The unit changes the meaning
One arcminute equals 60 arcseconds. A value of 15 arcseconds is therefore 0.25 arcminutes, not 15 arcminutes. WANSHSIN’s WSHD page expresses backlash in arcseconds, while its WVRB page uses arcminutes and precision grades. We normalize the numeric filter to arcminutes and preserve the original condition in each configuration note. Without that conversion, a filter can silently exclude the more precise unit or suggest a false equivalence.
Turn the angle into an application question
Three arcminutes is 0.05 degrees, or approximately 0.000873 radians. At a 100 mm effective radius, that angle corresponds to about 0.087 mm of tangential travel using displacement ≈ radius × angle. This is a geometric illustration, not a prediction of a machine’s total positioning error. Backlash, elastic deflection, encoder resolution, bearing compliance, load direction and control strategy must be considered separately. Decide whether a particular backlash limit fits your axis error budget before paying for a tighter grade.
Keep the precision grade attached
The WVRB table separates P0, P1 and P2 backlash grades. The standard P2 specification also differs between the smallest frame and larger sizes, and between one-stage and two-stage units. Our current configuration rows explicitly identify P2. If a quotation specifies another grade, ask the supplier to confirm its availability, lead time and measurement conditions for the exact frame and ratio. A family-level best figure is not an automatic property of every order.
Backlash is not total positioning error
Clearance on reversal is only one part of a motion system’s behavior. Elastic deflection, bearing compliance, coupling stiffness, the machine structure and control tuning can contribute to the result. Transmission accuracy and repeatability describe different characteristics from backlash. Ask what is being measured, at what load and temperature, and whether the figure is a limit, a typical value or a result from a particular sample.
Match the test to the application
A robot joint with an offset load can impose moment loads as well as drive torque. A measurement on an unloaded gearbox does not describe the complete joint under acceleration. Provide the payload, center of gravity, arm length, orientation and motion cycle. Ask for permissible bearing loads and torsional rigidity alongside the precision specification. The aim is not to collect the lowest number; it is to understand the deflection and reversal behavior that matter to the process.
Read the torque condition with the precision figure
The WSHD table labels rated torque at 2,000 rpm input and separately lists allowable start/stop, average-load and instantaneous torque values. Do not substitute one for another when selecting a precision reducer. A low-backlash gearbox operated outside its load or speed envelope is not a sound precision solution. Keep the rating condition visible in the purchase specification and request the latest manufacturer drawing and catalog revision.
Put the acceptance method in writing
Agree the measurement setup, load, warm-up condition, direction of approach and instrument resolution before using a precision value as an acceptance criterion. Distinguish the gearbox test from the assembled-axis test. Record the exact unit and precision grade being supplied, and retain the agreed method with the order. This makes supplier comparisons more useful and avoids disputes caused by different interpretations of the same word.
Gearbox types and documented products in this guide
Planetary Gearboxes
- Industrial Planetary Gear Reducers · SGR
- DFT17T3 Hydraulic Travel Reducer · Dongyu Hydraulics
- FG090 Precision Planetary Gearbox · KOFON
Cycloidal Reducers
- BXJC-C Precision Cycloidal Reducer · Tailong
- WRA Precision RV Reducer · WANSHSIN
- BLD Cycloidal Geared Reducers · GUOMAO
Harmonic Reducers
Continue reading
The combined limits trap in gearbox sourcing →
Planetary vs worm gearbox: compare the machine, not just the ratio →
How to verify gear heat treatment before placing a gearbox order →
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