Hi everyone,
I have a model i made and i want to blow it up then cut it in 3 pieces so i can print each one filling up most of my printable space and in the end i will glue them together for a very large print.
The problem im having is when i try to Boolean it im left with a hole.Im still pretty newb so im not sure why this happens sometimes and other times it works how i want.
Anyone have an idea of what i can do to cut this up and keep it watertight?
Thanks in advance
Aaron

Heres the actual file if that helps.

Hi Aaron, it's hard to say for sure what might be going on there just looking at a screenshot instead of being able to examine the actual model itself.

Is there any way you can post the 3DM model file? You may need to use some kind of file sharing service if it's pretty large.

Are you 100% sure that your first result is a closed watertight solid? How is it that you are determining that, are you checking the object type in the properties panel?

If the original object is not a closed solid then you would get that kind of result. But also you can get that kind of thing if there was some difficulty in forming a completely closed intersection curve calculation during the boolean. There are various things that can get in the way of that like if some areas are self intersecting or the cutting plane possibly just grazes a single endpoint on a pointy area or things like that. It looks like you have a significantly complex intersection there so it would take some investigation of the actual geometry to see what might be going wrong.

One thing you can try to possibly pinpoint problem areas would be to extrude a plane from your line and then select the plane and your base object and run Construct > Curve > Isect. That will calculate intersection curves between things and then if you look around the curve and see missing areas those would be problem spots.

It's just hard to give you any specific details without being able to examine the model though, there are a lot of possible problems many of which can't really be identified just from a screenshot.

- Michael

Hi Aaron, thanks for posting the file. So your problem in this case looks like your object is not really a watertight solid - if it was then when you selected it, it would read "Solid" in the object type indicator here:



Note that yours says "Joined srf" there - that means you've got an object that is made up of multiple surfaces but it's not a closed watertight solid, there are some openings in it.

The best way to find the openings is to set up a script on a shortcut key that will display "naked edge" which are edges that belong to only one surface rather than being joined between 2 surfaces. Those are holes that need to be patched up in order for your object to become a watertight closed solid.

See here for how to set up the script:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6051.2


When you run that there will be 4 naked edges found, they are right in this area of the model:





The problem there is that you've got a sort of zero width pinched together shape in that spot, that's bad because it means the vertical edges from 2 different sides are running right over top of each other, making it a self intersecting area of the model without a clear volume being defined in that spot:



So that may need a little bit of surgery in that spot to make a cleaner shape that doesn't have a "zero width" typed pinched together zone like that. It's a little tricky here because you've got a complex model with different heights around that spot as well. But you will sort of need to decide on a different kind of shape at that point right there rather than having 2 different chunks just exactly grazing each other with edges overlapping right over top of one another.


I guess maybe the easiest approach would be to (looking from the bottom here) draw in a line like this:



Then use that to hack off some area like this:




Then possibly a couple of surfaces from the other area will need to be deleted and rebuilt, then joined in to make a fully closed solid.

- Michael

Hi Aaron, I've attached an edited version of your model where I've sliced off that little bit I showed above and that seems to have fixed it up ok.

The process I used was to select just those immediate surrounding faces and use Edit > Separate to break those off of the main object. Then I drew in a cutting line like I showed above and used Edit > Trim to cut that with the line and discarded that touching piece, then Edit > Join to glue the surfaces back together and then select the object and run Construct > Planar to seal off the planar hole that was left by doing the Trim.

The result is now a solid volume and it should behave more like you were expecting during the booleans.

Basically the booleans look at what volume different pieces are contained inside of in order to determine which things to keep and which to discard. When your object does not enclose a volume and is just an open surface it will just get cut up as a surface as well.

Hope this helps!

Also when you do some more cuts you may need to be a bit careful about where you place the cutting line to avoid the same kind of situation of 2 different things just barely grazing each other at a point making things become self intersecting. In order to have a well defined solid each edge must be joined just between 2 surfaces and in a case like you had originally you've got 4 edges are running over the exact same area.

- Michael

Aha,ok that makes sense.
Great info ,Ill definitely try to avoid doing this in the future thanks so much for all the help and the fast reply.