Q&A about Gears – Gear Technology Insights –
In this “Q&A About Gears” section, we supplement the textbook with essential gear-related terminology. Understanding the proper use of gears encompasses various factors such as calculating strength and size, materials science, and drawing standards. To aid your learning, we frequently refine this section based on actual technical queries and their resolutions.
Kexin offers a professional and reliable service.
Procurement and Customization of KHK Stock Gears
Where can I purchase KHK Stock Gears?
KHK Stock Gears can be bought through a local distributor in your region. They are not available for direct purchase from us. Please refer to our network of international distributors here.
Can I request modifications or custom-made gears from KHK Stock Gears? What will it cost?
While we do accept requests for secondary operations and custom-made gears, they must be directed through a local distributor. Prepare your drawings and specifications for a quotation from the distributor, who will confirm if production is feasible, pricing, and lead-time.
Is it possible to request a design for custom-made gears or gearboxes?
We do not provide design services for custom gears or gearboxes. Please approach a professional designer for gear designs. However, we do manufacture custom-made gears but not gearboxes.
Do you manufacture gears with smaller bores than KHK Stock Gears or with no bores?
We do not produce gears with smaller bores than those in our stock due to manufacturing limitations. We can make gears with no bores, but these are custom gears with higher costs and longer lead times. For quotes, contact your local distributor.
Do you manufacture plastic gears from materials other than MC901 (MC Nylon)?
Depending on the gear's shape and required material, we accept custom orders for plastic gears made from commercially available materials such as POM (Polyacetal), MC602ST (a stronger variant of MC Nylon), and PEEK (known for its chemical resistance). We do not manufacture gears from fiber-reinforced resins like CFRP or GFRP.
Can I ask for the positioning of gear-teeth and keyways in KHK Stock Gears?
KHK Stock Gears do not feature pre-positioned teeth and keyways. For custom gears, we can align keyways with the teeth's top and bottom lands, but positioning accuracy is roughly ±0.1mm.
Are Raydent or other plating treatments available?
We offer various plating treatments, including Raydent, Electro-galvanizing, and Electroless nickel plating. However, plating may affect bores' smooth insertion due to uneven film thickness. Always ensure proper lubrication is used.
Can you reproduce a broken or used gear sent to you?
We cannot reproduce exact gears from broken or used samples because it is challenging to determine precise specifications from worn or damaged pieces.
Can I consult with you about gears from other manufacturers?
We do not offer inspection or troubleshooting for other manufacturers' gears. If you plan to replace other gears with KHK Stock Gears, please contact us for advice.
Can you measure gear products from other manufacturers?
We do not provide measurement services for other manufacturers' gears. Please consult the original gear manufacturer or a gear-measurement instrument provider.
Are products with model numbers absent from the catalog no longer available?
Check our list of Discontinued KHK Stock Gear Products here. For items not in production, we may offer equivalent or custom-made alternatives, except for One-Cycle Clutches.
Understanding Gear Technologies
What is "Module"?
Module is a unit of measure that indicates gear size, representing the pitch diameter per tooth. CP, or Circular Pitch, and DP, or Diametral Pitch are also used.
What is DP (Diametral Pitch)?
DP indicates the size of a gear tooth. To convert DP to module: 1 inch (25.4 mm) ÷ DP (e.g., DP 8 = Module 3.175).
What is "Reference Diameter"?
The reference diameter, or pitch diameter, is the diameter of a gear’s pitch circle, essential for determining gear size along with the number of teeth and module.
What is "Pressure angle"?
Pressure angle is the angle formed by the radial line and the tooth profile at the pitch point, affecting the direction of transmitted gear force. Common pressure angles are 20°, 14.5°, 15°, 17.5°, and 22.5°.
How can you identify right-hand teeth (R) from left-hand teeth (L)?
When placed on a flat surface, left-hand gear teeth incline to the left, while right-hand gear teeth incline to the right.
Direction of spiral and thrust for gears.
The meshing of helical gears, spiral miter gears, spiral bevel gears, screw gears, and worm gear pairs generates thrust, with specific directions dependent on the gear type. Spur gears are an exception, as their teeth are straight and parallel to the shaft axis.
What is "Center distance"?
Center distance is the measurement between the shaft centers of two gears, influencing backlash, with positive deviations increasing backlash and negative deviations decreasing it.
What is "Crowning"?
Crowning involves slightly removing material from the tooth center outward, making the tooth surface slightly convex to ensure central contact and prevent edge contact.
What are "Gear tooth modifications"?
Gear tooth modifications are intentional deviations on the gear tooth profile to prevent excessive stress or deflection. Techniques like chamfering are commonly used.
What is "Semi-topping"?
Semi-topping chamfers the tooth tip's corner during tooth generation to prevent burrs and dents, maintaining tooth integrity during cutting and shipping.
What is the "Shaft angle"?
The shaft angle is the angle between the shafts of intersecting or nonparallel gears, typically set at 90°, critical for tooth contact and backlash.
What is Seizure?
Seizure occurs when the lubricant film is sheared, causing direct contact between mating gear teeth surfaces, leading to rapid wear and damage.
What can ensure smooth gear rotation?
(1) Maintain proper backlash: gears need adequate clearance to rotate smoothly. (2) Ensure proper lubrication: too little or too much can cause issues. (3) Adjust tooth contact properly: uneven contact causes wear and noise; gears with post-heat-treatment grinding offer smoother rotation.
What is "Tooth thickness"?
Tooth thickness is the measurement of a gear tooth's size, not the face width. It is usually smaller than the basic dimension to allow for backlash, measured by div measurement for spur or spiral gears, or over pin measurement for racks and worm gears.
What is "Contact Ratio"?
Contact ratio, either transverse or overlap, indicates the number of teeth in contact during rotation, affecting noise and strength; higher ratios distribute load better.
Does the reference diameter vary for profile-shifted gears?
No, the reference diameter remains constant for profile-shifted gears, although the center distance changes with the working pitch diameter.
How can I distinguish between Transverse and Normal systems?
It is challenging to distinguish between Transverse and Normal systems just by viewing actual gears.
What is "Black oxide coating"?
Black oxide coating is a rust-prevention treatment, forming a film of ferrosoferric oxide on the gear surface.
Can black oxide coating be removed?
Yes, black oxide films can be removed by acid pickling, but this makes the gear surface prone to rusting.
How often should you apply lubrication?
The lubrication frequency depends on torque and operational conditions. Perform tests or rely on experience and knowledge to determine the intervals.
How much torque can be transmitted with a set screw for fastening a gear to a shaft?
Set screws offer simple fastening, but combining them with keys or dowel pins ensures secure attachment.
What are the available methods for fastening gears to shafts?
Common methods include keyways, frictional fasteners like Power-Lock, Lamp-Lock, or Mechalock, and for smaller diameters, dowel pins, set screws, and press fitting.
Understanding Backlash in Gears
What is "Backlash"?
Backlash is the clearance space between mating gear teeth, required for smooth gear operation.
How much backlash should be set?
Backlash data for KHK Stock Gears is available in our Web Catalog as theoretical values. Backlash varies per machine manufacturer and is influenced by experience and technical know-how.
Are gears without backlash problematic?
Yes, gears need backlash for smooth rotation. Insufficient backlash causes lubrication issues and excessive noise. Precision gears have fewer problems with minimal backlash but zero-backlash should be avoided.
How can I entirely remove backlash?
No KHK Stock Gears allow for zero backlash. Certain gears can minimize backlash, such as Tapered racks & pinions and Duplex worm gear pairs, but absolute zero-backlash is not advised. Refer to our reference book for more details.
How to calculate backlash for gears with varying center distances?
Refer to our reference book or KHK Catalog for basic calculation methods. Note these calculations may have errors, particularly with profile-shifted gears.
Evaluating Gear Strength
What differentiates Bending strength from Surface durability?
Bending strength is the resistance to tooth root breakage under force from power transmission. Surface durability is the endurance against wear on the tooth surface from repeated contact.
Should I consider Bending strength or Surface durability when selecting gears?
Both factors are important but sometimes, particularly for low-frequency or hand-rotated applications, only bending strength is considered. Always select gears according to usage conditions.
How to use a gear with low surface durability compared to its bending strength?
Heat treatment can enhance surface durability by 3-5 times but may increase noise and decrease precision. Grinding tooth surfaces post-heat-treatment improves both durability and precision.
What is the surface durability of plastic gears?
MC Nylon gears boast excellent wear resistance, often exceeding their bending strength, and thus surface durability isn't usually a concern. For DURACON gears, consider surface durability in the absence of lubrication.
How much does quenching increase gear strength?
Quenching enhances surface durability by 3-5 times but may reduce precision and bending strength. Grinding post-quenching can restore accuracy.
What materials are stronger than S45C-made gears with induction-hardened teeth?
Materials stronger than S45C, in descending order, include: SCM415 (carburized), SCM440 (induction hardened post-thermal refining), and S45C (induction hardened post-thermal refining).
What is the lifespan of a gear?
Gear lifespan cannot be precisely calculated but typically, gears last long if used correctly under specified conditions, avoiding breakage or wear from lifespan issues.
Can you calculate the surface durability of Free-Cutting Brass gears?
No, because free-cutting brass does not have specified allowable hertz stress in JGMA formulas.
Specialized Gear Applications
Can gears be used in high-temperature environments?
KHK Stock Gears are designed for normal temperatures (~40℃). High temperatures can cause distortion, precision loss, and lubrication issues. For metal gears, ensure temperatures stay below 150℃. Plastic gears: below 120℃ for MC Nylon and below 95℃ for DURACON.
Can KHK Stock Gears be used in clean rooms?
No specific KHK Stock Gears are clean-room compatible. Enclosed devices, like gearboxes, should be used in clean room environments.
Which gears are suitable for food machinery?
Stainless steel and plastic gears, such as MC Nylon, are ideal for food machinery to avoid rust and oil contamination. MC Nylon can be used without lubrication and is suitable for boiling sterilization, though dimensions may change with water absorption.
Which gears are resistant to rust?
Stainless steel and plastic gears resist rust well. It's recommended to pair plastic gears with metal gears to reduce heat and expansion issues affecting backlash.
Which gears are suitable for high-speed rotation?
Strong, high-precision gears like spiral gears and ground tooth gears post-heat-treatment are best for high speeds.
Which gears are quiet?
High-precision, ground tooth gears and helical gears are quieter due to better contact ratios. Plastic gears are inherently quieter but less strong.
Are there any gears that can run without lubrication?
Metal gears must be lubricated to prevent wear and seizure. Plastic gears can operate without lubrication under light loads but it's better to lubricate them and pair with metal gears.
Can gears use grease lubrication?
While oil bath lubrication is standard, grease is suitable for open gear systems like racks & pinions operating at low speeds. Grease must be maintained to prevent decay and is not recommended for worm or screw gears due to their heat generation and lower cooling effect.
Gear Calculations and Specifications
Can I request gear calculations (recalculation)?
We do not offer calculation services for custom gears. Gear strength for KHK Stock Gears can be calculated in our Web Catalog. For other gears, use GCSW (Japanese version only).
Do you provide information on ISO or DIN Standards?
No, we do not field inquiries on these standards. Please contact the Japanese Standards Association (JSA) for international standards information.
Can rotations over 3600 rpm be calculated?
According to JGMA methods, strength calculation is limited to rotations under 3600 rpm and peripheral speeds below 25m/s. Gears might still be usable outside these limits but without strength data.
Is CAD data for tooth profiles available?
Our product CAD data does not include tooth profiles. Contact us to discuss your needs for Straight Bevel Gear.
What is gear efficiency?
General efficiency data is available in our reference book. Worm gear efficiency calculations exist but practical accuracy is challenging due to bearing loss and stirring resistance.
What do the numbers (0 to 60) in the Involute Function Tables represent?
These numbers indicate “Minutes” in DMS (Degrees/Minutes/Seconds). For example, at 21°20′, the value is 0.018217, found at the intersection of the “21°” row and the “20” column.
How is thrust force in a radial direction calculated?
Refer to our product catalog and gear technology references for calculating gear forces.
Spur Gears Explained
What is the allowable center distance for spur gears?
We recommend a plus tolerance of H7 to H8 for center distances. JGMA suggests targeting zero tolerance as per JGMA 1101-01(2000).
What distinguishes MSGA from MSGB Ground Spur Gears in KHK Stock Gear series?
These gears have identical specifications except for their bore sizes.
Can gears with undercutting be used?
Yes, if the gears are strong enough and have a contact ratio of 1 or more. Undercutting occurs in non-profile shifted, 20° pressure angle stock spur gears with 17 or fewer teeth.
Why do gears with fewer teeth have less strength?
Gears with fewer teeth have weaker profiles at the tooth root and smaller
Comments
All Comments (0)