I can't seem to find a way to do this.



I'm trying to trim the knurled cylinder using the curved surfaces. I just need the knurled area within those surfaces, not the rest of the cylinder.

I tried making the knurled cylinder a solid tube and using boolean. That didn't work either.

Maybe I'm going about it the wrong way. But I've tried everything I know. Any clue as to how to get the desired effect?

I tried to attach the file, but it's rather large and is encountering problems during the upload. Still, any ideas?

Could you post a .3dm of the (two?) curved cutting surface(s)?

Do the cutting surfaces go all the way through the knurls?

Hi propmaster - it's hard to know what might be going wrong just from a screenshot, I need to be able to examine your actual geometry in order to really give you good advice.

Is it possible that the cutting surface is self-intersecting, meaning does it criss-cross or fold back over top of itself? If so then that kind of thing will definitely confuse surface/surface intersection calculations such as trimming or booleans.

- Michael

Also like Brian mentions in order to be able to cut the knurl the surface must fully divide it into different sections.

It looks like you may have some areas where the cutting surface is only partially submerged in the knurls and not fully dividing it, like in this area I've circled in red here:




If possible it can be easier to use a 2D profile curve as the cutting object rather than a 3D swooping surface.

- Michael

It seems I can upload only the file with the curves. The one with the knurled cylinder gives a 500 internal server error.

But yes, I can confirm that the cutting surfaces go all the way through. See attached image.

Hi propmaster - is the full file with the knurling of particularly large size? If so then probably it exceeds some kind of upload limit in the forum software.

In cases like that for particularly large files you would need to use a file sharing service to host the file and then post the link to it, rather than using the forum's built in attachment mechanism.

There are various free file sharing services out there, 2 common ones are dropbox and Windows Live SkyDrive:

https://www.dropbox.com/
http://skydrive.live.com/

- Michael

From what I can see on your partial file you uploaded, your cutting surfaces look ok.

Maybe there is some problem with the knurl part instead - I can't really tell that from a screenshot though.

A couple of things you might try are to use Construct > Curve > Isect to generate intersection curves between the knurl part and the cutting surfaces and see if there are bad looking intersection curves in some areas, then examine more closely in those areas.

Also you could try removing chunks of the knurl and trying to trim a smaller piece of them at a time to see if that is successful and might help to narrow down a problem area.

Another thing to try is to select everything and scale things up by 10 times in size, it could be possible that the knurls are small enough that they are running into some tolerance problems.

At any rate, those are some of the things that I would be doing to the file if I was examining it myself.

- Michael

Yes, it is 29MB. Here is the Dropbox link. Hope this works. I've never used the service before.

https://www.dropbox.com/s/yvllp3m1o6c1x0b/Knurl%20Post.3dm

This is to confirm that trim of a hollow cylinder, or a solid cylinder, with the two cutting surfaces works.

Boolean difference works also.

There is a difference between solid vs hollow...(?)

Yup, that worked fine for sending the file, thanks.

By doing the Construct > Curve > Isect test it looks like it's getting confused about some areas where some edges in the knurls just barely graze over the cutting surface, making the intersection more complex.

Here's one such area:



And here's an area where it did not generate one little piece across a part of a knurl, probably because the area traversed is so close to the fitting tolerance:




This kind of intersection through a tremendous number of separate tiny little pieces is a quite complex calculation and things involving little tiny distances close to the fitting tolerance or just barely grazing and coincident pieces will cause difficulties.

Probably the first thing is to scale up by first 10 times or 100 times in size and see if that makes things better, that can help to avoid having little tiny intersections that don't get processed since the area traversed by them is already under the fitting tolerance.

If you still have problems you would then probably want to go along the intersection curves generated by Construct > Curve > Isect and select any faces that are around a problematic area like the ones that I show above and separate those out from the main object, then trim the main object and do some more custom individual work on the pieces that had difficulties.

- Michael

I guess another step would be needed for solid...

And once you do a Construct > Curve > Isect, you can see the high complexity of what's trying to happen there just by how many separate little segments are generated - doing an Edit > Separate on the intersection results and you get 609 objects.

In order for the Trim to go well all of those 609 little segments have to make a well formed closed and non-self-intersecting loop that divides the surface area of the joined knurls into distinct regions. If there was any problem in even just one little area that would prevent the full Trim from working properly.

Since the intersection results get joined together into 18 pieces at first, there's probably around 18 different locations along the trimming boundary that have some of those problems (either grazing an edge making for an overlap being generated or a gap as shown in above screenshots) that will need some individual attention.

If you had a more regular 2D cutting curve instead of a 3D swooping one it would probably be less likely that you'd have some of these issues like as much grazing / edge-overlapping-cutting surface type stuff.

- Michael

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.