# Thread: Basic Spur Gear design/formula help.

1. ## 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?

John.

2. Originally Posted by john_morgan
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..

3. 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. 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..

5. 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

6. 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. 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. 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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