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

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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Originally Posted by pipeclay

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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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

There must be wear on the hercus as the small gear is 1.625 od.

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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Originally Posted by pipeclay

There must be wear on the hercus as the small gear is 1.625 od.

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If the Hercus small gear is OD 1.625" , this does not work out to 16 DP for 23 teeth ? DP = number of teeth +2 divided by the OD of the gear Mike 25 divided by 1.625 = 15.3846

I am sure the xperts will be able to help you better,good luck.

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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Originally Posted by allterrain50

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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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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Originally Posted by oldtech

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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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.