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Thread: Hercus Change Gear Diameter
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12th June 2009, 03:56 PM #1
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Hercus Change Gear Diameter
Im thinking of turning up a Gear Blank to suit a 16Th change gear,I am not quite sure of the OD of the blank.
I have measured 1 at 1.053".
I know that when I do the calculations (16+2) /18 equals 1 for an involute cutter of 18DP.
Could any of the members who may have an 16TH gear measure it for me so as I can get an idea of either the OD Hercus used or an average,Thankyou.Last edited by pipeclay; 12th June 2009 at 03:57 PM. Reason: Wrong figure.
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12th June 2009, 06:56 PM #2
Cranky Old Phart
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Just measured mine; 1.051 Findlay.
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13th June 2009, 06:47 AM #3
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1.056 here.
Just to confirm you are going to use a 20 deg PA 18DP gear cutter right? Not 14.5 deg PA.
alRemember if the ID exceeds the OD the hole will be on the outside!
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13th June 2009, 09:13 AM #4
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This seems to be the issue,whether 14.5 or 20.
If 14.5 in theroy should be 1".
If 20 in theroy should be .9"
It appears an OD of somewhere between 1.051"/1.056" is the going size.
The only reason I can see for the increase in OD is to allow for a Greater Wall Thickness for the Keyway,would this be correct or does someone else know why the change from standard 1" OD.
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13th June 2009, 10:44 AM #5
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hmm mine measures .996 on digital ...just so it will turn in the jaws of the calipers or 25.03mm on the mitutoyo
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13th June 2009, 01:35 PM #6
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I've made one of each diameter and the only difference I can see is the tip diameter width and the slight difference in root diameter and the keyway.
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15th June 2009, 01:24 AM #7
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Pressure angles
I was referring to the PA = Pressure angle of the tooth profile, not to be confused with the DP Dia Pitch.
I have cut some gears for a Hercus 9" restoration and the first one I cut was a 14.5 PA and was WRONG so I hadda buy more cutters at 20 deg PA.
Hope this helps.
alRemember if the ID exceeds the OD the hole will be on the outside!
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15th June 2009, 01:41 AM #8
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I understood what you meant . Can you explain what you mean by wrong please.
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