knurling

[niall mcginnis]

how do i Knurl a solid object using AutoCad 2000. in case this is not a word used throught the world, knurling is the diamond shaped cut that is used on thumb screws and such like.
i have tried and tried and can not work this one out.
somebody must have done this, please help.

[CADTutor]

This is not easy. If I'm right, you want to etch a knurled surface on a cylindrical knob.

As you probably know, you can subtract one solid from another. So, if you can construct a positive version on the knurl, you could subtract it from the cylinder. Essentially, a diamond shaped pattern on a cylinder could be constructed using two helix, one clockwise and one anti-clockwise. You could construct the helix path using fuccaro's LISP routine here http://www.cadtutor.net/forum/viewtopic.php?t=74 and extrude a triangle along the path. These triangular section helix could then be subtracted from the cylinder to produce your knurling.

If you manage to do this, I'd love to see a picture of it.

[Mr T]

Using 3darray on a thin disc version of the cylinder, with the correct patern would work.

Also go into 'help' and search for 3d polyline then PEDIT and see the cool example of a spiral shape there.

Nick

PS Post a drawing of it and I'll draw it for ya. Since you are a fellow scotsman !

[fuccaro]

As you probably know, you can subtract one solid from another. [...] You could construct the helix path using fuccaro's LISP routine here http://www.cadtutor.net/forum/viewtopic.php?t=74 and extrude a triangle along the path. These triangular section helix could then be subtracted from the cylinder to produce your knurling.

The lisp routine HELSURF generate a surface, not a solid!
Please try to send a freehand sketch. If you have no other possibility, post it as attachment to my address and I will put in on the forum.

[Mr T]

I think using a 3d polyline then extruding along that path would be best.

nick

[fuccaro]

I think I realized what knurling means. The cutting edges of the triangular shape are driven along a helix on the surface of the cylinder, keeping a vertex a bit under the surface and pointing the axis. To cover the whole surface, the cut is mirrored and repeated uniformly more time. Between two consecutive intersections the helix segment is almost a line. Even the “real” helix used in AutoCAD (and in other CAD programs) is basically a 3d polyline formed with a lot of small line segments. The approximation is better if the cylinder radius is larger and if the cuts are more dense. So I replaced the extrusion along helix path with simple extrusion. Nobody will notice the difference. Even so, the model is a test for the computer’s speed (and for the user’s patience).

(if the image is not here, you may visit my web site http://fuccaro.netfirms.com)

[CADTutor]

Hey, fuccaro - great image. Now we're just waiting for the automatic knurling LISP routine

When you say "I replaced the extrusion along helix path with simple extrusion", what exactly do you mean?

[gcp310]

Good job, now, in laymens terms,how did you do it?

Love the image,ve avoided trying to knurl anything in the past due to high
rendering times.

[fuccaro]

OK, Mr. Cadtutor, your humor was very appreciated by my friends. Knurling is not one of the daily operations working with AutoCAD, so the effort to write a Lisp routine is useless. But if requests from the forum readers will change my opinion, it is possible I return to this theme.
Now, it is hard (for me) to explain the way I worked the model I posted above. The resulting solid is not perfect, but the errors are –in my opinion- small enough.
Draw a cylinder, and look at it from the front side, so you have on the screen a circle centered in the UCS’s origin. Draw a square with the lower left corner at the northern quadrant. Rotate it around the northern quadrant of the circle with 45 degrees, than drag it down a bit, so it intersects the cylinder. Extrude the square, the height of the extrusion may be equal with the radius of the cylinder. Now you got a cylinder and a prism. Rotate the UCS around the Ox with 90 degrees. Rotate the prism with 45 degrees around the middle of its height. This will be a cutting edge. Mirror it relative to Oy axis and make a union of the two prisms. Return to the previous UCS and polar array the two_prism_solid around the center of the cylinder. Rotate again the UCS around Ox with 90 degrees, and array all solids but the cylinder along the Oy axis. Subtract everything else from the cylinder. The end.

[CADTutor]

aha! hmm...

WOW!

I'll definately try that when I've got a few spare hours