Trochoid generation for Gear root fillet 2

[bhavbhuti302]

thread406-61473

Hi Can anyone explain me about how to create trochoid for the gear root fillet. I found this thread which was good and informative, but still I couldn't find answer how to construct it. In Dudley's book it says various given parameter (as hobbed) that is not clear to me. Can anyone explain about this.

Regards,

 

[Occupant]

This might not be of much help, but that's how I do it. I wrote a small Visual Basic program where I rotate the cutter around the gear much like it would behave when you mill the gear. This program creates an Autocad script file that draws a polyline to represent the root form. Obviously, the gear and exact cutter parameters are required to successfully do this. One problem with this is that I rarely bother to get exact cutter dimensions. The one shown in the center of the picture is simply an extension of the tooth.

 

[bhavbhuti302]

Hi Occupant,

This looks promising to me, how can I get this program? I am doing analysis on the gear tooth, by modifiying it's profile, So I am expecting to have proper geometry. This is why I need some proper geometry.

thanks for your answer.

 

[Occupant]

That's where the problem is. I never took the time to compile it, so you can only run it in Debug Mode provided you have Visual Basic. Not only that, it has no prompting screens so you have to enter all the required info into the code manually. It works for me, but hardly for anybody else. It would probably be easier if you leave the gear/cutter data here and I'll post a spline or whatever. But keep it to less than let's say 10 gears otherwise it balloons into real work and who needs that?

 

[bhavbhuti302]

I can give you gear data, but I have no Idea about hob data, what sort of hob data would you need.
For gear,

Gear 1 :
No of teeth 26
PCD : 96.84
Face width : 60
Normal Pressure Angle : 22.5
Helix Angle : 20
Normal Module : 3.5

Gear 2
No of Teeth : 27
PCD 100.565
Remaining Data are same

Thanks.

 

[Occupant]

For instance I just copied from the internet a randomly selected file (attached) that shows profiles of this manufacturers cutters.

 

[bhavbhuti302]

Hi I found this standard rack, which has all the major dimensions that are multiplied with the module, and you can get the dimension that you want for the hob. I hope this helps you.

Regards,

 

[Occupant]

The file you uploaded doesn't show anything about the tooth profile. Besides, a standard rack doesn't do any good, it is the milling cutter profile you need. Look at the attachment on my last post.

 

[israelkk]

Why do you need the trochoid? If the gear is manufactured by a gear cutting machine such as hob or a rack (Maag system) the trochoid is automatically created during the hobbing process. The common reasons to draw the trochoid is when you design a molded plastic gear and you want to manufacture the mold cavity using wire EDM. Another reason can be when you want to manufacture the gear on a standard milling machine or EDM wire cut and you need to create the G-code.

If you still need the trochoid you can use a program such as GearTrax for Solidworks that will create the gears including the trochoid even for profile or rack shifted gears.

 

[bhavbhuti302]

I am doing analysis of gear pair for the Root stresses, and for that I want to get exact profile of trochoid.

 

[israelkk]

If you can get Geartrax you will be able to create a 3D model of the accurate gear automatically. Why do you want to do root stresses? This is an academic approach. Gears are commonly designed by based on known codes using empirical formulas based on many years of experience and testing of gear design and manufacture. You can use either standard from AGMA standards, ISO, DIN, JIS, etc.

 

[dinjin]

Not only do you want to draw the trochoid but you must also know how to determine the amount of undercutting that the hob would generate. If you look at occupants hob simulation drawing, you can see that the how undercuts away the involute curve of this small pinion or gear.
The only fault I see is that the tooth form in the center should show the hob radius at the tip which would then not undercut the profile as much. For a 20 degree pressure angle the approximate radius would be 1.5 time the clearance where the clearance is the difference between the addendum and dedendum. Check the Machinery's handbook for examples of rack for stub, full depth and different pressure angle to determine the hob tip radius.

 

[gearcutter]

You need to get hold of these books;

Gear Geometry & Applied Theory by Faydor L. Litvin

Analytical Mechanics Of Gears by Earl Buckingham

On The Geometry Of External Involute Spur Gears by T. W. Khiralla.

The equations on the images below will help you figure out how to plot the trochoid generated by a rack cutter.

Cheers,
Ron Volmershausen
Brunkerville Engineering

http://i200.photobucket.com/albums/aa127/ronvol/general/ToothGeometry1.jpg

http://i200.photobucket.com/albums/aa127/ronvol/general/ToothGeometry2.jpg

http://i200.photobucket.com/albums/aa127/ronvol/general/ToothGeometry3.jpg

 

[bhavbhuti302]

Hi Ron

Thanks for sharing these images, I will surely try to solve these equations and will see what I get. They are really informative. Just wondering though, have you used these equations before for your real case. It looks like that you might have used them before. Yeah I have been using litvin's book as my best reference, but I will try to find another books and see how it helps.

Thanks again.
Regards,

 

[gearcutter]

If you intend on running FEA then bellow is a link to an excellent thesis available on-line which describes how to run FEA on spur gears.
Oh....and it's free.

Cheers,
Ron Volmershausen
Brunkerville Engineering

Numerical & Experimental Analysis Of Spur Gear In Mesh.
Jiande Wang.

http://espace.library.curtin.edu.au/R/?func=dbin-jump-full&object_id=14464&local_base=GEN01-ERA02

 

[jjbeard]

Hi! Thanks for posting this great set of formulae - it is the only one I have ever seen that is explicitly given. I have tried to code it up in Python to use it as an extension for a free vector graphics application, but I can't quite get it to work. The involute has little "spurs" on the end and the trochoid doesn't line up with the involute base.

When the formula gives an (x,y) value, is it just that, or does it get transformed somehow into another coordinate system?

You can see what I generated so far in the image.

Thanks!

 

[bhavbhuti302]

Hi All,


Thanks for all your posting. I still am trying to get it in working condition. But I really appreciate for this help, and will let you know if I get it correct.

Thanks...