Also there's a bit of a problem in the "seam" area where the knurls close up - if you do a highlight naked edges (the script mentioned here: http://moi3d.com/forum/index.php?webtag=MOI&msg=4869.5 ) you'll see that there is a line of naked edges running down the "seam edge" of the cylinder area.

That can probably be repaired by doing a Join but Join won't work on just one single object piece, you need to separate out at least just one little face from the current object, then select that little face and the whole other part and then do Join and it should then get that seam area glued up.

Was this created from using Flow? There probably needs to be a tune-up to Flow to join these things up when opposite sides of the original object end up touching one another in the flow result.


Once you do that "separate one face and then join it back", to get the seam joined, then you can use Construct > Planar on it to make the knurl thing into a solid with capped ends.

- Michael

Understood. I tried it by scaling up and using a 2D curve. Only one of the curves would trim.

Would it help if I scaled up when creating the knurl - before I get to any of the cutting? It's the same flow technique as seen in a tutorial posted here previously.

Well the main problem is that the cutting surface in some areas swoops right along hugging some edges of the knurls - that confuses the intersection process, it can get stuff like an intersection for both that overlapping edge as well as some pieces from the surface/surface intersection as well.

Probably the best way to get a result would be to generate intersection curves and then select the intersection results individually and look near the ends - there will be things like additional intersection results overlapping the end (in areas where edges skimmed close to the cutting surface), and some of those will need to be deleted. Once you get the curve to be one single long closed curve then use the curve as the cutting object in the Trim.

Before doing any of that I'd probably scale everything up by 10 or 100 times, and get the seam area joined up by doing that separate one piece and rejoin step.


The basic problem though is areas where edges of the knurl happen do not cleanly intersect the cutting surface but instead skim over it for some amount of overlapping. That type of situation confuses the intersection mechanism. Maybe in the future I can experiment with a mode that will suppress generating intersection results along edges instead of only between surfaces, but certainly in other situations that would cause other problems.

- Michael

> Would it help if I scaled up when creating the knurl - before I get to any of the cutting?

So, to answer your question - no I don't think that this would help since the main difficulty is more about grazing conditions between the cutting surface and the edges of the knurls.

Grazing conditions make for a lot more difficulty in getting a clean intersection - in general when things punch more clearly through each other rather than grazing along each other for some shared area it is easier to generate clean intersections.

In your case here, I know it looks like you've got the cutting surface punching clearly through the object, but remember your object is not just a cylinder even though it has that general shape, you've got a lot of little edges on the knurl pieces and when some of those edges come very close to aligning with the direction of the cutting surface it causes a grazing situation where the edge skims over some common surface area with the cutting object rather than the cutting object dividing the edge neatly into 2 pieces.

- Michael

> I tried it by scaling up and using a 2D curve. Only one of the curves would trim.

Try making the 2D curve cut through some of the middle area of the knurls rather than having it hug right along some of the edges of the knurls.

- Michael

So I think you noticed that one surface cuts ok without any problem - the one that cuts more easily is this one here, note how it does not skim right along the knurl edges:




The one that has a lot more difficult looks like this - notice here the skimming type situation where it's trying to slice right through the same line as where the knurls have their own edges running in that same direction:




If you pull that problem one either up or down by just a little amount it will probably then intersect much more cleanly without a lot of edge coincidence happening to confuse things up.

- Michael

I've attached here (in the .zip file) a 3DM with that one more difficult cutting surface just moved up slightly so that it does not have any area where the knurl edges skim right along the surface, now it should trim without any extra messing around needed:



But depending on what you want to do with these pieces it seems like you may want to have a 2D cutting curve instead, the 3D cutting surface is banking around and adds a kind of extra angle to the cut up result, that may make it more difficult to get the results connected up to other pieces - a 2D cut will be more uniform and simple in its result.


You could get the one in your original position to work but it will probably involve a fair amount of clean up work, you'd need to generate the intersection curves and then go in and clean up the messy parts and then once you've got a good curve with no overlapping/backtracking type pieces in it use it as the cutting object.

- Michael

You're right. That's pretty messy.

Would it do the job if I just 2D cut a plain extruded tube surface and flowed the knurl pattern onto the remaining pieces?

In any case, thank you all for your contributions.

"Was this created from using Flow? There probably needs to be a tune-up to Flow to join these things up when opposite sides of the original object end up touching one another in the flow result."

Yes Please :) when using flow for rings, I normally have to take the STL output to netfabb to join up the area where the object ends touch :)

> Would it do the job if I just 2D cut a plain extruded tube surface and flowed
> the knurl pattern onto the remaining pieces?

No, that wouldn't really make any difference - Flow works on a full "underlying surface" - if you cut out a hole in the middle of something it does not make any difference as far as how Flow will be used on it.

Does the model that I attached above that will trim work ok for you?

- Michael

Hi Michael,

Sorry I didn't get back to you. I was dealing with a medical situation that arose and was nowhere near my computer for most of the week.

Yes, your model did the trick, although it wasn't immediately apparent. I had to cut it in half diagonally to better allow my computer to crunch the numbers.

Ended up making a solid tube out of the knurled section. Cut that in half diagonally. Then I used my sweeping curves to cut out the shapes and isect to make cutouts from the sweeping curves. Then I joined everything to make solids again.

Here's the result:



As you might be able to tell, it's the rubberized grip on Count Dooku's lightsaber. I got a replica for Christmas and immediately set out to model it. It's excellent practice and compliments my Luke and Obi-Wan virtual models.

Thank you so much for your help and insight.