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# Implementation of GD&T on Gear

01/06/2016 6:27 AM

hello,

I'm new to preparation of Gear drawing and implementation of GD&T into it, but i have prepared one and attached here, so could someone please check and let me know is that correct or tat can be improvised with other GD&T symbols & tolerance value.

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#1

### Re: Implementation of GD&T on Gear

01/06/2016 7:10 AM

Is it the drive gear of a gear pump ?

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#2
In reply to #1

### Re: Implementation of GD&T on Gear

01/06/2016 7:40 AM

Yeah exactly..

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#3

### Re: Implementation of GD&T on Gear

01/06/2016 8:24 AM

It's too small for me to see but as long as you know what the purpose of the tolerances and dimensions are, then you should know if you have labeled all information needed for that purpose...and I might add that if you are following a standard then what is required is clearly defined in that standard...

"Geometric dimensioning and tolerancing (GD&T) is a system for defining and communicating engineering tolerances. It uses a symbolic language on engineering drawings and computer-generated three-dimensional solid models that explicitly describes nominal geometry and its allowable variation. It tells the manufacturing staff and machines what degree of accuracy and precision is needed on each controlled feature of the part.. GD&T is used to define the nominal (theoretically perfect) geometry of parts and assemblies, to define the allowable variation in form and possible size of individual features, and to define the allowable variation between features.."

https://en.wikipedia.org/wiki/Geometric_dimensioning_and_tolerancing

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#4

### Re: Implementation of GD&T on Gear

01/06/2016 9:21 AM

Fax it to six machine shops for a manufacturing quote and they will tell you if they need more information to make an accurate part.

As Solar mentioned the quality of the picture is not clear enough to read the dimensions and datum etc.

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#6
In reply to #4

### Re: Implementation of GD&T on Gear

01/07/2016 6:10 AM

Fax? Wonderful idea! It gets attended to by the first person at the other end who picks it up. Far preferable to an email. GA :-)

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#8
In reply to #4

### Re: Implementation of GD&T on Gear

01/07/2016 6:35 AM

Hi Massey,

I have mentioned tat i'm new to this gear domain, and my bad luck i don't have any contact too with Gear manufacturing people.

Thank you!!

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#10
In reply to #8

### Re: Implementation of GD&T on Gear

01/07/2016 8:43 AM

I don't know where you are located but here are some that would tell you:

http://www.classicgears.com/

http://www.rushgears.com/

http://www.martinsprocket.com/

http://themachinecenter.com/

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#5

### Re: Implementation of GD&T on Gear

01/06/2016 9:54 AM

Based on the size of the print, I don't have much to offer other than the following:

First, I see no consideration for Feature Size in your tolerance. Would either the inclusion or exclusion of MMC, LMC, or RFS impact your desired end-result?

Second, alternative Datum's to consider would be Shaft Centers, if permissible.

Third, the text is pretty small so I can't tell for sure but I think some of your tolerance zones (Datum B and its opposing face) are going to have a percentage of their Feature Allowance eaten up by your surface finish. As a separate example... you can't apply a size tolerance of +/- 0.001" on a shaft with a designated surface finish of 125um as the allowable variations due to the finish will soak-up the entity of your size tolerance. Just something to look at and verify you're good on.

Fourth, the second part of GD&T is how a QC would be applied. What would the fixture look like that interfaces Datums A and B and checks the Total Runout? And does the specification of TR require the part to be rotated about Datum A? I'm not saying your application is correct or incorrect... I'll leave that for you to figure out, but you should always be prepared to answer the inevitable question: "How do I inspect this and make sure it is in tolerance?"

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#7
In reply to #5

### Re: Implementation of GD&T on Gear

01/07/2016 6:28 AM

Thanks for the suggestions..

first of all i have attached the drawing in PDF format for better clarity.

and regarding first point, i dint feel using the MMC or LMC, so meanwhile RFS will come into picture in the absence of MMC/LMC modifiers as of my knowledge.

for second, i have considered the shaft axis itself as a primary datum. is tat wrong?

for third, what i understood from your point is "the size tolerance i have given for feature size is "0.002" and perpendicularity tolerance on both the faces of the FS is "0.01" and this tolerance exceeds the FS tolerance, so i need to increase the FS tolerance to maintain the 0.01 surface finish on both the sides or vice versa". is this what u meant isn't it?

for Fourth, i thought like that only as you mentioned above, like keeping the poppet dial on the gear tooth surface by rotating the part about datum A and maintaining the datum B surface perpendicular to the primary datum again with the help of dial. and could you please explain me the best way of measuring and validating this part with respect to existing size dimensions & GD&T or the other way with by changing the GD&T.

.

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#11
In reply to #7

### Re: Implementation of GD&T on Gear

01/07/2016 11:17 AM

"first of all i have attached the drawing in PDF format for better clarity."

This has not impacted the apparent resolution so the numbers are still not readable. But, it doesn't matter as we are talking application of GD&T Standards and not Gear Design.

"and regarding first point, i dint feel using the MMC or LMC, so meanwhile RFS will come into picture in the absence of MMC/LMC modifiers as of my knowledge."

In regards to Tolerances of Position, RFS, MMC, or LMC must be specified on the drawing. For all other Geometric Tolerances, RFS applies unless specified otherwise.

"for second, i have considered the shaft axis itself as a primary datum. is tat wrong?"

No, it is not wrong. What I was trying to point you at was there is no need for a Primary and Secondary Datum, but rather you could have one Compound Datum make for easier fixture creation to facilitate post-manufacturing inspection.

Imagine if on both ends of the shaft you put in a countersink using a Standard 60-degree Center Drill. Dimensioning, I would have an extension line coming off the 60-degree surface and label the left one Datum A and the right one Datum B. Every subsequent Geometric Tolerance would then related to the Compound Datum of A-B. That is if Shaft Centers are permissible, some Designers don't want them or applications or subsequent operations don't warrant them.

"for third, what i understood from your point is "the size tolerance i have given for feature size is "0.002" and perpendicularity tolerance on both the faces of the FS is "0.01" and this tolerance exceeds the FS tolerance, so i need to increase the FS tolerance to maintain the 0.01 surface finish on both the sides or vice versa". is this what u meant isn't it?"

The best way I can explain it, without drawing it, is... for your particulate application:

Tolerances of Feature Size will impact to what degree your gear is trapezoidal. Imagine LMC at the OD and MMC at the interface of the gear and the shaft.

Your Perpendicularity tolerance is providing for how much this Trapezoid can morph into a parallelogram.

The combination of the two will result in an overall limit of space the feature must fall within. What you want to look for is that one tolerance doesn't provide additional limits on the other in their combined state.

My original point is that the surface finish applied to the feature takes away from the combined tolerance zone. The rougher the finish the wider your surface, the wider your surface the less available zone you have left to allow for variations is size and shape.

"for Fourth, i thought like that only as you mentioned above, like keeping the poppet dial on the gear tooth surface by rotating the part about datum A and maintaining the datum B surface perpendicular to the primary datum again with the help of dial. and could you please explain me the best way of measuring and validating this part with respect to existing size dimensions & GD&T or the other way with by changing the GD&T."

The 'best way of measuring and validating' is influenced by the tools and capabilities of the shop that would inspect the part... and how much you want the part to cost. Because the theoretically 'best' way might not be feasible in regards to cost. So you may elect to use a way that is 'good enough'.

Either way, you generally don't inspect gear runout on the gear surface, but rather off a sequence of pins that are placed within the tooth form. But this usually occurs after you've inspected profile and pitch/index of the teeth. Because what is really important on a gear isn't it's overall OD.

This might be a great training opportunity for you, if you can talk your boss into letting you go:

https://www.agma.org/events-training/detail/2016-gear-manufacturing-inspection

Otherwise, there are plenty of free resources online - do a search for gear inspection techniques or methods. Once you become familiar with how a gear is made and inspected - the tolerance application will reveal itself to you like the sun from behind parting clouds.

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#9

### Re: Implementation of GD&T on Gear

01/07/2016 7:44 AM

Hi,

To specify a GD&T on a drawing we should know interfaces and function. This drawing is not clear. I can't see diameters values. I'm not sure, but it seems that the 2 diameter near to the gear are for bearing interface and the end of the axis has another interface not known.

Another important consideration that you have to define Standard you are applying (ASME or ISO). It seems you are using ASME Y14.5.

According to item 2.10 from ASME Y14.5, you have to specify which diameter from gear you are controlling. Then, you have to put under total runnout control PD if you are controlling pitch diameter. I suggest to define datum B on another bearing interface diameter, then put A-B on the same box instead of separated one. It's important to make a stable control.

To control the end of the axis, I suggest to apply circular runnout instead of concentricity and put A-B on feature control frame. Circular runnout is easier to control (I'm assuming you have an interface as another gear or pulley).

To control perpendicularity you may establish A-B on feature control frame. I didn't know interfaces and these suggestion can change.

Regards,

João Baker

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#12

### Re: Implementation of GD&T on Gear

01/08/2016 2:48 PM

re the axial gaps automatically presure compensated or fixed by axial tolerances? This is an important aspect. For which pressure is the pump thought ? One of the problems a hydraulic pump has to fight is the fluid leak. Tolerances for the external diameter and gear sides perpendicularity are related intimately with above mentioned items.

Tolerances are to be specified so that for the whole temperature working range and depending on the different materials leaks are maintained at a minimum in order to obtain a good efficiency. Please consider that leaks are proportional to the 3rd power of the gap and 1/viscosity tolerances cannot be specified without considering it.

Normally to manufacture the part you will need to have centering cones at the ends as well for the gear cutting as for grinding the bearing surfaces. Il would be logical to make the control and thus specify the tolerances using same basis. For the gear it self the control should be done with a counter gear and by measuring the center axis variations there are specific rigs for it.

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