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mkdev2004
Member

Join Date: Jun 2010
Location: Bangalore, India
Posts: 5

Spur Gear Span Measurement With Grinding Allowance

06/02/2010 6:15 AM

Dear Friends,

Can you explain to me the calculations for finding the span measurement of the spur gear at hobbing stage. I have the span measurement value at finish stage. The following are the data of the finished gear I am having:

No. of teeth 31,

Pressure angle 20 deg

Module 4.5

Tip circle dia 147.6 mm

pcd 139.5mm

bcd 131.1

addendum modification -0.095

corrected addendum 4.07

corrected dedundum 6.1

root dia 127.4

span across 4 teeth = 48.16

back lash max 0.3

The stock for grinding per side of the tooth is 0.15mm

Can you help me and explain the method?

Thanks in advance,

Dev

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Pathfinder Tags: Hobbing Span measurement Spur gear
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rahulpshinde
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Join Date: May 2010
Posts: 9
#1

Re: Spur Gear Span measurement with Grinding Allowance

06/02/2010 6:29 AM

you will just need to add twice the grinding allowance to the finish dimensions.

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mkdev2004
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Join Date: Jun 2010
Location: Bangalore, India
Posts: 5
#2
In reply to #1

Re: Spur Gear Span measurement with Grinding Allowance

06/03/2010 7:09 AM

Dear Rahul,

I dont think this is the correct method. There are some calculations involved in this to find the span with grinding allowance.

Krishnadev

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Anonymous Poster
#3
In reply to #2

Re: Spur Gear Span measurement with Grinding Allowance

06/03/2010 8:48 AM

Of course it is not correct. The span measurement you do is at basic PCD. The grinding allowance is as we call stock at tool point.Since the teeth are not parellel to each other, the stocks will have to be converted trigonometrically.

So the direct add/subtract is invalid.

BTW: MK I don't have the calculations, of course it is possible to do, but it may b available readymade with some CR4 members?
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rahulpshinde
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Join Date: May 2010
Posts: 9
#4

Re: Spur Gear Span Measurement With Grinding Allowance

06/03/2010 9:35 AM

Dear Mr. Krishna and Dear Guest

The span is a measure of the base tangent length, which is perpendicular to the tooth profile, so as per my knowledge the grinding allowance or the material stock thickness would be directly added without any trignometric modification to achieve the hobbed (pre-grinding) dimensions.

I maybe wrong and this discussion may add to my knowledge.

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mkdev2004
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Join Date: Jun 2010
Location: Bangalore, India
Posts: 5
#5
In reply to #4

Re: Spur Gear Span Measurement With Grinding Allowance

06/25/2010 3:19 AM

Dear Friends,

Finally I got the formula for span measurement from Machineries Handbook. The formula is:

Span M= R*CosA*[(T/R)+(6.2832*S/N)+F], where, R= Pitch radius of the gear; A= Pressure angle; T= Tooth thickness along the pitch circle; N= No. of gear teeth; S= No of tooth spaces between caliper jaws; F= 2*Inv(A).

To find the hobbing stage span measurement, we have to add the grinding stock to tooth thickness T.

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