A question for the gear guys.

[atex57]

I have a question for the gear gurus. The first gear has 54 teeth, 7.980 OD and measures 7.935 over .247 pins, yes, the teeth are higher than the pin. Measure 8.074 over .288 pins. The DP appears to be 7 and 20PA as checked with my pitch gages. Measuring span it comes out to 1.545 over 4 teeth, 1.963 over 5 and 2.382 over 6.

The second gear is 30 teeth,5.795 OD, measures 5.665 over .288 pins and 5.864 over .345 pins. Spans are 1.383 over 3 teeth, 1.900 over 4 teeth, and 2.422 over 5 teeth. None of this comes out close to anything even as far as numbers. Big question is what in the world am I working with? Help a guy that is still learning.

An included pic may tell you more as it shows the first gear profile and a .288 pin.

Thanks, Ed.

 

[4GSR]

Are you certain they are 20° PA? I've seen gears with up to 25° PA. Where are you coming up with the pin diameters used? And how are you determining you measurement over the pins is not coming our right?

 

[BajaFire]

How old are these gears? Possibly 14.5 degree pressure angle

 

[EmGo]

Where are you coming up with the pin diameters used?

Normal for externals is 1.728"/DP He said they are 7's so .24686" wires. Real gear wires are better than a tenth on accuracy, not that it usually matters that much.

I was more confused by why op is using two different wire sizes and several span measurements and why the teeth look so abnormal. There's more going on here than just pressure angle.

So I just shut up for a change.

 

[guythatbrews]

Are you sure your span measurements are across the involute profile? The span difference on the first gear is .418 and .419. The second gear is .517 and .522. The span difference should be exactly the same, unless the gears are really crummy or damaged.

Look at that again, and then check against the base pitch tables. The span difference you have now doesn't quite match anything.

 

[Garwood]

Does not look like 20PA to me.

 

[atex57]

Are you certain they are 20° PA? I've seen gears with up to 25° PA. Where are you coming up with the pin diameters used? And how are you determining you measurement over the pins is not coming our right?

My pitch gages show 20 degrees and 7DP are the closest. Pin diameter is standard (close) for 7DP.

 

[atex57]

Normal for externals is 1.728"/DP He said they are 7's so .24686" wires. Real gear wires are better than a tenth on accuracy, not that it usually matters that much.

I was more confused by why op is using two different wire sizes and several span measurements and why the teeth look so abnormal. There's more going on here than just pressure angle.

So I just shut up for a change.

I checked several different ways to give options to interpret. The second gear is from a different set, sorry for the confusion.

 

[atex57]

Are you sure your span measurements are across the involute profile? The span difference on the first gear is .418 and .419. The second gear is .517 and .522. The span difference should be exactly the same, unless the gears are really crummy or damaged.

Look at that again, and then check against the base pitch tables. The span difference you have now doesn't quite match anything.

The second gear is from a different set, sorry about that. I threw the span measurements in in case that helps anyone.

 

[EmGo]

The second gear is from a different set, sorry about that.

Ah. That's a start anyway

Do they both roll smoothly with your gage ? And just for fun, do they roll together or are they entirely different ?

 

[David_M]

The second one sort of looks like a 4.5 module. It seems like wear in the tooth flanks is causing the pin measurement to be smaller (and/or it was cut undersize), and maybe the tooth tips need filing to remove displaced material, which is causing the OD to be oversized. Shown below is a 4.5 module.

 

[guythatbrews]

Use the base pitch charts to determine the PA and pitch. They are foolproof and work for standard or modified pitch diameters, as long as you can get span measurements on the involute profile. You must have precise span measurements. The span difference between teeth equals the base pitch.

 

[David_M]

The 54-tooth, 7-dp gear. The pressure angle seems to be 25 degrees (as shown). I placed the small gage pins where the OP measured, then rotated the right and left tooth flanks until they achieved tangency with the pin. I then added the large gage pins with the tangent, tangent, radius command. Changing the pressure angle the smallest amount would get the span measurements to agree with the OP's.

It almost looks like a sprocket.

I believe the only tooth spans that can be measured accurately on this gear are 7, 8, and 9.

(((54/7)*pi)*cos(25))/54 = 0.40674998 if the lookup table isn't convenient.

 

[john.k]

if these gears are from a lathe ,its quite common for odd gears to be used to get a desired ratio........you will never get a commercial gear ,or a commercial gear maker to match the gear.

 

[David_M]

30 tooth Gear
4.5 Mod
20 PA

(((30/(25.4/4.5))*pi)*cos(20))/30 = 0.523015 Base Pitch for 4.5 mod, 20 pa

 

[David_M]

I promise to quit after this.

The 54-tooth gear looks like one of a set that might be used on a sheet-metal roller.

Looks like a non-standard hob would be needed—extra deep teeth.

 

[rjwalker1973]

I promise to quit after this.

The 54-tooth gear looks like one of a set that might be used on a sheet-metal roller.

Looks like a non-standard hob would be needed—extra deep teeth.

why stop? some like me are learning new stuff. Most I have done is set-up hobs and shavers to make them. Never did learn a lot of the nuances to gears.

 

[David_M]

I have to break my promise. Sorry.
I looked at the OP's photo:

I see very little wear. So, my method of rotating the tooth flanks to match the over-pin measurements isn't the best.

These gears are profile-shifted to the inside. The only way to do this right, IMHO, is to generate an involute curve based on the profile shift, as below:

By changing to 5.5 dp, I got the OD to match up with the OP's.

If I get the time, I'll redo the 54-tooth gear. My gut feeling is that it will have a 20 pa.

Generating the Involute with the cutter moved for the profile shift:

 

[EmGo]

These gears are profile-shifted to the inside.

Maybe. Or maybe something entirely different. They sort of look like extra-extra-deep teeth, which some people have played with for various reasons.

That's why I hate these kind of questions. What's the point ? Just someone throwing up a few photos to be cute ? They aren't even a pair, who knows what the hell they go to, what's the purpose ? Gear teeth are made all kinds of weird different ways for different reasons, someone just putting up a question like this to prove how speshul they are, then they instantly disappear, flock me, I'd rather look at the macy's lingerie ads, it's more useful.

 

[David_M]

Maybe. Or maybe something entirely different. They sort of look like extra-extra-deep teeth, which some people have played with for various reasons.

If you look at his pic, the extra depth makes it look like it comes from a secondary operation. The radius at the bottom looks too round, like it was milled.

That's why I hate these kind of questions. What's the point ? Just someone throwing up a few photos to be cute ? They aren't even a pair, who knows what the hell they go to, what's the purpose ? Gear teeth are made all kinds of weird different ways for different reasons, someone just putting up a question like this to prove how speshul they are, then they instantly disappear, flock me, I'd rather look at the macy's lingerie ads, it's more useful.

I agree with you about posters who post and then disappear. I hate to be blunt.