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Single Pass Bevel Gears

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Captain Jerry:
Yesterday I downloaded a 3D cad (STEP format) of a mitre/bevel gear from Rush Gears and imported it into Alibre to help visualize and analyze.  It seemed to me that there should be a easier and more accurate way to machine these gears than the commonly used 3 pass / constant depth method.  It seems so simple that I was reluctant to think that it could be done.  Today I went to the shop to give it a try.  I think it works!

I had some difficulties based on my equipment and material.  I was just barely able to get my RT/Div head set over to the correct angle and get the cutter to traverse the face at the correct depth without hitting the chuck jaws.  It was only possible to cut in the Y axis direction and the cut had to be made cutting away from the chuck.  In order to get maximum travel, I had to remove the "X" scale from the back of the table. These problems are solely the fault of my poor choice of RT.  Other RT or indexers may not be so limited. 

I do not have a gear cutter so I had to grind a single tooth flycutter style.  This is really not that difficult.  I already had the head which I had used to cut spur gears previously.

The only material that I have that is near the right size  (1/2" diameter) that is not already committed to another project is steel of unknown specifications.

My poor lighting and cheap camera don't do justice to the results but the gears mesh and turn very smoothly.

I will barter (against some future service to be rendered) for my wife's better camera and see if I can get something that you can see.

How? Easy. 

The gear blank is faced at a 50? angle instead of 45?.  The RT axis is set over at a 40? angle instead of 45?.  The cutter profile is a compromise  that only approximates the correct profile but then so is every other cutter except for curves generated by elaborate gear production machinery.  The depth of cut, for which I have no mathematical basis, was set to .040" (for a 1/2" gear).  The result is a tapered tooth of variable depth (height) that is greater at the outside than at the inside and has an effective contact angle of approximately 45?.

The attached gear cross section shows the relative angles.   

HA! You may laugh!  Humph! You may scoff!   :stir: I'm going to post this and run for cover.



EDIT:

Sorry. I forgot to add the attachment. Here it is.

Bezalel:

--- Quote from: Captain Jerry on November 12, 2012, 01:49:53 AM ---My poor lighting and cheap camera don't do justice to the results but the gears mesh and turn very smoothly.


--- End quote ---

Too right Skipper, I can't even see where they mesh   :stir:
 
Bez
PS looking forward to the macro photos  ;D  hope the negociation goes well
 

Bogstandard:
Jerry,

You have proved that in this little game we play, lots of times we don't require the exact precision of correctly made gears, but something close will usually achieve what we want.

I'm not saying that imprecise gears should be used all the time, but in those non too critical functions that we come across, they work just fine, so allowing us to make our own 'special' gears.

Nice one :NotWorthy:


John

Jo:
I made similair tapered bevels for my Grasshopper, they work adequatley and allow the "balls to fly" but they don't have to actually operate the governor.

Jo

swilliams:
I like it

Steve

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