[ErnieD]

I have just run into a problem where I am trying to subtract a cylinder from an object. When I choose boolean subtract, select the item that I want to keep, select the item that I want to subtract, right click in the work area and left click ok, the item to be subtracted does not go away. If I slide the cursor across the entity on the screen everything is selected as if it were one solid. It is as if the subtract button is now the add button.

Has anyone encountered this phenomenon and if so what did you do to correct it?

Thanks,

Ernie

[jrmach]

if you have not closed the program yet,go up to edit and start undoing operations and see if you can figure it out from there

[BurrMan]

I have just run into a problem where I am trying to subtract a cylinder from an object. When I choose boolean subtract, select the item that I want to keep, select the item that I want to subtract, right click in the work area and left click ok, the item to be subtracted does not go away. If I slide the cursor across the entity on the screen everything is selected as if it were one solid. It is as if the subtract button is now the add button.

Has anyone encountered this phenomenon and if so what did you do to correct it?

Thanks,

Ernie

Hey Ernie,
This could be an indication that one of the objects is not a "solid" (Closed watertight surface) If you just made a simple cylinder for the subtraction, then look at the other object.... We could look at it for you if you can provide the file here... Review/inspect that other object closely for open areas in the surface or malformed surfaces in it...

[ErnieD]

Burr,

I have tried to attach the file. Take a look and see what you think.

Ernie

[ErnieD]

I could not attach the file. Need direction. I just tried using the add button and it subtracted the cylinder. What would cause the buttons to be reversed?

Ernie

[BurrMan]

It's probably an open surface and not a solid, but "open" because of malformed geometry, not a missing surface..... Right clcik the file and choose "send to-compressed zip". This will make a zip file that can be attached here...

[ErnieD]

S3-17-K- Return arm.zip

Burr, I hope it works this time.

Ernie

[SeanDa]

The issue has to do with the surface normals being reversed. The normals are in the simplest terms, the direction in which the surface faces. A lot of factors go into how this is determined. I cannot say for certain as you were able to accomplish the subtraction by doing the opposite, which is the tell tale signs of a normals issue. There is a method within BobCAD to both check and reverse normals. If you wish, I can post the steps to accomplish this on here.

Sean P Daugherty
BobCAD-CAM Technical Support

[BurrMan]

S3-17-K- Return arm.zip

Burr, I hope it works this time.

Ernie

Hi Ernie,
Yeah, you have some open gaps in the model, which will cause these types of issues.. I have attached a model here that is closed and should boolean as you expect. There is also a little fragment surface that should be removed...



The red area is a surface that shouldnt be there. I have assumed that the 2 holes going through the object are supposed to be going all the way through it... If you look in this area here, note that this is just an "open surface" for both of the holes.. To fix the model I unstiched it to surfaces and then I deleted the surface marked with a red X here in the picture and any "Hole wall surfaces" and then I extracted the edges of the 2 openings of the holes at top and bottom (Green). Blanked all the surfaces, then ran "Cross section" on the 2 sets of circles that were extracted (Control clcik 2 circles in the same place using the cross section command)

Then you can stich all the surfaces back together into a solid.

[BurrMan]

The issue has to do with the surface normals being reversed. The normals are in the simplest terms, the direction in which the surface faces. A lot of factors go into how this is determined. I cannot say for certain as you were able to accomplish the subtraction by doing the opposite, which is the tell tale signs of a normals issue. There is a method within BobCAD to both check and reverse normals. If you wish, I can post the steps to accomplish this on here.

Sean P Daugherty
BobCAD-CAM Technical Support

Hi Sean, although this is correct in a sense, the underlying issue is the open surfaces. With a closed volume, the normals are written as they should be. (Outwards of the volume)

Setting the proper surfaces normals would fix the "reverse boolean" it would still produce unexpected results for Ernie, as the boolean operations would still only be doing "surface trimming" and not volume subtraction... Surface modeling is a more advanced method and should only be undertaken by advanced modelers. (Unless you are a glutton for punishment )

[ErnieD]

Sean, Yes please post the steps.

Burr, Thanks for pointing this out. I guess I should use the zoom button more vigorously in the future to look for this sort of thing.

Thanks to both of you,

Ernie

[SeanDa]

1. Turn Surface Normals on through the view column or by hitting the "N" button on your keyboard
2. Under the Utilities tab, thi sis a selection that says Reverse Surface Normals
3. Look at the how the Normals are placed on the surface
4. Reverse the Normals that are facing the wrong direction

As Burr stated in his post, this is something that is for advanced Modelers, as it is something that you must be accustomed to seeing.