Short answer: a complete sample can be reproduced to the dimensions the original was built to, and a damaged one can be reproduced as far as the surviving geometry reaches. Two things change on the way to the new part. The process changes: the original was cast, moulded or stamped against tooling paid for once and divided across tens of thousands of pieces, while your ten pieces are machined from solid — so the price per piece goes up and the minimum order drops to 1. The material should not change unless you can say what the old one was doing. On a light machine an aluminium gear at 2.70 g/cm³ is light and soft for a reason, and a harder, heavier copy moves the wear onto the shaft, the bearings and the mating gear.
How much of the original is left
The condition of the sample decides how much of the job is measurement and how much is reconstruction. A complete part — worn, seized or cracked, but all there — carries every dimension needed, and copying it is a measuring job rather than a reconstruction. A part with a section missing, or with the functional face eaten away, has lost the information that matters most, and that information has to be recovered from somewhere else before anything is cut.
Wear is what makes reverse engineering possible in the first place, because wear is never even. The tooth flanks of a gear wear while the tip diameter does not; the loaded side of a shaft wears while the unloaded side stays near nominal. Measure the faces that do not carry the wear, and take the worn feature at its nominal value rather than copying the damage into the new part. Where the worn feature is the critical feature — a valve seat, a needle hole, a sealing land — the number has to come from a catalogue entry, a second part off another machine, or the mating component. More on that in which surface to measure on a worn part.
| Sample condition | What it gives on its own | What closes the gap |
|---|---|---|
| Complete, little wear | Every dimension, including fits and threads | Nothing — a drawing is issued for your approval before cutting |
| Complete, worn in service | Form, hole pattern, unworn faces, material | Worn features taken at nominal; a catalogue value or a second part confirms them |
| Broken, both halves kept | Full geometry once the fracture faces are aligned | Post both halves together, unglued |
| A section missing | What survives, plus the envelope | The mating part, a photo in the assembly, or a second sample |
| Corroded or burnt | Outline, thread sizes by gauge, hole positions | Original specification for the attacked faces; material analysis on sound metal |
Getting the shape off the part
Three routes take the geometry off a sample, and most jobs use more than one. Hand measurement with calipers, micrometers, radius and thread gauges is the fastest route for turned and flat parts and the one that reads intent: a shaft that measures 24.98 mm was drawn as 25 h7, and the drawing gets 25 h7. Material analysis answers what the part is made of, which the geometry never tells you. 3D scanning handles free-form shapes — castings, housings, impellers, trim — where there is no set of dimensions that describes the surface.
Scanning captures surfaces, not intent. A scan of a worn housing returns the worn housing, down to the dent. The scan becomes a solid model, and the model is then rebuilt to nominal values, given proper tolerances and turned into a drawing you approve — that step is the work, not the scanning. The same applies to material analysis: it reports what the alloy is, not why the designer picked it.
Why the copy costs more per piece than the original did
This is the part that surprises buyers, and it has nothing to do with where the part is machined. The original price was a mass-production price. The part was cast in a mould, pressed in a die or moulded in steel tooling; that tooling was bought once and its cost divided across tens of thousands of pieces, until it disappeared into the unit price. You need ten. The same tooling route has nobody to share the cost with, and the numbers we quote against — aluminium bridge tooling at $1,500–4,000, production steel moulds at $5,000–20,000 and up — would be the entire budget before a single part exists.
So the copy is machined from solid. That reverses the arithmetic in your favour on everything except unit price: no tooling charge, no minimum quantity, a drawing change costs a line of code rather than a new mould, and production runs 5 working days after the drawing is approved. What it does not do is beat the catalogue price of a part that is still in mass production. Machining loses at volume and wins at one.
If the part number is still live, buy it from the OEM. A catalogue part beats anything we can machine in ones and twos, and we will tell you so instead of quoting it. Reproduction is for parts that are discontinued, never sold separately, or wanted in a size the shelf does not carry.
The same logic settles the shape of the new part. The original may have been two pieces welded together, or a casting with a machined face, because that was the cheapest route at 50,000 pieces. At twenty pieces, one solid milled part is cheaper and has no joint to fail — copy the geometry the machine needs, not the production method the factory happened to use.
What the catalogue cannot give you
Before quoting a reproduction we check whether the part is buyable. Most of what reaches us is not, and for reasons that repeat:
| What you need | In the catalogue? | What we do |
|---|---|---|
| Two spares of a part whose maker closed | No — the number is dead | Reproduced from your sample, drawing approved first, MOQ 1 |
| The original in its cast form, 10 pieces | No — patterns and moulds are scrapped when a line ends | Machined from solid to the same geometry and material class |
| A gear in a module the shelf skips | Stock gears come in standard modules and bores only | Cut to the measured module, pressure angle and bore |
| The as-new diameter of a worn shaft | Not a catalogue value at all | Taken at nominal from the unworn band, confirmed against the housing |
| A part sold only as a complete assembly | Only as the assembly, at assembly price | The single failed component made on its own |
| A standard part that is out of stock | Yes — it exists, it is back-ordered | We say so; machining one costs more than waiting, unless the machine is down |
The material: match first, change second
Match the original material unless you can name what the change is for and what the old material was carrying. A reproduction looks like an opportunity to improve the part, and sometimes it is. But the alloy in your hand was a choice made by someone who knew the whole machine, and a copy that is stronger in isolation can be worse in place.
Mass is the clearest case. Steel is 2.9 times the density of aluminium, so the same shape in steel carries 2.9 times the mass — and every start, stop and reversal loads the shaft, the bearings and the drive with 2.9 times the inertia. Hardness is the second case: in a light drive the softer member is often the intended wear part, the one meant to give way first because it is cheap to replace. Harden it and the wear does not stop, it moves to whatever is left softest, which may be the shaft or the motor pinion.
| What the original material may be carrying | Symptom of changing it without checking |
|---|---|
| Low mass and low inertia (light drives, moving arms, rotating parts) | Heavier part loads bearings and shafts on every start and stop |
| Sacrificial wear (the soft member wears so the expensive one does not) | Wear moves to the shaft, the mating gear or the housing |
| Matched thermal expansion (aluminium part in an aluminium housing) | Fit tightens or loosens with temperature; seizure or play |
| Galvanic pairing (which metal is allowed to corrode) | The wrong pairing makes the housing the anode instead of the part |
| Electrical or thermal conduction | Loss of function in a part that still fits |
| Damping and noise (plastic and bronze gears in light drives) | A metal copy runs louder and transmits shock instead of absorbing it |
The weight check, in numbers
Before agreeing to any material change, compare the mass of the same geometry in both materials — the part weight calculator does it from the envelope in a few seconds.
| Material | Density g/cm³ | Same shape, mass vs 6061 |
|---|---|---|
| 6061 aluminium | 2.70 | 1.00× |
| 7075 aluminium | 2.81 | 1.04× |
| POM / acetal | 1.41 | 0.52× |
| C45 / 42CrMo4 steel | 7.85 | 2.91× |
| 304 stainless | 8.00 | 2.96× |
| Brass CuZn39Pb3 | 8.50 | 3.15× |
A change of material is agreed, not assumed, and there are three cases where it is the right call: the original grade is obsolete and the modern equivalent is a direct replacement (see case-hardening steel equivalents); the part failed by a mechanism you can name, such as a bolt that shears every season; or the environment changed, such as an indoor part now working outdoors, where 304 or 316 stainless replaces plated steel. Strength alone is not a case — 7075 in place of 6061 buys yield strength and costs corrosion resistance and weldability.
Two jobs, two routes
The route a reproduction takes depends on how much the part interacts with the rest of the machine, and the gap between the two ends is wide.
A gear from the United States: sample, analysis, and a material left alone
A customer in the United States posted a gear over to us. Material analysis came back aluminium. The first instinct was to improve it — a harder, more wear-resistant material for a part that had worn out. The reason we did not: the machine is a light one, and the original designer picked a light, soft metal for it. A harder and heavier gear would have held its teeth longer while feeding more inertia and more shock into the shaft, the bearings and the mating parts around it for the rest of the machine's life. The gear was reproduced in aluminium, with the tooth geometry restored to nominal rather than copied off the worn flanks. How a discontinued gear is reproduced covers the parameters that get captured.
A safety pin from France: photographs and four dimensions
At the other end, a customer in France needed a lock pin reproduced, and sent photographs with the dimensions that matter written on them — diameter, length, hole position, ring size. That was enough to draw it, approve it and make it. No sample crossed a border, no scan was needed, no material question arose: a pin of that type is a bar diameter, a length and a cross hole. Lock and safety pins with retaining chains are made the same way every week.
Between the two ends sits everything else, and the question that places a part on that scale is: what does this part have to agree with? A pin agrees with a hole. A gear agrees with another gear, a shaft, a housing, a load and a duty cycle — and each of those agreements is a value someone once chose, which a copy either honours or breaks.
Before you ask for a quote
EKINSUN LTD is a custom parts manufacturer in Guangdong, China that reproduces discontinued and obsolete parts from a sample, a photograph or a sketch — MOQ 1 piece, no tooling charge, quote within 12 hours, production typically 5 working days after the drawing is approved. What speeds a reproduction quote up:
- The part itself where it has fits, threads, teeth or sealing faces — or clear photographs with the key dimensions written on them for simple turned and flat parts. Samples come back with the new pieces.
- The mating part, if you have one. It is the cheapest way to confirm a fit that the worn sample cannot prove.
- What the part does: what it drives, how fast, how hot, wet or dry, indoors or out. This is what decides whether the material may be changed.
- Whether it failed or just wore out. A part that broke early is telling you something; a part that lasted for years is telling you the original choice was right.
- How many, and how often. One spare now and five a year is a different quote from fifty once — and above a few thousand a year, a tooled route beats us, which we will say.
No CAD file is needed at any point: a sketch, a sample or the obsolete part itself is a starting point, and the drawing we build from it is yours to approve before anything is cut.
Frequently Asked Questions
Because the two parts were made by different processes. The original was cast, moulded or stamped against tooling that was paid for once and divided across tens of thousands of pieces. A copy of five or twenty pieces cannot carry that tooling, so it is machined from solid and priced per piece. The copy gains what the original never had at that price: a minimum of 1 piece and no tooling charge.
It can be copied, but the missing geometry has to come from somewhere else: the mating part, a second sample, a catalogue entry for the dead part number, or a photo of the assembly. A complete sample, even a worn one, needs none of that. The more of the part that is gone, the more of the job is reconstruction rather than measurement, and the more confirmation is needed before anything is cut.
Match the original material unless you can name what the change is for and what the old material was carrying. Low mass and low hardness are often the specification, not a saving: on a light machine an aluminium gear at 2.70 g/cm³ is also the part meant to wear first. A harder, heavier copy moves the wear onto the shaft, the bearings and the mating gear. Where the original grade is obsolete or the failure mode is known, a substitute is agreed before machining.
Photos with the key dimensions are enough for simple turned or flat parts, such as a pin, a spacer, a washer or a bracket. Send the part itself when it has fits, threads, gear teeth, sealing faces or a wear pattern that has to be read, or when the material has to be analysed. Samples are returned with the new pieces.
One. A machined reproduction has no tooling to amortise, so a single spare and a batch of fifty are the same kind of order, with price breaks quoted on quantity. Typical production is 5 working days after the drawing is approved, and the quote comes back within 12 hours.