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dimension over pins, dop, dop measurement, spur gear
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  #1  
Old 8th July 2008, 09:12 AM
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Please Help! Spur Gear DOP (Dimension Over Pins) Measurement - 2 or 3 Pins?

One of our foreign suppliers is disagreeing with my gear DOP measurement method. I have been taught that when measuring spur gear DOP, one always uses two pins - no matter if the gear has an even or odd number of teeth. I have used this method for 15+ years without problem. (You would use three pins or balls for worm gears or screw threads.) The foreign "expert" says that you use three pins for odd number of teeth on spur gears.

I can find trade literature to back up my method. But I do not know of a standard or anything more formal to back up my position. Is there anyting out there that anyone knows of?

Thanks,
Scott

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Old 8th July 2008, 10:27 AM
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Re: Spur Gear DOP Measurement

This isn't my field of expertise. What is a gear DOP measurement method?

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Old 8th July 2008, 10:38 AM
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Re: Spur Gear DOP Measurement

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In Reply to Parent Post by Marc View Post

This isn't my field of expertise. What is a gear DOP measurement method?
I believe diameter/dimension over pins.

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Old 8th July 2008, 10:50 AM
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Re: Spur Gear DOP Measurement

Quote:
In Reply to Parent Post by ScottyWM View Post

One of our foreign suppliers is disagreeing with my gear DOP measurement method. I have been taught that when measuring spur gear DOP, one always uses two pins - no matter if the gear has an even or odd number of teeth. I have used this method for 15+ years without problem. (You would use three pins or balls for worm gears or screw threads.) The foreign "expert" says that you use three pins for odd number of teeth on spur gears.

I can find trade literature to back up my method. But I do not know of a standard or anything more formal to back up my position. Is there anyting out there that anyone knows of?

Thanks,
Scott
I am not an expert on this but according to my experience it depends on how the designer has calculated the " diameter over pins ".

In most cases I have encountered the designs were made using 2 pins but I have seen cases measured over 3 pins.
So it depends.

Best regards,

Antoine
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Old 8th July 2008, 11:03 AM
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Re: Spur Gear DOP Measurement

DOP = dimension over pins (or dimension over wires).

Two wires are placed 180 apart in the gear teeth and a measurement is made over the wires. (On odd number of teeth gears, the wires are placed as close to 180 as possible.) Gives a relatively quick and easy meausrement of size and tooth thickness at pitch diameter. We use doble flank gear testers ourselves, but the supplier does not have this capability - thus we also measure the DOP.

I have seen and can cite *many* references to using two pins. I have not seen nor can find any references to using three pins, unless it is a worm gear or screw thread.

From the Machinery's Handbook:
Attached Thumbnails
DOP4.jpg  

Last edited by ScottyWM; 8th July 2008 at 11:45 AM.
Thanks to ScottyWM for your informative Post and/or Attachment!
  #6  
Old 8th July 2008, 11:54 AM
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Re: Spur Gear DOP Measurement

Quote:
In Reply to Parent Post by ScottyWM View Post

DOP = dimension over pins (or dimension over wires).

Two wires are placed 180 apart in the gear teeth and a measurement is made over the wires. (On odd number of teeth gears, the wires are placed as close to 180 as possible.) Gives a relatively quick and easy meausrement of size and tooth thickness at pitch diameter. We use doble flank gear testers ourselves, but the supplier does not have this capability - thus we also measure the DOP.

I have seen and can cite *many* references to using two pins. I have not seen nor can find any references to using three pins, unless it is a worm gear or screw thread.

From the Machinery's Handbook:
I looked it up in my copy of the Handbook of Dimensional Measurement. It mentions only using two pins and then says to look up the details in the Machinery Handbook. Most splines are specified as being measured over two pins.

I'd ask the foreign expert for his standards.
  #7  
Old 8th July 2008, 06:07 PM
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Re: Spur Gear DOP (Dimension Over Pins) Measurement - 2 or 3 Pins?

Quote:
In Reply to Parent Post by ScottyWM View Post

One of our foreign suppliers is disagreeing with my gear DOP measurement method. I have been taught that when measuring spur gear DOP, one always uses two pins - no matter if the gear has an even or odd number of teeth. I have used this method for 15+ years without problem. (You would use three pins or balls for worm gears or screw threads.) The foreign "expert" says that you use three pins for odd number of teeth on spur gears.

I can find trade literature to back up my method. But I do not know of a standard or anything more formal to back up my position. Is there anyting out there that anyone knows of?

Thanks,
Scott
Scott,

Look at this magazine "Gear Solutions", page 25.

That may help a little....

Stijloor.
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