Number of teeth on gear

[Kunstmaan]

LS,

For a school project i have to produce a simple demonstration pinion/gear combination.

The used material wil be multiplex (lasered) .
I am intending to use a 190mm diameter disk using the script from: http://www.britishideas.com/2013/04/25/involute-gears-in-alibre-design/

The question how do i calculate the number of teeth on a gear for a given module

Any suggestions would be helpful.

Mareike

 

[Lew_Merrick]

Mareike -- Typically, the number of teeth on a gear are selected to create a specific ratio of rotation with respect to another gear. The
Tooth Module (Diametral Pitch for inch-based gear) is selected based on the torsional load being carried. The Contact Angle made by the Teeth also plays into the torsional load carrying capability, the friction encountered, and the meshing noise generated.

Does this help?

 

[albie0803]

ok, first off, your question should be "How many teeth in a gear of a given size for a certain module?"

second, the description in that wizoscript is wrong in that the diameter needed is actually the Pitch Circle Diameter and not the Outside Diameter.

For metric module gears, the OD of a gear is (Number of Teeth + 2) x Module.

1 module =1 mm

So using the script example:
Pitch Diameter = Number of teeth x module | 30 = 20 x module | module = 1.5
Outside Diameter = (Number of teeth +2) x module | 22 x 1.5 = 33

90t x 1m = 90 PCD | 92 OD
45t x 2m = 90 PCD | 94 OD
30t x 3m = 90 PCD | 96 OD so 28t x 3m = 84 PCD | 90 OD

Get the idea?

 

[protarawizard]

The attached AD_PRT file will allow you to model any gear size you desire.

There are values in the Equations Editor (prefixed by CONTROL_) for the number of teeth, module etc etc. The Equations Editor will also display the PitchCircle size etc etc.

 

[albie0803]

Close, but no cigar.
Your idea is good but technically incorrect as the tooth flank radius is not a radius but an involute curve. You also don't allow for oversize/undersize gears, where the OD, root Dia and addendum are non standard.

Bearing all this in mind, here is my version, which also gets no cigar, as it also only creates an approximation, but it allows you to set the desired OD (important to the turners), root and number of teeth. It also will do helical gears by giving it a helix angle.

As above there are values in the Equations Editor (prefixed by a_)

 

[Kunstmaan]

ok, first off, your question should be "How many teeth in a gear of a given size for a certain module?"

second, the description in that wizoscript is wrong in that the diameter needed is actually the Pitch Circle Diameter and not the Outside Diameter.

For metric module gears, the OD of a gear is (Number of Teeth + 2) x Module.

1 module =1 mm

So using the script example:
Pitch Diameter = Number of teeth x module | 30 = 20 x module | module = 1.5
Outside Diameter = (Number of teeth +2) x module | 22 x 1.5 = 33

90t x 1m = 90 PCD | 92 OD
45t x 2m = 90 PCD | 94 OD
30t x 3m = 90 PCD | 96 OD so 28t x 3m = 84 PCD | 90 OD

Get the idea?

so or that would then be:
Disk diameter = 190mm
Number of theet = (190/2+2 = 97theet

Correct?

 

[JST]

Of course, the answer to the "how many teeth in a gear of a certain size for a certain module" may have NO answer, or at least no sensible one.

You have number of teeth, diameter, and module. Any TWO of those FIXES the third, for a standard gear. Actually it fixes the third for ANY type of gear, stub tooth or whatever.

You have only certain numbers of teeth that are possible, all integers. For a given module, you have only certain diameters that are possible, because you must have an integer number of teeth.

Given number of teeth, the diameter is set by the module, or vice-versa.

So the question really is phrased wrongly, because the answer may come up with fractional teeth, obviously not an option with normal gears.

You could ask "what is the diameter of a gear with X number of teeth and Y module?". Or , "what module must I use for a gear of approximately Z diameter and X number of teeth?"

The second question can have an exact answer at the desired diameter, if you can choose any module, regardless of whether there are standard cutters available to make the teeth. For any diameter and number of teeth, there is a tooth size that will be exact. But it may not be a standard size.

 

[albie0803]

As JST has commented, gearing is a funny thing. The module of a gear is set by the amount of force you want the gear to transmit. The larger the force the larger the module, the larger the tooth. The larger the tooth, the bigger the gear diameter has to be for the same number of teeth.

Think of it in shoe sizes. ten size11 shoes side by side will take up more room than 10 size1 shoes. Each shoe is a tooth and the shoe size is the module.

So back to your original question; 38t x 5m = 190 PCD | 200 OD
38 5module teeth will create a gear with a 190 PCD and an OD of 200

Using the wizoscript which runs a 1:3 ratio you will get a 38t pinion and a 114t gear that has a 580 OD

I would suggest you alter the values of lines 15 & 16 to
15 Gear1Teeth = 16
16 Gear1Diameter = 80

and change line 29 to
29 Gear2Teeth = Gear1Teeth * 2

to give a 16 & 32 tooth gearset without using too much material.

Hope this helps.

 

[Kunstmaan]

Thanks everyone for the help