Cutting up a ring

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 From:  mickelsen
5594.1 
I have created a solid ring using the sweep command. I would like to cut it into four pieces. I have created a surface with the right shape to use for this cutting. I placed one of the cutting surfaces in the ring and then reproduced it into the correct locations using a circular array command. However, I can't get these surfaces to cut the ring into four pieces. I just want four pieces with relatively square ends, but when I try to cut the ring it gets cut in very strange ways. I've tried the trim command and the boolean command but neither works. I guess I've done something strange in creating the ring, but I don't know what or how to create the ring correctly.

I'm attaching the drawing page with the ring. Can someone please help me.
Thanks,
Mark
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 From:  Michael Gibson
5594.2 In reply to 5594.1 
Hi Mark, the file you posted only seems to contain one curve in it, did you mean to post a file that had the surface you are having problems cutting with?

But one thing I noticed about the curve you posted is that the ends of it are not in vertical alignment - have you possibly swept that in some way that the upper piece is overlapping back on top of itself making a self intersecting surface? If so then that would be the problem - you'll want to get those ends aligned so that you are not creating a self intersecting result which will not be able to be cut properly.

Also if you are making a circular shape it tends to be better to use Construct > Revolve rather than Sweep around a circle path - Revolve is able to make a 100% precise circular shape, while sweep goes through a fitting process and will be circular within tolerance but will be generally more complex with more points created in the resulting surface.

Here's a screenshot of what looks like a vertical misalignment of the ends (I've added in a vertical line to help show it):



Hope this helps!

- Michael
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 From:  mickelsen
5594.3 In reply to 5594.2 
Michael,
I'm sorry! I attached the wrong drawing page. (...but I'm not stupid, duh) Here is the correct one.
Mark

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 From:  stevecim
5594.4 In reply to 5594.3 
I only have the non-save version of MoI with me at work, but is this what your after





I reform the joined surfaces has a solid.... hopefully you have the solid saved. the just used the curves you used to make the cutting surface, joined to form a single curve, , used the end control points on the curve to make it a little longer, then just used boolean->merge to cut the solid.

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 From:  Michael Gibson
5594.5 In reply to 5594.3 
Hi Mark, yeah like Steve writes above probably your best bet is to make a 2D curve as the cutting object, and have the ends stick out a little instead of trying to make something that directly hugs the outer surface. It's fairly easy when making things just skim along each other that they might not quite fully cross the entire piece, by having things stick out a bit it eliminates any problems related to that.

I've attached a 3DM file with a version set up like that - this is ready to boolean, select the ring solid, run Construct > Boolean > Difference, and then pick the 4 curves as the cutting objects and it will divide it up into 4 pieces.

When possible it can be good to use 2D curves as cutting objects rather than messing around with constructing cutting surface pieces, it just saves some steps.

- Michael

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 From:  shayno
5594.6 
Stevecim is right but you need to use a boolean difference to cut the band. not the merge

I find that if you first join the cutting lines check they are on the same plane (ie thickness 0) then extrude them through the object. this often gives a better cut, also you can visually check the it goes right outside the object to be cut.

Your posted 3dm has the parts chopped into 12 or more parts (was this from the aborted cutting)
cheers
shayne
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