45 degree worm M2.5

[ArtF]

>>Just out of curiosity what do you mean when you say "the actual profile is used". How do you it convert the profile >>(a diagram) into coordinates?

  Yeah, I should explain.. :)

    I use the tool shape drawing you'll find on the DXF's.  While I could use the formulas you suggest for spurs, I couldn't use them anyway for helicals, the tooth shape of a helical is not an involute when viewed from the side. You have to turn a helical to the helix angle to see an involute shape. A helical is larger than a spur by the cos of the helical angle, so the involute shape gets stretched out of proportion when viewed transversely. But then helicals come in two flavours, transverse helicals and normal helicals. These terms refer to the way you view the tooth. If the tooth shape should be involute when viewed from the side you make a "Transverse Helical", which means you dont increase its size. (You check the box labeled "Dont resize")
      If you want a helical which is involute across its normal (the helical axis), you design a "Normal Helical". (The one your cutting is a "Normal Helical", this means the tooth is not really an involute when viewed side on, which means a cutter must follow a non-involute curve to cut one.).   
    The tool shape stored with each gear type is stolen from the gear outline before its teeth are copied around the gear. I design one tooth and copy it in all gears except non-circulars where each tooth is different. In the case of your helical for example, the non-involute result of the calculations is stored, then re-zeroed and kept in memory as "ToothShape" - a series of points referenced to 0,0 being top center of the tooth. When the toolpather goes to make a helical toolpath( or any toolpath), it looks to that stored tooth, does collision calculations and curve fitting operations to find any point intersection with that curve. SO when its rooting for example, I start at the top and ask the intersection calculator "How far to the left before I hit the profile at this depth?"  I subtract the clearance and tool radius from that and thats how far over I go. Each depth is different width of course. This allows a sprocket, pulley..anything to be machined with the same strategy.

  For toothing, same deal. My intersection calculator returns not only the intersection point of the toolcurve for any given depth, but it also returns the normal for that point. So I then rotate that normal to 0 degrees, move the tools edge to that point, and do a pass. That means the tangent and rooting passes use the same points and same intersection calculator. It why I can say with some certainty that its not the points being wrong. So to check numbers, I need only to look at a spur gears toolpath. I can measure on screen using the tape how far the edge of the path is from the profile on every line on the Y cutting axis., and Im always getting toolradius+clearance distance.. BUT, as the profile lies flatter and flatter on the cutting pane, a root path looks closer and closer to the edge as we discussed on the first optical illusion. It is the right distance from the edge of profile, but AWFULLY close to the point beneath it.
    The thing that confuses me the most is why your clearance appears to make the root wider...the path seems to indicate its getting narrower...

>>I will have a go at a straight spur later today.

  That will be an interesting result.

>>Yes trying to have this type of discussion basically by email is very frustrating.

  Been saying that for over 10 years. :) . Hey, I live this stuff, I dream in 3d at this point and normals, vectors, tangents and such roll around between my ears. I see things you cannot simply because Im involved in their math every day. On the other hand this blinds me to things I dont do every day ..like cutting gears. It makes it hard for me to see what your saying in exactly the same way its hard for you to see what Im saying. In the end its only about getting enough evidence to point to the trouble. It all helps though, I now know how many more config items I have to add when I redo the 4th axis to its own tab. I agree with you, more step size choices need to be available, Ill make that happen..

  Im off insulating my attic today, so dont rush any tests on my account. Ill be sweating in other ways.

Art

[philbur]

  Im off insulating my attic today

Better late than never. I thought you said things were warming up. lol

Phil :)

[BobL]

Phil;

He lied...

Friggin cold and wet..

:D

[philbur]

Trying to run the straight spur but there seems to be something wrong with the gcode values versus the gear blank thickness. See attached. The gear blank is 5mm thick but the x axis only cycles between X+1.5 and X-1.5, which is the tool diameter. clearance is zero!!!

Phil :)

[ArtF]

Damn..what the hell did I break while in there... Ill fix that very shortly.

Art

[ArtF]

Phil:


  Set your final depth as a positive number.. In 4th it translates to "final Thickness" and a negative number had an unknown effect.. (Ill fix that..).
Had me wondering why it worked here.. till I saw the final depth.. Now Im wondering if that affected other cuts, it basically caused a mirror of the path on my system...

Art

[philbur]

Then I'm confused. What has final depth got to do with the blank thickness, final depth should be fixed at the distance the root is below the top of the blank (the z = 0 point). Why does the CNC processing redefine the blank thickness This is confusion total confusion!!!!!!

Phil :)

[ArtF]

Phil:
 
  Not so confusing when you consider its history. We started with 2.5D only. Now consider that a person designs a gear with a facewidth of 5mm.
So they go to cut it in 2.5D. Its unlikley they will use 5mm as their depth of cut, the actual thickness considered is taken from the object, but is overridable by "Max Depth.". This allows a person with that 5mm thick gear to cut it from 12mm material or whwtever they wish. So far so good, now he can cut 5mm or 12 mm or whatever, by using the "Max Depth." field.

  Now consider the 4th axis. "Max Depth" has the exact same function, it allows for a thicker cut. Its unfortunate that the term to a gear designer
refers to the depth from tip to root, but then that's not a setting that would be usefull at all, who wants to cut a tooth to a variable depth, a tooth
is always cut to its design depth or it simply isnt usefull. But having the "Max Depth" work  in 2.5D and in 4th axis having the same effect made sense.

  As Ive said this was all done and explained at the time as a holder, a better system than GM's, that would be redone in  grander scale
when all else in GT caught up.  Its simply a handy way of making the gear thicker without having to go back and redesign it. I did fail
however to catch negative numbers.....

  Most of the settings will become more intuitive when its recoded, but "Max Depth" is simply a thickness modifier. You cannot, nor I suspect would you want to control the depth of a tooth in the toolpath generator.

Art

[philbur]

Of course, I had assumed that total depth related to the cut depth in 2.5D and had nothing to do with the 4th axis. It's difficult for the user to guess that you also use total depth in 4th axis to vary the gear thickness to avoid having to go back to the design stage. Seems to violate the whole principle of what you design is what you get. Total confusion for the user comes from throwing all parameters in one box  then later using a parameter for another total unrelated, none intuitively function. Clearance seems to be another example. This is all very frustrating.

I've been using negative DOC since the start but I don't recall ever see a blank that was wider than the cut or have gcode that had an x move less than the blank width ( I would remember that) until today. I see that the my same helical input today doesn't generate the same gcode as yesterday with respect to the x axis travel?

Phil  :(

[philbur]

Art, here's the M2.5, 4 tooth spur

Phil :)

[ArtF]

Hi Phil:

  The paths HAVE changed for sure over the course of this. When I have my fingers in there I tend to change things I see that arent right.
The negative DOC wouldnt have affected you till I fixed it yesterday. Till then only the spurs were affected by DOC. SO it likely didnt affect
anything you did up till now anyway.
  The X axis travel should have stayed the same... at least if the DOC is set to the same width you had set for the helical yesterday.
The DOC should fill in with the designed thickness when you select the gear, its only an override if one wishes. ( Kinda handy to have though..)

  Ill run a few more checks. It wont be long before the tabs get separated and Ill rename variables them to stop any confusion and allow settings for
some of the stepping values.  Once it has its own tab the 4th wont have to share variables with the 2.5D

(Your photo didnt take :)... The forum is pretty picky about used names and such.. if you post a photo, name it something weird .)

Art

[philbur]

Regarding the missing photo. When I post with an illegal format attachment it rejects the whole post. When I correct the attachment and try to repost it says its a duplicate post and rejects it. So I copied the text, closed the site then reopen, pasted the text and posted it to see if it would be rejected before going to all the trouble of adding the attachments. It accepted the post so then I modified the post by adding the correct attachments. I tell you all this in the hope that you can change the site so it doesn't reject a repost when illegal attachments have been corrected.

I on a couple of occasions I have rearrange the text a bit but it's not fooled so easily. :'(

Phil :)

[philbur]

Art, I thought we pretty much had a solution in post #49 and were only trying to avoid the tool marks on the tan shaving by lowering the cutter a little bit?

Phil :)

[ArtF]

Oh I agree, #49 looked pretty good. And we figured raising the bit a bit woudl stop the problem..wish I knew what changed..

(Ill find it..obviously I messed up something in other fixes I was doing..) :)

Art

[philbur]

And we figured raising the bit a bit woudl stop the problem..wish I knew what changed..

I though lowering the tool was the solution. It puts the flank at the tangent point, not the tip?

Phil :)