Making a Marking Gauge with Wooden Thumbscrew

This is the culmination of the wooden screw rabbit hole I've been in for several weeks.  It started from a Worth marking gauge I was given some years ago, the screw from which didn't fit the inside threads in the fence very well.

It all started from this

It turned out that the inside threads were the problem - they got wallowed out a bit and the screw would no longer hold.  So with my experience a few years ago making larger wooden screws and with the help of some online videos, I figured out how to make threads of the appropriate size: 3/8" major diameter at 10 threads per inch (3/8" - 10, for short).

To pull it all together, I made a new marking gauge.  The major challenge with this one was making the wooden thumb-screw.  I'll get to that in a little bit.  But first, I made a prototype marking gauge fence from scrap wood to see if I could create inside threads through the top and extending to the mortise that houses the beam.

I needed the prototype marking gauge to be at a specific height in
the threading box, so I planed a scrap piece and super-glued the fence to it.
Then ran the tap through the fence to make the inside threads.

And it worked very well.  Here's the original wooden screw
in that tapped hole - a nice snug fit.

Later I made a fence blank from walnut and repeated the procedure on the real thing.

Here's the walnut fence getting threaded

and I got a nice fit here, too

The walnut took the threads pretty nicely

Next I tested a 3/8" diameter piece of walnut to see how well it would take outside threads.  I had soaked it in mineral oil for a few days, and it worked out pretty well.

Testing a 3/8" walnut dowel for outside threads

And it fits an inside thread nicely

With that adding confidence, I laid out a wooden screw on a walnut blank.  I was careful to lay out precisely to keep things aligned.

Laid out the shape using the original as a guide

Then sawed and rasped the to-be-threaded end a little oversize and
tapped it through a dowel plate for a fairly accurate 3/8" diameter.

The extra material on the right in the above picture is so I could mount it in the threading box.  I formed that into a 5/16" diameter so I could use one of the couplers I'd already made (I realize that might only make sense if you had read the previous posts about threading small diameter wood).  Then I cut the outside threads and tested them in the walnut fence.

It fits nicely and it locks the beam solidly!

I cut off the extension on the back end and shaped the thumbscrew head similar to the original.  I also cut off about 1/2" of threads so that there's only about 1/8 to 1/4" of threads above the fence when the screw locks the beam.

At this stage, there's just a little shaping to do and then some coats of shellac.  Like my last marking gauge, I added wax to all outside surfaces, except the bottom of the beam.  That exception will help ensure the beam won't slip in its mortise during use.

It's looking like a marking gauge

I added measurement lines on the side of the beam that is visible to me (a right-hand dominant person) when in use.  I find the lines very useful on the original Worth gauge, and I don't know why more marking gauges don't have this feature.

I laid out these lines carefully - they go out to 6"

Almost forgot to mention - I made the pin from an old 3/32" drill bit.  It was annealed (though it was still very hard after annealing) with a torch and sharpened using a drill and hand-crank grinder.  It was a little loose in the 3/32" hole in the beam, so I bent it a little bit and now it holds well.

And here is the glamour shot.  When the screw is tightened, the beam will not go anywhere.  It clamps as solidly as a rottweiler on a postman's leg.

It's a beauty

I'm done with wooden screws for now.  It's time finally to move on to other things.