How to cut off a corner?

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Janosik
Posts: 3
Joined: Thu Mar 26, 2020 10:11 am

How to cut off a corner?

Postby Janosik » Sun Jul 12, 2020 12:43 pm

Cutting off a corner as shown in the first image is easy...
Sketch -> Extrude -> Cut . That's it.
Image

But how can I cut off a corner as shown in the second image?
Image
Reynard1066
Posts: 27
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Location: Scotland

Re: How to cut off a corner?

Postby Reynard1066 » Sun Jul 12, 2020 1:37 pm

Create 3 Datum Points at the co-ordinates you need.
Create a Datum Plate onto these 3 Datum Points.
Sketch a shape (Rectangle maybe) that encompasses the three Datum Points.
Pocket the shape in the correct direction. Probably reversed.
Attachments
Corner Cut.png
Corner Cut.png (19.83 KiB) Viewed 398 times
drmacro
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Re: How to cut off a corner?

Postby drmacro » Sun Jul 12, 2020 1:48 pm

Reynard1066 wrote:
Sun Jul 12, 2020 1:37 pm
Create 3 Datum Points at the co-ordinates you need.
Create a Datum Plate onto these 3 Datum Points.
Sketch a shape (Rectangle maybe) that encompasses the three Datum Points.
Pocket the shape in the correct direction. Probably reversed.
Make sure the MapMode property of the datum point/s is set to Deactivated and not attached to generated geometry. (to avoid the topo naming issues)

;)
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Reynard1066
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Location: Scotland

Re: How to cut off a corner?

Postby Reynard1066 » Sun Jul 12, 2020 2:01 pm

Hi drmarco,

I created the Datum Points onto the XY-Plane. That way the local and world co-ordinates matched up.

Can't work out how to get the Sketcher to snap to the Datum Points to draw a triangle to pocket. Seems not possible.

Reynard
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papyblaise
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Location: France

Re: How to cut off a corner?

Postby papyblaise » Sun Jul 12, 2020 2:31 pm

One of solution
on a edge do a triangle (white)
on the other edge do a line for path (green)
and do a soustrativepipe
Attachments
cut angle.PNG
cut angle.PNG (16.41 KiB) Viewed 369 times
jmaustpc
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Re: How to cut off a corner?

Postby jmaustpc » Sun Jul 12, 2020 2:36 pm

Reynard1066 wrote:
Sun Jul 12, 2020 2:01 pm
Hi drmarco,

I created the Datum Points onto the XY-Plane. That way the local and world co-ordinates matched up.

Can't work out how to get the Sketcher to snap to the Datum Points to draw a triangle to pocket. Seems not possible.

Reynard
map a datum plane to the datum points and then map the sketch to the datum plane....i.e. don't attach the sketch directly to the datum points.

Before datum planes existed in freeCAD, we used to do something like pappyblais has posted above, although of course the profile does not need to be a triangle it just needs to be anything larger that the piece you want to remove, could be a rectangle for example. If you were to do it that way its actually better to make it wider so that the cut tool is wider than the cut out so that you don't run a risk of invalid solid due to a cut with a coincident edge, which could leave an infinitely small face behind.
Janosik
Posts: 3
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Re: How to cut off a corner?

Postby Janosik » Sun Jul 12, 2020 2:58 pm

Thank you Reynard1066, and everybody else who added to this thread. After some 'trial and error' (which is a good thing ;)), I got it working :!:

To draw the sketch, I used "create an edge linked to an external geometry" and placed a point on each of the DatumPoints. I then connected those with "create a line". Perhaps not the "most elegant way" to go, but it works.
drmacro
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Joined: Sun Mar 02, 2014 4:35 pm

Re: How to cut off a corner?

Postby drmacro » Sun Jul 12, 2020 3:15 pm

Reynard1066 wrote:
Sun Jul 12, 2020 2:01 pm
Hi drmarco,

I created the Datum Points onto the XY-Plane. That way the local and world co-ordinates matched up.

Can't work out how to get the Sketcher to snap to the Datum Points to draw a triangle to pocket. Seems not possible.

Reynard
Specifically, don't attach.

In the following there are 3 datum points, none attached, i.e. Deactivated in Properties MapMode. Each with a specific Placement. (See Property Placement)
Note the Sketch properties: Support is the 3 datum points, Map Mode is ThreePointsPlane.
Attachments
CornerCut.FCStd
(19.45 KiB) Downloaded 11 times
CornerCut_annot.png
CornerCut_annot.png (122.83 KiB) Viewed 321 times
Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."

My beginners, written treatise: Learning FreeCAD
jmaustpc
Posts: 10222
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Location: Australia

Re: How to cut off a corner?

Postby jmaustpc » Sun Jul 12, 2020 3:18 pm

There are always many ways to do this, I took a short cut which leaves you to potential topological naming issues if you edit it too much. It would have been a more robust model for editing if I had attached the datum points to the xy axis plane and then adjusted their offsets from there.

I selected just the edge, then added a datum point, attached with centre of mass which puts the datum point in the centre of the edge of the cube. I did that for each 3 edges/datum points, then I adjusted their attachment offset to move them to 1/4 of the edge length.

One you have the three Datum points, select all three, then click Datum plane, it will attach to those datum points. Then slect the datum plane and create a new sketch that will then attach to it. Draw a large enough profile, then pocket (tick reverse pocket).
Screenshot_20200713_010706.png
Screenshot_20200713_010706.png (9.34 KiB) Viewed 317 times
here is the demo file
cutcubecorner.FCStd
(21.18 KiB) Downloaded 12 times

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Reynard1066
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Location: Scotland

Re: How to cut off a corner?

Postby Reynard1066 » Sun Jul 12, 2020 4:14 pm

Thanks drmarco,

That's a different method. Got rid of the Datum Plane.

None of my Datum Points in my original reply were attach to the model. I avoid topo issues like the plague.

Reynard