GearHeads Corner

Hi Folks - newbie here
I recently purchased this amazing software and have been designing up
an external Lantern type gear train. My question is of the accuracy of the tooth depth.
I noticed that after "creating" the pinion and wheel, there is a small gap at the bottom of the tooth where
the pin should seat into the radius. After measuring, it looks like about .033" of space which doesn't show up in the original
gear layout under the "lantern" tab. I selected a zero backlash in the pop-up dialog box before generating the gear model so I assumed that
the pin-wheel and pinion would fit together air tight (for registration purposes) Any thoughts? Also - after comparison to a cad generated model
using the same geometry, there is a distinct .033" difference between the pitch diameters.

(The blue model was generated in Gearotica, Orange - I hand modeled up in Inventor using geometry I found in an old machinery handbook of gearing (1916)

any thoughts would be great. If i commit to making this pinion out of metal, I really want it to run smooth.

Cheers! - JD

Update: Ok well........ it looks like it's my weak math skills  ;D.
But - I'm still a bit perplexed. Here goes:

12 teeth x 1.5" spacing (center to center) -or- 12 x 1.5" = 18" circumference.

18" / (Pi) = 5.7295" Pitch Dia. (D)

N (Number of teeth) / D = 2.0944 Diametral Pitch (Dp)

Now, when I measure the center to center distance of 2 pins, it comes out 1.4829" - not 1.5" like I thought.

Is this because it's a circumference measurement rather than a point to point measurement?
And - does it matter as long as both gears match each other?

::) Thanks folks - JD

JD,

I'm not an expert, but I'll try to help.  It looks like your calculations are correct.  The only issue that I see is that 5.7295 is the diameter of the gear, not the diametral pitch. 

The spacing of the teeth on a gear is indeed along the circumference, so in your case, it is 1.5".  Also, since you are measuring along the cord, the distance is 1.4829, which is also correct.  I can't speak for others, but I never use the chord dimension, it would just confuse things for me.  What really matters, in your example, is that the teeth are 30 degrees apart.

Since you are just looking at the same thing two different ways, they should match.

Steve Fox

Hi:

  Without crunching the actual numbers, that does sound right to me. You have to
watch out for chordal vs distance numbers they will throw you out by the tan of the angles
involved. I suspect you'll find the mesh is fine. GM always generates its lantern spurs to perfect fit.

  Very shortly Ill be doing the new module for lanterns and Ill add better backlash methods for it
just as we've done for ellipticals and normal spurs..

Art

Thanks guys - I sure appreciate the Input!
I never got higher than general math in school.
Too concerned about music and girls - lol
Now I'm paying for it - ha

I'll keep chewing on this. I realize that a lot of folks here are making their
gears out of wood but I'm looking for nice waterjet pattern maybe.

cheers - JD

Jon:

>>Thanks guys - I sure appreciat e the Input!
>>  I never got higher than general math in school.

  Me either, the 60's were good to me and I never finished high school.. Ive lived to regret that
many many times. Teaching myself calculus, motion dynamics for Mach3 and now gear math for Gearotic
has been painful at times. ( Stay in school kiddies.. :) )

Art

School? That's where I learned to defy authority -- actually a very valuable lesion.

>>that's where I learned to defy authority

lol..wish I had a nickle for every time Ive heard that term...

Art