Determining pressure angle on gears

I'm trying to repair a DaeJung 560 lathe. It seems the importer walked away from this critter a long time ago so I need to come up with the right gear
spec to fix it. There is a plastic gear in feed drivetrain that is designed to be the sacrifical gear should a brain fart occur. Well at some point in time a brain fart occured. (NOT ME)
I used a program to generate gear data from WM Berg http://www.wmberg.com/Tools /
GearSpec is the program. (Thanks to Sam on a.m.c aka PrecisionMachinist)
It generated this data for 14.5 and 20.0 pressure angles. By juggling module and DP values I think I have the gear narrowed down to these two below.
http://wess.freeshell.org/usenet/rec.crafts.metalworking/95_14.5_GearSpec%20-v2_5_1.pdf http://wess.freeshell.org/usenet/rec.crafts.metalworking/95_20_GearSpec%20-v2_5_1.pdf
The only real difference is base circle but that isn't some thing to measure since I believe it is below the gear surface.
So are there any quick and dirty methods of estimating pressure angles?
And while I'm at it what kind of plastic should one use to make the gear if I can't find a blank? The only thing I know about the gear is that the plastic is blue.
Thanks,
Wes
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The last time I was trying to match a pressure angle, I took the offending gear, set it in my scanner, ran a high res scan of it, then viewed the tooth close up. Compared the tooth profile to Machinery's handbook, pretty obvious what I had.
If you really get stuck, you can download an evaluation copy of Feature Cam http://www.featurecam.com/general/software/latest_version.asp It has a gear program buried in it, you can draw any gear you want and print it out a 1:1 size picture. The eval version won't generate the code or save it but you don't need those functions.
Wes wrote:

http://wess.freeshell.org/usenet/rec.crafts.metalworking/95_14.5_GearSpec%20-v2_5_1.pdf
http://wess.freeshell.org/usenet/rec.crafts.metalworking/95_20_GearSpec%20-v2_5_1.pdf
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Wes wrote:

http://wess.freeshell.org/usenet/rec.crafts.metalworking/95_14.5_GearSpec%20-v2_5_1.pdf
http://wess.freeshell.org/usenet/rec.crafts.metalworking/95_20_GearSpec%20-v2_5_1.pdf
Get youself a Martin Gear catalog and plop down the gear on top of the page with the two illustrated pressure angles.
John
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I found these folks real helpful. http://www.sdp-si.com /
--Andy Asberry-- ------Texas-----
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the purpose of the plastic gear is interesting. surely a simple shear pin would be easier to implement if brain fart protection was the aim. I thought the plastic gear in a gear train was for noise attenuation.
the lathe I've been looking at recently has all steel gears and is a hell of a lot noisier than my old belt drive hercus (south bend clone) I think it needs a plastic gear in the train.
Stealth Pilot
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On Wed, 19 Sep 2007 21:39:22 +0800, Stealth Pilot

Shear pins are too cheap and easy to replace with alternate strength materials. Gerry :-)} London, Canada
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