Cogs and shapes
Cogs and shapes
(OP)
I feel the need to design a module or two of a cogwheel.
While I have seen many a nice picture on the net, I haven't come across a good description of how to actually design a cog tooth.
My aim is a standard metrical spur cogwheel.
This problem has bested even "Karl Bjorks lilla gula"
While I have seen many a nice picture on the net, I haven't come across a good description of how to actually design a cog tooth.
My aim is a standard metrical spur cogwheel.
This problem has bested even "Karl Bjorks lilla gula"





RE: Cogs and shapes
If you have access to AutoCAD, there are only about a thousand "gear.lsp" programs available for it.
Mike Halloran
Pembroke Pines, FL, USA
RE: Cogs and shapes
But I would like to make a drawing with all the data so as to be able to produce the modules.
RE: Cogs and shapes
You don't need a drawing of a gear in order to get a physical gear produced. A drawing would help you communicate any special requirements, but gearmakers don't need a drawing to produce the gear per se, and in particular they don't need an accurate drawing of the tooth profiles, which are generated by machines. The traditional convention for pencil drawings is a single simple tooth with trapezoidal flanks, and phantom circles to imply that there are more than one. AutoCAD can, with help, generate an accurate image of a tooth profile, and can array that to give an exact representation of a gear, but the effort is not necessary to procurement of an actual gear.
If your objective is production of an _image_ of an actual gear, you can do that, with a little more difficulty. You could, for instance, use Excel to calculate the coordinates of the transverse section of a single tooth, enter them and connect them with a spline or polyline, and array that to produce a full image, or whatever you want.
Mike Halloran
Pembroke Pines, FL, USA
RE: Cogs and shapes
I guess I want to produce a image of an actual gear by your definition. It is the measurements I lack. Failing searching the net for two hours made me turn to Eng-tips.
I want to do it, partly to be able to, and partly to understand it.
If only I can draw one tooth, I can then copy it all the way around.
RE: Cogs and shapes
http://www.du.edu/~jcalvert/tech/trochoid.htm
If you can't find an add-in for your CAD program, it may be easier to do it with pencil and paper.
This would be a good time for you to snag a copy of "Machinery's Handbook", which will tell you all you need to know, and then some.
Mike Halloran
Pembroke Pines, FL, USA
RE: Cogs and shapes
I appreciate it. It is closer than what I succeded with. Not perfect, but it's a step in the right direction.
RE: Cogs and shapes
The key word is involute. That is the curve made by the end of a string as it unwinds from a spool.
If you know the pressure angle and pitch diameter, you can graphically solve for the base diameter from which the string "unwinds".
I have a SolidWorks model which uses this process to generate a geartooth. Ask, and I will post it.
http://www.EsoxRepublic.com-SolidWorks API VB programming help
RE: Cogs and shapes
Know though, that I use neither Solidworks or Windows, but Qcad (www.ribbonsoft.com) on Linux
RE: Cogs and shapes
It might have been done already, had you told us the gear module and number of teeth.
Mike Halloran
Pembroke Pines, FL, USA
RE: Cogs and shapes
You might want to check the
acad forum.
Are you trying to draw external
involute spur gears?
Dudley and Buckingham both have
some excellent texts to show you
how to design these.
You will find some help too on the
gear and pulley engineering forum.
RE: Cogs and shapes
Lisp? I can't say, but I am willing to try.
Acad? I'll check it out. Got an address? I tried Google, but found everything but CAD forum.
External spur, yes
RE: Cogs and shapes
RE: Cogs and shapes
RE: Cogs and shapes
RE: Cogs and shapes
ok, why ? i'd have thought that gear geometry was something machinists understood, so all you should need to do is to specify a "X-Y-Z" gear geometry; no?
RE: Cogs and shapes
RE: Cogs and shapes
RE: Cogs and shapes
RE: Cogs and shapes
rather than the full depth form for your design.
Also check out thread406-103836 for a lisp
program and simply accept all of the defaults
the first time thru to get some idea of what
it does. The thread mentioned above in in the
Gear & Pulley Forum which is part of this
general Forum.
RE: Cogs and shapes
RE: Cogs and shapes
"Art without engineering is dreaming; Engineering without art is calculating."
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: Cogs and shapes
Mike Halloran
Pembroke Pines, FL, USA
RE: Cogs and shapes
cog, cogs, cogwheels, gear, spur, and a few others. Yet another set of Swedish words too.
As you may be able to figure out, I came up with nothing. Much to my surprise.
Yes I would like to buy the suggested book and more. I bet "Karlebo handbok" (Swedish machinists cult handbook) would contain the information as well, but it cost an arm and a leg. But there is a limit to my use of that sort of information.
So I am grateful for the help I have gotten.
RE: Cogs and shapes
"Art without engineering is dreaming; Engineering without art is calculating."
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: Cogs and shapes
RE: Cogs and shapes
Here is a link to a gear catalog from Boston Gear. Towards the end of the catalog is a section on gear development and nomenclature that should help you out.
http
Timelord
RE: Cogs and shapes
Those teeth are made according to the system used in the US only. But the information is indeed very good.
RE: Cogs and shapes
http://www.meshingwithgears.com/faq.htm
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