Thursday, February 21, 2013

The Fourth Dimension

At the Woodworking Show a few weeks back, I was introduced to an interesting take on the dial caliper by Andy Chidwick.  He was mentioning that this measuring device was one of his favorite tools because it allowed him to transfer a single measurement, from one place to another, in four different ways.  I knew about three, but what was this fourth dimension that Andy speaks of?  Did he find it at the back of a wardrobe?

The dial caliper has also been one of my go-to measuring instruments for some time now.  Years ago while spending time with Dad in his shop I was admiring his dial caliper and asked him where he picked it up.  As soon as I returned home I logged into the Highland Hardware website and ordered myself the six inch fractional model.  Dad had taken note of my interest and the day after my six inch model arrived, a four inch model of the same design showed up on my doorstep.  Boy, he was always like that.  He said he was sure I’d use the four inch model ten times more than the six…and he was right.  The six inch model is almost too big for the type of work I’m usually doing with a caliper, so it never even comes out of the box.  The four incher hasn’t been back in its box in years.
Let’s take a quick look at this incredibly versatile measuring device…

The first measurement is the most obvious.  Just open’er up and give the object a friendly little pinch to determine the outside dimensions.
Once you’ve captured the measurement, in this case the width of one of the legs for my Rietveld Red and Blue chairs, you can hold the setting by tightening this lockdown screw.

With our measurement of 30m captured between the lower, outside measuring jaws, we can see that the upper, inside measuring jaws are holding that same width and could be used to transfer our 30mm dimension between two interior surfaces such as the inside of a box or the walls of a mortise.
Last weekend I used the calipers to confirm the width of the dowel stock for the joinery on the Red and Blue chairs, and then compared that same width against the test holes I drilled with a Forstner bit on my drill press.

The dial caliper is an excellent tool for measuring the width of round objects as the full extent of the piece’s width can be captured between the jaws, and consequently interior measurements of round or curved surfaces can be easily captured by the upper jaws.  No more guessing or measuring from multiple points above the opening to narrow down the widest distance.

That 30mm measurement is also converted to a depth measurement using the sliding bar at the end of the caliper’s beam.  This is the perfect little gadget for confirming the depth of holes or mortises.
So there you have the three standard instances of our same 30mm measurement provided by the tool.  In fact, these are the only three points of measurement that the instructions accompanying this caliper describe.  Hold onto your hats now, as we enter…the fourth dimension!

You won’t, in fact, find it at the back of a wardrobe, rather on the back of the tool.  No really…flip it over right now!
That’s right…you’ve probably been holding this gateway to an alternate universe of measurement right there in your hand this whole time.  That distance between the end of the beam with the outer jaws and the end of the beam with the inside jaws is our same 30mm measurement.  Now that flat end of the outer beam can be used to reference the caliper against the surface you want to measure from, and the inner beam forms a shoulder that can be used to “hook” onto the other end of your desired measurement.

This is a great way to measure the length of a tenon by referencing from the end of the tenon to the base of the shoulder.  Then you can use the sliding bar at the end of the caliper’s beam to check the depth of your mortise. 

I know!  Your mind is blown too.  Try to take some deep breaths…flirting with the space-time-measurement continuum can take a lot out of you.  You’ll need your composure for our next adventure.  We’re going to actually traverse between two worlds in a matter of milliseconds…no, wait…come back, you don’t need your passport!  Just lean in and look real close…see that 30mm setting at the top of the scale?  No, on the picture and zoom right in there.
Now just relax and let your eyes drift down just a hair…BOOM!  We’ve just converted from Metric to Imperial.  Who knew that 30mm is exactly 1 3/16 inches?!  It’s a lot to take in, I know.  Perhaps we’d better call it a night.  If you have a hard time sleeping in inches though, it’s just a quick hop through the measurement wormhole to get you back to the safety and comfort of the Base 10 Metric system.  I know that fractions can be scary for some.

Sleep tight and don’t let any cosmic insectizoid type creatures that have escaped the fourth dimension bite.


Chris Bagby said...

I really enjoyed reading your excellent article about using what we years ago started out calling "the woodworker's dial caliper." I would like to correspond with you via email about possibly using the article in our monthly newsletter. Thanks!
Chris Bagby, owner
Highland Woodworking

Pete said...

Thanks Chris! I really appreciate that! E-mail sent.