45 degree worm M2.5

[philbur]

It still looks wrong to me.

The roughing stil does the overcut at the tip.

[ArtF]

Hi Phil

  Proably important for me to use the same model.. I see its about 8mm dia? What module is it..

Actually, save the project and attach it here..Ill try some tests with that one to see why its failing..

Art

[philbur]

Hi Phil

  Proably important for me to use the same model.. I see its about 8mm dia? What module is it..

Actually, save the project and attach it here. Ill try some tests with that one to see why its failing..

Art

Hi Art, I'm still not sure what you mean by "save the project" I have attached the summary, I guess that should be enough. It's a M1.0.  I think any module, 4 tooth, helical involute gear produced by tangential shaving will show the same rooting error. I used a gear thickness of only 0.1mm so that the error is more easily seen.

Phil :)

[philbur]

Hi Art, with the toothing tool path is the orange line the edge of the end mill or the centre line. If its the centre line then the cuttingedge possibly goes over the involute line. See attached screenshot:

Phil :)

PS: the amount of overlap appears to be influenced by the gear thickness. Which I can understand if the overlap appeared only one side of the tooth profile, in the direction of the helix, but it's on both sides? I'm probably miss something!!

[ArtF]

Phil:

  There will always appear to be overlap on both sides of the flank and this will be influenced by the
thickness of the gear. Remember, the profile you see is in the center of the blank, so the helix moves on each
side by a function of the helical angle. For  45 degree for example, the tool is moving 22.5 degrees on either
side.
          Rotate the drawing around and watch the center profile, see the way the toolpath wraps around the center
profile to either side of it and youll see what I mean.

  I think I see the problem, its a matter of too few teeth I think, the fewer teeth the more it has to rotate from center tooth
to clear the trochoids, and when that angle gets critical the bit is shaving the opposite flank while trying to clear the trochoid.

Im looking into it to set a maximum rooting angle so that it cannot hit the opposing side. I suspect this is why I havent seen it
before, never tried a 4 tooth. :) , good news is I think its fixable, just a matter of calculating that maximum angle of tangency..

Art


 

[ArtF]

Phil:
New version uploaded. I found the error. I added a routine a few months ago to
straighten up the root walls during a rooting. It had a bug that would grow increasingly unimportant as the gear got larger.
Try this one and it shouldnt gouge your teeth at all. BUT, its not the cleanest root either..though I know what I need to
do now to make it right. For the meantime, this version will stop you I think from chewing up the teeth during the
rooting..

Art

[philbur]

Hi Art, it still doesn't look right. The overcutting at the tip of the tooth during rooting still seems to be there.

Phil :)

[ArtF]

Hi Phil:

    I just uploaded a new version that should correct it all. The toolpath will still look like its cutting off until you rotate it to see where its hitting.
(But it shouldnt hit anywhere anymore.)

  Check image1 .. looks like cutoff, but rotate to image 2 and you can see it doesnt..image 3 shows both flanks are clear.

Helical toolpaths are very very hard to look at to see if cutoff is occuring.. I dont think it is anymore..


Art

[philbur]

Hi Art when run for a very thin gear (0.1mm) it still looks an awful lot like the gear I produced with the tooth tip error:

[ArtF]

Phil:

  Unlike before though, the red lines seem to show a proper relationship..

What does it look like when tilted around so you can see the profile.?

Art

[ArtF]

Yeah, Im still seeing things I dont like as well.. Still testing, Ill let you know..

Art

[ArtF]

Phil:

  lol..that display is really hard to analyse by eye, I now need thicker glasses. Anyway, try a thickness of .1mm and a tool of .1mm in diam.. does it look quite clean now?
I think the overlap your seeing is due to the correction pre and post slice for the tool diameter. Looked at straight in with a larger than 0 diam , it gets more and more overlapping at that scale. With a dia of .1 on the tool you can more easily see the shape of the tooth at center.

  The reason this is so hard to see is we're dealing with a 4mm  radius object being cut with a 1mm bit.. thats quite a ratio, try it with a
50mm radius and a 5mm bit ( 10:1 ) to see much better whats going on. Try a 12 tooth for example, it becomes much more obvious that the path is correct.. Even a 10 tooth of the same module shows a nice path..its just the smallness of the numbers on that 4 tooth that makes things very hard to grasp.

  There WAS definitely an error though, the roughing was badly broken in terms of the numbers and I can easily see it causing what happened
on that cut, so at the very least its probably worth a retest if you wish, Im pretty confident of the numbers now. (Not that thats  a definitive proof. :-) ), so we owe you a thank you for the bug, it was a bit complex to find, but your cut showed the proof.

Art

[philbur]

Hi Art, still seems to be the same problem. The lower tooth "space" has been run with rough and fine and on the upper tooth "space" I just allowed the fine to carry on and cut a second space with out any roughing.

I'll be away working until next weekend so no chance to try anything until then.

Phil :)

PS: using version referenced in post #27

PPS: the surface finish on the upper fine looks much worse in the photo than it actually is.

[philbur]

It's an M2.5 cut with a 3mm end mill.

here's the project file:

[ArtF]

Phil:

Thanks, that test was invaluable. I can see the  change from what I did, Im a bit stymied , but Ill analyse it and
see what needs to be done..

Art