Check Bubble Level and Rafter Square Accuracy

Sola Big Red 3 Box Spirit Level Action Drawer

Whether you’re just starting out or have worked for years in the trades, you should know that tools need to stay accurate. One of our favorite tool maintenance tips centers around how to check bubble level and rafter square accuracy. Levels can get knocked out of level if they are roughly treated or dropped one too many times. Squares can go out of square if dropped on a corner. Even tape measures can stop reading true. This is why you have your measuring devices and, I have mine that you shall never, ever touch!


Check Bubble Level Accuracy

To check bubble level accuracy, place it on a surface that reads level. Then, rotate the level 180 degrees. It should still read level. Now flip the level over and see if it still reads level, then rotate it 180 degrees again. In all four positions, it should read the same.

This is also the test you should perform in the store when buying a new level to make sure it is a good one.

Milwaukee MLDIG48 level top display

Check Rafter Square Accuracy

Speed or rafter squares are less likely to get out of square, but it can still happen. This especially holds true when these tools lie flat in the bottom of your tool bag. When all your tools get dumped on top, these levels can warp over time.

You can easily check rafter square accuracy by following this tip. You can also, however, use the same technique for machinist squares, drywall squares, etc. All can be checked for accuracy by either drawing a line in one direction against a straight edge and then flipping the square over and drawing another line over the top of the same line.

Check Bubble Level Rafter Square Accuracy

If the square is at a true 90 degrees, you should see only one line. If the square is off, you will see the lines you drew diverge (see photo). A second method, if available, is to put your square up against the table edge of your table saw and line it up with the miter saw slot which will be a perfect 90 degrees.

SawStop Jobsite table saw fence square
Slide your square (usually metal), to the right to see if it lines up perfectly with the miter slot.

Hopefully, that was helpful. If you have a tool maintenance tip of your own, please leave it for us in the comment section below.


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