Backlash on Gears

[dchib]

Just for clarity, can you confirm the following regarding creating backlash (=greater clearances) in gears

On spur gears backlash is achieved by reducing the tooth width from 0.50 to say 0.49  (or less if more backlash is desired to reduce chance of gears binding)

On circular planetary gears backlash is achieved by increasing the tooth width to say 0.51 (or more if more backlash is desired)

On elliptical gears backlash is achieved by increasing the tooth width to say 0.51 , same as for planetary gears.  Does this apply for all non-circular gears?

Apologies if this is clarified elsewhere (I'm sure I saw it somewhere, perhaps on one of the videos) but I haven't found it again.

Thanks
David

[ArtF]

Hi David:

  Generally , yes. We used to simply shift the shaft a bit in position, but that wasnt ideal.
Now all comp for backlash is done using tooth width variance.

Art

[HaveToDo]

I don't know how many generate dxf gears for wood, but I just started.  If I use them exactly as generated, the shafts cannot be inserted into the holes because the gears are too tight.  I measured the gears with a digital micrometer when they came off the CNC and they are very slightly larger (around 10 mils).  When I saw this thread, I dropped the tooth width to .45 and tried again.  Better, but still too tight.  I then put the tooth width up to .47, imported the dxf into VCarve Pro and change the sized of the gears to 98% of the original.  Very good fit and they move freely.

I will add that these gears are small - 0.6" and 2 at 1.5" diameters.  As the gears get bigger, the tweaks would probably not need to be as large.  I guess I'll find out.

What do others do when milling wood gears?

Pete

[ArtF]

Pete:

I typically as well use about 98% as a sizing for my 3d printer. In wood I tend to tell
the program the tool is just slightly smaller by the amount I wish to loosen the fit.

Art