Inset object along XY

[kefir]

I have a design that was made by importing an SVG drawing (path), making it a face, and then extruding that along the Z axis. It turns out that the SVG was based on a sketch that was made by overlaying a part on paper and tracing a line around it with a pen - so the sketch was offset around 1-2mm outside the perimeter of the original object.

As a result, I'd like to virtually shave off a couple of mm around the perimeter, or do a negative offset (inset?) of the outline of my object on the XY plane. Is this practically feasible? Do I have to go back and try to do this with the SVG, or the original sketch? I don't want to shrink the entire object, that would result in wrong measurements other places. I want holes/gaps to be bigger, but the outline to be smaller.

fcstd attached.

OS: Ubuntu 16.04.2 LTS
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.16.6707 (Git)
Build type: None
Branch: releases/FreeCAD-0-16
Hash: 5465bc47c95db45e0be85dc0e2872419efadce0f
Python version: 2.7.12
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17

[chrisb]

- You could use a fillet around the face. The inner edges are then offset by the fillet radius.
- Next you can Draft downgrade until you get the faces.
- Delete all fillet faces, and keep the inner face which is what you wanted.
- Last you can Part->Extrude the face again.

[bejant]

Or you can just hide the things you aren't going to use, but that makes for a bigger file size. The attached file uses the method explained by chisb, but I didn't delete anything. The blue outline is the original shape and grey is 2mm offset (the odd coloration of the top surface is the result of z-fighting):

20170311.png (23.82 KiB) Viewed 2579 times

20170311-016-sample-bejant.fcstd

(237.56 KiB) Downloaded 29 times

OS: Ubuntu 16.04.2 LTS
Word size of OS: 32-bit
Word size of FreeCAD: 32-bit
Version: 0.16.6707 (Git)
Build type: None
Branch: releases/FreeCAD-0-16
Hash: 5465bc47c95db45e0be85dc0e2872419efadce0f
Python version: 2.7.12
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17

[Willem]

hi, a more simple method
Extrude SVGface with the extrude function in part design, this is what you already did, but change the taper angle to -10 or another angle that creates the inset you want
In draft workbench make a facebinder to the smaller top face
Extrude the facebinder

[kefir]

Thanks for the suggestions! I think chrisb's suggestion is the simplest since I know the distance I want to inset, with Willem's suggestion I need to do some (simple) calculation.

A drawback I think so far is that I'd like to script this, and doing the Draft -> Downgrade I get lots of faces. How will I know which face to keep? I guess I could traverse all App.ActiveDocument.Face* and sort by .Shape.Area, keeping the second largest.

Also, another shape I have just disappears when I try to create a fillet of 1mm or more. I can manage a fillet of a bit less than 1mm, but I think that's too little. None of the details are that small, as far as I can tell. Any ideas why it won't fillet?

[kefir]

Seems like insetting in inkscape may be easier. Editing the SVG in inkscape, I could simply choose Edit -> Preferences -> Behaviour -> Steps to define the inset distance, and then simply select the path and choose Path -> Inset. I use this "script" to convert to an object:

Code: Select all

from FreeCAD import Base
import importSVG
import Part

def extrudeSVG(filename, thickness):

    doc = App.ActiveDocument

    # Import SVG
    importSVG.insert(filename, doc.Name) # returns None
    Gui.SendMsgToActiveView("ViewFit")
    # Get latest object in document:
    SVG = doc.Objects[-1]
    # Gui.ActiveDocument.activeObject()
    # Gui.ActiveDocument.path3400
    # All objects: App.ActiveDocument.Objects[0] etc

    # Create face, hide SVG
    tmp = Part.Face(Part.Wire(Part.__sortEdges__(SVG.Shape.Edges)))
    if tmp.isNull(): raise RuntimeError('Failed to create face')

    doc.addObject('Part::Feature', 'SVGFace').Shape = tmp
    del tmp
    SVG.ViewObject.Visibility=False

    # Extrude face
    SVGFace = doc.Objects[-1]
    SVGExtrude = doc.addObject("Part::Extrusion", "SVGExtrude")
    SVGExtrude.Base = doc.SVGFace
    SVGExtrude.Dir = (0, 0, thickness)
    SVGExtrude.Solid = (True)
    SVGExtrude.TaperAngle = (0)
    doc.SVGFace.ViewObject.Visibility = False
    doc.recompute()

# Demo use:
# extrudeSVG(u"/path/to/file/design.svg", 4)

[DeepSOIC]

Last but not least, in 0.17 Part workbench got a 2D Offset tool.

[chrisb]

Any ideas why it won't fillet?

I cannot tell for sure, but here seems something going wrong (please have in mind that filleting is performed by the OCC kernel, lying out of scope of the FreeCAD developers):