Yes it is a South Bend and I believe they are 20 DP. The one you posted the link to on eBay looks right but doesn't have any real info about it. I may try to contact the seller to find out more details. His price isn't too awful painful. Thanks for the help.
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80 Tooth Idler gear
- Thread starter RWanke
- Start date
Yes it is a South Bend and I believe they are 20 DP. The one you posted the link to on eBay looks right but doesn't have any real info about it. I may try to contact the seller to find out more details. His price isn't too awful painful. Thanks for the help.
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- Jul 2, 2014
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Know that an idler gear can have any number of teeth without causing a change in the delivered gear ratio. The only purpose of an idler gear is to increase the reach of the other gears. If the 80 tooth gear is also needed for a drive gear or a lead screw gear in other combinations, then you need 80 teeth. The lack of a keyway leads me to believe it is only an idler. Any gear might be made to work if it has the correct pitch, the correct pressure angle, and will fill the space you need to fill.
Thanks for this info. I'm just going by the screw thread chart on my lathe to get all the possible combinations I might need for threading. The diagram shows 4 different setups using 3 different idler gears (80 tooth, 72/18 tooth, and 54/18 tooth). I also found a formula on another site for figuring the DP of the gears I have.
DP=(N+2)/OD
DP - Diametral Pitch
N -Number of teeth
OD - Outside Diameter of gear
I measured all my gears and came up with 18.0something on all of them so I am hopefully assuming I am correct that the gears on my South Bend are 18 DP.
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If the 80 tooth gear is only spacing the gears and reversing the direction, then the tooth count does not matter beyond influencing diameter. The double count gears you mentioned are the same, but only if you are just using one of the gears, leaving the other unused. If you are using both sides of a double gear, then you are doing compound gearing, and then there is a calculation for each tooth count, and everything affects the end result.
I can see using the 72 tooth in a single idler setup when threading 8 through 30 TPI (at least if it will reach). But when threading 4 through 7 1/2 or 32 through 120 TPI I need a combination of the 72/18 double gear and the 80 tooth at least according to the gear chart. There may be other possibilities but that would involve me doing lots of math. 
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That would be great if true!
I have been asked to 3D-print a gear for a friend. I have gear tooth gauges for Diametral Pitch gears, but not for Module Pitch gears. I won't know what it is until he removes the old, stripped gear from the equipment.
However, I was looking for gear tooth gauges just the other day, and this site shows 14.5 and 20 degree pressure angle gauges for both diametral and module pitch gears:
http://www.fujitool.co.jp/eng/products/measuring_tools/000092.html
-brino
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I picked up a set of gear tooth gauges from Boston Gear years ago. It is a series of flat almost rectangular "leaves" on a key ring. Each leaf is stamped with the diametral pitch at the end, and has teeth cut down each long-side; one side is 14.5 degrees, the other is 20 degrees. Unfortunately I cannot find it on their site now.
I am also certain that I saw some full-size gear tooth silhouettes printed in a text book that could be used to help determine pressure angle. I'll try to dig up that reference, but my collection of machining book is large, and my memory is weak.
The pressure angle difference should show-up as a slightly thinner or fatter tooth.
It can be difficult to be certain.
-brino
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One simple method I've seen was to roll the gear in clay, then cut that so it looks like a rack gear and use a protractor to measure the angle
of 14.5 or 20 deg.
Never tried it myself though.
I usually have a known gear to compare to the one in question. The tooth thickness is visibly evident when comparing the two together.
I also have a set of the leaves in DP and I was trying them in the 80 tooth I have and one is very close but not quite right. The answer was right
on the gear it was stamped 80 m=2 it is a #2 module 80 tooth gear.
of 14.5 or 20 deg.
Never tried it myself though.
I usually have a known gear to compare to the one in question. The tooth thickness is visibly evident when comparing the two together.
I also have a set of the leaves in DP and I was trying them in the 80 tooth I have and one is very close but not quite right. The answer was right
on the gear it was stamped 80 m=2 it is a #2 module 80 tooth gear.