Large Spur Gear and Pinion Problem 2

[BEMPE16524]

Hi Guys,
I'm designing a set of gear. My problem arise when my gear is very big, more than 2.5mtr diameter.
I have to keep my pinion around 120-150mm diameter. Velocity ratio will not effect my problem.
Force on teeth is very low as not much load to carry.

When i use standard pressure angle, 14.5 or 20 degree, it gives wrong value of base diameter and dedendum diameter.
It suppose to give a dedendum dia. smaller than base diameter but instead it is the other way.

So, then i try my stupid analysis to try make different pressure angle, i tried 6 degree, it gives quite reasonable value.
but when i try to plot the involute, it doesn't seem right.

I need someone expert here. Attached is the analysis i did (sheet 3).

 

[Occupant]

Why is the root dia. supposed to be smaller than the base dia.? In your case for 20[sup]0[/sup] and 15 teeth it's true but not for 297 teeth, so what? Up to 7.25[sup]0[/sup] it's true, but not after that.

 

[BEMPE16524]

what are you trying to say? if not true for 297 teeth, what is the applicable formula then? please advise.

 

[gearcutter]

conantar,

You need to go and research the reasons behind a phenomenon that occurs with involute gearing generally referred to as 'undercut'. Put basically; it's a function of the number of teeth and pressure angle and how these affect the diameters that you're talking about.
A quick search with Google reveals heaps of info.

That's a neat little spread sheet that you've come up with.


Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[mfgenggear]

Conatar
A simple formula
#teeth/diametral pitch=pitch diameter.

And as long as the true involute is above the base diameter. You are good.
And It is not necessary to have the root below that base diameter. I did not look at your data. But these are elementary gear subjects.

If know the basic center distance of the pair gears. You can reverse calculate to get the correct # of teeth.

Mfgenggear

 

[Occupant]

I've drawn the pinion and inserted a straight sided tooth. When you have 297 teeth in the gear it is almost like a rack, go with that and insert that tooth at the proper location for CD and PD.

 

[tbuelna]

conantar-

As gearcutter noted, you will have undercutting with a 15T pinion unless you tweak your mesh geometry. One other option would be to go with a 20T pinion that would not undercut, plus a slightly different module and a 396T gear to maintain the same PCD.

Hope that helps.
Terry

 

[BEMPE16524]

Guys,

Thanks a lot for your information.

Regards,

Conantar