Threading Small Diameter Wood

A couple weeks ago, I made a new fence for an old Worth marking gauge.  In the original, the beam of the gauge got clamped in position using a wooden screw through a tapped hole in the top of the gauge's fence.  The screw was about 3/8" diameter and about 10 threads per inch.

The original from the Worth gauge

For the new fence, I used a machine screw and a threaded insert.  But it got me thinking (again) about wooden screws and nuts.  A couple years ago I finally had success making wooden screws and nuts, but the diameters I was working with were much larger than this (the smallest was 13/16").  So I thought I'd give it a try.

My plan was to start with a screw having 1/2" major diameter and 8 threads per inch.  A 3/8" diameter just seemed too small for now.  Using 8 tpi, (1/8" thread pitch) makes the numbers come out nice.  I started with a 1/2" square blank and on each face, I knifed and penciled lines every 1/8".  The lines on each consecutive face were 1/32" offset from the prior face.  After planing the workpiece round, The lines were still visible and I could connect them with pencil.

Ready to connect the layout lines and get filing

After filing the threads with a square file

This worked fairly well, but I still needed to see if it would fit into a nut with the same thread pitch.  For the nut, I first tried using the method I had success with a couple years ago.  I made a block with a 7/16" hole (the minor diameter of the screw) through a face and then cut a saw kerf in an edge at an angle down to and a little bit into the 7/16" hole.

You can see the 7/16" hole through the front face, as well as
the slanted kerf at top of the block

The kerf fits a slim card scraper - you can see the scraper extending
into the hole just a little bit

That 7/16" diameter stick in the above picture has a shallow spiral kerf sawn into it.  This stick was laid out very carefully and sawn very carefully.  This was the second try - the first was made from a very porous wood that was clearly not suitable for this purpose.  The one above is maple.

The first attempt got destroyed in use.  There is just not enough
meat around those kerfs to withstand a little stress.

A little below those threads, I drilled a 1/8" hole and fashioned a tiny cutter, which is just press-fit into the hole.

The cutter can be seen here - it's got a (roughly) 90 degree point

In use, this spiral-kerfed piece gets placed into the block (the block with the 7/16" hole and slanted kerf), and the slim card scraper engages the kerf.  As the cylinder is turned, it gets pulled into the block and the cutter can cut an inside thread in a workpiece that is clamped to the block.

Here's the cylindrical piece engaged with the card scraper in the block.
Note the spacers taped to the front of the block.

Here, I've added a workpiece that had a 7/16" hole bored through it.
The block and workpiece are clamped in a bench vise.

In this view from above, you can see the spacers allow you to see between
the workpiece and the block.  This way you know when the cutter exits
the workpiece as the cylindrical piece is turned.

At first, the cutter is barely showing as you turn it through the workpiece.  After retracting the cutting cylinder, you advance the cutter and run it through again.  And again.  And again ... until the threads are well formed and deep enough.  For threads this size it only takes a few passes.

Here are the internal threads that were just cut

And the screw fits!  Success!

Well, so this post doesn't get too long, I'll end here and pick up next time with a second method.  I'm fairly excited about it because it doesn't rely on the spiral kerf cut into the cutter stick.  Maybe eventually there can be some success with 3/8" diameter sticks!

New Fence for a Marking Gauge

About 12-15 years ago, I met a man on a plane who noticed I was reading a woodworking magazine and we struck up a conversation.  Short story shorter, he ended up surprising me by sending a few tools that he was no longer using.  Among these was this marking gauge labelled "Worth", a name I didn't and still don't know anything about.  EDIT - an internet search came up with a thread on a "Garage Journal" forum where people identified Worth as being a brand from Bigelow and Douse Hardware of Boston, MA.  They further noted that the Worth tools were probably manufactured by Peck, Stow and Wilcox (Pexto) for the hardware store.

The Worth marking gauge

It had a wooden screw to clamp the beam in place, approx 3/8" x 10 tpi

Like many similar gauges, the wooden screw had become loose as the wood fibers were worn away.  Also, the mortise hole in the fence wasn't a great fit for the beam, so this gauge has been sitting in a drawer for a long time.

At first, I addressed the beam looseness problem by putting some blue masking tape on the beam to get a tighter fit in the fence.  Obviously not a long-term solution.  Then I thought about putting a threaded insert in the screw hole and using a metal thumb screw.

Brass threaded insert

It turned out that the brass insert was still a little loose in the hole, so I decided that I'd make a new fence.  If I was making a marking gauge from scratch, I'd mortise the fence first and then plane the beam to fit just right.  For this one, I wanted to use the Worth's beam, both for nostalgic reasons and because I like the scale printed on one side.  It was a little tricky to make the mortise just the right size to fit the existing beam.  I ended up using a caliper to measure the beam's width, locked the caliper at that measurement, then stabbed the inner diameter measuring fingers of the caliper on the new fence to mark for the mortise walls.

Mortise chopped and upper and lower facets shaped for the
curved top and bottom surfaces of the beam

At first, the fit seemed a little too loose, but after some shellac it fit very well.  Next, I bored a hole through the top, down to the mortise.  I had shaped and placed a stick in the mortise so that I wouldn't blow out the mortise's top wall.  The threaded insert went in that hole.

You can see the insert within the mortise

I used a leather punch to make this plastic "coin" (?) so that
the thumb screw would not damage the top of the beam

I get a good solid grip of the beam when the thumb screw is tightened

Then the screw was cut down to length.  To make the thumb screw more comfortable, I inset the "thumb hold" part of the screw into two small pieces of walnut that were carved out to fit the thumb hold and then glued together.  It was then shaped to make a much more comfortable grip and look a bit more like the original.

The new thumb screw next to the original

After shaping the fence for comfort, I gave the parts a few coats of shellac, then waxed all but the bottom of the beam - that's what gets pressed against the lower mortise wall when the screw is tightened and I don't want that to be slippery.

So I now have a nicely working marking gauge.  It looks a little funny being two-toned, but I got to preserve some of the gift I was given and give it new life.

Glamour shot #1

Glamour shot #2

BTW, I changed one thing in my fence from the original: there is more meat below the mortise in the walnut fence.  I like having that extra bearing surface when using a marking gauge.  The original had less than 5/8" of bearing surface to reference against a workpiece.