LASER CUT 15 DEGREE HELICAL GEAR OFFSET HELP!

[Dan Mauch]

I have had some limited success with cutting the right side of a herringbone gear at 15 degrees. I am using Mach3 to control laserworks 6. M3 controls the B axis and rotates it to 15 degrees. The C axis is controlled by mach3 and indexes a 40 tooth gear. In my set up I align the laser beam with the Y axis engraved on the blank. The engraved line is aligned with the Y axis. After jogging the laser to this line and out to the edge of the blank i then order  mach3 to rotate the B axis to 15 degrees.plus 1/2 of the width of a tooth.
However, that is where the problem comes in. The first cut tooth isn't centered over the engraved centerline. I used the attach screen shot to show my calculations. There should be a offset of .625" or15.875MM. I enter that value into LW and can see that the value isn't correct. so I have been fudging by eye and adding or subtracting a partial mm at a time to get it centered. But it has me baffled why my calculated offset isn't the right amount of offset. I have attached a screenshot of my cals.
Also while it is not a good video that shows the offset problem it gives you and idea of my setup. Any help would be appreciated. https://www.youtube.com/watch?v=Nigk3ZXL-2E
Dan Mauch

[ArtF]

Dan:

Not sure I follow perfectly, bu is it possible its the thickness of the blank? Or is the center
of the blank ( in Z), perfectly on the B axis rotational plane? The rotation I would think would create its own offset equal to the tangent of the 15degrees times the depth
of the top of blank to center on the low and high ends?

  Where I dont fully understand the amount of offset I could be way off.. :)

Art

[Dan Mauch]

Thanks for the reply. Yes the B axis is in line with the centerline of the C axis and the Y axis. When I designed the motor mounts for the B and C axis I made sure that everything was going to be in line. And yes I made the radius of the B axis with the C axis so that the blank would be even with the top of the c axis stepper motor. I really would like to figure out where my calculations off but tomorrow I plan to test an idea I have. That is that once I have the laser line up with the centerline of the horizontal C axis In laser works I can query the location of the X axis and record it. Next  rotate the B axis 15 degrees. Then jog the laser over to the new centerline location and record that reading. Then add one half the tooth width. Last test. I should be able to figure out the actual movement and see how that compare to the calculated and maybe come up with a corrected formula that will allow me to compensate according on other gear diameters.

Dan mauch

[ArtF]

Dan:

Good approach. The formula may point you to why it is so..

Art