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

[KM]

We have some old equipment (1940s), low speed, intermittent service, outdoors. <br>
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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.<br>
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We are sending out a sample gear for testing to determine tooth profile (involute vs. cycloidal) and pressure angle. <br>
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What other information would we need to include on the drawings? What would be needed to manufacture spare parts?

 

[cowski]

KM, sounds like you have been pretty thorough in your documentation of the gears.&nbsp;&nbsp;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).<br><br>My advice would be to grab a couple of catalogs from gear manufacturers and pick the gears you want to use.&nbsp;&nbsp;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.&nbsp;&nbsp;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).&nbsp;&nbsp;Besides potentially reducing replacement costs, you may also get the benefit of more efficient, stronger gears.<br><br>This redesign approach may take a little more time up front, but I think it will pay off in the long run.<br>Hope this helps.

 

[Luslugger]

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

 

[Luslugger]

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

 

[BrianDengel]

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.