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# 1/4 pitch gears?

#### Sandro29

##### Plastic
Hi all, new member here. I'm a maintenance tech in a manufacturing facility, and one of my responsibilities is correctly sizing gearing for production machine format changes. So the vast majority of our machines use either 8 or 10 pitch gears, which makes figuring out the sizing easy. However a few machines contain what are supposedly "1/4" (quarter) pitch gears, which are very close to 12 pitch but not quite. The trouble I'm having here is this: no matter how much digging I do I cannot seem to find any info online about these "1/4 pitch" gears, and the (fairly expensive) gear pitch gauge set I bought doesn't include a leaf for these "1/4 pitch" gears. So what exactly is a 1/4 pitch gear, and why is it named as a fraction instead of the normal pitches (6, 8, 10, 11, etc)?

#### Dan from Oakland

##### Titanium
Yes, circular pitch gears do exist. Its an old standard carried over from worm and worm wheel practice. Finding circular pitch gears on line will probably be difficult, but any gear shop should be able to cut them for you.

#### Sandro29

##### Plastic
Yes, circular pitch gears do exist. Its an old standard carried over from worm and worm wheel practice. Finding circular pitch gears on line will probably be difficult, but any gear shop should be able to cut them for you.
Ok, so then it's just an older system of gear sizing...makes sense because the machinery it's being used for is around 50 yrs old. Thanks. Any idea where I can find a tooth gauge for these circular pitch gears?

#### kevin johnson

##### Cast Iron
There is a set of circular pitch gear gages on Fleabay with a buy it now. Circular pitch is a component mathematically of diametral pitch gears. Cast gears are based on circular pitch. .25 CP is between 12 and 13 DP.
I would buy a a used copy of Machinery’s Handbook and do the math to figure out what I had. The math is not complicated.
Best of luck!

#### johnoder

##### Diamond
"Pi" divided by Diametral Pitch is circular pitch

Say you had 8 DP

"Pi" / 8 = .3927 CP

Conversely, "pi" divided by CP is DP

"Pi" / .25 = 12.5664 DP

The 1923 Pratt & Whitney tools catalog has all the CP cutters for sale

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#### ratbldr427

##### Stainless
Our Kidder flexo presses use 1/4" Cp change gears gears and our older sheeters we had used them also. It makes it easy to choose the correct tooth count for whatever repeat length you need; a 30" repeat would use a 120 tooth gear. Our Kidders came from England and had 1cm pitch gearing. I had to have the bull gears made with (I think)754 1/4 cp teeth. Spencer-Pettus in Bessemer City NC cut all our change gears. Good people and reasonable pricing.

#### David_M

##### Hot Rolled
When I worked for Union Camp/International Paper in Savannah, Georgia, their W & H presses (Windmöller & Hölscher) used 1/4 circular pitch gears.

We had a Newlong shopping bag making machine (press) that used 10mm circular pitch gears.

#### 10 fingers

##### Hot Rolled
Interesting. I have yet to encounter metric, circular pitch gears. Our printing press customers use a verity of CP sizes including, 1/3 CP.

#### David_M

##### Hot Rolled
Interesting. I have yet to encounter metric, circular pitch gears. Our printing press customers use a verity of CP sizes including, 1/3 CP.

I did some checking to make sure that I wasn't imagining the 10mm cp.

The Newlong machine(s) came from Japan.

Here is one of the lists of hobs showing it:

Edit:

I see that someone from engineering mistook a couple of the stub hobs for fractional diametral pitches when they converted the diametral pitch to circular pitch.
Another thing I see on the list is a 13.2131 dp hob. That one makes 1/4 transverse cp gears if hobbed at 18 degrees. It's been 20 years since working there, so I am re-remembering some of this stuff.

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#### ratbldr427

##### Stainless
As mentioned above our Kidder presses from England had 1cm(10mm) cp gears. They were built in the late 70's.At the time we had a lot of that type of work so the company bought 6 of them, 4 & 6 color ci's.We rebuilt them and converted the gearing to 1/4 cp.Before all the electronic registration came about all the web fed sheeters and printers used gearing to set repeat lengths and the ones I delt with were 1/4 cp.

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