Reverse engineering a part without a drawing means measuring an existing sample, identifying its material and finish, and creating a new drawing and 3D model that can be used to machine replacement parts. A machine shop with CMM and gaging equipment can do this, but the customer should review and approve the resulting drawing before production, because a measured sample shows what was made, not necessarily what was intended.
Replacement parts for legacy equipment, obsolete components, and parts from suppliers that are no longer in business often have no drawing. This page explains how reverse engineering works for machined parts, what information the shop needs, and where the risks are.
The reverse engineering process
| Step | What happens |
|---|---|
| 1. Sample review | Shop examines the sample for wear, damage, and features that affect function |
| 2. Measurement | Dimensions measured with CMM, micrometers, bore gages, thread gages, and optical comparator |
| 3. Material identification | Material determined from records, markings, or testing by an outside lab |
| 4. Mating part review | Fits and clearances checked against the mating parts if available |
| 5. Drawing and model | Measured values rounded to design intent, tolerances assigned, drawing and STEP model created |
| 6. Customer approval | Customer reviews and approves the drawing before production |
| 7. First article | First part machined and inspected against the new drawing, then test fitted |
Measuring a worn sample
Most samples come from service and show wear. Journals, bores, threads, and sealing surfaces may have worn away from the original size. The shop measures unworn areas where possible and uses standard fits, thread sizes, and bearing dimensions to estimate original intent. For example, a shaft that measures 0.9992 in at a bearing seat was probably designed to a standard fit on a 1.000 in bearing, not to 0.9992 in.
Identifying material and heat treat
Material affects strength, wear, and corrosion resistance, so it should not be guessed. Sources include the original equipment manual, part markings, and the customer's maintenance records. When those are not available, chemical analysis and hardness testing through an outside laboratory can identify the alloy and condition. If the part was heat treated or plated, those requirements must be added to the new drawing.
Information the customer should provide
- The sample, or several samples if available, including a less worn one.
- The mating parts or their dimensions, if possible.
- What the part does, its loads, speeds, temperatures, and environment.
- Any known material, finish, or heat treat information.
- Any failure history: why the part is being replaced.
- Quantity needed now and expected future use.
Improving the design during reverse engineering
Reverse engineering is also a chance to fix known problems. If the original part wore quickly, cracked, or corroded, the customer may choose a different material, add a heat treat, or change a finish. Any such change is a design decision for the equipment owner, and it should be recorded on the new drawing so future orders match.
Risks and how to manage them
A reverse engineered drawing reflects measurement and judgment. Risks include copying wear into the design, missing an internal feature, or choosing the wrong material. The customer approval step, a first article, and a test fit reduce these risks. For safety-critical parts, involve the equipment owner's engineering function in the review. For parts under government contracts, confirm that a reverse engineered source is permitted.
Reverse engineering at Wexmar
Wexmar measures samples on Brown & Sharpe CMMs and a Mitsubishi optical comparator, along with thread gages and hand gages, and can produce a drawing and model for customer approval before machining. Material testing is arranged through outside laboratories when needed. Replacement parts are then made on CNC lathes, horizontal machining centers, or Swiss-type machines, depending on the geometry. See inspection and quality and parts.
Reverse engineering checklist
- Best available sample, plus mating parts if possible.
- Function, loads, and environment described.
- Material and heat treat known or tested.
- New drawing reviewed and approved by the customer.
- First article inspected and test fitted before quantity production.
Getting a quote
Contact Wexmar to discuss a part with no drawing. Photos with a scale reference and approximate dimensions help the first conversation. If you have any partial drawing or sketch, you can upload a drawing for an instant estimate, or call (315) 400-2654 to arrange sending a sample.