Runout on Gear Callout 4

[vc66]

Hi All-

I am redesigning a power transmission system, and currently doing the drawings of the gear and pinion. One of the main problems on the original design was the concentricity of the pitch diameter to the mounting hub. I would like to put a runout callout on my drawing, but have never called out runout on a gear before. My question is, in order to do this, do I just dimension the P.D. and attach the runout callout? Is it more difficult than that, or am I just over complicating things?

Thanks in advance.

Regards,

V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[MintJulep]

I don't see how you could ever measure the runout of the pitch diameter, seeing as it isn't a physical feature and all.

 

[vc66]

Sorry, I meant O.D. Thanks for the lack of help, and sarcastic comment though.

Is it safe to say that the runout of the O.D. is related to the pitch diameter? If not, what is the best way to specify if a gear is running concentric?



V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[MintJulep]

You ask a question about how to do something that can't be done and it gets your panties all bunched up when it's pointed out to you?

How is anyone supposed to know that you meant O.D. when you write both "P.D." and "pitch diameter" in your question?

 

[vc66]

First, no one was supposed to know. That's why it's called a typo. I DID mean pitch diameter in my first sentence. That's what I'm trying to relate to the O.D. The second time P.D. was supposed to be O.D. (they're right next to each other on the keyboard, and I have fat fingers ). Second, I didn't get my panties in a bunch, I was simply returning sarcasm with sarcasm.

Seeing as though you have posted two replies--neither of which really help me, I would appreciate it if you kept your future replies to the question I posed or don't reply, as I don't wish to banter about using the preview post button before I submit my post.

My question again... Can the runout of the outer diameter of a gear be related to the pitch diameter? If not, how is it usually called out on a drawing to specify that the gear should be concentric to the hub?

Thanks,



V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[Xplicator]

ASME Y14.7 covers gear specification standards and that there is probably something to address your issue there. My issue is the 1971 version so don't want to mislead you form an old standard. I would find an updated one and go from there.

Now in regards to applying GD&T based on your scenario, you first have to determine which geometric characteristics you want to control. You stated that historically concentric variation of the pitch diameter(PD)led to problems. If you could be more specific about the error that would be beneficial to determining what type of control you really need.

Concentricity controls location and orientation w.r.t. a datum axis. Now you have stated that you want to use a total runout which controls location, orientation and form. Is that what you really want? Furthermore these are both relatively expensive requirements to produce and inspect.

I would like to suggest that you look at either position or profile as a means of controlling the geometric characteristics in question here.

Hope this helps.

 

[MintJulep]

I think you need to control this by calling out a concentricity requirement.

If the gear is pressed onto a shaft, concentricity of the gear hub ID to the gear OD would probably do.

If the gear is loose fit, with a key and set-screw, or other mechanical mount, then concentricity of the shaft OD to the gear OD on the assembly would be necessary.

 

[vc66]

A star for both of you. Thank you for the help.

Xplicator- We have a central gear. Then there is a pinion, and an encoder with an anti-backlash gear. The problem has been that historically, we've been breaking shafts of the pinion and encoder (~3 of each). It was decided by someone with more business clout than me, that the best idea would be to better control all the tolerance elements regarding these parts. You suggested looking at profile of surface. What would be the difference between using runout and profile of surface? If you have any other suggestions as to what it could be, they would be appreciated.

MintJulep- Thank you for your suggestions. The gear is connected mechanically, with a key.

If there are any other failure modes that anyone can think of, please let me know.

Thanks again,

V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[drawoh]

vc66,

Gears are fabricated to AGMA tolerances. You need to talk to your fabricator and see what they can do and what specifications they understand.

You can do measurements to the gear's pitch diameter. You measure across pins which are seated between the teeth. This is described in Dudley's Gear Handbook, by Dennis P. Townsend, McGraw Hill books. I am sure some other references describe this too. This is not absolutely simple, but it is feasible.

JHG

 

[MikeHalloran]

You _can_ measure the pitch diameter runout, by meshing the gear with a known good 'master gear', and measuring the radial movement of the master gear's axle as the gear under test is rotated on a known good spindle.

The master gear is of course suitably restrained by a simple linkage, typically a lever arm (so it moves 'radially' in an arc).

I think there used to be illustrations of the setup in Berg/PIC/SECS catalogs, all of which I have misplaced.



Mike Halloran
Pembroke Pines, FL, USA

 

[Xplicator]

First off, I am by no means a gear expert so anybody can pipe in here and correct me as necessary. Again, I would get a copy of the ASME Y14.7 standard and figure out if what I needed can be addressed in this standardized method of specifying gears. I also know that AGMA has quality/tolerance classes for gears this could also address your needs.

In regards to the interrelationship of the gear to other features on the component or even in a sub-assy from a higher level functional standpoint, I have always used the PD as the "feature" to control or reference to employing position or profile. Now realize that the PD is actually a theoretic perfect cylinder mathematically derived from the specified/measured nomenclature of the gear. It is what ties the gear tooth profiles to the axis. This is method used when I have created models for 3D variation simulation analysis.

Since there is no surface to actually place an indicator on and rotate the gear 360 to indicate median points, as is the case for concentricity or to determine FIM for total runout. Conventional inspection equipment won’t validate these. However, as mentioned in other post there is some special measurement equipment out there to achieve this, but I choose not to use these two controls if I can help it.

Thus the use of profile or position, an actual pitch diameter or AME can be derived using a CMM with the right setup and algorithms. This is a less expensive way using common equipment to validate and have the same control over the chosen characteristics as the previously mentioned controls.

A robust callout like a surface profile can control size, location, orientation and form all at once or even a combination of, depending on how it is applied and what you’re looking for.

Again, I hope this helps.

 

[israelkk]

vc66

Gear dimensioning is different than part dimensioning. If you follow AGMA guidlines you define the AGMA class which gives terms such as the "total composite error" and "tooth to tooth composite error", "testing radius" etc. which are defined with reference to a feature such as a center hole of the gear or the hub or the shaft. This is only part of the dimesioning data needed to define the gear dimensions. In order to correctly design a gear you need to familiar yourself with the gear dimensioning terms otherwise, there is no meaning to the dimensions you give.

 

[vc66]

To all who answered-

Thank you. I spoke with a friend of mine who worked at Philly Gear for 30+ years. He suggested controlling the hub with a profile of surface, call out an AGMA 10 rating in the gear data, and then put a runout control on the pitch diameter of the gear. He said that they will check the gear exactly as MikeHalloran said, and that this would probably the best way to control the gear for my purpose. Since, I agree with him this is what I will use.

Thank you all again for your help, and suggestions.

Regards,

V

Mechanical Engineer
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[israelkk]

vc66

Using a master gear with AGMA call out is the way to go. However, AGMA only gives the "alternating sinuses i.e. TCE and TTCE" deviations of the gear. It doesn't give the diameter the "alternating sinuses" are riding on. Therefore, either you define minimum and maximum "testing radius" of the gear which is the best if you already use master gears, or dimensions over pins or any other mean of measuring the actual size of the gear.

The trick is to know how to calculate the testing radius based on the AGMA gear accuracy class, tooth thinning, tooth profile shift, etc.