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Thread: Back gear pressure angle
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24th September 2014, 09:39 PM #1
Back gear pressure angle
Hi
Would anyone know if the Hercus 9 backgear teeth PA is different to the Sheraton backgear teeth PA ?
I've got a feeling the Hercus is 20 degrees and the Sheraton is 14.5 degrees ?
Mike
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24th September 2014, 10:33 PM #2GOLD MEMBER
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The hercus is 14.5 and as the knowledgeable will inform you if you mix and match a 14.5 with a 20 on a precision machine such as these at the high speeds and high workload they do ,you will cause irapairable damage.
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24th September 2014, 11:05 PM #3
teeth count
Yes I agree with that
I just solved a puzzle
My Sheraton back gear has 24 teeth on the small gear end and 62 on the large gear end
I bought a replacement back gear for the Sheraton and it has 23 teeth on the small gear and 62 on the large gear ( from a Hercus I think )
Both the Sheraton and Hercus gears are 16DP . The Sheraton small gear has a OD of 1.625" - the Hercus small gear is OD 1.5625 "
BTW I am going to repair the original Sheraton back gear and sell the Hercus one , if anybody wants a good Hercus 9 back gear PM me
Mike
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24th September 2014, 11:14 PM #4GOLD MEMBER
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There must be wear on the hercus as the small gear is 1.625 od.
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24th September 2014, 11:20 PM #5GOLD MEMBER
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Are you sure that you haven't mixed up the back gears you have as the figures mentioned don't relate to your tooth counts.
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24th September 2014, 11:21 PM #6
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25th September 2014, 12:05 AM #7GOLD MEMBER
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I am sure the xperts will be able to help you better,good luck.
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25th September 2014, 06:47 PM #8Senior Member
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headstock gears
The Sheraton is 16dp 20 pa, the Hercus is 16dp 14.5pa. Sheraton went for the quieter option and Hercus for the stronger. There is a common practice among the various manufacturers to have gears with a one tooth adjustment,that is to say, the 24 tooth diameter(1.625) is cut with 23 teeth. There are many places throughout the machines where this became necessary in confined spaces with mated shafts, or where there is not sufficient space to achieve the standard. During the remaking of parts for the Hercus and Sheratons I have come across quite a few examples of this. I'm not quite sure why there is a tooth adjustment in that particular instance but I'm sure they had a reason, which I'm sure someone else with greater knowledge will explain.
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23rd October 2014, 06:18 PM #9New Member
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Pressure Angle etc
The 20deg pa is the stronger; 14.4deg the quieter. Yes it is common to cut say 23 teeth on a blank sized for 24 teeth, but you need a machine that generates gears (ie shaper or hob) to cut proflile shifted gears successfully. This is possible with involute gears because it is the base pitch that determines whether gears will mesh correctly or not.
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23rd October 2014, 10:11 PM #10Senior Member
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Thankyou for the correction. I had assumed the thinner top of the 20 deg would make it more likely to chip, and the shape would have more of a sliding action and therefor quieter. The reverse seems to be true. Thankfully I have all my gears are hob cut, so correct shape is not an issue.
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