45 degree worm M2.5

[ArtF]

Phil:

Thx, Ill take a look at it. Its my plan to totally recode the Gcode section, at the moment its all one class, Im going to subdivide it so
each can work independently. I suspect I screwed up whatever was wrong with saw even more with the new tool profile, an angled
axis woudl require the previous transverse I think as a planning shape.. ( Perhaps not, Ill be looking into both..

Art

[philbur]

It seems that the involute bit (I assume this is single tooth involute cutter) cuts the helical gear correctly. This is strange because I think the cutting process for the B&S cutter should be the same, the only difference is the number of cutting teeth!!!

Phil :)

PS: I see that the cutter type is not as I thought so ignore the above.

[ArtF]

Hi Phil:

  We'll look at each routine one by one in near future.. :), I do think theres a thickness limit
for that type of helical cutting due to cylidrical wrap on larger widths... anyway..later..

  I have had to redact yesterdays changes, I jumped the gun. The tooth
profile which I thought had to be corrected..was correct. I should have known this as I cut
several helicals with it myself. I changed it to correct for profile , but that was wrong and
wasnt your trouble. I have uploaded the program with those changes removed.
  This happened because I duplicated your problem and could see the same shape..
surprisingly , when I redacted my changes and tried again, the paths were correct.
  Thats very weird, and always worries me. Hopefully you didnt waste time or material
on testing that version. I need now to try to reproduce your paths for that worm..
( well..long helix anyway.. :) )

  Ill let you know what I find and perhaps ask you to verify it. You should probably redownload..and see if
that path still looks screwy..sometimes a touch error in the compiler allows a modification to not compile till
I make another change, this may have happened here. I cant explain why the path looks OK to me today.

  Last night I tried it and the rooting and toothing matched the profile in the center of the gear. (This is one way
I verify, when viewed from various angles one can see the toolpaths touch the profile when dia of the tool is zero
in the toothing, and for rooting ( where 0 wont work), I enter a small diameter and see if the root paths just miss
the center profile). Last night they matched perfectly for some reason, yesterday early they matched yours..
something is afoot....now to find it..


Ill comment more later..

Art

[philbur]

Hopefully you didn't waste time or material on testing that version.

Hi Art unfortunately I just came back in the house from trying yesterdays revised version and yes it doesn't generate the correct form. I appreciate that using the helical form to produce a worm is probably stretching it a bit and I'm not even sure if it is the correct profile. A worm cut on a lathe is done with a straight sided "v" cutter!

However the worm allows for very large ratios in a relatively compact space and gives many possibilities.

Phil :)

[ArtF]

Phil:

  Todays version does appear to generate the correct form, at least differetn from your original test, but
Im not sure why its different. Redownload and see if the toolpath looks different.. I wouldnt cut anything till
we at least figure this out in theory. Although it may not be a proper worm, its my opinion that it shouldnt overcut the way it did. Your fine pathing looked and seemed to work great, so its just the rooting that something seems screwy on... and while Helicals shouldnt by spec have undercuts, I fail to see why GT
couldnt make them anyway...

Art

[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