STANDARDS IN GEARS

[roltek1]

Hi,
How are you caculatin g backlash in the gears. Depending on different materials and how they are used will decide how much backlash to use. I would aslo like to be able to change center distance which will change operating pitch's and preasure angle's using standard tooling.  Are you also looking at doing stub tooth's or full fillet for strength.

[ArtF]

Hi:

 As the video on spurs states, Im really waiting till I see how users requirmen ts add up. Stub teeth, addendum correctio n or profile shifting is possible to add, and if people want it they will be added.
Stubbing should probably be added anyway just so belt cogs can be done, but profile shifting. .hard to
say if hobbiests need it as yet.
    As to backlash, nothing yet has been added, shaft centering adustment could be done to allow for the backlash, but I guess we'll see as people begin to cut.

Thx
Art

[roltek1]

If they start to cut gears with no backlash they will not turn any .oo1 out of concentri cwill bind gears

[ArtF]

hI:

 True, but adding backlash distance to shaft center distance is the generally accepted backlash injection to standard spurs. The distance shift is equal to the backlash coefficie nt.

  Im looking into profile shifting as a possible addition , but profile shiting really is used more to change the shaft centering distance, not so much a backlash item..

Art

[ArtF]

Hi:

  Let me detail that one a bit, as I stated in the video's, I dont consider myself an expert on gears..
but here's the general philosphy on gear backlash. You dont "cut" a gear with backlash. The curves of a gear are set by math, as are the tooth sizes. To proprly consider backlash in two spur gears the only thing you do is shift the center distance between any two gears. Profile shifting. .or Adendum correctio n depending on where you live , allows two gears to mesh at a further center distance. This means the "perfect fit" distance between 2 gears changes. You'd still need to add a backlash distance to the shaft centering .

   If you profile shift, the addendum of the gear is shifted out ( or in in negative shift) and the meshing gear or pinion has a choice of being shifted the same shift, or a negative shift. If the sum of the profile shifts are zero, then the shaft center doesnt change. IF the shift is summed negative the gears "perfect center" is less than normal, if the sum is positive, the shaft distance is greater than normal. But profile shift isnt a backlash correctio n, not is any real gear creation co-efficient, only shaft distance makes sense as a backlash correctiv e measure.

  Profile Shift IS used though to modify the shaft centering distance. . IT has no real other use near as I can tell. (Please correct me if Im wrong.. )

    Again, I could be very wrong, but as I research it seems there is little real standard on this issue. The math however seems to follow that view.

Thx
Art

[Mac The Knife]

I have seen some clock gears that only have one side of the tooth profiled, since they only rotate in one direction .  That would only work for the first, and last gear in a train.  It was for a wooden clock, and made for plenty of backlash for humidity compensat ion.

http://garysclocks.sawdustcorner.com/fancy-gears.html

[ArtF]

>>I have seen some clock gears that only have one side of the tooth profiled, since they only rotate in one direction .  That would only work for the first, and last gear in a train.  It was for a wooden clock, and made for plenty of backlash for humidity compensat ion.


  I too have seen that. Makes sense for clocks only in one way to me.. it lightens the gear. But in terms of keeping backlash down, slightly changing the gear center would work better as the tooth would maintain its size thus is stronger. Specially if its made of wood which tends to age badly at times. I think Id prefer a full tooth, but a bit of backlash for swelling and such. I made a wooden clock and its the swelling that kills me.
  Designing with a bit of looseness helps. Theres a lot to discuss when it comes to clockwork s and how to do them right. ( And Im SURE theres many people out there much better than I on that topic. Ive only made one clock and while it does run well, its high enough friction that I get only 4 hours on the weight before it runs out. ). Ive seen where the true experts say if the gears run with just blowing on them , they will work in a wooden clock.  I can do that for a couple gears , but by the time I get to 3600:1 blowing just wouldnt work at all. ,but you have to admire the work done on all those wooden clocks out there. )

  I guess we'll see what everyone thinks.. ..

Art

 

[ArtF]

btw ,, Heres what my clock looked like in the end.

Art

[BobL]

Hi;
 For the record I'm no expert on gears either but find the concept interesti ng . If I understan d the backlash question correctly, both (profile shift) and (backlash) control would as I see it be needed depending on your applicati on. Example, if you were to generate new gears for a new project, I would give the required backlash by moving the center of shaft, but if I'm replacing an existing gear from some assembly with fixed centers, I would then use profile shift ( - or +) to create the offset needed in order to adapt to the existing gear. My vote is for both controls to make it versatile for all designers .

Thanks
Bob
 

[ArtF]

Bob:

  Good point. Backlash via shaft displacem ent will be necessary I think, Ill add that right away. Profile shift in order to perhaps match an existing gear into a device will be necessary as well. Ill add that before release.

Art

[alenz]

Hi Art,
Machinery’s Handbook (page 2039 in twenty-sixth edition) states that ‘in spur and helical gearing, backlash allowance is usually obtained by sinking the cutter deeper into the blank than the standard depth’ It has a table showing the depth coefficie nts for various pressure angles.

Example, for a 20 deg PA, the depth of cut is increased by 1.46*B if the backlash is cut all in one gear or by 0.73*B if it is cut one-half from each gear, where B is chordal measured by inserting a feeler gage between meshing teeth. To convert to circular, Backlash = B / cos PA.

They also mention 4 or 5 other options including changing the center distance.

BTW, I’m NOT suggestin g that this be incorpora ted. Just happened to have the book on the shelf within arms reach and thought I would look it up FWIW.

Can’t wait to see more videos. Fascinati ng!

Al

[ArtF]

Al:

   Thank you. Its a volume I didnt read. , so apparentl y profile shift is used for backlash. I guess it goes to prove we will need a profile shift. ( Sinking the cutter
deeper is exactly what profile shift is when applied to digital creation of a gear, or
pulling it out .. ).
    It does make a logical sense, though in the terms of Gearotic motion its as easy to
change the centering distance. That having been said, I can see where if one were to replace a gear already existing you may need a profile shift. Ill dig into adding profile shift before I release the program. Should only delay me a day ro two I think.

Art
 

[roltek1]

Hi,
I would like to explain the differenc e between backlash and profile shift so you dont get them mixed up. Backlash is an even amount of profile thinning between a set of gears this is different from thinning one gear. Most gear designers calculate gears as sets.When you get into profile shift of gear sets the backlash is already calculate d in with center distance and then you do a profile shift where 1 gear is increased in tooth thickness and the mating gear is decreased in tooth thickness this is usally done for case constrict ions or to equal out jay factors in gears to increase strength.

[BobL]

Thanks for the info.

[ArtF]

Thanks for the pointers guys. Ive added stubbing, profile shift and tooth width ratio to the spur gear creation. Ive also added backlash correctio n via shaft distance. Tests well, so it will stay that way for release.

 Preciate the feedback.


Art