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Ask The Expert—Questions and Answers

Welcome to Gear Technology's Ask the Expert—a regular feature intended to help designers, specifiers, quality assurance and inspection personnel in addressing some of the more complex, troublesom gearing challenges that never cease to materialize.

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Questions already answered

Bevel Gear Mounting—Proper bearing preload for optimum tooth contact pattern
Efficiency of High-Ratio Hypoid Gears
Runout and Helix Accuracy
Maximum Number of Teeth in a Shaper Cutter

Questions needing answers

Aug 06, 2012 -- I am planning on using a 14.5 deg 24 pitch 20 tooth spur gear to drive a 14.5 deg 24 pitch 60 tooth spur gear. What is the maximum torque which can be applied to the 20 tooth gear? Both gears have a face width of .25".
posted by Anonymous

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Jul 13, 2012 -- Bevel gears used in differentials seem to be forged in most automotive applications. Old developments are Gleason Coniflex cut developments, but it seems modern developments are computer generated. I have never seen anything about who does this and wonder if this is true and why it is not in the news.
posted by Jimmy Ream, QMS Inc.

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Jul 05, 2012 -- External involute gears are very tolerant of Center Distance variations.

What are the Center Distance constraints/parameters for internal gears?
posted by Anonymous

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Jun 19, 2012 -- We are refurbishing an Allis Chalmers ball mill. The herringbone bull gears and pinion gears are worn. Can you reverse engineer these gears?
posted by Anonymous

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Jun 19, 2012 -- What kind of data must be considered when we grind a gear with profile shift?

A few days ago we received a series of gears that need to be corrected (Profile shift), and our engineering department has a question about this topic. They told me that they do not know how to calculate the gears with profile shift. They suspect that with each profile shift factor the pressure angle also changes.

A friend in Texas told me "you cannot make a profile shift gear with a normal cutter. For each correction factor you require a cutter according to the modification." Is this correct?
posted by Anonymous

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May 29, 2012 -- Do you have any suggestion regarding calculation of:
-Hob life cycle
-how often shall the hob sharpened

We are a gear cutting machine maker, and we recommend hobs from other suppliers to our customers. The customers would like to understand and evaluate the hob life cycle.

Do you have any idea or calculation manner that could give a rough idea?


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May 28, 2012 -- It is very difficult to set a pair of bevel gears by trial and error in order to get the ideal backlash and contact pattern. For our regular gear technicians at sites, this involves a lot of time for assembly. Often, we have to hire outside professionals, even after paying high charges for spares.

Can there be a faster/easier method to arrive at the ideal combination?
posted by Anonymous

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May 23, 2012 -- We manufacture gear hubs and gear sleeves with spur profiles. These together form gear couplings for mechanical power transmission between drive and driven equipment.

One of our customers requires the teeth of components to be case hardened and depth of case hardening should be 0.8 to 1.2 mm.

Please guide us which material we should use for the gears and the process of hardening.

The profile of hardening should be parallel to that of gear tooth profile. Teeth width is small, in the range of 4 to 5 mm.
posted by Anonymous

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May 23, 2012 -- What are the various reasons for grinding crack of gear components, and how can grinding crack be prevented?
posted by Bhupendra patel, Elecon Engineering - Gear Division

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May 23, 2012 -- How can i calculate the differential constant (helical gear train) in an older machine, if no data is available.
posted by Anonymous

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May 23, 2012 -- I work for VALEO since 1999 manufacturing Motor Wiper Systems and I've never found a method to inspect correctly the tip and root diameter or radius of our gear parts (pinion and wheel with spur or twisted teeth in plastic POM or worm in steel).

Most recently, we have used a caliper, but this method does not give satisfactory results (R&R > 30%). I would like to know if there are some other methods to inspect these dimensions, such as optical or LASER methods.

For your information, our modules are between 0.5 to 1.5 mm, the dimensions to inspect are between 8 to 65 mm and our tolerances for the tip or root diameter are between 50 to 350 μm.

Thanks for your answer.

Best regards,
posted by Christophe Lassalle, VALEO Wiper System

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May 23, 2012 -- We are doing Pinion Gear hobbing process (Module 1.75 and Helix angle of 20degrees). During Hobbing the Helix angle Lead error maintained within 20 microns. But after Heat treatment in Sealed Quench furnace, Helix angle lead variation observed up to 70 microns.

Is there any improved process to minimize Heat treatment distortion, so that Lead values can be controlled?

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