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Old 04-26-2006, 12:01 PM   #17
RalliSpec
Former Vendor
 
Member#: 39
Join Date: Jun 1999
Location: Hainesport, NJ, USA
Vehicle:
98 Prodrive WRC

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Quote:
Originally Posted by fliz
Quick question regarding these two paragraphs.

I broke an aftermarket gearset. Since it's no longer manufactured, I had to have a custom replacement made. The original was helical, but I asked for a straight cut second on the new shaft. I was under the impression that spur gears are stronger, ince they don't produce the axial loads that a helical gear design does. Is a spur gear design less likely to produce shaft flex?

If the spur design is not going to be as strong...I may have to call and change my order.
Yes, a spur gear produces much less axial load than a helical gear. The axial thrust loads must be absorbed by the bearings. The high thrust loads create increased frictional losses which is why most racing gear sets opt for a spur gear (more power delivered to the wheels basically). But in terms of the actual strength of the gear....a helical gear is stronger than a spur gear all other things being equal.

A spur gear is actually going to create more shaft flex because nearly all the reaction forces are going to be in the direction that would bend the shaft. A helical gear, as mentioned, has a portion of those forces going along the length of the shaft in the axial direction. However, I believe that a spur gear can operate with less critical gear mesh so the gears need to separate more for it to become a real issue.

If you have this gear made I would suggest consulting an engineer to make sure that the gear being produced is as strong or stronger than the gear it is replacing.

--Dave
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