STANDARDS IN GEARS

[John S]

Usually a profile shift of 0.5 will create stub teeth.

If you use a known DP like say 20 DP, a profile shift of 0.5 and a pressure angle of 30 degrees you will get a 20/40 DP involute spline.

I used this same method to generate a multiflut e gear cutter for some special shafts.



Where I can really see this program having practical use [ as opposed to playing, but there's nothing wrong with that !! ] is corrected gears.

It is possible to cut different numbers of teeth on the same PCD and still have them mesh correctly .



All these three gears are from identical blanks, if they are put on pins at the correct centre distance apart they will all run smooth and can be swapped in any order, the 22 tooth one is correct, 20 and 21 are corrected .
It's easy to do when hobbing but the off the shelf Brown and Sharpe type cutters don't exist for the 20 and 21 tooth forms.

Often you need to alter a ratio where it's hard to change as a pair, when we were racing we used to use this half tooth method to close ratio's up because things like the final output gear would have been far to expensive to make but the mating gear was usually just a simple pinion that could be changed easily.

BTW, first post here and thanks for having me.

John S.

[ArtF]

Hi John:

  Welcome, we need experts like you.

 I have a few questions about shifting actually.

  Im finalizin g the profile shift, or trying to, but some of the numbers dont seem to work.
Im told a gear with a negative shift and a posative shift gear will mesh fine at the same
center distance. Mine do not as yet. Im trying to figure out why.
   If I profile shift .5 and -.5 on two 22 tooth gears, save them to dxf, and overlay them with
shifted gears from another program out there, they overlap perfectly, but they do not mesh.
Im trying to figure out why..

  Do you have any way to properly generate a 22 tooth, 20 degree 5 module gear shifted .5?
( or any shifted gear) in dxf so I can also try an overlay of that one? Seomwhere the math is wrong and
Im trying to figure out why. If I mesh a 22 tooth 5 mod 20 PA gear shifted .5 with a nonshifte d gear
they do mesh at a modified center distance created by the extended pitch of the shifted gear,
but for some reason it isnt a perfect mesh..tho ugh close..


  Im hard at this one as I want shifting to work as perfectly as it can. Stubbing works fine, shifting is a bitch as some of the dcoumenta tion seems to disagree on the numbers..

Art


Im not sure why your phtos dont show..

[John S]

Unsure about your reply in that stubbing works fine but profile shift is a bitch. I may be wrong but I was under the impressio n that the profile shift produced the stub tooth form. ?

I know you have the same program as me, involute, which can generate the dxf but I don't have any way to rotate these to check for mesh. Usually they come under corrected gears in many of the books, not read Machinery Handbook, I find this publicati on of more use to stop the dog getting the food out of the kitchen cupboards .

Pictures should be OK now, problem was at our end as we have to give sites permissio n to prevent hot linking.

John S.

[ArtF]

Well, shifting does stub teeth a bit, but really its more of just a center displacem ent and thining or fattening thing for the teeth. Stubbing is just a tooth height ratio, so its stubs the teeth down for timing belts or whatever.
  The shifting though does make gears that looks like yours in the photos. But the math says they shoudl mesh tohether at the same center distance. So in your photo, the foirst and third gear shoudl mexh together at the same distance as to of the second gear would.

( assuming both are shifted negative to each other. )


  I sent you a prelim version, try it and see..

Art

[ArtF]

John:

   I dont know if you use VCarve, but if you load a dxf from Gearotic you can then imporrt and DXF and rotate it around to math up..

Art

[John S]

The gears in the photo do mesh together in any order but they were cut on a hobbing machine. Basically depth of cut was set for a standard gear and that was cut, then without changing anything on the machine the ratio was changed to cut 20 then 21 teeth.
On my hobber it's easy as it's electroni c, you just alter the thumbwhee ls to read the correct number of teeth so there is no working out shift etc.

I can't use these gears as examples as I no longer have them but it's easy to cut some more as long as it's a DP I have a hob for.

As an aside I also have about 6' shelf space of gear books by various authors so if anyone wants some details from a known copy I may be able to help.

Off to watch some tutorials ......... .....

[Edit] Just read your last post, yes I have the full suite of Vectrics software all though doing a static rotate I can do in Fastcad.

[ArtF]

John:

  One other note. If you used the program "Involute" to do your shifting, then mine will work identical ly as I checked mine against that programs output as a safety. BUT.. I suspect we're both wrong in the shifting somewhere as they should mesh at normal center if sum of shift is zero. ( According to the machinist s handbook) . The math is a bit above me ( not that thats unusual), but Im getting close to figuring out why..

( I really wish the machinist s handbbok used metric, I hate swithcing to standard. .numbers are always too small fer me. )


Art

[ArtF]

Ahh right, I forgot you were a hobber.. lol


  Those gears do look amazingly like mine though.. but its the small details that will kill you.

Art

[ArtF]

Hi Guys:

  Hopefully, less than 3 weeks till release of the program. A sincere Thanks to John Stevenson for helping me with the particula rs and testing of the profile shifting, stubbing and width clearance s. I still have some work to do on Gcodeing for 4th axis gears. ( Helical is the only 4th axis gear that will be in the release. ). If the program is popular, than after a few months Ill start adding other types of gears and assemblie s based on what you guys determine youd like to have in your designs.

  Just a not of how things are going..
Art

[John S]

Got bogged down on what I was doing, what should have been a simple drive change on a raid system has now turned out to be open heart surgery.
So no email hence the message here.

Normal service will be resumed as soon as I smack small son round the ear.