Conversion of Bevels to CAD files.

[ArtF]

Hi All:

Thanks to thinktink for this writeup on how to convert bevels to cad files.  The newer bevels can also be
converted this way but will not have the hoels and errors in the first steps as they are now lcosed manifold and
a single body.

Thx
Art

[thinkntink]

Hi Art,

I have the latest beta release, I think (V4.890).  Unless I am configuring something wrong, the bevels are still coming out with 2 bodies (gear form, and "pallet") and InStep still reports "pierced facets". Sounds kind of Goth.

Rhino 5.0 also imports the STL as 2 distinct bodies. See attached screen shot.

On the other hand, Rhino 5.0 can now import it VERY fast and repair the mesh directly.

[ArtF]

Interesting....


  Ill look into it, I have added 2d dxf's and 3d dxf's in a different way so they export all 3d contours as contours in space, we'll see if that helps. The STL's shoudl be good, Assimp reports no holes as does Up! .. Ill dig deeper to see why Rhino migth act that way..

Thx for the report..


Art

[ArtF]

Weird:

  I use Rhino 4.0 and it loads them fine. Im curious how it knows to lower the tooth rack down in Z away from te rest of the gear.. ( which is what appears to be happening..). Ill give it some thought, but it dos sound configurationish to some degree. Those vertices all have Z's that line the teeth with the rest of the bidy, I cant figure how just the body Z's change..

  Pirced traingles are , I suspect, a result of the angled tooth back being triangulated on a bevel, its a low level error that most programs woudlnt notice. More a warning than an error.. Weird on Rhino though..

Art

[ArtF]

Think..

  Dunno whats up with the stl. I downloaded Rhino 5.0 just to see if I could repeat it. My Rhino loads
the stl fine. It also loads the new 3d-dxf's. I have changed the 3d dxf's to not put out face data as before,
I figured stl was fine for triangle based output, the new 3d dxf puts out the outside contours with thoughts
you could make them solids yourself. That will be in the next release.

Thx
Art

[thinkntink]

Hi Art,

Sorry if my image caused confusion. I separated the 2 meshes in Rhino to show that 2 bodies were being created, not one.  When originally imported, the core and gear face meshes were stuck together (just like in GM)

I am continuing to investigate the conversion of STL into CAD ready formats and keep running into the same problem. I have attached a PDF showing what I mean.

• [I design a gear set in GM V4.89/li]
  • [li]Using the measuring tool (VERY HANDY) I measure the Bevel Diameter and Shaft diameter to make they agree with the dimensions listed in the screen
  •       the bevel diameter and the shaft diameter measurements match what is shown on the screen. 
  •       however, the face angle is very different (64.32 deg. vs 58.32
  • I exported the main wheel into an STL which I open in Rhino 5.0
  • I deleted the core mesh to leave only the gear faces that I repair and then fill the holes.
  • I measured the  Bevel diameter and Shaft diameter but they have now changed (see attached). Oddly enough, the face width has only changed very little and the face angle is the same as I measured in GM
  Any idea of what might be going on here?  I need to create a CAD drawing to send to our shop to make up a number of pre-forms that will be sent to the gear cutting house. The pre-forms have to have the correct angles and face width already formed so that all they have to do is mount the pieces in their hobber, set the angle and cut the teeth.
  
  My question is, which angle should I use? The one shown in text in GM or the angles derived from the CAD drawings. Please advise

[ArtF]

Ron:

  Thanks. Ill double check my bevels, they shoudl share vertices on all collars making them
indivisable..

  As to numbers, your quite correc t. I verified that the display is wrong onscreen and correct in the dxf.
The pitchcone angle is correctly the angle to the pitch circle , but the addendum was being subtracted, not added,
the root angle was similarly wrong, it shoudl be smallest of the three angles.

  I have corrected this for the next release. Also, Ive made the 3d dxf output actual contours of the teeth ( if that helps..it may or may not... ). SO the 64 degree's woudl be correct, and you can double check that in the dxf output of a bevelk as it will show the angle of the face properly..

( GT displays it now as Tip Angle)

Art

[ArtF]

Ron:

Weird thing about the rhino issue. Your two separate parts are missing a small disk type edge coming up from the closed teeth, yet when I look at the gear sideways on loading into Rhino, I can see mine is joined all the way round..
  ( Im not good at rhino, and Im not sure how you got it to separate that way.. ), in theory its one STL with no
breaks, yet yours does seem to show it as two pieces.. Im still not sure why..

Art