multiproducts
Mechanical
What could happen to the pinion/gear teeth if you have a 20deg pressure angle pinion driving a 14.5 deg. gear?
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20deg. Vs 14.5deg. 3
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eromlignod
Mechanical
- Jul 28, 2006
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It'll be hard to assemble, hard to turn, and grind the teeth all to hell.
Don
Kansas City
Don
Kansas City
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multiproducts
Mechanical
Thanks,
We use AGMA 6 gears. As a test I assembled a gearbox with 20 deg Vs 14.5 and it assembled and turned just fine, sounds OK also. I was wondering what the affect it will have on tooth wear and roll.
We use AGMA 6 gears. As a test I assembled a gearbox with 20 deg Vs 14.5 and it assembled and turned just fine, sounds OK also. I was wondering what the affect it will have on tooth wear and roll.
scarecrow55
Mechanical
I'd agree with eromlignod. They might feel OK by hand turning but under load they'd get destroyed.
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I do not understand why are you guys even try to answer this question. I would refer multiproducts to the literature to gain a basic knowledge before asking questions which shouldn't be asked at all. I do not dare to think what was the question if this was a gentic or stem cells forum.
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multiproducts
Mechanical
I can't find anything written about mixing pressure angles.
We have a 12T 48 pitch pinion driving a 48T 48 pitch gear. The pinion is at 400 RPM.
We have a 12T 48 pitch pinion driving a 48T 48 pitch gear. The pinion is at 400 RPM.
You will not find anything written about mixing pressure angles because this is not done. Look for the basic law of gearing, i.e. the properties of the involute, the tout string etc.
You could as well use pin gear system as seen in the old western movies to pump water but these don't follow the laws or gearing.
To keep the laws of gearing the pressure angle has to be the same in order to get constant transmission ratio along the tooth action even with variable center distance.
You could as well use pin gear system as seen in the old western movies to pump water but these don't follow the laws or gearing.
To keep the laws of gearing the pressure angle has to be the same in order to get constant transmission ratio along the tooth action even with variable center distance.
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multiproducts
Mechanical
Thanks,
We had a 20deg Vs 14.5deg mix-up that was fortunatly cought at first piece inspection. Afterwords the question came up "what happens when you mix pressure angles?" and I could not find a specific answer.
We had a 20deg Vs 14.5deg mix-up that was fortunatly cought at first piece inspection. Afterwords the question came up "what happens when you mix pressure angles?" and I could not find a specific answer.
I had always been taught that you could
not mix pressure angles and I was curious
why they worked for you at 400 rpm and
I assume it was on the same center distance.
Were these plastic gear in that you did
hear any disturbances? Really strange.
not mix pressure angles and I was curious
why they worked for you at 400 rpm and
I assume it was on the same center distance.
Were these plastic gear in that you did
hear any disturbances? Really strange.
eromlignod
Mechanical
- Jul 28, 2006
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Let's look at it geometrically.
Two involute gears with the same pressure angle result in the two curved gear faces contacting at a point where the line of centers of the two gears intersects the pitch circle. The pressure angle is perpendicular to the common tangent plane.
Now, if one gear's pressure angle is different, that means its involute tooth profiles are generated from a different base circle diameter. For a larger base circle (smaller pressure angle) the teeth would be wider at the crest and narrower at the base than teeth generated by a smaller base circle, which makes narrow crests and wide bases.
Teeth with thicker bases also have narrower root widths between them at the same pitch, so you're mating a tooth with a wider crest in a slot with a skinnier width, which won't work. When the pair is rotated half a pitch more, to where the skinny top mates with the wide gap, then you have backlash.
That's why if you mate two gears of differing angle, the resulting motion vibrates and grinds as alternating interference and clearance occur at each tooth.
Don
Kansas City
Two involute gears with the same pressure angle result in the two curved gear faces contacting at a point where the line of centers of the two gears intersects the pitch circle. The pressure angle is perpendicular to the common tangent plane.
Now, if one gear's pressure angle is different, that means its involute tooth profiles are generated from a different base circle diameter. For a larger base circle (smaller pressure angle) the teeth would be wider at the crest and narrower at the base than teeth generated by a smaller base circle, which makes narrow crests and wide bases.
Teeth with thicker bases also have narrower root widths between them at the same pitch, so you're mating a tooth with a wider crest in a slot with a skinnier width, which won't work. When the pair is rotated half a pitch more, to where the skinny top mates with the wide gap, then you have backlash.
That's why if you mate two gears of differing angle, the resulting motion vibrates and grinds as alternating interference and clearance occur at each tooth.
Don
Kansas City
Well Gentlemaen - none of the answers given so far have gotten to the crux of the issue.
It is customary to design gears that mesh with the same pressure angle, only because it is also customary to design gears with the same Normal Modules or Normal Diameteral Pitches. ie a 20 degree pressure angle pinion meashes with a 20 degree pressure angle gear. This is due to simplicity in design.
The real criteria however is that the pinion has the same base pitch or in the case of helical gears; normal base pitch.
The equation for normal base pitch in metric mm is:
Pi x Cos (Pressure Angle) x Normal Module
and in inches is
Pi x Cos (Pressure Angle) / Normal Diametral Pitch
For a 14 1/2 degree pressure angle pinion to properly mesh with conjugate action with a 20 degree pressure angle gear, we need to solve the equation as follows (in metric mm):
Pi x Cos(14.5) x Normal Module Pinon = Pi x Cos(20) x Normal Module Gear
Reducing we get
Normal Module Gear = Normal Module Pinion x Cos (14.5)/Cos(20)
Incidentally - this concept of gears requireing the same Normal Base Pitch to have conjugate action is the main reason why gears are noisy. To tourbleshoot noise problems, try to measure the normal base pitches. If the two gears match, they will will run quiet even if both gears of off spec by the same amount.
It is customary to design gears that mesh with the same pressure angle, only because it is also customary to design gears with the same Normal Modules or Normal Diameteral Pitches. ie a 20 degree pressure angle pinion meashes with a 20 degree pressure angle gear. This is due to simplicity in design.
The real criteria however is that the pinion has the same base pitch or in the case of helical gears; normal base pitch.
The equation for normal base pitch in metric mm is:
Pi x Cos (Pressure Angle) x Normal Module
and in inches is
Pi x Cos (Pressure Angle) / Normal Diametral Pitch
For a 14 1/2 degree pressure angle pinion to properly mesh with conjugate action with a 20 degree pressure angle gear, we need to solve the equation as follows (in metric mm):
Pi x Cos(14.5) x Normal Module Pinon = Pi x Cos(20) x Normal Module Gear
Reducing we get
Normal Module Gear = Normal Module Pinion x Cos (14.5)/Cos(20)
Incidentally - this concept of gears requireing the same Normal Base Pitch to have conjugate action is the main reason why gears are noisy. To tourbleshoot noise problems, try to measure the normal base pitches. If the two gears match, they will will run quiet even if both gears of off spec by the same amount.
Go back to the typical definition of "pressure angle". It is the angle between a tangent to the involute at the "pitch circle" and a radial line through the point of tangency. A gear tooth that includes a 20° pressure angle also has a point closer to the root where the pressure ange is 14.5°. If the pitch of the gears is the same at the circles where the pressure angles match, they can run fine if there are no interferences and the center distance is properly chosen.
Using "standard" gearing, the best design practice is certainly to match DP and PA, but it is not impossible to find a combination where different PA's can be well mated with different DP's.
Using "standard" gearing, the best design practice is certainly to match DP and PA, but it is not impossible to find a combination where different PA's can be well mated with different DP's.
Spurs & Gearmold,
Can you give a specific combination of gears with different pressure angles that run together? If you are
speaking only of operating pressure angles, I could agree.
I know a long addendum gear running against a standard addendum gear will operate with no problem, but at different pressure angle. These are cut with the same standard pressure angle tooling. I have not see a set of gears with one having a been cut with 20 pressure angle tooling that operates with a gear that is cut with 14.5 pressure angle tooling.
Can you give a specific combination of gears with different pressure angles that run together? If you are
speaking only of operating pressure angles, I could agree.
I know a long addendum gear running against a standard addendum gear will operate with no problem, but at different pressure angle. These are cut with the same standard pressure angle tooling. I have not see a set of gears with one having a been cut with 20 pressure angle tooling that operates with a gear that is cut with 14.5 pressure angle tooling.
Well, you could call this a "mathematical trick", but the mathematical truth is that the curve we know as the "involute of a circle" is really just a single curve. There is no 14.5° involute or 20° involute or whatever. It's just ONE curve on which we base all "involute form" gear teeth. If pressure angles match, regardless of the "nominal" pressure angle of a specific component, then we will have the conjugate action afforded by the involute form. This insures that noise generated by mating gears arises from
a) sliding action and hence, surface finish
b) inaccuracies in the generation of the involute form and/or
c) tolerances in the position of the involutes (shaft sizes and positions, etc.)
Likewise, wear will depend on these factors plus lubrication. Notice that nominal pressure angle ISN'T in the list.
The concept of "operating pressure angle" is an extension of this idea. One of the greatest advantages of the involute profile is the fact that teeth still mesh in conjugate action even if center distance is changed a bit. The "operating pressure angle" (angle between a normal to the line of action and the centerline of mesh), will change, but the action is still purely conjugate. This design flexibility is not strictly applicable to cycloidal tooth form designs.
No, I cannot give a specific combination. We don't normally design gear trains using different nominal pressure angles for mating gears, and I'm not going to spend time creating an example. My point was only that it is conceptually possible to find such a combination.
You can see practical applications of this if you do a lot of double-flank gear rolling with non standard DP gears or both English and metric gears. Suppose you have to check a .4 module, 20°PA gear, but don't have a .4 module master. Do you spend $800 for a new master and wait for delivery, or just use a 64 DP master and calculate the difference?
a) sliding action and hence, surface finish
b) inaccuracies in the generation of the involute form and/or
c) tolerances in the position of the involutes (shaft sizes and positions, etc.)
Likewise, wear will depend on these factors plus lubrication. Notice that nominal pressure angle ISN'T in the list.
The concept of "operating pressure angle" is an extension of this idea. One of the greatest advantages of the involute profile is the fact that teeth still mesh in conjugate action even if center distance is changed a bit. The "operating pressure angle" (angle between a normal to the line of action and the centerline of mesh), will change, but the action is still purely conjugate. This design flexibility is not strictly applicable to cycloidal tooth form designs.
No, I cannot give a specific combination. We don't normally design gear trains using different nominal pressure angles for mating gears, and I'm not going to spend time creating an example. My point was only that it is conceptually possible to find such a combination.
You can see practical applications of this if you do a lot of double-flank gear rolling with non standard DP gears or both English and metric gears. Suppose you have to check a .4 module, 20°PA gear, but don't have a .4 module master. Do you spend $800 for a new master and wait for delivery, or just use a 64 DP master and calculate the difference?
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