I recently threw out two combo square heads because I found out they were not accurate. I bought a new one recently, and checked the 90 degree edge and all looks good.
But it got me thinking….
How do I check the 45 degree edge? I have never seen a reliable test for doing this. If anyone can give advice or point me to an on-line article, I would appreciate it.
Thanks
Replies
I've done it by drawing two long 45's from a straight edge, which then intersect at 90. You then place a known good (framing or drafting) square into the corner, and verify that the lines you drew are both parallel to the sides of the square.
Also, combination square heads can be tuned in with an auger bit file if necessary.
Regards,
Tim
Edited 4/28/2008 1:34 pm ET by tsgraz
Geometrically, the two 90 degree legs of a 45 degree triangle should be equal. If you draw lines along the edges of the square and join them with a straightedge, the opposite and adjacent sides to the 45 degree angle should be equal when measured accurately.
Start with a good 90 degree corner angle on a board, or another media of your choice.
Scribe a line bisceting the 90 degree angle using the 45 degree edge of the square.
Flip the square to the other edge of the 90, and the straight edge should fall exactly on the scribe line. If not , you should be able to see how it is off and to what degree.
Ya might want to try a drawing triangle that you might have used in mechanical drawing in high school. Got a 45 and a 30 60 90 triangles work great for checking out tools.
Edited 4/30/2008 9:14 am ET by GW52
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