topic Spur gear wrong diameter in Inventor Forum

Spur gear wrong diameter

DavidTunnard — Wed, 17 May 2023 08:05:25 GMT

I have a gear that we have been getting manufactured for years. Going to get a version watercut for a test rig. However, I need the actual tooth profile (and not just a representation/note on the drawing).

I don't normally have a problem using the design assistant, but this time it's giving me the wrong OD for the gear.

It's a mod 3 gear with 198 teeth. I make that to be 594mm OD. This is also the OD we have been manufacturing to. The design assistant is giving the centre distance as 594, however, when I measure the OD it is coming in at 600mm.

Can someone show me where I have gone wrong?

Here are my inputs

Re: Spur gear wrong diameter

Alexander_Chernikov — Wed, 17 May 2023 08:33:21 GMT

Can you add here the arhive with assembly and parts (gears)?

Re: Spur gear wrong diameter

DavidTunnard — Wed, 17 May 2023 08:38:17 GMT

yeah, but I mean it is just 1 gear created with the design assistant fyi.

Re: Spur gear wrong diameter

Alexander_Chernikov — Wed, 17 May 2023 09:34:38 GMT

Maybe I misunderstood the question, but if you open the part and turn on the surface of the dividing cylinder, its diameter is 594. And the outer diameter of the circle of the teeth is 600.

The external diameter da=m(z+2)=600.

Accurate involute profile can be obtained by exporting the tooth shape

Re: Spur gear wrong diameter

JDMather — Wed, 17 May 2023 12:01:34 GMT

@DavidTunnard wrote:

I make that to be 594mm OD.

Can someone show me where I have gone wrong?

Gears are not specified by their OD.

They are specified by their Pitch Diameter.

Pitch Diameter + Addendum = OD

What is the center-to-center distance for the shaft between the two mating gears?

How many teeth are on the mating gear (is it 1:1 as you show)?

@DavidTunnard

Where are you located in the world.

When would be a good time to continue this discussion?

What version of Inventor are you using? (I do not own a license to a rar extractor - so I cannot extract your files.)

Re: Spur gear wrong diameter

jan.vonasek — Fri, 19 May 2023 12:15:52 GMT

Hi,
With given inputs (module and number of teeth) is possible to reach OD=594 mm using Unit Correction = -1
OD is shown as "da" in right panel.

Note: to extract rar file can be used for example 7zip extractor or Total Commander.