# Checking Perpendicularity Between Shaft and Its Hole

A blue round bar is inserted into the hole of of the grey shaft.
Ensure no gap there.
V-block and the shaft are arranged vertically.
Small error in verticality does not affect the checking result.
The shaft always contacts V-block thanks to two pink springs.
There is a red ball at the shaft bottom.
Checking steps:
1. Put a bubble level (in orange) on the bar to get angle between bar axis and horizontal direction E1.
2. Turn the product 180 degrees.
3. Put the bubble level on the bar to get angle between bar axis and horizontal direction E2.
Error in perpendicularity P:
If the level’s bubble moves in opposite directions for the two attempts:
P = (E1+E2)/2
If the level’s bubble moves in the same direction (it may happen when the shaft is not absolutely vertical):
P = (E1-E2)/2
Here the error in perpendicularity P is understood as an angular error:
P = (B – 90) deg.
B is real angle between shaft axis and hole axis.
This method has advantage for checking bulky products.

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