Making a Set of Trammel Points

I've been in a woodworking funk lately.  I once read that when that happens, you can make some projects for the shop and that might ease you back into things.  That's what the miter sawing bench hook project was about, and that's what this project is about.

Occasionally I need to draw arcs to lay out some project part.  My previous jig was simple - long thin stick of wood with a little slot for a pencil point at one end and holes along the length for a screw wherever I need a radius.

Old arc-drawing jig

In his excellent blog, Dennis Laney posted in late 2014 about drawing ellipses.  In discussing this, he said "everyone needs a set of trammel points", and well, who am I to disagree with him.

So I looked on the internet and sketched a few things.

A few notes

I used a piece of oak 3/4" x 1/4" x 31" long for the beam.  I settled on a design that would use wedges in line with the beam and started work on a prototype trammel in pine.  The prototype was to look at shaping, but also to figure out the taper of the mortise for the wedge.  I used a wedge that was sitting on a shelf from some past project as a guide - I liked its taper.  I mortised the trammel, one end of which was angled for the wedge.

Tight fit on this side

Not so good on this side

The smart way to go would have been to lay out a rectangular mortise, hold the wedge to the layout lines and transfer the extents of the wedge to the trammel.  Live and learn.

The completed prototype

When I was satisfied with the prototype, I got a couple pieces of maple 7/8" square and about 8" long.  Each trammel would be about 2/7/8" long and I could get two out of one piece and a third from the second piece.

Mortising by eye

It takes some patience to ensure the mortise end wall is straight and without a hump.  But with careful paring and checking it came out fine.

Verifying that the mortise wall had no hump ...

... looking at both sides

As mentioned earlier, the other end of the mortise is tapered for the wedge and it's important to get it right.  But the smart way is to lay out the taper you want, cut the mortise, and then create the wedge to fit the mortise so that it locks the trammel tightly on the beam.

One of the trammels will be fitted with a 2" length of pencil.  I found the center at the end of one trammel and drilled a hole for a tight fit.  I also shaved off the arises of the hexagonal shaped pencil to make it more round and to fit better in the hole.

Hole drilled for first trammel

The other two trammels would each get a 1/16" hole, sized to fit a finish nail (with the head cut off).  As for shaping the trammels, the mortise area stayed relatively square and I gave them a taper towards the business end.

Before and after shaping

And here's the three musketeers, or stooges, or something.

Mo, Larry and Curly (or is that Shemp?)

I transferred the wedge shape of the prototype to a piece of maple and added a hump on the small end to keep it from sliding all the way out of the mortise when loosening it.

Wedge shape laid out and relief cut made

I pared close to the lines (picture was too blurry to share) and followed that with chiseling cross-ways to the line.

Sneaking up to the line

It's important that this side of the wedge is straight, so I took great care here.  When I was satisfied, I used the shooting board to trim the other side to get a perfect fit in the mortise.

Shooting for a perfect fit

Tight this side ...

... and tight this side

But I didn't like the way the wedge looked in the mortise when tightened - it wasn't "balanced".

Too much wedge on the right side

A couple shavings off the bottom of the wedge got it where I wanted it.

Much better balance

Then I rounded over the hump and all corners.  Since the three trammel mortises would most likely be slightly different, I fit each wedge individually to its trammel.  And to keep them straight I marked them.

"P" for pencil trammel, "1" and "2" for the two nail trammels 

I laid out some lines at 1" intervals on the beam to help me locate the trammels.  A couple coats of shellac and a coat of wax (except for where the wedges meet the beam) and this was done.

Stick a fork in it - it's done

Oh, yeah - the project is not really done until you've found a home for your new set of trammel points.

Hanging out on the side of my tool cabinet

I think these will be really useful and I'll love using them.  But I'll keep my old jig for when I need an arc with radius longer than 30".

Now I gotta get out of this funk and get on to some decent projects.