Change Gear Measurements By Mike Meagher

To: "''" <>
Subject: [7x10minilathe] Change Gear Measurements
Well, I checked some of the 7x10 change gears on an optical comparator this
morning, and here is what I have found:

 Circular pitch = 0.1245 in
 Pressure angle = 20°
 Bore = 0.4735 in
 Face Width = 0.3070 in
 Keyway Width = 0.1151 in
 Keyway Length (above bore) = 0.0563 in

I measured the 50-tooth and 60-tooth gears at several points to verify the
dimensions. At 100x magnification, the involute profile was, to put it
mildly, terrible. No clearly defined lines on the tooth form made it
difficult to get a true reading, particularly for the pressure angle. But
that is to be expected with a molded gear as opposed to a gear which has
been machined. 

Calculating diametral pitch (Pd) from circular pitch (Pc):

 Pd = pi/Pc = pi/0.1245 = 25.23

Not a nice even number, so it's probably metric. Determining the module:

 module = m = 25.4/Pd = 25.4/25.23 = 1.0067

Definitely metric, IMHO. If I were ordering gears from a catalog, here's
what I would look for:

 module = 1.0
 pressure angle = 20°
 bore = 12 mm
 face width = 8 mm
 keyway width = 3 mm
 keyway length (above bore) = 1.4 mm minimum

If there is anyone else in this group who also has the ability to measure
these characteristics on the change gears, that would be greatly
appreciated. That way, what I have measured and reported here can either be
verified of thrown out the window.

Carrollton, TX (at work)

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