Measuring tip - centering

[LCHIEN]

Marking the center of a piece of wood is a frequent task.
Its surprising sometims you mark the center, say the drill a hole and find out you're off a little.

Some of the problems are, you measure the width, and round off. The make a mistake dividing 3-13/32" exactly in half... quick what is it?, then there's the width of the pencil and the error reading or even marking the point from a ruler or tape measure.

Here's a couple of ways I solve that.

Method 1: Use a combination square. I can do math quickly and usually right but sometimes not. in the example above, half of 3-13/32 is about 1-1/2 plus a little more than 6/32 - or about 1-11/16
I set the combination square so that 1-11/16 is right at the right angle edge. Then I use the square against the edge of the wood, and use a .5 mm mech pencil to mark along the edge of the end of the rule.
Then without changing the quare I do the same from the opposite side. I'll end up with two marks that will be very close together.
If they're less than 1/16th apart I can mark and susequently draw or drill to the center between the lines. If they're more than 1/16th apart, then I've missed by quite a bit and I start over.


Method 2:
I use a centerfinder, there's several types any one will work. Usually they are for finding the center of a dowel or round object.
I use them to draw 45 degree lines from two corners at the end of the board. The lines will intersect at the exact center. I can then use a combination square off the end to draw a line down the center of the board. or one of those sliding marking devices that you slide down an edge and it marks a parallel line.

[RodKirby]

OR - work in millimeters - use metric rule(s) OK?

[Pappy]

Drill 3 holes in a small board, 6" apart. The center hole is drilled to hold your pencil from the top. Glue dowels in the end holes sticking out the bottom of the board. Run the dowels along the edge of your stock so the board is angled across the face of your stock and the pencil will be in the center.

[lcm1947]

I much prefer method #2. I have had problems doing method #1 before but your idea #2 should help me alot. I do have a centerfinder so it'll give me an excuse to use it. Seems I never mess with dowels so never get to use it. Thanks for the tip Loring.

[gonesailing]

Pappy has the right idea if you want to make a jig. Assuming the board is of uniform width, lay a ruler across it and then rotate the ruler until it measures an even number of inches (or for Rod Kirby, mm). Mark the center. Thats it, you have the center of the board marked. If it isn't in the right place, move the ruler down a bit and mark again, then connect the dots, that line is in the middle.

Mike

[monte]

They're all good ideas.

[Napoleon]

Here's link to Pappy's center finder: http://runnerduck.com/centering_tool.htm
Mark

[LarryG]

I mostly use Mike's method; I've used Loring's #1, too. And after reading Pappy's reply, I predict we'll soon be seeing another round of pictures from jigmeister Kirby.

The angled-rule trick also works when you need to divide something into multiple equal parts. Say you have a 2-9/16" wide board, and want three equal parts. Place the zero end of the rule at one edge, and angle the rule so that the 3" point is at the other edge. Place tick marks at 1" and 2". Presto, three equal parts.

Depending on the width of the board and the number of divisions, you might sometimes need to use less-than-full-inch increments on the rule. When that happens, just use something that's easy to work with, on the rule and in your head: 3/4", 1-1/2", 2-1/4", 3", 3-3/4".

(These are old tricks that anyone who's ever spent much time on a drafting board will know.)

[Tom Miller]

quote:Originally posted by gonesailing

...lay a ruler across it and then rotate the ruler until it measures an even number of inches (or for Rod Kirby, mm). Mark the center.

I like this idea a lot, but I always assumed I'd have a problem marking the board with this method, since you're trying to line up your mark with the end of a now-slanted ruler line. I think this idea really needs the jig.

But I ruled (unintended pun) it out before I even tried it.

I currently use Loring's Method 1.

And each time I read the "equal parts" method Larry mentioned I promise myself I'll remember it. But I never do.

Regards,
Tom

[mattc183]

I'm with Kirby, lately anytime I'm trying to be precise I read from the millimeter side of my combination square.

mattc

[rickd]

hi,

i use the lee valley 25' centre finding tape measure to find the center of any measurements i have to make - it's too easy!!

i've used a couple of the methods described above - and i really like pappy's method - it's simple and it works.

but, a few weeks ago i bought a lee valley "centre-finding" tape measure and now it couldn't be simpler. Just measure a board as usual(using the top gradation)i.e. if it's 6 3/8", then look at the bottom gradation(which is 1/2 scale) for 6 3/8" and that's the center point.

seems a bit like cheating - but it works for me.

[scorrpio]

A tip for ***cutting*** a piece into equal parts: Make a shim that matches your kerf thickness (3/32 or 1/8). Lay the shim on the edge of workpiece and angle your rule across piece+shim width. Then, make sure to place the blade on the other side of the mark from the shim.

[Scottydont]

Like Larry, I take a good measuring tape and place it at any angle diagonally until it lines up with an even inch number. Take that dimension divide by 2 and mark your center.

[Tom Slick]

you could also use a layout rule. it has 0 in the center then measures out left and right from 0.