Help with Involute Curve Gear(Scroll Gear)

Hello, I need help with the structure of the scroll gear(not the gear teeth just the diameter of the gear), if somebody could post a step-by-step tutorial that would be amazing! Even just some images would help. Thank you!

The dimensions are,

Diameter of gear = 2.5"

My wild guess is it might start off like this. I could be wrong though.

I'd start with the spiral and use that for the pitch line of the gears, and offset from the spiral for the body of the gears as well, but how you would do that in Inventor? This could prove interesting!

Nanobyte welcome to CADTutor, but couldn't you of come up with something a bit more complex for your first Question

In AutoCAD, it would be based on a spiral (helix) as Steven suggested... no idea about Inventor.

I moved your thread to the Autodesk Inventor Forum.

What program are you using for this design? Inventor or AutoCAD?

Do you understand how a true involute curve is generated?

What is your base circle diameter?

Decide on how many divisions you want to make of the circle. (angle)

Get the Arc Length dimension of one division.

Unwrap string (draw tangent line) equal to Arc Length.

Draw 2nd division tangent line equal to 2*Arc Length.

Draw 3rd division tangent line equal to 3*Arc Length.........

Connect the ends of the lines with a spline.

or

You could compare the Spiral to a true Involute curve.

I am using AutoDesk Inventor 2014, I have the concept of a Involute curve, but it is more of the diameter of the scroll gear that I am confused of. When the gear turns it does not lay against the curve of the opposite gear; it goes from laying against the opposite gear to slowly creating a gap in-between the two gears). I think the reason for this result if from the spiral not matching up with the diameter of the circle, like how nestly has shown, "http://www.cadtutor.net/forum/attachment.php?attachmentid=53080&d=1425385892".

I read somewhere that the sum of the radii of the two gears at the point of contact is constant. I don't know how that works in with predefined curves, but something seems amiss.

True involute gears are rather complicated to say the least, most descriptions go into a whole range of complicated formulas, from what little I know of involute gears, one of the more important values is the angle of pressure, and another is the pitch circle. With a spiral you don't have a constant pitch circle. What is the reason for doing this, does it need to be engineering quality or is more towards the hobby side of the spectrum.

Here is an example from a book on gear design. Not sure if it helps, but I'll post it anyway.

http://books.google.com/books?id=XUSHSYwdiV8C&lpg=PR14&pg=PA318#v=onepage&q&f=false

Another book http://www.amazon.com/Noncircular-Gears-Generation-Faydor-Litvin/dp/1107683521/ref=tmm_pap_title_0?_encoding=UTF8&sr=&qid=

... When the gear turns it does not lay against the curve of the opposite gear; it goes from laying against the opposite gear to slowly creating a gap in-between the two gears)......

Attach your assembly here and end all doubt.

It is more of a hobby.

In that case I would suggest picking a point in the middle somewhere, and drawing your involute, mirror it to create the size of tooth you want (you did say you were confident with that part), then measure the distance between the two points that have the correct pressure angle. From there it is more specific to Inventor and I can't help, in Autocad I would try turning that tooth into a block and use the measure command with the option to place blocks at set distances around the spiral, but it would need fine tuning to get the thing lined up correctly.

I really hope JD can help you further, I would be fascinated to see how this should be tackled properly in Inventor.

It is more of a hobby.

Why or how does that change the problem description?

Geometry is geometry.