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Thread: Basic Spur Gear design/formula help.

  1. #1
    Associate Engineer
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    Basic Spur Gear design/formula help.

    Designing a prototype for future manufacturing. I have referenced 4-5 different formula pamphlets etc. over the last week or so on Spur Gear design and ratio calculations. I have made an Excel spread sheet with the pertaining formulas embedded in the cells for personal improvement of understanding and future simplicity, yet have no way of verifying formulas etc.
    - I'm looking for some help with comprehending the formulas.
    - Looking for some (known) values of existing spur gears so I can (verify) my own knowledge of the formulas against them.

    Is there someone willing to spend some time working with me on this?

    Thank you for your help.

    John.

  2. #2
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by john_morgan View Post
    Is there someone willing to spend some time working with me on this?
    Most experienced engineers and designers are too busy for this sort of request. But, who knows..

    I would post the excel sheet, find existing design calculation examples, etc..
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    I appreciate that Kelly. After referencing 4 major spur gear manufacturers PDF's on gear design, I'm a little confuse on how the Pressure Angle effects the overall tooth design, outside the simple Involute curve of the tooth. I know, sounds weird to me also.
    Any help would be great.
    John..
    25 Spur Gear/Ring Gear Work Sheet Only
    Formula's Sun (In.) Planet (In.) Ring (In.)
    Pitch Diameter (PD) 0.236 0.354 0.944
    Center Distance (CD) 0.2950 0.2950 0.4720
    Pitch Circle (PC) 0.7414 1.1121 2.9657
    Number of Teeth (t) 8 12 32
    Pressure Angle (PA) 25.0000 25.0000 25.0000
    Diametral Pitch (Pd) 33.8983 33.8983 33.8983
    Circular Pitch (CP) 0.0927 0.0927 0.0927
    Outside Diameter (OD) 0.2950 0.4130 RD+choice
    Root Diameter (RD) 0.1770 0.2950 1.0123
    Addendum (A) 0.0295 0.0295 0.0295
    Dedendum (D) 0.0341 0.0341 0.0341
    Whole Depth (WD) 0.0636 0.0636 0.0636
    Circular Thickness (CT) 0.0463 0.0463 0.0463
    Module (m) 0.7493 0.7493 0.7493
    Base Circle dia. (BCd) 0.2139 0.3208 0.8556
    Gear Ratio (GR) 1.5000 2.6667 4.0000
    Clearance (C) 0.0046 0.0046 0.0046
    Backlash (BL)
    Contact Ratio (CR)
    Pitch (P)

  4. #4
    Administrator Kelly Bramble's Avatar
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    Pressure angle in relation to gear teeth, also known as the angle of obliquity, is the angle between the tooth face and the gear wheel tangent. It is more precisely the angle at a pitch point between the line of pressure (which is normal to the tooth surface) and the plane tangent to the pitch surface.



    My advice on gear design is to keep it simple.. Use industry standard profile, equations and design around standard cutting tools..
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  5. #5
    Administrator Kelly Bramble's Avatar
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    I assume you have already checked out the gear design resources here on Engineers Edge?

    Gear Design Engineering and Design Resources

    Elements of Metric Gear Design
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  6. #6
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    I appreciate the reply Kelly. Your explanation of the Pressure Angle is clearer than the PDF's I have. The bottom picture clears a lot up. I've been a maintenance manager in a high tech machine shop in the past. 3,4,5 axis CNC; Swiss Lathe; EDM cut off, plunge; urethane prototyping, SLS 3d printing, metal Sintering machines and injection molds. So I'm familiar with a lot of this. Just not actually working the formulas etc.

    My advice on gear design is to keep it simple.. Use industry standard profile, equations and design around standard cutting tools..
    The 4-5 PDF's I have from Gear Engineering firms have used various inconsistent formulas/nomenclature etc. from firm to firm. Its frustrating for me. The same happens in the electrical field. Most firms vary their nomenclature etc. Prior to registering on your forum, I researched the AGMA for the standards. They wanted some amount of money. I'm bootstrapping at this point. I'll research the links you added and rework my formulas and the excel formulas to match.

    I assume you have already checked out the gear design resources here on Engineers Edge?
    No. Initially at registration, new-be's are limited. So I just scanned about 4-5 pages in each forum looking for similar questions at first. I'll reference your links first before asking anymore questions.

    Thanks for the help.

    John.

  7. #7
    Senior Engineer
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    The choice of diametral pitch as 33.8983 is a puzzling. Usually a whole number is selected to simplify the purchase of cutters.

    Higher pressure angles can make the tooth a bit stronger at the base. However, the pressure angle affects the minimum number of teeth you can have without undercutting and reducing the strength of the gear tooth. With only 8 teeth you need a lower P.A. and you'll still have undercutting.

    What are you trying to do with this really tiny gear set?

  8. #8
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    What are you trying to do with this really tiny gear set?
    Trying to get a 3 or 4 to 1 speed reduction and a 1 to 3 or 4 torque increase within a 30 mm diameter space.
    Any help will, well, be of great help.

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