Sproket Design Problem

13 Apr, 2022 03:35 PM

Hi everyone,

I am having an issue modelling a sprocket using equations I have found from an example that originated from a textbook (American Chain Association Chains for Power Transmission and Material Handling handbook). The example (http://www.gearseds.com/files/design_draw_sprocket_5.pdf) walks through the steps and explains every point well however I have come across an issue that I am not quite understanding.

this section defines the tooth tip and it is based on a function 180/N where N = number of teeth. This works for the example perfectly fine however any other examples I try this logic doesn't work. The example I made used metric values I had gotten from a paper (https://www.researchgate.net/publication/341968409_Designing_and_Validation_of_a_Sprocket_Wheel_for_a_Formula_Student_Vehicle) however when I reach this same point in the design process using the values from the paper the design breaks.

If this angle is set to 4 degrees which are based on the calculation of 180/45 where 45 is the number of teeth the angle of 4 is too small to produce the tooth geometry.

Am I doing something wrong?

Bob Wiley

Apr 13, 2022

Just about every other value will change as a result of changing from imperial to metric and changing the number of teeth. It sounds like you haven't updated all the equations. Also the point where the tip intersection lands indicates your pitch circle is much too small for the number of teeth. Take a close look at your pitch circle calculations.

Given the original example, all other things being equal, if the number of teeth changed from 30 to 45 then the pitch circle would be about (not exactly) 1.5 times larger.

Carlos Soler

Apr 13, 2022

Carlos Soler

Apr 13, 2022

This image may help you, I think

Yohann Panthakee

Apr 13, 2022

These equations were taken from the book that I had mentioned earlier in the post however they are in imperial as mentioned correctly by bob Wiley however I can't find any metric versions for the formulas which I had a small hope that wouldn't make a difference if I just used metric dimensions and the same formulas, but I guess I was wrong.

Is there a metric version of these formulas?

Bob Wiley

Apr 13, 2022

Yohann Panthakee These equations were taken from the book that I had mentioned earlier in the post however they are in imperial as mentioned correctly by ...

The formulas are independent of the measurement units. Except for the roller clearances but those are easily converted to metric. However, all formulas must be recalculated based upon your new variables and all calculations must use the same measurement units. I must emphasize, ALL formulas must be recalculated based upon your new variables. If you change the chain pitch, roller diameter, or number of teeth, then you must start over at the very beginning with every single equation.

Bob Wiley

Apr 13, 2022

What you really out to do is layout everything graphically in your CAD system. (You're probably doing that anyway.) Place the formulas as parameters/dimensions in the sketch(s). Many formulas won't even be needed since the CAD system will be doing all the trig for you. For instance, the formulas for "M" and "T" are not needed to get the location for point "c". All you need is angle "A" offset by distance "ac". Both are easily obtained by knowing the number of teeth and the roller diameter.

These formulas were created empirically for those that had the key variables and only had access to trig tables or a calculator. It would do you good to understand these formulas but you're making this harder than it has to be. Let the CAD system do what it was designed to do and this is what CAD was designed for!

Carlos Soler

Apr 13, 2022

You can find Metric formulas in DIN 8196.

Carlos Soler

Apr 13, 2022

You can find Metric formulas in DIN 8196.

Carlos Soler

Apr 13, 2022

Gears

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Sproket Design Problem