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-GURU
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Tonights demo is about some simple layout tricks, truing and using squares. This is sort of a light lesson covering some useful things that many of us never learn or are not taught. It is not in depth coverage of layout.
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Figure 1b |
Most of us have framing squares in our shops or have used them in other's. There are a few details you have to watch for. Most but not all English framing squares have different divisions on some of the scales. They range from 1/8ths to 1/32nds and include tenths and twelfths. These are the ones that will get you in trouble if you don't look close. tenths look like eights and twelfths are close enough to sixteenths to be confusing.
You may ask, "Why tenths and twelfths?"
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-GURU
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Tenths are handy if you calculate a distance and it does not easily convert to a fraction. The parts smaller than a tenth you estimate.
Twelfths are handy for scaling architectural drawings that are often drawn using 1" = 1'. Each twelfth equals one inch on the drawing. Twelfths also let you divide things into thirds and sixths without guessing.
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-GURU
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Framing squares also come with rafter charts that include the sines of common pitches for calculating rafter length. There are many tricks to using framing squares and there are booklets on the subject so we are not going to get into that since most of it applies to carpentry.
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Figure 2 |
However, even if we don't use the technical aspects of the framing square in smithing and metal working we DO use them for layout and checking the squareness of things we build.
But how square is your square? Dropped once and most are severely out of square. Over a lifetime they get pretty messed up.
When a layout in our shop didn't jive I checked the square the machinist was using. It was out an 1/8" in two feet. . Too much for most jobs.
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Figure 3 |
To check and true a framing square is simple if you know how. First, check the square for dents and dings and file them out. Then, on a bench, board or sheet of plywood with a true straight edge make a mark at the edge of the surface and at the end of the square as shown. Then flip the square over and check it against itself. The error can go either way so check using the inside edge if you don't see your mark.
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Figure 4 |
To true the square simply takes a few taps with a large ball peen hammer or any hammer with a radiused face. This is done gently. The amount of material to move is almost invisible and a few gentle taps do it.
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Figure 5 |
Figure 6 |
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-GURU
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To "open" the square tap it near the inside corner where the circles are shown. To "close" the square tap it on the outside corner as shown. Check the squareness after a couple of taps. You want to sneak up on perfect.
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-GURU
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The straighter the edge you work off of the better and the finer the lines the better. Scribed lines on a metal surface are best but fine pencil lines will do.
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Figure 7 |
Other ways to check squareness is to measure a triangle and use the calculated hypotenuse. Easy for some, a headache for others.
However, there are two "magic" triangles where the sides come out even.
A 3:4:5 triangle and a 5:12:13 triangle.
These can be used in feet, inches or meters.
On large items (gates, doors, floors) multiples can be used.
Using nothing more than a tape measure you can layout or check any corner in the range of your measurements.
I like using a 5:12 pitch roof because the rafter length is 13 inches for every foot in span.
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Figure 8 |
To check an equal sided triangle with 45° corners the hypotenuse is the square root of two times the length of the sides. All you have to remember is to hit 2 and square root on any pocket calculator.
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Figure 9 |
When measuring a rectangular opening to put work into such as a fireplace, door or floor layout you always need to take FIVE measurements. Each side and a diagonal. Even if the opposite sides are perfectly equal the shape may be a parallelogram. The diagonal measurement lets you make an exact layout that will fit.
Be sure to check for straightness of lines and levelness. Don't trust your eyes. I've measured fireplaces that LOOKED perfect but were out 1/4" in every dimension and had a 3/8" arch to the hearth. This is one reason YOU want to measure things and not your customer.
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Figure 10 |
The other square common in shops is the combination square. These can also have odd markings if they are machinists squares including 1/50 and metric.
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Figure 11 |
One of the handiest things to use a combination square for is a "stock" gauge for cutting stock. Adjust and lock the square and then use if from the end of the work to the teeth on the saw blade. If you use the widest part of the blade your stock will be cut to within +/- .005" every time (depending on how square your saw cuts).
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-GURU
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Questions, Comments?
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Snow Smith
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Jock, ever use a mirror to check a square for truth?
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-GURU
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No, Snow-smith I've never used a mirror. I can see how it would work. On the other hand I don't keep much glass in my shop other than windows. It doesn't last long around metal working equip.
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Milt
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I don't think I follow the last item -- stock gauge.
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Terry-F
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Can you put the math in to formulas. it might be easier to understand.
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-GURU
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Terry, There is nothing above to put into formulas, that is the point. The triangles above come out even PERIOD. The square root of two is the the square root of two (1.4142. . .) as shown. Multiply the sides of an equal sided triangle by that and you get the long side.
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Snow Smith
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Agree with the glass comment.
Carry mirrors with me all the time work very well with stock that is irregular.
Also in a miter box with slop in guide!
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Pete F
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Good basic demo Jock..helpful as I'm self taught...thanks
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jj2k
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Thanks Jock. It's nice to get some basic info like this.
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-GURU
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When sawing or cutting stock in a saw or lathe repeatedly to the same length,
some folks go to the trouble of making a "stock gauge" to make the repeat measurements instead of measuring each time with a scale.
Just setting a common square to the right length saves a lot of effort and it has a built in scale.
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mike-hr
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I tried to order a tape measure in 1/10 inch, I got one in 1/10 foot!
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-GURU
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I had a fellow in the shop that didn't understand the difference between the inch side and the centimeter side of his dual unit tape measure. I took it away from him. . . Maybe he filled your order!
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Milt
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Guru --- Now I understand. Thanks for the demo. Good stuff.
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Links:
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Demonstration by Jock Dempsey
December 19, 2001
Figure 1b
You may ask, "Why tenths and twelfths?"
Twelfths are handy for scaling architectural drawings that are often drawn using 1" = 1'. Each twelfth equals one inch on the drawing. Twelfths also let you divide things into thirds and sixths without guessing.
Figure 2
But how square is your square? Dropped once and most are severely out of square. Over a lifetime they get pretty messed up.
When a layout in our shop didn't jive I checked the square the machinist was using. It was out an 1/8" in two feet. . Too much for most jobs.
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
However, there are two "magic" triangles where the sides come out even. A 3:4:5 triangle and a 5:12:13 triangle. These can be used in feet, inches or meters. On large items (gates, doors, floors) multiples can be used. Using nothing more than a tape measure you can layout or check any corner in the range of your measurements.
I like using a 5:12 pitch roof because the rafter length is 13 inches for every foot in span.
Figure 8
Figure 9
Be sure to check for straightness of lines and levelness. Don't trust your eyes. I've measured fireplaces that LOOKED perfect but were out 1/4" in every dimension and had a 3/8" arch to the hearth. This is one reason YOU want to measure things and not your customer.
Figure 10
Figure 11
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