A Gear Pressure Angle Question

99Panhard · Aug 28, 2020

I'm helping a friend with his 16-valve 1917 White touring car. The one part that is damaged is the water pump shaft, not from wear but from galvanic corrosion. It's an interesting challenge and is testing the limits of my skills but I think I can handle it. All of the early cars I've worked on used a 14.5 pressure angle on the gears and I'd say it's about 90% sure this one does to but the 20-degree pressure angle was known in 1917 and the White company clearly had their own ideas of how to do things...(the thread on that piece screwed into the front of the gear is 7/8-13). Can you tell by looking at the gear what it is? I could if I have a variety of gears to look at but I don't and none of what I have are 20-degree gears.

I should add, 20 teeth, DP8. The OD of the gear appears to be 2.88 but I will have to go back and measure that again. I measured it with my dial vernier and I really should have use a mic.

johnoder · Aug 28, 2020

And its a helical gear - not "straight cut"

(unless the camera is making it look helical)

A straight cut 20 tooth 8DP would be 2.75 OD (22 divided by 8)

The extra OD comes from it being helical

Phil in Montana · Aug 28, 2020

Looks like a 14.5 alright, being helical might kick your butt...Phil

99Panhard · Aug 28, 2020

I know. I've never done a helical before but you have to start somewhere. I remember you telling me the OD could be larger for a helical gear which is why I wasn't concerned. Thanks for putting my mind at ease on that. How abut the pressure angle? I searched on that and came up with a post you did years ago saying the 20-degree gears are a little "pointier" but I don't have anything to compare this one to. It looks like 14.5 to me but I'm just an amateur.

I'm going to take some photos tomorrow because I want to send it back to the gentleman who owns the car so he can use it temporarily while I muddle through making one. It's the strangest water pump shaft I've ever seen.

Mud · Aug 28, 2020

Don't be fooled that it has to be either 20 or 14.5, it can be just about anything a designer fancies. I make some 18.5°PA gears for a modern motorcycle because that's what the factory puts in them. FWIW other companies make the same gears at 20° and they seem to work out fine.
As to how to figure that out, I don't know with a helical gear. There are a few vintage posts here on PM about how to calculate PA from teeth spans and measurements over wires but I don't do helicals. The real headscratchers I send to Ash Gear and ask them to figure it out and supply a cutter.

johnoder · Aug 28, 2020

Here is a little scan from about 100 years back (Union Twist Drill). The 14.5 tooth space is visibly wider at the bottom compared to the 20. The 20 - with its wider base, is "stronger". You could say it was a higher performance item

What they don't say is it could be any thing between the two if that suited the requirements

If you intend making one, there is important info that can be extracted from the White:

Mating gear tooth count and center distance from one to the other

Then you can apply such handy published info such as this to arrive at helix angle

With helix angle you can determine LEAD that the milling machine needs to be set up to create - using table lead screw driven dividing head.

Lead calcs are here among others:

99Panhard said:
I know. I've never done a helical before but you have to start somewhere. I remember you telling me the OD could be larger for a helical gear which is why I wasn't concerned. Thanks for putting my mind at ease on that. How abut the pressure angle? I searched on that and came up with a post you did years ago saying the 20-degree gears are a little "pointier" but I don't have anything to compare this one to. It looks like 14.5 to me but I'm just an amateur.

I'm going to take some photos tomorrow because I want to send it back to the gentleman who owns the car so he can use it temporarily while I muddle through making one. It's the strangest water pump shaft I've ever seen.

1953chevB · Aug 28, 2020

I don't want to be the bad messenger.
Some retorical questions
What is the Din or AGMA quality? Precision of the the gear. Lead error, total composite error, tooth tooth composite error.
Is this gear Hobbed, and ground.
Is this case harden gear or through harden?
Does this gear have a profile shift. If it does how much.
What is the measurement over balls.

To get an exact measurement this of this gear it should be reversed engineered at a gear shop that can get the exact involute profile. They cnc gear checker that can nail it down.

Jim Christie · Aug 28, 2020

If you have or can get the use of a gear pitch gauge similar to the one shown here ,

https://www.practicalmachinist.com/vb/attachments/f19/283761d1585934373-early-hendey-dscf1057.jpg
It may help to determine the pressure angle .
gear tooth pitch gauge - Google Search
Those sets are getting more expensive now but perhaps you could find a deal on line somewhere and they are not that precise .
There are gear tooth vernier gauges too that are more rare and expensive that may be of some help if you can get your hands on one .
I remember being shown one at school 40 years ago but never mastered how to use it.
gear tooth vernier caliper - Google Search
You can probably use that to determine the pressure angle as well so maybe someone else will know .
With a helical gear you would need to swivel the gauge to the helix angle of the gear when checking the profile rather than square with the end as shown on the straight gears too get a more accurate comparison of the profile.
I don't have a helical gear handy at the moment to take a picture for an example.
As mentioned by Mud you may have to be prepared to deal with something that isn't made to the usual standard diametral pitch or pressure angle.
P.S.
I see 53ChevB has posted while I was typing so I'm bit late and behind in technology with my post.

Regards,

Jim

P.S. there is a section on milling Helical gears in this book that I have a copy of
Catalog Record: A treatise on milling and milling machines | HathiTrust Digital Library
Starting here
https://babel.hathitrust.org/cgi/pt?id=wu.89089665160&view=1up&seq=499&q1=Helical Gears
Brown and Sharpe equivalent is here and probably covers much the same material but I'm not familiar with this book
https://catalog.hathitrust.org/Record/009124290

gbent · Aug 28, 2020

Don't overthink this, guys. Its a 1917 car. OP, correct me if I'm wrong, but this vehicle will probably see less than 10 hours of running time in the rest of it's life. An undersize 14.5 pressure angle gear from aluminum will still look pristine when the car gets recycled.

1953chevB · Aug 28, 2020

Jim no worries
A gear caliper should be in a gear cutters tool box an works very well.
Set the addendum of a spur gear and measure the chordal tooth thickness.
For helicals the inputs are in the normal plane. #teeth, DP normal, PA Normal
And the helix angle., When the numbers are crunched, the normal and transverse Circular tooth thickness
Are calculated. As well as bunch other important data.
In a helical you have the normal plane and the transverse plane.
The differential gear train has to be precise with very little error.
Which equals the the lead error
In addition the indexing has to be precise.
I take a swag at the AGMA level of this helical gear to be Q10.

99Panhard · Aug 28, 2020

johnoder said:
Here is a little scan from about 100 years back (Union Twist Drill). The 14.5 tooth space is visibly wider at the bottom compared to the 20. The 20 - with its wider base, is "stronger". You could say it was a higher performance item

View attachment 297942

What they don't say is it could be any thing between the two if that suited the requirements

If you intend making one, there is important info that can be extracted from the White:

Mating gear tooth count and center distance from one to the other

Then you can apply such handy published info such as this to arrive at helix angle

View attachment 297943

With helix angle you can determine LEAD that the milling machine needs to be set up to create - using table lead screw driven dividing head.

Lead calcs are here among others:

View attachment 297945

Thanks again John, I'm going to print this out as it's very useful.

jp

99Panhard · Aug 28, 2020

gbent said:
Don't overthink this, guys. Its a 1917 car. OP, correct me if I'm wrong, but this vehicle will probably see less than 10 hours of running time in the rest of it's life. An undersize 14.5 pressure angle gear from aluminum will still look pristine when the car gets recycled.

Not with this car, and certainly not with this owner... He's one of the top people in the country for sorting out expensive pre-war cars and making sure they are as good, or better than they were new.

jp

99Panhard · Aug 28, 2020

Jim Christie said:
If you have or can get the use of a gear pitch gauge similar to the one shown here ,

https://www.practicalmachinist.com/vb/attachments/f19/283761d1585934373-early-hendey-dscf1057.jpg
It may help to determine the pressure angle .
gear tooth pitch gauge - Google Search
Those sets are getting more expensive now but perhaps you could find a deal on line somewhere and they are not that precise .
There are gear tooth vernier gauges too that are more rare and expensive that may be of some help if you can get your hands on one .
I remember being shown one at school 40 years ago but never mastered how to use it.
gear tooth vernier caliper - Google Search
You can probably use that to determine the pressure angle as well so maybe someone else will know .
With a helical gear you would need to swivel the gauge to the helix angle of the gear when checking the profile rather than square with the end as shown on the straight gears too get a more accurate comparison of the profile.
I don't have a helical gear handy at the moment to take a picture for an example.
As mentioned by Mud you may have to be prepared to deal with something that isn't made to the usual standard diametral pitch or pressure angle.
/QUOTE]

I have both. I used the gauge to determine the DP. I have a B&S gear vernier too but have never used it. Somewhere (I'm looking for it right now) I have the B&S book "Formulas in Gearing". I realize I'm in a bit over my head here but challenges like this are how I move forward. This forum has been a huge help in that...

99Panhard · Aug 28, 2020

As to it being an odd pressure angle. While I've no proof, that is very unlikely. White was a charter member of the ALAM (the Association of Licensed Automobile Manufacturers). When the Selden patent, which was controlled by the ALAM, ran out in 1911 the technical committee of the ALAM was reformed into the SAE which is its direct descendant. The standards adopted by the ALAM just carried over to the SAE. After WWI they undertook to standardize the threads used in automobiles because the army had so much trouble during the war with odd threads that it was decided that only vehicles using a standardized thread system could be purchased. There was already an ALAM thread system, some of which was folded into the new SAE system. The White uses ALAM threads and they seem to have adhered to the suggestions of the technical committee. There is no SAE handbook until the mid-20s but all of the other engines I've worked on from cars made by ALAM members used 14.5-degree gears.

Homebrewblob · Aug 28, 2020

Simple. Build a straight cut gear. And twist it!!

1953chevB · Aug 28, 2020

That cool history, who made this car, and what manufacturing abilities did they have back then?
To properly reverse engineer a gear of this quality. A gear would have to be sent to a metallurgical lab for a spectral analysis of what material it was made from, and the hardness of gear teeth profiles.
Section to verify if it was case harden or through harden.

A gear tooth bends under load. S& N curves are use to know the max gear tooth to tensile strength, the bending moment causes fatigue. If not calculated correctly it will self destruct in short cycle run. The other is wear, fretting if the gear teeth are not the correct hardness, pitting and fretting will occur. Hertz hardness.
If the gear teeth have manufacturing errors, as in my previous post, it will interference this will also cause failure.
You may have to use the mating part as a master gear check to make sure it rolls smoothly. They may have been made as a marched set, unknown.

Edit: not the info you are asking for but at least your aware.
gear calc on line https://www.tribology-abc.com/sub8.htm
Gear Generator

EmGo · Aug 28, 2020

99Panhard said:
As to it being an odd pressure angle. While I've no proof, that is very unlikely ... There is no SAE handbook until the mid-20s but all of the other engines I've worked on from cars made by ALAM members used 14.5-degree gears.

All this talk about "standards" .... with gears, these numbers only apply to 'standard' teeth on 'standard' center distances. If you take a pair of 8 pitch 14.5* pa gears and spread the center distance, the pressure angle goes up even though they are still cut with the same tools. With helicals it's even worse, you have the normal pressure angle and the transverse pressure angle, all the product of the same 'standard' cutter. (Not talking space cutters here, they aren't even accurate when used as specified.)

From the photo, those look like 20* teeth, but until you measure that hummer out, you can't really say.

I always think of it as, 'there are no standards, there's only common practice'. As soon as you move even a millimeter off the 'standard' numbers, everything goes out the window.

You're not likely to make a nice version of this part in a milling machine. Possible, but unlikely.

1953chevB · Aug 28, 2020

one more You need to register, Hope it Helps
Free Gear Calculator | KHK Gears

1953chevB · Aug 28, 2020

EmanuelGoldstein said:
All this talk about "standards" .... with gears, these numbers only apply to 'standard' teeth on 'standard' center distances. If you take a pair of 8 pitch 14.5* pa gears and spread the center distance, the pressure angle goes up even though they are still cut with the same tools. With helicals it's even worse, you have the normal pressure angle and the transverse pressure angle, all the product of the same 'standard' cutter. (Not talking space cutters here, they aren't even accurate when used as specified.)

From the photo, those look like 20* teeth, but until you measure that hummer out, you can't really say.

I always think of it as, 'there are no standards, there's only common practice'. As soon as you move even a millimeter off the 'standard' numbers, everything goes out the window.

You're not likely to make a nice version of this part in a milling machine. Possible, but unlikely.

modern gear calculations take into account special center distance, and that is dictated by the profile shift such as pinion gears.
that have to be enlarged to prevent under cutting, in addition to find the most efficient gears which it prevents as per my above post.
standard gears are for very low stress, very low loads, profile shifted gears, and the correct material and heat treat for specific loads and RPMs
all I have stated may be over kill, but that's OK because it's better to be aware. unknows from op's post
RPM, Load (torque), actual center distance of the shafts, these may be special designed gears on special center distance. not standard.

pavt · Aug 28, 2020

If possible, I would blue up one side of the gear with with machinists blue, and "print" it onto a sheet of paper, carefully to get the full image.. This can be scanned into a CAD program to make analysis much easier. The helix angle can be found with some angle gauge blocks while the gear is laying flat on the paper. Being from 1917, I wouldn't assume any sort of standards were followed that would translate into modern practice. I would also be happy to bet that modern, 4140 pre-hard is adequate -- and certainly much better than the original material.

A Gear Pressure Angle Question

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