Gear diameter problems

[Anonymous]

I am attempting to model a spur gear to have it 3D printed. I have tried using the built-in script and importing a DXF file, but with both methods, the gear does not appear with the correct diameter. The gear I am trying to model has 56 teeth, a pressure angle of 14.5 degrees, and a diametral pitch of 24. It appears that the "Diametral Pitch" option in the script corresponds to a different variable than my diametral pitch. 

[promm]

@Anonymous,

Can you provide some more information about the built in script that you are referencing?  Also what tool are you using to create the .dxf that you are importing.

Cheers,

Mike Prom

[Anonymous]

Mr. Prom,

When I click on the "file" icon one of the option is "Scripts and Add-Ins". Clicking on that gives me a list, three options of which are titled "SpurGear". I have tried all three with identical results. 

The .dxf file was created with a free tool online I found that is titled "GearDXF". 

[HughesTooling]

The problem with the gear script is it works in cm not inches. If your document is set to inches, run the gear script and enter the sizes you list above and OK after the gear generates select scale from the modify menu and select the gear and set the scale to 2.54 this should give you a gear with an OD of 2.417", I think that's the correct size as far as I can tell.

Mark

Edit a bit more info on calculating the OD and pitch diameters. To get the pitch diameter it's 1/24 * 56 = 2.333" To get the Od it's 1/24 * (56+2) = 2.4166

[Anonymous]

Mark,

Thank you very much. Scaling it did indeed work. 

[Anonymous]

I am having a similar problem. Attached is a screenshot of what I am trying to create. There is simply no way the pitch diameter can be 56mm. It seems like it is calculating the outer circumference and calling it the pitch diameter. How do I change that?

[etfrench]

56mm is the correct pitch diameter for a Module 2.8 20 tooth gear.

[Anonymous]

I am confused. By pitch diameter, are you referring to 2x radius or the outer circumference of the gear. If the outer distance between the teeth is 2.8mm and they are 20 teeth, what you are referring to as the pitch diameter is the circumference. Correct?

Sent from my iPhone

[HughesTooling]

The OD of the gear is number of (teeth + two) x module, the pitch diameter is teeth x module. So 2 gears with a 2.8 module and 20 teeth, the pitch diameter is 54mm and the centers between the 2 will also be 54mm. the OD of the gears will be 61.6mm.

Mark

[Anonymous]

Why I am confused is that when I build a spur gear with the following values: Module 2.8mm, Teeth 20, Backlash 0, Root fillet radius 1mm, Gear thickness 5mm, Hole diameter 5.8mm, I get an automatic Pitch diameter calculation of 56mm

However, when I look at the created gear and measure the module (distance between the teeth on the pitch diameter), I get 8.2 mm (originally entered as 2.8mm). So something is off. 

Can you run the same numbers or a similar one and tell me what you get. 

[HughesTooling]

Think you're confusing diametral pitch with module, see this LINK.

Mark

[HughesTooling]

Did you try setting the spur gear plug-in to inches for Diametral Pitch?

Mark

[Anonymous]

No. I entered my measurements in mm. so I used the metric calculator. Here is a screenshot of what I have. 

What I am saying is that if the module is defined as the "distance between the teeth on the pitch diameter" per the calculator. Then when I go to my newly created spur gear using those calculations, that module distance is clearly bigger. What am I missing. 

[etfrench]

Here's a screenshot from Gearotic.  You'll note that all of the numbers agree with the gear generator in Fusion 360.

What size gear are you trying to create?

p.s. When you're calculating the distance between teeth, you need to multiply the module# X Pi.  You also need to measure at the pitch diameter.  For this gear the distance should be around 8.2mm.

[HughesTooling]

If you want the distance between teeth around the circumference to have a 2.8 pitch divide 2.8 by Pi. The gear you'll get entering 0.8912 will not be a standard gear you'll get off the self. Oh and I guess the picture's wrong on the dialog.

Mark

[Anonymous]

Ok. I tried dividing my module distance of 2.8mm by Pi (0.89) but now it says the root fillet radius must be less than .5261879. Is there a correction factor for my root fillet radius based on what I am trying to do. 

[HughesTooling]

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@Anonymous wrote:

Ok. I tried dividing my module distance of 2.8mm by Pi (0.89) but now it says the root fillet radius must be less than .5261879. Is there a correction factor for my root fillet radius based on what I am trying to do. 

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I normally use 10% - 20% of the Module.

Mark

[Anonymous]

Ok. Thanks a lot. Let me try again. I will let you know if any issues.