In Need of a Knob
I am in the process of designing and building a horizontal mortise machine. For that, I needed a precise circle cut-out. To do that, I needed a circle jig. For that, I needed a knob, one with a threaded stud.
I had made one a while ago, and found my template, improved my technique a bit and went to work.
The Knob Concept
Most knobs are formed like a star, with five “pointers”. I took Inkscape to the rescue to create a template, here a picture:
It’s based around a 2 1/4” circle. I drew a hexagon inside that circle, and drew 1” circles at each corner of the hexagon. The hexagon is slightly larger than the circle, which results in less than a half 1” circle, which provides a better grip that a full half-circle.
With a bit of Inkscape magic, I made this template user-friendly for the drill-press, with markings for the center points where I will drill:
Please note that the image above is not to scale. If you want the proper sized template, you can use the link at the bottom of this little story…
This template is then printed out, and glued to a piece of wood, cherry in my case. The 1” holes are drilled first, with a forstner bit. Then I drill a 1/4” pilot hole for the 2 1/4” hole saw cut-out. But before cutting out the entire disc, which will be the base of the knob, I drill a 5/8” hole, just about 1/4” deep, in the center. This should fit the t-bolt I use for the knob, and the plug to hide it.
Finally, I drill out the entire thing with the 2 1/4” hole saw:
As you may have noticed in the image above, I have already started to chisel out a recess for the head of the t-bolt. This can be done, or at least started, with a forstner bit. The recess will keep the t-bolt from turning. It should fit tightly, one can check the fit by simply turning the t-bolt around:
The final shape has to be refined with a small chisel for a perfect fit:
Now it’s time to make a plug to hide the t-bolt. I had a small piece of ebony scrap, and turned it round, and a 5/8” dowel shape on one end. This should be pretty precise, so that the plug will fit properly:
Once the 5/8” dowel end is turned, I just cut off a plug, a bit over 1/4” in depth:
Here is the cut-out knob with the plug fitted:
Before I glue the plug on, I use some superglue to glue in the t-bolt. This is just extra security, since the t-bolt is in a recess, it shouldn’t be necessary. Then I glue in the plug, and “wipe off” the glue squeeze out with some of the ebony dust from the plug.
I made two knobs at a time:
The rest is just a bunch of sanding and finishing. I did a lot of this on my Shopsmith, with a disc sander, and a shop-made drum sander pin that is 1” in size. When using a disc sander, it is much safer and easier to simply build a mini-jig: A small board with a hole in it, into which the knob can be threaded. Then one holds the board when sanding, or mounts it down and moves the sanding disc.
The finish I use is shellac. It’s my favorite finish, I have hardly every used anything else…
Here is the final result, notice the ca. 30° angles that I like to shape on the edges of the points, which makes the knob much nicer to handle:
If you would like to make one of your own, feel free to download the Inscape template below. It has six knobs on one sheet:
I hope you enjoyed my little knob-making OCD :)
Oh—and in case you wonder why I called it the “Ternowski” knob: Ternowski used to be my family name, before my great-grandfather changed it. A weird story. Anyway, I picked it up to use as my artist name, there is also a very outdated website where I have some of my earlier art work: http://ternowski.com/