Pinion Gear Pitch?

Uglydog

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Yep, it's gear weekend!
I'm also working on two gears for my Boye & Emmes 16A apron.
One is a bevel for the powerfeed (whole different subject).
The other is a new pinion for the rack.
The rack has about 6inches of wear near the headstock.
I'm planning on flipping it end to end and redrilling.
The pinion has about half the teeth significantly worn the other half unscathed.
I've found some prints with measurements (microfiche). The prints show an 8DP. My measurement of the pinion shows the same. I count 13teeth.
I've got a 8P 12-15tooth 14.5 pressure angle involute cutter.
It just doesn't look right. Way to small at the bottom.
I've only cut one so far. Looks more like a 10P.

When making a pinion do I need a rack cutter? Other ideas?

Daryl
MN
 
Yep, it's gear weekend!
I'm also working on two gears for my Boye & Emmes 16A apron.
One is a bevel for the powerfeed (whole different subject).
The other is a new pinion for the rack.
The rack has about 6inches of wear near the headstock.
I'm planning on flipping it end to end and redrilling.
The pinion has about half the teeth significantly worn the other half unscathed.
I've found some prints with measurements (microfiche). The prints show an 8DP. My measurement of the pinion shows the same. I count 13teeth.
I've got a 8P 12-15tooth 14.5 pressure angle involute cutter.
It just doesn't look right. Way to small at the bottom.
I've only cut one so far. Looks more like a 10P.

When making a pinion do I need a rack cutter? Other ideas?

Daryl
MN
Daryl, look in Machinery's Handbook. They have full size drawings of different diametral pitch (DP) teeth you can compare with your gears. Don't use something magnified like microfiche or something off the internet that you do not know for sure to be a correct sized template. You must get diametral pitch correct to get started. The handbook also shows what number cutters are used for different tooth counts, starting at 12 teeth (IIRC) and going to a rack. There are eight cutters for each DP, and each does a portion of the possible tooth counts. Watch out, Chinese gear cutters are sometimes numbered backwards from US made ones, but they usually say the appropriate tooth counts, and depth of cut, on the cutter. Write it all down before you mount the cutter, because you cannot read the cutter when it is mounted on the arbor. Machinery's Handbook will also tell you what diameter the gear blank needs to be and the depth of cut.

mrpete222 made a series of YouTube videos recently on how to lay out, machine, and cut gears. They are quite well done, comprehensive, and lengthy for the whole set.

For me at least, the #1 rule of gear cutting is -- slow down, be careful, think each operation and action over several times before making chips. It is incredibly easy to make mistakes making gears and frustrating throwing oops parts in the scrap bin.
 
A "rack cutter" is only used for high tooth count gears and racks. The cutter to use for your pinion depends on its tooth count. The rack and the pinion use DIFFERENT cutters.
 
Is the actual pinion gear a 14.5PA? You could have a 8DP 20PA or other PA which would make a difference. Not sure what you have so you might want to check the PA on the pinion and make sure it is 14.5.
 
Daryl, look in Machinery's Handbook. They have full size drawings of different diametral pitch (DP) teeth you can compare with your gears. Don't use something magnified like microfiche or something off the internet that you do not know for sure to be a correct sized template. You must get diametral pitch correct to get started. The handbook also shows what number cutters are used for different tooth counts, starting at 12 teeth (IIRC) and going to a rack. There are eight cutters for each DP, and each does a portion of the possible tooth counts. Watch out, Chinese gear cutters are sometimes numbered backwards from US made ones, but they usually say the appropriate tooth counts, and depth of cut, on the cutter. Write it all down before you mount the cutter, because you cannot read the cutter when it is mounted on the arbor. Machinery's Handbook will also tell you what diameter the gear blank needs to be and the depth of cut.

mrpete222 made a series of YouTube videos recently on how to lay out, machine, and cut gears. They are quite well done, comprehensive, and lengthy for the whole set.

For me at least, the #1 rule of gear cutting is -- slow down, be careful, think each operation and action over several times before making chips. It is incredibly easy to make mistakes making gears and frustrating throwing oops parts in the scrap bin.

Thank you Bob,
These are vintage BS cutters. The microfiche type is from Boyee and Emmes. But, your point is well taken. Actually measure the existing pinion and do the math. Arrgh. I think I've watched every Tubalcain video at least twice. Some much more than that.

Daryl
MN
 
Is the actual pinion gear a 14.5PA? You could have a 8DP 20PA or other PA which would make a difference. Not sure what you have so you might want to check the PA on the pinion and make sure it is 14.5.

Valid point.
The vintage of the lathe suggests a 14.5PA. But, I am gonna have to figure out how to measure it.

Daryl
MN
 
Daryl,

Way back in my younger years, I had the privilege to work with a old lathe manufacture when the company sold and moved to Houston in the 1970's. Had a lathe made by them in the 1920's that had a worn out rack pinion gear. We pulled the rack pinion gear drawings on file for that size lathe, an 18". There were three different size gears, all had the same number of teeth, but the variation in pitch diameter was nearly 1/8". They made oversized, undersized, and nominal sized, pinion gears for that lathe size series. That's how much variation they had in the manufacture of the lathes back then.

So you maybe dealing with a undersized pinion needed for your lathe. If so, you may have no choice but to find someone with a gear hobber to cut the pinion gear for you, to get the root of the tooth profile correct.

Ken
 
Hey Ken, Great point. I ran into a extended depth gear recently that I had no idea they made. They are easily identified, a stub gear has very short teeth and the normal, well it is normal looking, the extended depth have very long teeth- normal looking just long.
 
Hey Ken, Great point. I ran into a extended depth gear recently that I had no idea they made. They are easily identified, a stub gear has very short teeth and the normal, well it is normal looking, the extended depth have very long teeth- normal looking just long.

It's not a stub tooth form he has or extended tooth depth. It's where they make the pinion OD oversized or undersized, depending where the pitch diameter needs to fall. The gear hobber hobs or generates the tooth form according to the P.D. needed. The depth of the tooth does not change, just the shape of the tooth. And it's this shape that cannot be cut using involute cutters to cut.

Ken
 
Thanks guys ,
Having read the thread I'm now beginning to understand why I'm finding it so difficult to fly cut a new thread counter gear that actually works each & every time I engage it.
 
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