Gears question

[PEU]

Hi, I registered long ago when Art commented about his new endeavor, but never posted before, so Hi to all :)

Im designing a machine for splitting leather, the standar design is at least a hundred years old and I plan to go along the same lines, I have a doubt regarding the gear train and Im sure someone here will point me in the right direction.

The machine consists of a couple of rollers to feed the leather and each roller has a gear axially attached to it, then one of the rollers have a second gear to allow a reduction for a hand crank.

My question is regarding the small gears of the same size and teeth count attached to each roller.
The rollers are 60mm diameter, the gears need to allow leather thickness of 5mm and still engage, so:

what would need to be the module of the gears to allow this 5mm displacement and still engage properly?

Here is a photo of an old unit:



and my design so far:


(placeholder gears there, they are not correct)


Thanks!


Pablo

[ArtF]

Peu:

  Id go with mod. 4.
This gives a 60mm diam, with 9mm teeth. So they will still mesh when they pull out 5mm, by about 4mm ( maybe 3.5 or so..).
This isn't a proper mesh. Gears only truly mesh at their pitch curves so they cant move in and out and still mesh "Properly".
However, the mesh of gears gains importance as speed increases and the inverse is also true. Its not important that you
get a proper mesh in such a machine, its important you have mechanical advantage and enough strength in the teeth
for the job at hand. Thickness of the gear is your friend here. Proper mesh allows rolling action thus lowering friction and wear.
In your case you'd be cranking a long time before worrying too much about wear Id think, so long as you build them strong,
and perhaps fairly thick. I wouldnt worry greatly about mesh. Of course thats just my opinion , Ive never used a leather
separator, perhaps their more finicky that Id think.. The gear reduction seems to indicate pretty slow speed.. so personally
Id not worry too much..
   
   

Art

[PEU]

I never saw one of these machines in person, but from the photos the gears appear to be 3/4 or 1" thick. There are many models and brands but most of them use the same gear arrangement for simplicity sake I guess. Will try around mod 4 in simulations and see if they engage properly.

Thanks Art


Pablo

[JustinO]

Big (fewer) teeth.
Smaller pressure angle.
Involute tooth form.
Minimizing backlash and pulsing would be the goal.

Or,
If you drive one of the rollers with a gear, and the other with a chain, from a gear and a sprocket on the drive shaft, you'll be able to adjust the center to center distance freely without introducing any backlash or pulsing.

[PEU]

Backlash here is not a problem because there is no back and forth movement, well unless the leather gets stuck and you need to backpedal...
I tought about a chain, but it would need to be crossing between the rollers because they need to turn in oposite directions.
But I will stick with gears, these are being used for more than a century and the machines still work.

What do you mean by involute? if you check the old machine photo the teeth seems to be wider moving away from the center.

Thanks

[JustinO]

The drive shaft with the crank handle, a pinion gear, and a small sprocket, would go CW.
The top roller with the chain drive would go CW.
The bottom roller with the gear drive would go CCW.
Because the rollers each are driven by the drive shaft, they can be swung toward and away from each other, pivoting around the drive shaft.


Involute vs cycloid. Involutes tolerate a little CtoC slop.

[PEU]

you lost me :) a photo of a hand drawing would help a lot!


Pablo

[JustinO]

The drive shaft has a gear and a sprocket and is rotating clockwise.
The upper roller has a sprocket and is rotating clockwise.
The lower roller has a gear and is rotating counter-clockwise.
The two rollers are rotating oppositely.
The chain and gear are always at optimal CtoC distance.

[PEU]

Justino.
Its a solution that complicates the build I think, the pendulum like movement of the small gear will make the build and hand cranking more difficult. I will stick with two gears and lousy engagement, in my last simulation I used module 5 and the engagement was reasonable.

In any case, thanks for the time you took to explain it.


Pablo

[JustinO]

Chances are really good that those old splitters were optimized.

[PEU]

what do you mean by optimized?