Mounting distance and backlash connect the gear geometry to the housing, bearings and shaft stack. They are not independent numbers that can be copied from a similar-looking gear. A useful RFQ defines where each value is measured and which assembly surfaces hold the pair in that position.
Mounting distance needs a real datum
A value becomes useful only when the reference surface, shoulder, axis or housing feature is defined. Put that datum on the drawing. If the project is a replacement, record the assembly before the old gears and bearings are removed.
When several surfaces could be used as references, identify the one that actually controls the position in service rather than the easiest surface to reach with a caliper.
Why backlash is an assembly outcome
Backlash is influenced by the gear geometry and by how the two members are positioned. Bearing seats, shims, shoulders and housing tolerances all contribute. If the machine specifies a backlash range, include that requirement and explain the assembly condition under which it is checked.
For precision or reversing mechanisms, the buyer may also care about repeatability after reversal. That should be described as an application requirement rather than hidden inside a vague request for “minimum backlash.”
What to measure during replacement work
| Measurement area | Recommended record |
|---|---|
| Gear position | Distance from defined mounting face/shoulder to the relevant gear reference |
| Shaft support | Bearing locations, shoulders and any shims that establish axial position |
| Mating gear | Tooth count, hand, bore/shaft interface and installed orientation |
| Backlash | Measured range and the method/assembly state used to obtain it |
| Housing | Critical distances between shaft or bearing references |
| Condition | Wear, looseness or damage that may have changed the measured position |
Do not use wear as the datum
A worn thrust face, damaged bearing or loosened shaft can change the apparent position of the gear. Note the condition of the assembly and separate “as found” measurements from the intended design reference. Legacy drawings or an undamaged mating member can help reconstruct the original position.
RFQ wording that reduces ambiguity
State the mounting distance with its reference, the backlash target with its checking condition, and whether the housing/bearing arrangement will remain unchanged. If adjustment is available through shims or another mechanism, describe the available range. That information lets the supplier understand whether the gear geometry must hit one fixed position or be installed within an adjustable system.
Fixed versus adjustable mounting
Some assemblies locate the pair with fixed shoulders and bearing seats; others use shims or another adjustment method. State which arrangement you have. In a fixed housing, the replacement geometry has less freedom to compensate for an incorrect position. In an adjustable assembly, the available range should be documented so the installation procedure and backlash target are understood together.
Do not hide an unknown housing dimension behind a wide backlash range. The supplier still needs the geometry that establishes the intended position.
Questions buyers often ask
Can backlash be set after installation?
Sometimes the assembly provides an adjustment method, but that depends on the actual housing and bearing arrangement. State the available adjustment and the target checking condition.
Is mounting distance the same as overall gear length?
No. Mounting distance is tied to a defined gear/assembly reference. Overall length may be useful for packaging, but it does not by itself define the working position.
Should I measure a worn assembly before changing bearings?
Yes. Record the as-found condition first, then note any bearing or shim changes separately so the original and corrected positions are not mixed.
Send the gear pair, drawing and duty in one RFQ.
The more clearly the mating relationship and assembly datums are defined, the faster the configuration can be reviewed.
Ordering & delivery guidance
MOQ is flexible by product type, manufacturing route and total order value. Suitable new projects may request 1–5 sample pieces at sample pricing. Mixed models can be combined when the order total reaches approximately USD 1,500. Orders of 1–2 pieces can be reviewed, although unit cost is normally higher.
Typical planning windows are 10–25 working days for standard parts, 20–45 working days for customized components and 45–120 working days for project-type equipment or assemblies. EXW, FOB, CIF and DAP are commonly supported; FCA, CFR, CPT, CIP and DDP can be discussed for the shipment.
