Center distance error in spur gears Design Accelerator

[wolterh6]

I am creating a couple of spur gears using the "Center Distance" design guide. I have fixed each gear to a cylindrical face, but when I click on the "Calculate" button, there is an error saying that the center distance is incorrect. I went back and edited my sketches so the center distance matched the one displayed in the design accelerator and attempted to calculate again, but the error persists. What am I not getting here?

[Inv_kaos]

You are best to have one end fixed and one end sliding and let DA calculate the length for you. If your sketch is correct it will place the sprocket exactly where your shaft is. It is logical to make the sliding end in the same plane as you tensioning / chain takeup.

[wolterh6]

Well I would prefer to have the shaft already because that way the motion constraints of the gears are added automatically, but I will fix only the plane until somebody else comes up with how far to set the second cylinder apart from the first one, i.e. which is the true center distance.

Edit #1: Also, I  have tried once again by only constraing the plane in which the gear is created, and it isn't placed adjacent to the existing gear

Edit #2: Well, to correct what I added on my previous edit, if only the plane is selected, the gears will be placed adjacent one to the other, but there will be a physical interference (volumes overlap), why does this happen? Shouldn't the gears be separated so far apart that overlapping does not occur? 

[Inv_kaos]

Sorry, I read the OP as sprockets (chain drive) for some reason. With gears it should work if you have the centre distance correct, see attached. Can you drag down the bottom of the window and post what error you have in red?

[Inv_kaos]

Same result if you change your input to number of teeth or enter the exact ratio, otherwise it may calculate a different centre distance. See attached.

[wolterh6]

Hm I think you may have spotted what the problem is without knowing 🙂 Is the unit correction 0 ul by default? I may have done some tinkering on a past occasion without knowing the parameter would be remembered by the Design Accelerator assistant. I will try with a 0 ul unit correction and let you know the results!

[wolterh6]

Well for some unknown reason I couldn't edit my previous post, so here is my feedback. 

I set the all the unit correction entries to 0 ul, which corrects the center distance (it is now the half of the sum of the pitch radii) but the following error appears:

The Unit Correction (x) is less than the Unit Correction Allowed Undercut (xd)

[Inv_kaos]

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@wolterh6 wrote:

Hm I think you may have spotted what the problem is without knowing 🙂 Is the unit correction 0 ul by default? I may have done some tinkering on a past occasion without knowing the parameter would be remembered by the Design Accelerator assistant. I will try with a 0 ul unit correction and let you know the results!

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I can't know what the problem is if you don't post any screen prints, all I can do is guess. But I do have a pretty good idea as to the cause.. 

I have left everything default except the centre distance, the rest was updated automatically. Why are you playing around with unit correction instead of doing it by any of the methods I posted?

What were your errors before you changed the unit correction?..

[wolterh6]

No I am not playing around with unit correction, I did it on a previous occasion. The screenshot attached illustrates all the settings I have selected:

[Inv_kaos · Accepted solution]

From memory basic gear design has a minimum number of teeth equal to 17 or 18 depending on your pressure angle. This is to avoid undercutting of the root of the tooth and is probably what your error is related to.

[Inv_kaos]

Did you manage to get it to work?

[wolterh6]

Oh yes thank you, I got it working. I had to add a non-null unit correction value because of the subminimal number of teeth on my gear though.