Eric Brown
07-02-2023, 5:26 PM
Have you ever used a center square and had to make four lines to end up with a small box in the middle showing center? The reason for this is that most center squares are made so well that it requires a knife held against the edge for best results. If your like me though you might use a pencil. Problem with pencils is that they are thick compared to a knife line and result in the line offset from the true edge. Experience users never rely on just two lines because of this. Another problem is if the center square is not square. Hers how to tell. Take a piece of wood or plywood that is wide enough to accommodate the full length of your center square. Make sure the board has two square corners and the sides are parallel.
Below you can see I used a 6" Ame's 1852 patent (#9,089 July6, 1852) center square to make the initial mark. These squares were made by Ames, then G. Holliday, then JR Brown and finally Darling Brown & Sharp.
503697
Then I used a carpenter's square to verify that the two sides were the same length. This verifies that the square is true.
503698
I then used a no name center square on a 24" hardened rule and compared it to the marked line. You can just see the line especially where there is a gap in the line around the 9" to 9 1/2" area.
503699
Looked good. So the next picture shows an out of square head.
503700
This particular head was made by Brown & Sharp using J.S. Chafee patent 2,085,461 (June 11, 1935) It is the only center head that I know of where you can adjust the head on the rule. There are two adjustable stop screws so you can adjust tilt or offset of the rule. Once in position the adjuster can be locked in with two additional side screws. Where this can come in handy is you can offset the rule to make your line exactly centered. Below shows the rule offset.
503701
Adjusting for square is easy too with simple adjustments.
There are many other center square available but check them out to verify squareness. The older cast iron models will be good as they don't bend but rather break. The newer aluminum ones might bend. The ones made from multiple pieces
might also be knocked out of adjustment is dropped.
Below you can see I used a 6" Ame's 1852 patent (#9,089 July6, 1852) center square to make the initial mark. These squares were made by Ames, then G. Holliday, then JR Brown and finally Darling Brown & Sharp.
503697
Then I used a carpenter's square to verify that the two sides were the same length. This verifies that the square is true.
503698
I then used a no name center square on a 24" hardened rule and compared it to the marked line. You can just see the line especially where there is a gap in the line around the 9" to 9 1/2" area.
503699
Looked good. So the next picture shows an out of square head.
503700
This particular head was made by Brown & Sharp using J.S. Chafee patent 2,085,461 (June 11, 1935) It is the only center head that I know of where you can adjust the head on the rule. There are two adjustable stop screws so you can adjust tilt or offset of the rule. Once in position the adjuster can be locked in with two additional side screws. Where this can come in handy is you can offset the rule to make your line exactly centered. Below shows the rule offset.
503701
Adjusting for square is easy too with simple adjustments.
There are many other center square available but check them out to verify squareness. The older cast iron models will be good as they don't bend but rather break. The newer aluminum ones might bend. The ones made from multiple pieces
might also be knocked out of adjustment is dropped.