The first question in timing belt selection is what the belt actually does. Does it transmit torque and phase between shafts, or carry workpieces through a machine? Both use toothed belts, but the calculations for drive capacity and conveyor effective tension are different. Mixing them produces the wrong belt width, pulley, take-up range and acceptance test. This guide helps Thai factory teams specify a new machine or replace a drive using documented inputs, comparable quotations and measurable FAT/SAT criteria.
The purchase description “pitch × teeth × width” cannot establish drive compatibility or life. Specify the belt family and tooth profile, matching pulley profile and tooth count, actual load, speed, duty, starting and stopping, installation tension, centre-distance adjustment, and environment as one system. Compare manufacturers only after their assumptions and rating methods are visible.
Why timing belt selection starts with the application
A power-transmission belt transfers torque and a speed ratio from a motor or gearbox to a driven shaft. Its assessment includes transmitted power, duty factor, small-pulley speed and teeth, ratio, belt family, engaged teeth and width. MISUMI’s power-transmission procedure first collects machine type, power, load variation, daily running hours, small-pulley speed, ratio, provisional centre distance, diameter limits and operating conditions; it then progresses to design power, profile, pulleys, length and width. Selecting a stock number first conceals start-up peaks and bend limits. Source 1
A conveyor belt carries a workpiece or an attached fixture. Mass alone is insufficient: friction with its support, incline, speed, load distribution, positioning and belt surface matter. MISUMI’s conveyor example assumes equal head and tail pulleys and proceeds from effective tension to design tension, belt type and width, pulley diameter, length, centre distance and take-up allowance. It is not the same calculation as a motor-drive power rating. Unequal pulleys, multiple shafts, reciprocating or vertical travel require a separate design. Source 3
Positive tooth engagement does not mean that tooth jump or positional error is impossible. Low tension, too few engaged teeth, overload, pulley misalignment, poor assembly or a jammed workpiece can cause them. In precision positioning, consider belt elasticity, backlash elsewhere in the mechanism, shaft stiffness and pulley eccentricity. Where tolerance is tight, measure the position of the actual workpiece in both directions and after temperature changes, rather than relying only on motor counts.
Nine inputs to gather before requesting quotes
First, state whether the task is shaft transmission, workpiece conveying, a positioning axis or synchronous conveying. Second, document workpiece or load mass, friction and incline; separate normal running from jam and stop peaks. Third, record motor rated power, torque, speed, reduction ratio and start/stop frequency, without treating rated power as peak torque. Fourth, note daily operating hours and the cycle: a continuously running axis and one accelerating dozens of times per minute have different duties despite similar average speeds.
Fifth, measure pulley diameter constraints, centre-distance tolerance, the motor-base adjustment direction and usable space inside the guard. Sixth, record temperature, dust, water, oil, cleaning chemicals, food-contact requirements and any static or hazardous-area requirements. Assess these against the selected product’s actual certification; a temperature claim for one belt is not a universal timing-belt limit. Seventh, quantify position tolerance, speed variation, allowable tooth jump, noise, debris and maximum repair time. Eighth, document the existing belt print, pulley teeth and profile, widths, tension procedure, failure location and replacement interval with photographs. Ninth, define procurement scope: belt only, or pulleys, bearings, guards, tension meter, spares and training as well.
This input sheet tells buyers whether quotes describe equivalent systems. For repeated failures, a wider replacement belt may not address the cause. Examine tooth wear, edge wear, bearing heat, tensioner position, start-up current and stop logs together.
Selecting a power-transmission timing belt
Begin with the power actually transmitted and the load profile. MISUMI’s general method uses design power derived from transmitted power and an overload factor, but factor definitions and rating tables depend on the belt series. Never apply one manufacturer’s factor to another manufacturer’s capacity table. Supply each vendor with the same load variation, hours and ratio, and ask for a calculation following its own documented procedure. Source 1
Next, choose a provisional tooth profile and pitch. HTD, GT, S and T names relate to geometry and pulley compatibility as well as size. Equal pitch alone does not prove that two profiles are interchangeable. For a replacement, match the belt and pulley part numbers, measured dimensions and manufacturer compatibility statement. For a new machine, include local availability of replacement parts in the decision.
Then set the speed ratio with small and large pulley tooth counts and check the chosen series’ minimum tooth count and speed limits. A very small pulley creates stricter bending and engagement conditions. MISUMI publishes minimum small-pulley teeth by profile and rotational-speed band; there is no single universal minimum. Check pitch diameter, shaft diameter, key or clamp, flange and surrounding clearance in addition to outside diameter. Source 2
Use provisional centre distance and pulley pitch diameters to estimate belt pitch length. Choose an available standard length and recalculate the actual centre distance. Manufacturers can define marked lengths differently; put the selected manufacturer’s pitch length, teeth and width on the purchase drawing and map them to the old belt’s markings. The motor base needs travel for both fitting a new belt and setting tension afterwards. A fixed-centre design must not require the installer to lever a belt onto the pulleys.
Verify belt width using the series’ capacity table and the number of engaged teeth. MISUMI uses basic transmission capacity, engagement correction and reference width to calculate a preliminary width, then rechecks a standard width. Engagement correction decreases when fewer teeth share the load. Width alone cannot remedy too few small-pulley teeth or excessive bearing load. Gates also requires the overhung load on a reducer output shaft to be checked against that reducer’s own permissible rating. Source 2 Source 5
Finally specify installation tension, pulley alignment, guard and maintenance. More tension is not automatically safer: excess loads bearings, while insufficient tension encourages tooth jump and vibration. State the manufacturer’s measurement method, span, belt condition, isolation procedure and reinspection point. Optibelt treats pretension calculation and adjustment as a distinct design step. This article also recommends validating the drive under conditions close to real use. Source 4
Selecting a conveyor timing belt
Draw the workpiece, fixture and belt support first. A belt sliding on a table, one supported by rollers, and one carrying a workpiece directly have different friction and deflection. Include total simultaneous payload, elevation difference, acceleration and local fixture attachment loads. A vertical or multi-pulley arrangement needs an application-specific assessment.
In MISUMI’s equal-pulley conveyor example, effective tension includes gravity times friction and lift terms. Its tabulated friction coefficients are general values for specified support materials, not guarantees for a dusty, oily or freshly cleaned Thai line. Measure or validate uncertain conditions in a trial. Apply the source’s operating-hours, belt-length and belt-speed corrections when obtaining design tension. Source 3
Compare design tension with the candidate belt’s permissible tension and check each pulley’s minimum teeth. Same pitch does not imply the same allowable tension. The cited conveyor table is for joined belts and cannot automatically rate endless or open-ended forms. Coatings, attachments and joints need their post-processing rating confirmed by the supplier. Check whether the belt can be replaced without dismantling major machine sections.
After selecting pitch and pulley teeth, use an available belt tooth count to determine pitch length and centre distance. Additional shafts and tensioners change wrap angle and straight runs. Translate both inward fitting allowance and outward tension allowance into the adjustment drawing. Verify tool access and whether an axle must be removed to replace the belt. For positioning, accept the actual stopped workpiece position, not merely a motor encoder count. Test maximum payload, hot operating hours, after cleaning and after extended running where relevant. Food-contact or chemical suitability must be verified against the selected material and certificates.
Worked geometry example: pitch length is only a first check
The following assumptions illustrate drawing review, not a certified product choice. Consider equal pulleys with 5 mm pitch and 40 teeth, separated by a provisional 500 mm centre distance. Their pitch circumference is 40 × 5 = 200 mm, giving a pitch diameter of about 63.66 mm. Two straight spans plus two half-circles give a pitch length of 2 × 500 + 200 = 1,200 mm. That corresponds to 1,200 ÷ 5 = 240 belt teeth. If a matching 240-tooth standard belt exists and the manufacturer approves it, the geometrical centre distance is (1,200 − 200) ÷ 2 = 500 mm. Source 3
Do not freeze the mounting holes at 500 mm. The belt needs inward travel for fitting and outward travel for tensioning. For the S5M belt in its stated conveyor table, MISUMI gives at least 10 mm inward fitting allowance and at least 5 mm outward take-up for centre distances up to 500 mm. These are source- and configuration-specific values, not a universal drawing rule. Manufacturing tolerance, actual stock length and maintenance access may demand more travel. The example says nothing yet about permissible tension, payload, speed, motor, life or cross-profile compatibility. Label every preliminary drawing value as an assumption and ask the vendor to return its validated calculation and standard part number.
Compare total quotations rather than belt unit prices
Design a small trial before ordering
If two candidates remain, test them under the most demanding relevant conditions. A dedicated test rig is useful, but even a short, instrumented run on one existing machine axis can answer practical questions. The purpose is not to declare one belt universally superior. It is to establish which matched belt–pulley set repeats the required performance under this machine’s load, speed, temperature and cleaning conditions. Freeze the belt, pulley, tension setting, workpiece and measurement procedure for each candidate; log any change during the trial.
For transmission, include start-up, the heaviest product, the most demanding acceleration recipe, and restart after a stop. Observe speed ratio, unusual noise and vibration, bearing-area temperature and lateral belt tracking. Plan safe measurement with a window or sensor rather than an extended run without a guard. For conveying, include maximum simultaneous and asymmetric loading, entry and discharge impacts, incline, friction after cleaning, and actual positional accuracy. One average product variant is not enough when several are manufactured.
Confirm that both candidates were tensioned to their respective specified settings. A noise comparison made at different incorrect tensions does not isolate belt material or profile. If old pulleys are retained, record the vendor’s compatibility approval and their condition; do not present a worn existing-pulley trial as equivalent to a new-pulley trial. At the end, list untested conditions alongside the pass/fail result. Several days cannot establish long-term life. Carry untested washdown chemicals or peak takt into SAT or later validation. When performance is close, local lead time, replacement access, maintenance training and common spares also belong in the purchase decision.
Columns in the comparison sheet should include profile, pitch, teeth, width; pulley part number, teeth and material; permissible power or tension; installation tension and measurement method; bearing load; replacement downtime; local stock and lead time; warranty exclusions. For a transmission, add duty factors and engagement correction. For conveying, add friction, incline and maximum concurrent payload. A premium belt can raise total cost if it requires new pulleys, while a narrower belt that meets the full system requirements may sometimes reduce machine cost.
There is no defensible single Thai-market price for a timing-belt installation. Freight, stock, quantity, pulley machining, installation, guard modification, commissioning and spares change the quote. Separate “belt only”, “belt and pulleys” and “installed modification” offers. State the permitted downtime and supplier responsibility. Choose spare quantity against replacement frequency and the cost of an unplanned stop, rather than copying another factory’s stocking rule.
For a servo axis, the shaft-coupling selection guide helps separate torsional stiffness and alignment questions from the belt’s own requirements. Where the belt is part of a positioning axis, the rotary-encoder selection guide helps decide whether feedback belongs on the motor or load side. Neither replaces a belt-capacity calculation.
Turn failures into a useful RFP
Similar symptoms call for different checks. Missing teeth in one location point to investigation of peak load, jams, engagement and pulley damage. One worn edge prompts alignment, flange and bearing checks. Uniform tooth wear suggests reviewing dust, material, tension and duty. A damaged back surface prompts inspection of tensioners, guards and handling. These are inspection priorities, not diagnoses. Log operating hours, products, maximum loads, tension, photographs, alarms, belt lots and whether pulleys were replaced. Repeated damage in the same place merits a machine-level investigation before specifying a stronger consumable.
If the old drawing is absent, photograph the belt print and measure pulley teeth, profile, width, pitch diameter, centre distance, shaft and flange. A worn belt’s outside circumference is a poor substitute for its original pitch length. Manufacturers encode belt length, teeth and width differently. Obtain a supplier cross-check of both belt and pulley; similar looking markings are not approval for substitution.
For new equipment, also confirm whether a belt is the right architecture. Chain or rollers may suit long conveying, while a screw or linear motor may suit some short precision moves. Compare force, stroke, speed, positioning, cleaning and replacement downtime. Divide responsibilities among the belt, guide, sensor and control system in the machine drawing.
The RFP should state process, payload, takt, annual duty and measurable position or stop requirements. Attach drawings, centre distance, diameter limits, allowable shaft/bearing loads, space, ambient conditions and contamination constraints. Require suppliers to disclose the load, correction factors, rating-table revision and exact belt, pulley and tensioner part numbers used in their calculations. For existing pulleys, demand written evidence of profile, pitch, width, flange and attachment compatibility; for new machines, quote belt and pulleys as one engineered package. Specify isolation, guard removal, loosening, replacement, alignment, tension measurement, test running and guard restoration in the maintenance scope. Gates’ preventive-maintenance manual describes isolation before service and a staged installation/tensioning procedure. Source 6
FAT and SAT: measure the complete machine
Before FAT, assign responsibility for confirming loads, approving the belt calculation, accepting the mounting drawing, and remedying site failures among the machine builder, integrator, belt supplier and factory maintenance team. The belt supplier may rate its component without knowing every jam, bearing condition or motion profile of the complete machine. Review motor and driven rotation, pulley position, tensioner contact side, guard opening, measurement span and the actual workpiece transfer points on the approved drawing. Ask maintenance to rehearse the proposed replacement sequence on paper, including the parts that must be removed for access.
At handover, reconcile installed belt, pulley and tensioner part numbers with the approved drawing, purchase list, spare-parts list and maintenance instructions. If a supplier changes a belt family or width, retain the reason and recalculation. A note saying “equivalent part” alone does not preserve pulley-compatibility or tension evidence for the next replacement. Keep photographs, part labels, measured tension and site test results in the equipment record.
Measurement conditions make acceptance results repeatable. A tension record reading “pass” is weak unless it identifies the calibrated instrument, span, belt state, temperature and moment of measurement. Follow the selected manufacturer’s instructions on any check after initial running; do not infer a universal retension interval. For positioning, test loaded and unloaded states, both approach directions, hot running and the most demanding product variants. If an error appears, investigate sensors, servo control, guides and fixtures as well as the belt. When headquarters FAT and Thai-site SAT have different teams, preserve test fixtures, load conditions and method in records or video. Explicitly carry site-only washdown or product variability into the SAT scope rather than treating the FAT pass as covering untested conditions.
At FAT, verify belt and pulley part numbers, profile, teeth and width, centre-distance adjustment, recorded installation tension, alignment, guard operation and replacement access. Test normal and maximum payload, starts and stops, fastest and slowest specified speeds, and reversal if required. Replace “operates normally” with measurable criteria for positional error, tooth jumping, product drop, temperature or abnormal noise. Agree thresholds for the actual product and machine; do not reuse this article’s illustrative numbers as acceptance limits.
At SAT, recheck shaft alignment and tension after installation, then measure real workpiece position and sustained operation. Site power, controls, heat, dust, washdown and product variation may differ from FAT. Record heat rise, edge debris and any belt tracking changes instead of dismissing them as running-in. Maintenance staff should be able to replace the belt by the agreed procedure and restore the same acceptance values. Keep identical part numbers, tension conditions, pulley positions, load patterns, running hours and photos in FAT and SAT records; otherwise later failures are hard to compare.
Frequently asked questions
Can a belt from another manufacturer replace one with the same pitch?
Pitch alone is insufficient. Check tooth profile, pulley geometry, width, length definition, tension, capacity and environmental suitability. Ask the proposing supplier or integrator for written compatibility and capacity evidence for the installed pulleys.
Is a wider timing belt always safer?
It may raise allowable capacity, but cannot cure inadequate engagement, excessive bearing load, wrong pulley diameter or poor tension. Calculate width with the selected series’ rating table and confirm surrounding machine space.
How should we compare conveyor timing-belt costs?
Use the same scope and acceptance criteria for belt, pulleys, tensioner, machining, installation, measurement, spares, local supply and stoppage. Public product prices cannot establish a Thai factory’s installed cost.
What should we inspect if a new belt jumps teeth?
Check profile compatibility, measured installation tension, pulley wear, engaged teeth, alignment, overload, emergency stops and jams. Save failure location and the load or alarm record at the time.
Summary
Choose a timing belt by separating power transmission from conveying and specifying real load, matched belt and pulley, stock length and take-up, bearing load, maintenance, and FAT/SAT criteria together. The geometry example checks dimensions only; it does not warrant capacity or life. Recalculate against the selected manufacturer’s current documentation and test with real products on site.
If your Thai factory is still deciding whether existing pulleys can be reused or how to compare quotations, contact TOMAS TECH with the drawings, belt markings and workpiece details available. Even an early-stage review can identify the design and acceptance questions that need answers.
