In addition to the above, it depends what purpose your model is serving. It can be a simple extruded disk, an approximated spur gear, or a true spur gear model. Look in Machinery's Handbook for applicable formulas, or contact vendors that may have available models for download.
[green]"Art without engineering is dreaming; Engineering without art is calculating."[/green] Steven K. Roberts, Technomad
Have you read faq731-376 to make the best use of Eng-Tips Forums?
Go to a reference book at specifies the geometry of your gearing. Draw it in the flat, two dimensional plane to show the profile. Extrude that profile into the third dimension to show thickness. Done.
The method is independent of your software. You can take this for the tip for today.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
An involute means the arc traced from a constant radius or length of string off of a second base arc. Perhaps the most common is the involute tooth with 14 1/2 degree pressure angle. There are others, 20 and 25 degree pressure angles are common.
These are covered in various elementry drafting textbooks. I can suggest, for example, Engineering Design Graphics, James H. Earle, 4th Edition, ISBN 0-201-11318-X. In this regard, Chapter 18 discusses the design and drawing of involute gears complete with necessary computations, while providing the support mathematics for the mechanics.
There are other design manuals, but I would suggest an engineering textbook from elementry drafting courses. These references provide the necessary detail and support documentation in a much more complete manner than what a website forum would provide. Good luck with it.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
I approach this in the same manner except I start with the o.d. of the gear and profile the area between the teeth and do an extrude cut. You wind up with the same thing. Just another way to skin a cat.
Dennis
SolidWorks 2006 SP4.1
Windows XP Pro, Pentium4 3.00GHz
1.5 GB RAM, Matrox P650
Logitech Marble Mouse, CadMan
to draw the involute. I believe Geargen can output the shape as a wireframe in dxf format, which can be imported into most 3D modelers and then extruded to create a 3D gear model.
The Geargen program indeed produces a true shape of the gear. Actually in many posts I recommended this program. However, if you want an exact gear dimension let say up to 0.001mm or even 0.01mm which are practical for the common AGMA 10 accuracy. Then you end up with hundred of thousands or even millions of data points. From my experience both Solidworks and Alibre design which I tested can not handle extruded files from such 2D sketches. They are too heavy and slowing the system up to the point that there is no point to work with those parts. By the way few years ago I reported Solidworks through their branch in my country and sent them examples but to my best knowledge they did not solve this issue. My Alibre Design Professional too choke on such models.
Basically I do not see the reason for accurately make a solid model of a gear shape. You do not manufacture a gear from the solid part on a CNC machine. The manufacturing process is usually made by a hob or fellow etc. Therefore, the manufacturing drawing is a common 2D drawing.
If one intend to use wire EDM or laser cut to cut the teeth (which is expensive and not so accurate) then the 2D dxf is enough.
The only point that I see to use "so called accurate" solid modeling of a gear is for FEA dynamic analysis but then how do you account for the imperfection and inaccuracy of the tooth shape and profile, contact problems, establishing how many teeth are in actual contact, etc.
It seems to me that designers and drafter are investing unnecessarily too much time and effort to create kind of exact modeling of gears because the solid modeling program allows them to do this but, to my opinion it is like trying to kill a mosquito with a cannon.
True it is nice for presentation but the managers or customers do not see how accurate the gear is.
Thanks for the input Stick1. I strongly disagree with several points raised by your comment(s).
Politically speaking, JCBM wanted to understand the process involved with 3D spur gear sketching. Perhaps he is new to the technology, perhaps he is Junior. I strongly commend his efforts and those of others who choose continous education to advance the technology.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
Thanks for the input IsrealKk. I strongly disagree with several points raised by your comment(s).
Politically speaking, JCBM wanted to understand the process involved with 3D spur gear sketching. Perhaps he is new to the technology, perhaps he is Junior. I strongly commend his efforts and those of others who choose continous education to advance the technology.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
Dudley's Gear handbook has instructions for drawing gears. This is a drafting procedure, not an accurate modeling procedure as per stick1, above. It generates good looking models of gears with small numbers of teeth.
For large numbers of teeth, you might as well model the tooth sides straight.
I understand that gears have been manufactured by powder metallurgy, without subsequent machining. Definitely, they are injection moulded from platic. This is another application for accurate geometry.
I hope that you're not just wasting time to make your model look "cool" on company time. This is a disease on the machine building industry these days. Draftsmen and engineers waste incredible amounts of time making their 3-D models with intricate detail and fancy colors, etc. instead of more wisely spending their time creating accurate and readable 2-D shop drawings so that the machine gets built correctly and shipped out the door on time.
While a cool-looking mockup of the complete machine that can be viewed from all angles and lightings might be fun to model and thrill the marketing department, it isn't of much use to the machinists, welders and mechanics that have to actually produce the machine.
Shop drawing quality is at an all-time low right now. I've never seen such poor drawings as those produced these days. I blame programs that automatically produce orthographic projections and dimensions. More time should be spent on the art of producing a crisp, clean part drawing that includes all the appropriate information and is easy to read without becoming a cluttered mass of chaotic dimensions and unnecessary hidden lines in an unreadable black morass.
I don't use Paint... er.. I mean Inventor, but if you are looking for some of the math behind the development of an involute gear profile, take a look at:
