Diametrical Pitch Gears, what do ya got

When I had this last one, I asked God to keep my mind intact. It looks as though He may have done it more or less. I have seen many stroke victims who had lost theit mental facilities but could still see and drive. My greatest concern was my mental facilities, my father was in a wheelchair when I was a teen. It didn't bother me near as much as losing my mind. To have that mental facility brought into question scares me more than I can state. I have always had a good memory and still depend on it to some extent. Hell of a way to spend retirement. . . Currently expounding on another thread that is more in my baliwick;

DIY dro from fridge magnet and 3 sensors​


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Finding the diametral pitch or module (same thing different numbers) is easiest by measuring the diameter of the gear from the top on a tooth to the bottom of the tooth opposite. Gives a close approximation of the pitch diameter.

Diametrical Pitch is a measure of tooth size and equals the number of teeth on a gear divided by the pitch diameter in inches. Diametrical pitch can range from 1/2 to 200 with the smaller number indicating a larger tooth. Module is a measure of tooth size in the metric system. It equals the pitch diameter in millimeters divided by the number of teeth on a gear. Module equals 25.400 divided by the diametral pitch. Module can range from 0.2 to 50 with the smaller number indicating a smaller tooth. In looking for gear cutters Module is the most often system used.

Deciding what the pressure angle is a bit harder. Luckily there are only 3 common angles used on spur gears. 14.5, 20 and 25. Bigger angles are less pointy. There are illustrations on line comparing them. I decided my change gears were 20 degree, and they all measured out to 1.25 Module. All meshing gears have to have the same angle and module.

Reference:
 
Larry$ said:
Finding the diametral pitch or module (same thing different numbers) is easiest by measuring the diameter of the gear from the top on a tooth to the bottom of the tooth opposite. Gives a close approximation of the pitch diameter.
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This effectively adds in the addendum of the tooth and subtracts the dedendum. The addendum is 1/DP while the dedendum is 1.25/D.P. which would result in the above measurement of pitch diameter being low by .25/D.P. For all intents and purposes, it will be close enough to determine the pitch diameter though.
 
Bill, I think that there is something to your sheet metal gauge. After all, 3.1 is just short of pi. There must be something that is being overlooked. P.S. I'm also getting to the age where my memory will play tricks especially trying remember peoples names. Hang in there my friend.
 
silence dogood said:
Bill, I think that there is something to your sheet metal gauge. After all, 3.1 is just short of pi. There must be something that is being overlooked. P.S. I'm also getting to the age where my memory will play tricks especially trying remember peoples names. Hang in there my friend.
Click to expand...
The proper notch length is Pi inches. I calculate Pi as 3.14159 in what I do. The nominal repairman in the field, who this guage is calculated for, might measure 3.14. Call it an inch and an eighth, full. The nominal shop measurement would be 3.1 or maybe 3.15, scant. In every case listed, the measuremant of 3.1 is so close as to make no never mind. In any event, this idea has been manipulated around showing the correct measurement method. I normally use such a method, this gimmick came out of my memory for field use. It was never intended for shop use.
 
There are a number of methods for measuring D.P.that will get you close enough to determine what an unknown gear is. Here is another quick and dirty way. Mrasure the length of a tooth and divide into 2.25. This works because the addendum is equal to 1/D.P. and the dedendum is 1.25/D.P and the total is 2.25/D.P. A careful measurement will get you close enough to identify the gear.
 
If the objective is to determine whether you have an inch gear ir a metric gear, it becimes a little more tricky as some metric gears are fairly close in size to inch gears. Here is a conversion table from modulus tro diametral pitch for metric gears.
Modulus Diametral Pitch
.4 63.50
.5 50.80
.75 33.87
.8 31.75
1 25.40
1.25 20.32
1.5 16.93
2 12.70
2.5 10.16
3 8.57
 
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