Initial estimation of diametral pitch in gear sizing

It is not very dificult to start to size a gearbox. Firstly, you have an initial ratio between the input shaft and the output shaft. You must consider that the better gearings you are going to find have a ratio between 2,5:1 and 4:1, then, you can use as an aproximate formula, r_total=r_mⁿ where r_m is going to be your medium ratio, (it could be, for example, 3,25, is only to have an aproximation) and the nearest natural number to n is going to be an aproximation to your steps number.

After that, you must think that in the first step is where you are going to have more noise. Having a little diameter in the pinion, the tangential speed is going to be little and noise is going to be reduced. Then, you must have in this step a ratio bigger than the others (for example, 4).

Last step is going to have the bigger torque, in this case, having a big diameter in the wheel reduces the tangential force in the teeth, another time, it is good to have a big ratio (in this case normally is easier to have biggers ratios than in first step).

For the intermediate ones you can divide the total ratio between the ratios for the first step and the last step. You are going to have a new ratio that you can introduce in the initial formula as r_total. Using the number of intermediate steps you have as n, you can find a new r_m to be used as ratio for intermediate steps.

Remember that in every steps , the number of teeth must be prime between them.

The gearbox size is going to be very important to calculate the distance between shafts, and this distances are very important to calculate the diametral pitch. In every step, you can calculate with the ratio, a number of teeth for pinion and wheel. To calculate this number, remember than the minimun theoric teeth number for the pinion is 14, but you could use little ones. Manufacturers use sometimes 7 or 8 teeths, but it is not very good. I recommend you to use a number bigger than 10.

Now, you have a relation between the diameter of the pinion and the diameter of the wheel. You could use the next formulas:

wheel diameter+pinion diameter+2,45/D.P=2*distance between centres.

(2,45 depends of the reference profile)

wheel diameter=pinion diameter*step ratio

Then

pinion diameter*(1+step ratio)+2,45 / D.P =2 * centres distance

pinion diameter = z (teeth number) / D.P.

Then

z (teeth number) / D.P.+(1+step ratio)+2,45 / D.P =2 * centres distance

then, you can calculate an initial D.P. (normally, the bigger one you could have). After that, you must choose a standard D.P. and recalculate the engagement to have a correct one, but having this aproximation is much more easier.

Hi, I use AGMA equations to define the dimensions of gears. The question is that this formulas are good for verification, that is,you have to know the dimensions. For that reason there are some formulas for predimensioning, asuming (thumb rules) values for differents factors.

I have a paper about this, if you want this information let me know.

Regards.

Gabriel

i would appreciate to see your papers as soon as i recieve ai will send you confirmation

thanks for your info.

Hi: I don´t know how to attach a file in this system, I am new in it. Can you tell me? Or send me an e-mail for this purpose.

Regards.

Gabriel

i would appreciate to see your papers as soon as i recieve ai will send you confirmation

thanks for your info.

Hi gabriel,

Thanks for your valuable post.Can you send the Papers to the following email id

nagaraj_meti@yahoo.com

Thanks in before

Nagaraja

Hi Nagaraj: I sent the paper. If some trouble let me know.

Regards.

Gabriel

Thanks for your valuable post.Can you send the Papers to the following email id

Hi Gabriel.

Can you please send this paper english version.

Best regards

nagaraja