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kkominiarek

Internal Gear guidance needed

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See attached file for gear specs.

 

I'm using the Mastercam gear c-hook.

(I also created the involute curves, which did not look correct either)

 

The 45 deg PA creates a tooth that almost comes to a point.

 

I hit most dimensions given.

 

The circular pitch comes very close .0391 (.0393)

 

The measurement between pins is .1987 (.2021)

The circular space width is .0196 ( .022-.024)

 

 

I still say the 45 deg PA is the issue.

 

If anyone has any thoughts....please LMK.

post-1005-0-40475500-1377693235_thumb.jpg

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I cant get it to look right either

 

 

I think the PA should be 14.5 and then it looks right

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I work in a shop that specializes in gears, my thought is it says its a serration on the image (ie most serrations come to a point), and also based on experience the vast amount of gear drawings look nothing like the gear/spline that's defined in the gear data.

 

I didn't have any issues getting the gear c-hook to make this gear and when I checked space width / tooth thickness it appears to be right.

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I work in a shop that specializes in gears, my thought is it says its a serration on the image (ie most serrations come to a point), and also based on experience the vast amount of gear drawings look nothing like the gear/spline that's defined in the gear data.

 

I didn't have any issues getting the gear c-hook to make this gear and when I checked space width / tooth thickness it appears to be right.

 

Can you post a pic and gear info for future reference ?

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I have attached a screenshot of the gear c-hook with the info typed in..

 

Just to double check I drew the Pitch Diameter in once I was back in Mastercam..

 

I then drew lines to the intersection of either side of a tooth, and either side of a space to determine the respective angles to allow me to calculate actual Circular Space Width and Circular Tooth Width and Circular Pitch ..

 

The tooth comes out at 7.5756 degrees and the Space is 11.37177 degrees combined they make up the Circular Pitch which is 18.94737 degrees..

 

Then with a bit of math.. we take .2375 (PD) * 3.14 (PI) to get Circumference = 0.746128255

 

then Circumfrence / 360 to get the amount of circular movement in one degree for a constant to multiply by and we get .. 0.00207257

 

So then muiltiplying by the original numbers for the angles.. we get

 

Circular Tooth Thickness = .015701

Circular Space Width = .02356

Circular Pitch = .039268

 

Those are the numbers given on the gear data so I am assuming it is correct.

 

Hope that helps..

post-18715-0-33697000-1377707617_thumb.png

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No wonder mine looked wrong. I was using 18 teeth not 19

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dj, see attched file.

 

All specs same as yours except for Circular Tooth Thickness.

 

After entering data into chook.....CTT and Roll Measurement auto fill to - .01961 and .197956

 

This seems correct to my calculations.

 

CTT or tooth thickness at pich diameter = 1.5708/P (1.5708/Diametral pitch)

 

1.5708/80 = .019635

 

 

Any thoughts? Your opinion counts as you work on more gears than I do.

 

 

You'll notice my gear is more "pointy" then yours, if I change to .0157 CTT then it looks like yours.

post-1005-0-31317500-1377787286_thumb.jpg

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You have to manually type in the roll measurement and roll diameter that's shown on your drawing, .2021 the circular tooth thickness will change to reflect the new roll dimension.

 

The roll diameter and dimension between pins is tied directly to the tooth thickness.. and therefore when you type them in and hit enter they will alter your tooth thickness.

 

Also the formula you give is only valid if the tooth thickness and the circular space width are the same.. if the gear was not modified from standard at all this might be the case but

in many cases gears and or splines are altered from standard..

 

On this spline they give the numbers on your drawing for circular space width , the circumference of the circle is always a constant based on the pitch diameter .. pi * diameter.. so therefore given 19 teeth and 19 spaces, you can do the math with the following formula which will give Circular Tooth Thickness

 

Circular Tooth Thickness = ((PI * PD) - (Number of Teeth * CSW)) / Number Of Teeth

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Good point. I have had to wire edm several gears that had been modified. I assume they do that so others have a harder time making them to fit. Always nice if I have either the male or female gears.

 

djstedman, Do you ever have to modify the Diametrical Pitch based on the OD ?

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Usually DP is a constant that is provided in the gear data, since it is integral to so many gear formulas it is unlikely to be monkeyed with.

 

As for the reasoning for the modification of gears and splines I believe it has more to do with center distances between gears as well as strength of materials based on the application.

 

I don't think its just cause the designers are trying to be evil... though I have no doubt some of them are in fact evil.. :harhar:

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A lot of times I get a sample or worn out gear with no info on it. Only thing I know for certain is the OD and Number of Teeth. I have a chart that gives me the formula DP=(N+2)/OD where N is number of Teeth. If I use that formula and say the DP comes out with a weird number, should I assume that maybe the OD has been modified and use the Standard DP that is closes to the numbers I come up with? Also, How do you come up with the Pressure Angle. The more I learn about Gears the more I realize I don't know crap. I always get it to work but usually by trial and error and test burns.

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I would generally assume DP will be something fairly normal.. and make the assumption that the OD has been modified.. OD and Root Diameters are tweaked a lot .. PD and DP should remain pretty constant..

 

That said I jumped in on this thread to give a hand with the gear c-hook using mastercam, now that that's covered I don't think I should say a lot more given I work in a place where this is our bread and butter.

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I would generally assume DP will be something fairly normal.. and make the assumption that the OD has been modified.. OD and Root Diameters are tweaked a lot .. PD and DP should remain pretty constant..

 

That said I jumped in on this thread to give a hand with the gear c-hook using mastercam, now that that's covered I don't think I should say a lot more given I work in a place where this is our bread and butter.

 

 

I understand. Thanks for the info though. Personally I do very few gears during the year and we always send stuff out for gear cutting unless it's just a 1 piece job for a walk in customer. :cheers:

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