45 degree worm M2.5

[philbur]

Regarding the tool marks on the tooth flanks. I checked for lost motion on my machine and I have only 0.02mm on the y axis and 0.003mm at a 10mm radius on the A axis. In any case looking at the code the y axis movements are all in one direction and the only cut where the end corner of the end mill is at the tangent point is the first cut. So the most probable cause of the tool marks may be left-overs from the rooting stage, although the number of marks doesn't seem to match the depth per step for the rooting. I may have to play with the rooting clearance some more. I'm not sure using the same tool clearance number as used at the end/beginning of each pass is a good long term solution.

Phil :)

[ArtF]

Phil:

  Good looking result, Im very pleased.

The marks are more from that plane thing I was talking about, as the plane of the profile goes flatter and flatter to one Z plane, the tangent functions approach infinity. ( Tan(90) = Infinity) and it causes such things. Raising the rooting path can help.

    Im unsure why the rooting was so deep, there is a bug that causes it to be weird if the stepdown is too large, the stepdown has to be small enough for at least 1 pass otherwise it fails to make any passes. Im looking into it.

That having been said, its a good result considering the near impossible angles involved. Not maky tangental shaving algorithms will handle a 4 tooth object in addiotn to sprockets and non involute shapes.. Im pretty happy, but Ill continue to work on making it better.

Art

[philbur]

Hi Art, I was beginning to think you might be away somewhere nice for the weekend.

The marks are more from that plane thing I was talking about, as the plane of the profile goes flatter and flatter to one Z plane, the tangent functions approach infinity. ( Tan(90) = Infinity) and it causes such things. Raising the rooting path can help.

Yes but the first tool marks are way down close to the base diameter so the tangent shouldn't be to tough down there, or should it? The tool marks are the same magnitude all the way up the tooth flank?

If I raise the rooting path will this increase the root diameter?

Phil :)

[ArtF]

Phil:

  Your right... How about just increasing the clearance setting. It affects only the rooting, so upping it a bit will not affect the end size, just how much the rooting takes off..

Art

[philbur]

Sorry Art but I don't think we are there yet. See attached photo: Left tooth space is set to 25% clearance and the right tooth space is set to 50%. The tooth profile includes the toothing cut in both cases. I'm not sure I still have the file but I think yesterdays run must have been set at 10% clearance.

Also the tool marks are from the toothing cut not left over from the rooting cut. I managed to get close enough to see what was happening. Z may stay constant but because of the blank rotation the tool tip effectively rises up the tooth flank for each rotation step. If the tool flank shaved at the tangent point rather than the tool tip at the tangent point then the tool marks would be avoided. Probably much easier said than done. Possibly all that is needed is to subtract a small % of the tool diameter form the z height. for each toothing pass.

Phil :)

PS: If I try to load a none allowed file and then correct the mistake it tells me I have already loaded that post!!!!!

PPS: I just checked the gcode from yesterdays good run, it was only 10% clearance.

PPPS: Why not use the tangent shaving algorithm to do the roughing above the base circle. and keep the rooting for the root.

[ArtF]

Phil:

  Shows every sign of a clearnace thats backwards... Im not sure how that can happen..

Did the toolpath show it getting wider as you increased the clearance or narrower ( Should be narrower)..
  Ill check it. As to the tip..I know in GM I made it keep the tip down to the base circle.. Im pretty sure I still do. Problem is that sharp angle again.. By the time you get tangent with that damn flat plane,
the base circle is probably up near the tangent point.. (Ill look into this.. ) In essense I think we're seeing limitations about the small tooth count again. (But that clearance looks backwards.. It isnt here so I need to check that..

Art

[ArtF]

Phil:

  Still not sure why your clearance appears to increase the amount taken. I did have time to check the tangents though. They work the way I remembered. The tool is not being raised for each shave, its being kept at what it figures is the base circle. BUT your rotating so much that that level is climbing the profile quite sharply. Again, I think most of that is the limits of the tooth count. Really your not supposed to shave a gear with undercut and a 4 tooth has a lot of it. On the other hand perhaps I can allow a drop to the root level if its an involute..that would probably relieve those tooth marks on the profile. Im still considering why the clearance error....maybe its the tool is too tight for clearance.... If the tool just fits in the root, and is then told to back away from the edge by .5mm, it will cut into the other side. Ill bet thats what happened. I failed to check for that so Ill add that tomorrow. Ill also consider if its possible to drop the tool to root level instead
of base curve level..that should clear up a lot as well if its possible..

  Thx for the info, Ill try to get a version out tomorrow with some corrections...

Art


 

[philbur]

I'm still curious as to why you can't use the tangent shaving routine to also do the roughing above the base circle. That would solve the original problem and you wouldn't need to add clearance for the rooting phase?

Phil :)

[ArtF]

Phil:

>>I'm still curious as to why you can't use the tangent shaving routine to also do the roughing above the base circle

  I used to do that in early GM. Users found though that it made the flute take too much off. It cause the flute to flex overly so that in the end rooting was extended to take up as much as possible. There are differences though from GM. I did find tonight that while GM keeps the depth at the base radius, GT was recalculating that value on each tangental step. Ive stopped that for tomorrows version. Now the Z will not move while doing the tangent. It will stay at Base radius. It can be argued that the depth could be a bit deeper so the tangent point is always above the tip, but as I recall we tried that in GM and it didnt work well for many gears as it causes overshoot where it shouldnt occur.... Ill look at a way to automate that better.

  Some of this is because the routines are meant to do sprockets and such as well, unlike GM which could do ony involute gears on 4th axis...so the profile follower is trying to be intelligent about it.. Ive told it to stop that for involute gears only. We'll see how that smooths things out.. I may allow for an option to not root above the baseline..though that can leave a high load on small bits..

Art

[philbur]

Users found though that it made the flute take too much off.

Can't you step the shaving across and down like you currently do the rooting.

1. Run the end mill straight across the middle with a user defined step down per pass.
2. Run the tangential shaving above the base circle with a user defined step across and down per pass.
3. Run rooting below the base line with a user defined step across and down per pass.
4. Then add a finishing cut if chosen.

That brings me to the layout of the CNC screen. It?s very confusing as to which parameters work with which machining strategy. A separate box for parameters for each strategy (and sub strategy) would make it much clearer and also help greatly with the users understanding of how each strategy works.

Phil :)

[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