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Making spare gears from existing: what info is needed?
2

Making spare gears from existing: what info is needed?

Making spare gears from existing: what info is needed?

(OP)
We have some old equipment (1940s), low speed, intermittent service, outdoors.

We are undertaking to make drawings of all parts, including gears, so that we can have spare parts manufactured. For the gears, we have already recorded overall (outside) diameter; rim, hub, and spoke dimensions; and of course the number of teeth. Just looking at them we can see the gears are castings.

We are sending out a sample gear for testing to determine tooth profile (involute vs. cycloidal) and pressure angle.

What other information would we need to include on the drawings? What would be needed to manufacture spare parts?

RE: Making spare gears from existing: what info is needed?

KM, sounds like you have been pretty thorough in your documentation of the gears.  The only thing that you didn't mention would be the pitch of the gears (number of teeth per inch - which would probably be included in the tooth profile measurements, but I mention it just in case).

My advice would be to grab a couple of catalogs from gear manufacturers and pick the gears you want to use.  All you would really need is the ratio between the mating gears and the pitch diameters of the gears in mesh to fit your space constraints.  This method would eliminate the cost involved with sending the gears out to be inspected and the potential cost of manufacturing a style of gear that is no longer a stock size (ie cycloidal teeth and some pressure angles are not too popular these days).  Besides potentially reducing replacement costs, you may also get the benefit of more efficient, stronger gears.

This redesign approach may take a little more time up front, but I think it will pay off in the long run.
Hope this helps.

RE: Making spare gears from existing: what info is needed?

The centerline distance is helpful. You may find the exact copies are very expensive and may decide to use stock gears for replacements.

RE: Making spare gears from existing: what info is needed?

The centerline distance is helpful. You may find the exact copies are very expensive and may decide to use stock gears for replacements.  Very few gear teeth on old equipment are cast.  You could be looking at pitted worn-out teeth.  If they were cast this machine must allow a lot of backlash.  The bronze bearings used on old machines required more backlash or aquired more backlash than modern roller bearings.  I mention this because if you are able to update the bearings,  you may update the gear design also.

RE: Making spare gears from existing: what info is needed?

When replacing gearing, it is best to replace all of the components together. This way the problems of pressure angle & tooth form can be avoided. In order to reproduce a gear what is need is: the pitch, the number of teeth, the pressure angle, the bore, the hub diameter, the face width and the overall length. In order to confirm that a gear is cut to standard dimensions, the OD should measure module*(the number of teeth + 2). If the gear appears to be modified from standard then the number of teeth in the mating gear and the center distance between the two gears is required.

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