Spare parts without drawings: making a part from the original

November 2, 2026  ·  Indumor

1 Worn part · 2 Measurement · 3 Drawing · 4 New part.

What do you do when the sprocket on a machine nobody makes anymore breaks, and the broken sprocket is all you have?

You bring it to the shop. With the part in hand, a caliper and a micrometer, the drawing you never had comes out. A sprocket for 5/8" pitch chain is defined by the pitch, the teeth, the width and the bore with its keyway. A spur gear needs the module, the tooth count and the pressure angle, almost always 20°. Bushings, sleeves, knives and wear plates are surveyed the same way.

The part you bring no longer measures what it used to

A bushing that ran for five years is oval, and copied as it is you get one that is worn from day one. One that came into the shop with a 40.61 mm bore and measured 40 when new does not get copied as found. You measure where the part did not work, the edge that does not rub or the end under a circlip. If nothing sound is left, you measure the mating part or the bushing on the other side of the machine. With an H7/g6 fit as a reference, the original size is rebuilt.

Then comes the material. Rockwell or Brinell hardness tells whether it was heat treated, the spark on the grinder separates a carbon steel from an alloy steel, and a handheld spectrometer confirms the alloy. From that follows the treatment: quench and temper for a shaft, case hardening for a sprocket, nitriding for a sleeve.

Nine times out of ten, hand instruments are enough; the 3D scanner is kept for housings and curved surfaces, as we explain in measuring and 3D scanning. If the machine is imported and the spare takes months, see what to do with an imported machine with no spare parts and how to build the stock for Chinese machinery.

With the plant down there is no room to think it over. The part is surveyed the same day, goes on the lathe, gets fitted, and that is that.

If you have a broken part, bring it over or send us photos with dimensions. At Indumor we survey it, make it and deliver it with its drawing, so the next spare comes out of a file instead of a broken part.

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