter mounted in a mortise through the dowel.  The second is a special "nut" that pulls the dowel and cutter into a workpiece.

First the nut - a block of wood and a piece of steel .  I needed to make a 1 3/4" hole in a block of poplar.  I have a 1 3/4" Forstner bit, but with my drill press in storage, my holes when using a power drill were not even close to square to the surface. I have expansive bits for the brace, but for the life of me I can't get them to work well for holes this size. Though it was far slower, I had better results marking the hole centers on front and back, marking the holes with a compass, sawing with a coping saw and paring to the lines with an incannel gouge.

Poplar block with 1 3/4" hole

There needs to be a piece of steel let into this block and I used a piece of a mending plate.  It's thickness was in the range of .030 or 0.040" - something that would fit a saw kerf reasonably well.  In the pic below, you can see that I inserted it into a saw kerf that was cut at an angle into the top of the block.  The kerf extends about 1/3 of the way into the hole.

Sheet of metal in the angled kerf

The angle is the same as the angle of the threads that will be cut and is calculated as follows.  For my screw's root diameter of 1 3/4", the circumference is pi times diameter, or 5 1/2".  The block above is 5 1/2" long, same as the circumference.  For a thread pitch of 3/8", I cut the kerf in the block so that the right side is 3/8" further away from the front of the block than the left side.  When the piece of steel is inserted, it is marked for the arc of the hole and then shaped with hacksaw and file to leave about 1/8" to 3/16" showing inside the hole.  The ends of that arc are also rounded to make it easier for the cylinder to start threading onto it.

The metal piece is shaped to leave about 1/8" arc of steel within the hole

The cylindrical dowel starts out as a squared up piece of stock.  As you'll see later, I chose rather poorly the first time using Douglas fir.  Poplar worked much better.  It's far better to mark this out while it's square.  First, I drew centerlines and octagonizing lines on all four faces.  Then I marked a knifeline every 3/8".  On each adjacent face, these lines were offset from the previous face by 3/32".

Marking center and octagonal lines

Using a 3/8" setup block, square and knife to mark every 3/8"

It's also far better to mark out and chop the mortise for the cutter and wedge while the stock is square.

Chopped the1/4" x 3/8" mortise for the cutter / wedge

The opposite side is 3/8" x 3/8".

1/8" x 3/8" piece of O-1 steel and wedge

Fitted to the mortise - cut the length down later

Making the dowel octagonal with jack and smoothing planes

Rounding with homemade spokeshave

Testing for high spots and fit in a pine scrap with 1 3/4" hole

Once the dowel was round, I penciled in the spiral by joining the 3/32" offset knife lines that had been struck earlier.  The dowel started out at 1 3/4" square, so no material needed to be removed at the center of each face when rounding the dowel, thereby keeping the knife lines.  Then I sawed the spiral kerf.

Setting sawing depth to 3/16" with blue tape

Sawed the kerf along the laid-out spiral

Sawed and ground the cutter to shape

First test cut on that same pine scrap

It's working!

With deeper cuts, ran into difficulty

The Douglas fir tap was not up to the challenge ...

The kerfed tap completely disintegrated

Starting with a new poplar dowel and better method of ensuring depth of kerf

Testing in a piece of poplar, using grippy mat to turn the tap

Relieved some material in front of the cutter to give shavings a place to go
Wow!  This is exciting, but ...

... the cut at end grain was very rough

So I wetted the end grain areas with mineral oil, waited a while
and made a few more passes.  Got a MUCH smoother cut.

OK, so I got a nut made.  Now to make a screw.  The geometry of this thread pitch made it necessary to use a dowel with 2 1/8" diameter.  Normally one would make a screw box to make the outside thread, but I wasn't ready for that yet - maybe next week.  For now, I'm going total Neanderthal and using a saw and chisel.

Started by laying out and cutting a kerf similar to the tap.
Added a spiral pencil line centered between kerfs.

Then got to chopping with help from a mirror and bevel gauge set to 45°

After chisel work - note pencil lines remaining

After filing with a course square file

Testing in the nut.  Needed a little extra filing on a few threads, but it's a damned good fit!

Well, this is exciting!  What am I going to do with this wooden screw and nut, you ask?  I don't know yet; I was just having fun.  But the possibilities are many.  For now, though, I'm going to look into making the thread-box.  That's the part I had no success with a few years ago.  Until then ...

Thursday, May 6, 2021

Simple Rustic Frame for Needlepoint Art

For a few years now, my wife has wanted a frame made from very old, weathered wood for a picture or other art.  When she first asked, I went out and bought two pieces of what I can only guess were old fence boards that were thinned to 1/2" and sold for great profit (they were junk, destined for landfill, when someone caught on to the craze for weathered wood).

The wood was so weathered that it was coming apart at the ends.  So I stabilized the wood by using some 1x4 pine, thinned to about 1/4" and glued to the back of the weathered wood.

The wood for the project

The weathered wood was just shy of 3" wide and the pine was made 1/2" narrower so that when glued on it created a 1/2" rabbet.  I needed the rabbet to be deeper, so I got to use a woodie rabbet plane to deepen it.

This old D.R. Barton skew rabbet plane works very well

One might notice that the backer pine board in the above picture is much longer than the weathered board.  This is how I'm joining the parts together.  It will look like a butt joint from the front, but the extended length of the backer on the rails will be glued to the undersides of the stiles.

Here's how it will look

This pic shows how the horizontal backer extends to the edge of the stile.
The glue joint between the rail's backer and the stile is how the frame stays together. 

The backer pieces were beveled so that they won't be seen as easily

Et voila!  A simple little project.  All that's left is for the wife to get a piece of mat-board to mount the needlework art on.  Then I'll use glazier's points to keep the art in the frame and then mount it on the wall.

Wednesday, May 5, 2021

A Blacksmith's Post Drill

This one's mostly for Bob, of the Valley Woodworker blog.  He's been working on an old post drill that he mentioned was a "blacksmith's post drill", more for drilling in metal than wood.

On a trip last week to California's "gold country", we stopped at Jamestown's Railtown 1897 State Historic Park.  I'm not much of a train guy, but for those who are, this would be a good place to get a fix.  I saw, in a building that looked like some blacksmithing went on in there, a huge post drill.

Post drill in blacksmith's shop

It's not so easy to get the magnitude from this picture, but it was huge.  Unfortunately I couldn't get closer for better pictures.  The top-most horizontal wheel was probably about 7 feet off the ground.  It's bolted to a plank that is about 4" x 8", and the plank is affixed to the timber-frame post that is probably about 8" x 8".

Look at the crank/handle on this thing.  I'd love to see it in action.  If others are interested in these old human-powered drills, follow along with Bob as he gets his in working shape.  (No pressure, Bob.)