45 degree worm M2.5

[philbur]

Taking into account the problems also on the other 4th axis thread would things not be much more manageable if you have a separate algorithm for each machining strategy. Also then the risk of any future changes having unforseen consequences would be greatly reduced.

Like any tool, if you try to design it for multiple functions it never works as well as a dedicated tool, too many compromises.

Just a thought
Phil :)

[philbur]

Really your not supposed to shave a gear with undercut

I'm no expert but I thought the no undercut (for straight involute gears) was: a) because it weakens the tooth and, b) because a B&S type cutter can't do undercut due to the way it functions. 12 involute teeth is the lowest tooth count on a straight involute without undercut. Clocks gears don't have a big need for tooth strength and tangential shaving can achieve undercut. Clocks do however need small tooth counts because of the desire for high ratios.

Looking at the profile of the 45 degree helical gears, even with a 4 tooth, there is effectively no undercut! So I wonder how a 4 toothed helical would come out when cut with a B&S type cutter . It will be interesting to see once you have fixed the tool path for the helical, involute saw strategy???

Phil :)

[philbur]

The involute bit strategy for helicals looks like it is correct. Possibly it could be used also for the involute saw as is, providing I can angle the blank ( my mill head is fixed so I can't angle the cutter)???

So now all I need is to convert my B&S semi-universal dividing head to CNC, another project!! I already have the parts, but not the time.

Phil :)

[ArtF]

Hi Phil:

  the screen layout will change, at the moment its all one class , but its my intent to make 4 classes, one for each type of output. The cnc screen was "roughed" in to be better than GM's and allow me to see the path, but its become obvious it will need its own variables screen for each type..

  I dont think I see much difference in most of those stategies, they pretty much are whats done, except they cant be individulaly controlled in parameter as yet. But the number of segments for the tangential is setable and these passes
always keep Z at base circle for each pass.

  Several changes are made for todays version, ( which Ill be uploading in a few minutes), Ive removed some
passes that cut in the air, Ive stopped the Z from moving in tangential and locked it to the same height GM uses,
which has worked well for a long time. We'll see how that looks.  Ive changed the roots so that the clearance shouldnt
allow any back correction on one flank from impinging on the other flank.

  Im trying simply to make it error free in the way it operates for no, when I recode the 4 machining types into their own classes, Ill add more capabilites as well as a post processor.

Art

[ArtF]

Phil: <et al.>

&nbsp;New version is now online. Heres a phot of how my test 4 tooth output looks. All numbers crunch well,
Ive blocked clearance from being able to push back beyond center, so the flank erasing shouldnt happen anymore,
(Im hoping that was it as I cant find any other excuse for why clearance increasing erased your flanks.)

&nbsp; Youll notice now the rooting doesnt try to cut outside the blank at all, the tangential passes no longer move the Z
at all, Z stays at the calculated base circle value. Im going to make that the true base radius for involutes, but since sprockets, pulleys and other types dont have base circles, Im hoping the AI works in that regard.But I dont mind doing code that recognises Involute gears for special handling..

Art

[philbur]

I can't see the photo. Also my 4 tooth rooting now shows the same tool path as toothing!!!!!!

Phil :)

[ArtF]

Phil:

&nbsp; Sry, I fixed the photo..

>>Also my 4 tooth rooting now shows the same tool path as toothing!!!!!!

&nbsp; Youll need to explain that one?

art

[ArtF]

>>Also my 4 tooth rooting now shows the same tool path as toothing!!!!!!


&nbsp; On rereading that I think I might see what your saying. But, urn off rooting and youll see
toothing is quite different. Its still the same tangential, but it doesnt move in the Z, the old one
was trying to move around the Z to match the tangent point, this one stays at base circle.. ( Calculated base)
which means it tends to keep the tool tip below the tangent point. Since it doesnt move, the path looks a bit
different, but its the same.

Art

[philbur]

&nbsp;Youll need to explain that one?

Tool paths are the same for Rooting and Toothing!!

Ooops my mistake, involute bit selected by mistake.

Phil :)

[ArtF]

lol.. had me for a minute.

Seriously, I know its hard doing this back and forth..but its usefull to not only us but others who view the thread. While I'm not sure how great we can make a 4 tooth, its worth trying.&nbsp; Keep up the good work. :)

&nbsp; It may be easier though, if you cut a nonhelical first, if that works and the helical doesnt we at least know where the error is. Non helicals are mcuh easier to visualize on the toolpaths display..

Art

[philbur]

here's a very thin helical. Still seems to have that anomaly close to the tooth tip?

Phil :)

[ArtF]

Its funny, I keep trying to rotate these images to look behind. :)

&nbsp; Switch to a non helical, its easier to see it properly, that mess is just the helical portion derived from having to
hang the tool in front of the blank.. If you use a spur or a .1 degree helical you'll see what I mean.. As the tool moves to the fron of the blank to cut the helix, it must be definition continue the helical angle past the front and rear, so the paths look bad and overwriting the profile, ( which is in the center..). All in all it makes it very hard to intuitively see whats going on. Switching to a very very low angle helical or a spur will show how close the path is to the profile.
&nbsp;

&nbsp; Im of the opinion that there is no difference between helical an non-helical in terms of how they cut, but the non helical is certainly easier to see the path properly..

Art

[philbur]

Quote "that mess is just the helical portion derived from having to hang the tool in front of the blank.."

If that were the case wouldn't the tool path pattern at least be uniform all the way up the curve.

Phil :)

[ArtF]

Phil:

&nbsp; Youd think..but its another of those visual effects. What your seeing as non uniform motion is the delta of an involute angle amplified by the almost horizontal plane of the profile. Another optical illusion of sorts.

Im pretty sure about the helical angular code, which is the only difference between a non helical and a helical. Thats why I say look at the equivalent spur. The exact same code generator makes the toolpath, the only difference between the two is the helical angles added in. So if a spur works and a helical doesnt, it can only be the angular changes for helicals that are a problem, and since Im pretty sure about the helical angle, the only question remaining is "does a 4 tooth helical with .1 degree helix ( or a spur) cut properly".

&nbsp; Should a spur fail, then it points to one thing, should a spur work it points to another. The problem with looking at a helical toolpath is the assumptions youll make about the way it looks, which is very non-intuitive unless you think better than I in 3d space. The spur is much easier to tell and easier to see where its failing. Im still pretty sure the normal tooth count gears are cutting fine ( at least up to the changes Ive made for this problem..but even those shouldnt have affected them.). Its warming here, soon Ill be able to cut a couple myself to see where I can make things better. ( Christ I hate the cold..). In the meantime, if you test, Id test a spur of equivalent size, if its fine, the helical should be as well.

Art

[philbur]

No optical illusions, it looks like the tool path in post #70. Its cut on the same blank from yesterday. Todays tooth flanks are at 12 o'clock and 2 o'clock

Phil :)