Does anyone know where to find these gears?

For an off season project relating to a gearbox I have been looking for a 7-8 inch spur gear and a 4" inward facing gear. However, it seems that no one carries this size. Does anyone know where to buy these?

do you mean in internal ring gear?

they’re kind of hard to find in a size you want…

Yes, that is what I mean for the second one.

check out , you can have custom gears made if you have CAD for them, in addition to the endless list of standard gears they have. They aren’t cheap, but they can get them to you darn fast and are about the most reliable way to easily find non- standard gears like you are looking for.

You can look here: sdp-si

They switched-up their UI and catalog since the last time I ordered from here, but you can find pretty much any size of gear you can dream of.

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Depending what it’s for, it may be easier to find an external gear and an internal gear of the size you want, drill a hole the size of the internal gear, then either weld or use a key way (with something else to restrain axial movement). If you go with welding, you might need further heat treatment depending on the application.

Thanks for the ideas. Are these gears going to cost hundreds of dollars, or is there any way to get them cheaper?

Really we need some more info to give any kind of guess on what cost would be. type of gear, depth of gear, pitch size, number of teeth, hub-ed, hub-less, weld on, keyed, etc. how will it be mounted? what does it need to be made of? nylon, brass, bronze, steel, aluminum? And how fast do you need it? 3 days vs “sometime before next season.” These are all huge factors when discussing price.

Definitely the former, regardless of how you do it. I would try making sprockets or something to save money.

Likely the only way to find them inexpensive, is to find something that is used for another application, and make your gearbox fit the gears.

If there is an existing planetary gearbox with a ring gear the right size, that might be a start. but 4" is kind of in between what you’d find for robotics gearboxes, and automotive gearboxes…there are slightly larger internal ring gears used in automatic transmissions in cars, for example.

You could water-jet these gears, but I would suggest something like 16DP or smaller. Any CAD program can generate the profile.

If you have a well equipped shop (large Lathe & Mill) you can cut your own spur and internal gears. You would turn an approraite blank on the lathe. You would then use the appropriate gear cutter, and an indexing rotary table in the mill to cut the gear teeth. There are unique gear cutters for each DP and range of tooth counts.