Full Chisel Blog

January 15, 2009

The uses of the compasses

Now Joseph Moxon does give us three sentences with one of them describing their office of describing circles and to set off a distance from the rule…

Compasses

[The above are a bit later than Moxon’s time and the distance between prickers can be set with the quadrant and thumbscrew.]

This is another tool that I think Moxon may have not gone on about because of its ubiquitous nature.  This tool is used by sailors at sea to plot their course, surveyors to measure maps, carpenters to transfer measurements, turners to replicate work, joiners, cabinetmakers, instrument makers, &c,

Everyone knew how to use the compasses, right?  Well today we call them ‘a compass’, perhaps ‘a pair of compasses’, although not that common or more often ‘dividers’.  We think circles and certainly they are used for that, more often they were used to scribe parallel lines.  Or they were used to scribe odd shapes by maintaining an equal measuring distance.  For scribing coped moldings, to scribe odd shapes, etc.

A pair of dividers can be set at a certain distance (taken from a rule) and that mark transcribed repeatedly.  One wing of the dividers can act as a fence, ride along the edge of a board and scribe a uniform mark as with a marking gauge.  The compasses can be used to walk off (and leave a mark if you push the pricker hard) distances.

Cutting dovetails?  The most important mark when gang cutting tails of dovetails is the square across the end-grain.  Using a compass will put both marks on the end-grain with just one set of the square.  Reduces time in layout for dovetails and the length of mortises.  Also great for laying out the extra shoulders on tenons when a marking gauge just won’t quite fit.

If you can’t read numbers, can’t see well, only have a metric rule or are otherwise encumbered, the compass give an accurate representation of what you are measuring, properly transfer the measurement and not transposed numbers or the like, the compasses ascribe accurately.  And they can make two marks at once.

Then there is determining the number of segments in a circle, laying out a Dutch star, walking off distance and the other things that this fine philosophical instrument is capable.  Again I think this tool doesn’t get the attention of fancy tools like saws and hand planes and its capabilities are not fully realized.  I also think trammels or a beam compasses are also largely overlooked tools and go beyond the span of a pair of dividers.

So pick up a compasses and be mindful of the two sharp prickers and you will see it is more than I described.

Stephen

5 Comments »

  1. Stephen

    Absolutely! Which is to say, I agree with you. It’s good to see attention given to the more prosaic of tools. I have a variety of compasses, ranging from tiny Starett machinist models up through a big coopers style. They get use for all sorts of activities. I hadn’t really thought about the vision part, but it’s true. Instead of picking up a rule, I tend to grab a compass, straight, inside or outside.

    Gary

    Comment by Gary Roberts — January 15, 2009 @ 11:29 am

  2. Excellent post Stephen! I use mine all the time. It’s probably the most used “measuring” tool in my shop, though I rarely measure anything.

    Bob

    Comment by Bob Rozaieski — January 16, 2009 @ 7:07 am

  3. Hi Stephen,

    Do you know of a publication that can teach the ways a compas can be used for a joyner or woodworking in general. If you know of more techniques, please tell us.

    Charles

    Comment by Charles-William Roy — January 16, 2009 @ 7:48 pm

  4. Gary,

    These are indeed handy and under utilized tools and very little is written about them.

    Bob,

    The advantage is that you don’t get the numbers wrong when using compasses as you can with a ruler.

    Charles,

    The Romans called them ‘circinus’ and Mercer said they were used by more trades than the carpenter. There were three of these found in Nova Zembla from the 1596 Dutch ship wreck. There is more information written about using them in the carpenter trade, about using the framing square for roof and stair work. Coopers would use the compasses to determine the size of a barrel head. The compasses are set to walk out six equal steps around the croze (groove for the barrel head). Once the six equal steps are marked out that is the radius of the circle, so no math was required to make that determination.

    Sorry I can’t give you any more direction on the uses of the compasses as so little was written.

    Stephen

    Comment by Stephen Shepherd — January 19, 2009 @ 8:21 am

  5. Well, Stephen, you have inspired me to use my own more often. I have been endevouring of late to measure less, transfer more. I started using a folding rule (with a sliding out bit) which is great for this. I often also use calipers to transfer; they are nice because they can transfer an inside distance to an outside distance without paying any attention to the numbers. However, it occurs to me a compass would be much less fussy and delicate for many of those operations, so I’ll give it a whirl.

    Comment by Paul Kierstead — January 26, 2009 @ 12:12 pm

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