I am new to gears I need help

[horizon]

Hello I am new to gears. I need to figure out what type of gear I have here, and my only option to make is with a gear cutter. I dont have a hob machine or shaper. The OD is 1.865 and it has 12 teeth. When i did the calculations I came out ot 7.5 Diametral Pitch which isnt a thing apparently. When I calculated as a module I got closer to a 3.5. So i bought some gear tooth gauges that have both 14.5 and 20 degree profile. Neither of them match the gear I have. I could not find it on google search or youtube.

 

[Dan from Oakland]

Unfortunately you cannot cut that gear with a standard involute space cutter. Because of the low number of teeth that pinion has been designed with what is referred to as "long addendum". The operating pitch diameter of the gear has been enlarged to prevent undercutting. If you notice the very pointed appearance of the gear tooth in your picture that is a dead giveaway. If you have no other options to cut the gear, hand grind up a HSS single tooth flycutter and fit the shape to your existing tooth space. The only way to produce the correct tooth form is to generate it using either a hobbing machine or gear shaper.

 

[bob]

Maybe they screwed up when they made it. What does the mating gear look like?

 

[gbent]

Is that a power transmission gear or an oil pump gear?

 

[Joe Henderson]

Sort of looks like a gear for a slip roll.

 

[johnoder]

Hello I am new to gears. I need to figure out what type of gear I have here, and my only option to make is with a gear cutter. I dont have a hob machine or shaper. The OD is 1.865 and it has 12 teeth. When i did the calculations I came out ot 7.5 Diametral Pitch which isnt a thing apparently. When I calculated as a module I got closer to a 3.5. So i bought some gear tooth gauges that have both 14.5 and 20 degree profile. Neither of them match the gear I have. I could not find it on google search or youtube.

As Dan commented it is "big". If we simply make it some smaller it will be an 8 DP.
For instance, imagine the OD was 1.750 and if you use that the DP will be 8. This is not something actually done because the larger is what works in this assembly

 

[horizon]

Unfortunately you cannot cut that gear with a standard involute space cutter. Because of the low number of teeth that pinion has been designed with what is referred to as "long addendum". The operating pitch diameter of the gear has been enlarged to prevent undercutting. If you notice the very pointed appearance of the gear tooth in your picture that is a dead giveaway. If you have no other options to cut the gear, hand grind up a HSS single tooth flycutter and fit the shape to your existing tooth space. The only way to produce the correct tooth form is to generate it using either a hobbing machine or gear shaper.

the stem material seen here is 17-4. I wonder how long hss would hold up. so do they make odd shapes for a hob or shaper that they normally dont make with a single profile cutter.

 

[horizon]

Maybe they screwed up when they made it. What does the mating gear look like?

no its not messed up. we sent it off to be done, just trying to do it in house

 

[implmex]

Hi horizon:
Why do you want to do it in house?
In your first post you remarked you don't know much about gears and you admitted you're not equipped to do this.

Did you think you can eventually make better gears than what you can buy from professional gear makers?
Did you think you can make the gear cheaper than you can buy it?

If you need lots, you need at a minimum, the proper equipment not only to make them but to measure them.
If you only need one, or a few, get them wire EDM cut.

There are lots of good places to go...one I know and like is WJR at this place:

American Machine & Gear Works

American Machine & Gear Works, Surgical, Medical, Dental, & Industrial Machining, Rapid Prototyping, & Gear Making

www.thegearmaker.com

Give him a call...he's a good guy and very knowledgeable.
He's also very well equipped.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com