I fear one wrong millimeter can stop a job. I have lived that pain. I want proof first. This is how I make accuracy certain before I buy.
I verify accuracy before any order with a clear pack: 2D drawings with all critical dimensions and tolerances, a CMM-based first article report, optional third-party inspection, and a live video measurement. I can also approve a physical sample, so fit is proven on my machine.
Here is my simple promise. I make the data visible. I show the method. I let you measure with me. Then I lock the spec. So you can order with confidence.
Can you provide detailed technical drawings with all critical dimensions?
I worry that missing one critical dimension can cause a no-fit. I want drawings that show everything. I also want the tolerances that matter.
Yes. I provide fully detailed drawings and native CAD. Each critical-to-fit dimension is marked with clear tolerances and GD&T. I share a critical dimension checklist, and I include our first article results to match each callout.
What you get before you commit
You get a complete drawing set with every interface feature marked. I include blueprint views for bores, ODs, faces, pitch, and bolt patterns. I also include a 3D STEP model if you want to check form and clearance in your CAD. I list each critical-to-fit (CTF) point. Examples are track link pitch, bushing OD, pin OD, sprocket pitch diameter, idler OD, roller shaft seats, and bolt hole positions. I call each CTF item out on the drawing and in a separate checklist.
I also align our drawing with your brand’s OEM reference. I confirm part code, revision, and machine models. I add notes for heat treatment, surface finish, and coating thickness, because these can shift dimensions if we do not control them. I map the control plan to the drawing. So each CTF point has a tool, a method, a frequency, and an acceptance rule.
Drawing content and GD&T
I use clear GD&T only where it adds value. I apply position on bolt circles, runout on large ODs (idlers, sprockets), parallelism on roller seating faces, and perpendicularity on flange faces. For pitch, I use cumulative pitch tolerance across a set number of links, plus a dedicated gauge fixture. I put general tolerances on non-critical features using ISO 2768 1 1 2 (mK) unless you tell me a different standard. I state datum scheme with a big, legible stack so you can follow the setup.
Sample and third-party verification
If you want to verify yourself, I can ship a pre-production sample. You can measure with calipers, micrometers, bore gauges, or a height gauge. Measure the bushing OD, link pitch, idler OD, and hole positions. If shipping is slow or costly, I can do a live video session. I place the part on the CMM or optical comparator. You watch the probe hit points and see the screen readouts. You can ask to re-measure any point. If you want extra certainty, I can book SGS, BV, or TUV 3 3 4 to issue an independent dimensional report that lists nominal, tolerance, and actual results for every CTF item.
Below is the exact pack I deliver for pre-order verification.
| Item | Format | Contents | When Delivered |
|---|---|---|---|
| 2D drawings (rev-controlled) | PDF + DWG | All dimensions, CTF tags, GD&T, materials, heat treat, finish | Before sample or FAI |
| 3D model | STEP/IGES | Full geometry for digital fit checks | Before sample or FAI |
| Critical dimension checklist | XLSX | List of CTF with nominal, tolerance, gauge, method | Before sample or FAI |
What quality control tools (e.g., CMM) do you use to check dimensions?
I have seen shops rely only on calipers. That is not enough. I want the right tool for each feature. I want proof of accuracy as well.
I use a CMM for core fits, plus bore gauges, micrometers, height gauges, and an optical comparator. I keep all tools calibrated. I run MSA (gage R&R) on critical gauges. I can measure live on video.
Core metrology for heavy undercarriage parts
Different features need different tools. I inspect bores and shafts with classed bore gauges and micrometers. I check large ODs, like idlers and sprockets, on a CMM with rotary table or with a large diameter mic. I check pitch with a dedicated fixture and confirm on the CMM using center-to-center points. I check bolt circles with CMM and optical comparator for edge definition. I inspect runout by putting the part on V-blocks and using a dial indicator, then confirm on CMM. I use a height gauge with granite surface plate for step heights and flange thickness. For small profiles, I use an optical comparator with overlays. I verify surface finish with a roughness tester 5 5 6 when it matters for seals or bearing fits.
I track all instruments in a calibration system. Each tool has a unique ID, a calibration due date, and a certificate traceable to national standards. I lock out expired tools. I keep a metrology log in the job traveler. Operators scan the gauge before they measure.
Calibration, MSA, and method standardization
On critical-to-fit features, I run gage R&R to be sure the tool and the appraiser do not add too much variation. If R&R P/T is high, I switch method. For example, if a caliper shows too much spread on pin OD, I move to a micrometer or CMM. I write a standard work sheet with photos. It shows setup, clamping, temperature note, and the exact probe points. I control temperature near 20°C for tight measurements. I place parts near the room for equilibrium before measurement.
Live measurement options you can witness
If you cannot receive samples fast, I set a live session. I put a camera on the CMM screen and another camera on the part. You can see the probe go to the bore, face, or hole center. You can see each value as it appears. You can ask me to repeat points or measure 10 pieces in a row. I record the session and send the file.
Here is how I match tools to features and the typical uncertainty.
| Feature | Primary Tool | Typical Accuracy/Uncertainty |
|---|---|---|
| Bushing OD (e.g., 90 mm) | CMM or micrometer | ±0.005–0.010 mm |
| Pin OD (e.g., 50 mm) | Micrometer | ±0.003–0.008 mm |
| Link pitch (center-to-center) | CMM + pitch fixture | ±0.02–0.05 mm |
| Idler OD (e.g., 580 mm) | CMM or diameter tape + CMM sample | ±0.05–0.10 mm |
| Bolt circle position | CMM | ±0.02–0.05 mm |
| Runout (idler/sprocket) | Dial indicator + CMM check | ±0.02–0.05 mm |
What are your accepted dimensional tolerances (e.g., +/- mm)?
I dislike vague tolerances. I want clear numbers that fit heavy equipment reality. I also want GD&T that helps, not noise.
I use ISO-based general tolerances for non-critical features and tighter, feature-specific limits for fits. Typical examples: bushing OD ±0.02 mm, pin OD ±0.01–0.02 mm, idler OD ±0.20 mm, pitch ±0.10 mm per link, runout ≤0.15 mm.
General tolerances
For non-critical dimensions, I apply ISO 2768-mK 1 1 7 by default. This gives practical limits for heavy parts without over-processing. I list these on the drawing notes. If your standard differs, I align to your rule. For threads and standard fasteners, I follow the relevant ISO/ASME specs 8 8 9. For fits between bores and shafts, I select ISO 286 classes that match your install method. For press fits like bushing into link, we set the interference based on your assembly force and thermal practice.
Critical undercarriage examples
I will share typical numbers that we use often. Please treat them as a starting point. We agree the final values together.
- Track link pitch: 203.2 mm nominal, tolerance ±0.10 mm per link, with cumulative control over 10 links ≤±0.30 mm.
- Bushing OD (e.g., 90.00 mm): ±0.02 mm after heat treat, with roundness ≤0.01 mm.
- Pin OD (e.g., 50.00 mm): ±0.01–0.02 mm, surface finish Ra ≤0.8 µm on bearing zones.
- Idler OD (e.g., 580.0 mm): ±0.20 mm, total indicator runout (TIR) ≤0.15 mm.
- Sprocket pitch diameter: ±0.15 mm, tooth profile within template limits, runout ≤0.15 mm.
- Roller shaft seat: ±0.02 mm diameter, cylindricity ≤0.02 mm.
- Bolt hole position: true position ≤0.10 mm at MMC relative to primary datums.
- Flange thickness: ±0.10 mm, parallelism to datum ≤0.05 mm.
I also include heat treat distortion control plans, because hardness steps can shift size. I measure after final temper and grind if needed to hit the tight numbers.
Here is a quick view you can use to compare with your spec.
| Feature (example size) | Typical Tolerance | Typical GD&T note |
|---|---|---|
| Link pitch 203.2 mm | ±0.10 mm per link; 10-link cum ≤±0.30 mm | Position to pitch datum |
| Bushing OD 90.00 mm | ±0.02 mm; roundness ≤0.01 mm | Datum A on bore axis |
| Pin OD 50.00 mm | ±0.01–0.02 mm | Cylindricity ≤0.02 mm |
| Idler OD 580.0 mm | ±0.20 mm; TIR ≤0.15 mm | Runout to face datum |
| Bolt hole Ø18.0 mm | True position ≤0.10 mm @ MMC | Datums A, B, C |
| Roller seat Ø60.00 mm | ±0.02 mm | Parallelism ≤0.03 mm |
Agreeing and controlling the final tolerances
I do not force a one-size rule. I start with your machine’s fit needs. I simulate thermal conditions if you plan hot or cold assembly. I run a first article inspection (FAI) with 100% checks on CTF features. I track process capability (Cpk ≥1.33 target) on these features in pilot runs. If Cpk is low, I adjust the process or relax a non-functional limit after we agree. I lock the final tolerances in the control plan and the drawing revision. I then keep samples as golden masters with serialized labels. I store them for the life of the part.
How do you guarantee my parts will fit OEM machines perfectly?
I know that “close” still fails in the field. I want a real fit guarantee. I want fast fixes if anything goes off-spec.
I guarantee fit with a golden sample process, a CMM-backed FAI, and 100% inspection on critical features. I run try-on checks with gauges and jigs. If any delivered part deviates, I replace, remake, or refund fast.
Golden sample and FAI that lock the spec
First, we agree a master, also called a golden sample. You can receive it and validate on your machine. Or we can validate together by video with CMM proof. I tag this sample and lock it in storage. Second, I run a First Article Inspection on the first production piece. I check all critical dimensions on the CMM. I also check general items per plan. I send you an FAI report that lists nominal, tolerance, and actual numbers. I include photos of the setup and the measurement points.
100% inspection on critical features
I do not risk CTF with sampling only. I check 100% of parts on the critical dimensions that control fit. For example, I check every bushing OD, every pin OD, every pitch on a link set, and every bolt circle position. I use go/no-go gauges where that makes sense. I also use automated fixtures for pitch so I can measure fast and without bias. For non-critical features, I use AQL sampling unless you ask for more.
Fit verification with jigs and try-on tests
I keep control jigs that simulate the machine interface. I check a running sample from each batch on a jig: link pitch engagement with a sprocket template, idler runout on a mandrel, or bolt patterns on a master plate. For custom parts, I can build a fixture from your CAD that replicates the mating geometry. I store jig records with serial numbers.
Live proof and traceability
If you want, I do a live proof for each shipment. I open random boxes, measure on camera, and show labels and serials. I keep traceability from heat lot to final pack. If any issue comes, I can trace back to the lot and the operator.
Clear remedy if anything goes wrong
If the delivered parts differ from the approved sample or the locked drawing, you get a priority fix. I can replace the affected parts, remake them on an expedited schedule, or refund. I pay the return shipping on confirmed nonconformance. I also cover reasonable re-install labor if we agreed in the contract. I open an NCR, run root cause analysis, and share a corrective action plan. I also align stock, so you do not run out. I offer a temporary price credit if the delay hurts your schedule.
What if you cannot receive a physical sample?
If shipping a sample is not possible on time, I do a high-resolution video and a live session. I put the part on the CMM, on the optical comparator, and on gauges. I show each reading. I also invite a third-party inspector 10 10 11 to attend the call. If you still want physical proof, I can ship a set of “measurement coupons” that include the bore section, the tooth profile section, or the bolt-circle slice. These coupons are fast to ship and good for fit checks.
Conclusion
You get drawings, CMM data, sample or live proof, and a fit guarantee. You see the numbers, the method, and the fix plan. You order with certainty.
Footnotes
1. Explanation of the ISO 2768 standard for general tolerances. ↩︎ 12
2. SGS provides independent verification of dimensions. ↩︎ 13
3. Overview of roughness testers for surface finish checks. ↩︎ 14
4. Details on ISO 2768-mK tolerances for machining. ↩︎ 15
5. Comprehensive guide to ISO/ASME specifications for fasteners. ↩︎ 16
6. Importance of third-party inspection agencies like TUV. ↩︎ 17