I designed a bevel drive base gearbox a while back and the team has decided on making it. We have now acquired a CNC sponsor and we have no idea what tooling they have but they are not a hobbing shop. They should be able to handle all of the structural prices just fine but we want to CNC the bevel gears as well. Being that this would be the first thing we ask them to make I dont want to walk in there with an impossible part. How difficult would this be to machine? It does not have to be perfect when it comes out of the mill we would be willing to clean them up. I know a decent amount on CNC but not a bunch so I don’t really know.
That would take a 4th axis (or at least an indexer) and also a specialized involute profile gear cutter. Not sure how it would be programmed but it doesn’t seem like it would be terribly complicated.
What kind of tooth profile?
What diameter?
What material?
What kind of bore/hub?
Not optimal by any means but they could be 3d contoured on a 3 axis.
Yeah I wasn’t going to mention that but since you brought it up… Need a really high spindle RPM, tiny ball endmil, lots of program memory, and still not sure how you’ll get it to cut on a true involute profile.
Okay I had a feeling it would not work out well especially since they are so small. For custom gearing we could spend upwards of $500 including spares. Any ideas on other manufacturing techniques that may work. I was thinking of 3D printing a mold of the gear then casting it in plastic. Would that be too soft for a drive base?
Why do you need the gears to be custom?
It’ll be really difficult to cut the profile of a gear like this without specialized equipment. That said, you likely don’t need a totally custom gear.
I don’t think plastic has much of a chance of holding up in a drive application.
Is there a way to modify your design so that it uses bevel gears from McMaster?
If you’re doing a large reduction with this gearset, you might consider using a worm gear instead.
It is possible I’m sure.
The main thing that will be difficult depends on the size of the part, what kind of parts the shop normally does, and how deep you wanted the teeth.
Is it not possible to get an off the shelf bevel gear?
How about casting it in metal?
It all depends on the type of plastic and where it is in the gearbox. You should work on the gearing calculations if you want to do custom gearing to make sure that the widths of gear can handle the stress. That being said, the best way to go about this is to redesign the gearbox to use off the shelf bevel gears. This would be much easier for cost, replacement parts, and time.
Thank you guys for all of the replies and the reason being for a custom gear is to try and keep the box as small as possible. I am going to toy around with the CAD and see if I cant get the small bevel gears to work from mcmaster.
You should check out SDP-SI, they have a better selection for gears. http://www.sdp-si.com/eStore/CoverPg/Gears.htm
Fur custom gears you could try Rush gears. For off the shelf units you could try Boston Gear or WM Berg.
Rethinking my original plan to cut it, I don’t think a traditional gear cutter tool would work, because of the tapered teeth.
Cutting bevel gears isn’t something that a typical “CNC sponsor” does often. Gear shops usually use more specialized equipment. In theory you might be able cut FRC sized gears with a small endmill, but that would probably not be the best use of a new sponsor. Real bevel gears have a variable tooth profile which are a more challenging. If it can’t be redesigned to use COTS bevel gears (which is what I recommend), you can make fake bevel gears with a knee mill, an indexer, cutters like this http://www.ebay.com/itm/Lot-8pcs-Dp20-14-1-2degree-PA-1-8-Involute-Gear-Cutters-/181370271060?pt=LH_DefaultDomain_0&hash=item2a3a82b554 as detailed here http://homepage.ntlworld.com/corromant/bevel_gears.htm
I think this is a situation where the tradeoff between a easier to get, less optimal COTS part and a custom, higher performance part pretty definitively leans to one side.
QTC is also in the same corporate family: http://www.qtcgears.com/RFQ/BevelGears.htm. You’ll have better luck getting appropriately-sized bevel gears from them, than from most other suppliers. Call them to discuss, and to get a quote, and summarize the interaction here.
Casting aluminum gears…
Another option and quite possibly faster and safer, have Shapeways print the gears:
I vote QTC. Rush Gears has a minimum order on the level of $1500 regardless of number. The gears from QTC are of pretty good quality even at the lowest quality they offer for metal gears, and you can buy ground gears if you need to. They have a very wide selection too.
It’s very easy to modify the bevel gears if you sue a machinable collet to hold them; I have been shortening the hubs and widening the bores slightly for a project.
Vex sells small and cheap 15T Bevel Gears