how to construct symmetrical sketches

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scrungy_doolittle
Posts: 121
Joined: Thu Jun 21, 2018 11:15 pm

how to construct symmetrical sketches

Postby scrungy_doolittle » Wed Jul 11, 2018 2:48 am

I have about decided to start over and construct this from scratch, by measuring from one of the other sketches, and constraining this as I go.
I've learned enough from the discussion to think that I might be able to do this.
So I have some questions:

I have a horizontal and vertical line set crossing at some point. Unfortunately, it appears that this is in the ZY plane, rather than the XY plane.
How do I change the planes?

I have set symmetrical constraints on the center points of the circles, and the line at 90 degrees to them, so they are constrained symmetrically, and
I have set the distance between them to the proper values.

Secondly, I have established point on object constraints for the center points of the 4 circles.

1. What kind of constraint do I need to put on the 4 of them, so if one is changed, they are ALL 4 changed?
2. I have a left hand arc built. I want to mirror it to the other end of the sketch (the right side,) and flip it and lock it in the same relationship to the
center point of the small arcs, and set so that if the left arc radius is set, it will change the right arc radius., but such that it matches what what has been done so far.

How do I do that? I find no easy way to select an object, and flip it along the vertical axis, like I can in most drawing programs.
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symmetrical_start.FCStd
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chrisb
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Joined: Tue Mar 17, 2015 9:14 am

how to construct symmetrical sketches

Postby chrisb » Wed Jul 11, 2018 7:44 am

You should have opened a new topic, since this is far away from dwg conversion. I can split the topic if you give the post a new and sensible name.
scrungy_doolittle wrote:
Wed Jul 11, 2018 2:48 am
I have a horizontal and vertical line set crossing at some point. Unfortunately, it appears that this is in the ZY plane, rather than the XY plane.
How do I change the planes?
Open the placement dialog by clicking on the ellipsis button right to the property. Set the rotation angle to 0°. To keep the object a bit more tidy you can change the rotation axis to Z (or X or Y).
I have set symmetrical constraints on the center points of the circles, and the line at 90 degrees to them, so they are constrained symmetrically, and
I have set the distance between them to the proper values.

Secondly, I have established point on object constraints for the center points of the 4 circles.
Your sketch contains a redundant constraint: Remove one of the point-on-object constraints of the circles on the vertical axis. it is implied by the symmetry and the other point-on-object constraint.
1. What kind of constraint do I need to put on the 4 of them, so if one is changed, they are ALL 4 changed?
Do you mean the radius? You simple select the arcs and apply an equality constraint.

2. I have a left hand arc built. I want to mirror it to the other end of the sketch (the right side,) and flip it and lock it in the same relationship to the
center point of the small arcs, and set so that if the left arc radius is set, it will change the right arc radius., but such that it matches what what has been done so far.

How do I do that? I find no easy way to select an object, and flip it along the vertical axis, like I can in most drawing programs.
You do it in the same way as before: Apply a symmetry constraint on the center and equality on the arc.
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bejant
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Re: dwg conversions

Postby bejant » Wed Jul 11, 2018 1:02 pm

scrungy_doolittle wrote:
Wed Jul 11, 2018 2:48 am
I have about decided to start over and construct this from scratch,
This time you might want to model only one fourth of your model, meaning that your Sketches will have white geometry in one quadrant only. When you have that quarter of the model to your liking, use mirror on it and join the fourths together. This method will make your Sketches much easier and simpler.
scrungy_doolittle
Posts: 121
Joined: Thu Jun 21, 2018 11:15 pm

how to construct symmetrical sketches

Postby scrungy_doolittle » Wed Jul 11, 2018 2:44 pm

Chrisb
Lets do that. Because this is something that every noobe needs.
scrungy_doolittle
Posts: 121
Joined: Thu Jun 21, 2018 11:15 pm

Re: dwg conversions

Postby scrungy_doolittle » Wed Jul 11, 2018 2:51 pm

chrisb wrote:
Wed Jul 11, 2018 7:44 am
Open the placement dialog by clicking on the ellipsis button right to the property. Set the rotation angle to 0°. To keep the object a bit more tidy you can change the rotation axis to Z (or X or Y).
? I have set the rotation axis to 0, and x. But the XYZ indicator on the lower right bottom did not change. So it seems that we are still in the z,y plane.
bejant wrote:
Wed Jul 11, 2018 1:02 pm
This time you might want to model only one fourth of your model, meaning that your Sketches will have white geometry in one quadrant only. When you have that quarter of the model to your liking, use mirror on it and join the fourths together. This method will make your Sketches much easier and simpler.
That is precisely what I intend to do. But where is "mirror" in sketcher?
Ah, got it. You have to get out of the sketch, select an object and mirror then shows up.
2. To mirror an item in a sketch, exit the sketcher. Make sure the sketch is visible. (a space bar in the labels & attributes panel on the sketch will do that). Select one of the items, in this case an arc. hit mirror, and then select mirror around the origin, and it will be mirrored.
However, you now have a sketch and a mirror and they are separate. So you need to select the sketch and the mirror and combine them. If you want to keep a copy of the sketch and mirror, first select them in the panel, do a copy and paste.

I created another arc, and based on a point on a line, which was fixed by a constraint to another point. That works, however, WHERE does one get
access to the start and end angle of an arc so you can know the degrees and tweak them?
Last edited by scrungy_doolittle on Wed Jul 11, 2018 3:51 pm, edited 1 time in total.
scrungy_doolittle
Posts: 121
Joined: Thu Jun 21, 2018 11:15 pm

how to construct symmetrical sketches

Postby scrungy_doolittle » Wed Jul 11, 2018 3:04 pm

scrungy_doolittle wrote:
Wed Jul 11, 2018 2:51 pm
Do you mean the radius? You simple select the arcs and apply an equality constraint.
The moment I did that, I got an error asking me to remove redundant constraints. That made no sense, but when I started looking at the ones, they were all radius constraints on the other circles. In this case, since they were set to equality, that makes sense.

I intend to try to turn this into a clean tutorial thread, so here is fact 1.

1. When you apply equality constraints to a group of objects such as circles, you need only 1 set of constraints on one object. The program will automatically link the constraints of the other objects to the one you set the constraint on. In the case of circles, specifically, a radius constraint only needs to be on one circle in the group.

I wrote-----
2. I have a left hand arc built. I want to mirror it to the other end of the sketch (the right side,) and flip it and lock it in the same relationship to the
center point of the small arcs, and set so that if the left arc radius is set, it will change the right arc radius., but such that it matches what what has been done so far.

How do I do that? I find no easy way to select an object, and flip it along the vertical axis, like I can in most drawing programs.

-----
chrisb wrote:
Wed Jul 11, 2018 7:44 am
You do it in the same way as before: Apply a symmetry constraint on the center and equality on the arc.
So I have a symmetry constraint already on the middle 0,0.
I just selected that and the n the arc and got
Select two or more compatible edges.....
What did I miss?
Do you mean to set a symmetry constraint on the origin of the arc? and an equality on the arc? Gives me an error.
chrisb
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Re: how to construct symmetrical sketches

Postby chrisb » Wed Jul 11, 2018 3:23 pm

scrungy_doolittle wrote:
Wed Jul 11, 2018 2:51 pm
? I have set the rotation axis to 0, and x. But the XYZ indicator on the lower right bottom did not change. So it seems that we are still in the z,y plane.
The indicator does not change, the sketch orientation changes
But where is "mirror" in sketcher?
That is not what you usually do. You mirror the created feature instead.

Nevertheless there is a "symmetric" function in sketcher: https://www.freecadweb.org/wiki/File:Sk ... mmetry.svg (Sorry to include the link, but referencing from the Artwork page doesn't seem work anymore.
scrungy_doolittle
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Re: how to construct symmetrical sketches

Postby scrungy_doolittle » Wed Jul 11, 2018 4:04 pm

chrisb wrote:
Wed Jul 11, 2018 3:23 pm
Nevertheless there is a "symmetric" function in sketcher: https://www.freecadweb.org/wiki/File:Sk ... mmetry.svg (Sorry to include the link, but referencing from the Artwork page doesn't seem work anymore.
That worked perfectly. Had to enter a couple more constraints.
Now I am using .18, so where is the DOF function? I now have a sketch laid out, but with 15 degrees of freedom, so I have to get those reduced.
version .18 is supposed to have a way to identify the degrees of freedom.
I have a lot of measurement lines in it so I know that it is the correct dimension.
Attachments
symmetrical_start_2.FCStd
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chrisb
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Re: how to construct symmetrical sketches

Postby chrisb » Wed Jul 11, 2018 4:16 pm

scrungy_doolittle wrote:
Wed Jul 11, 2018 4:04 pm
Now I am using .18, so where is the DOF function?
You find it in the menu under solver tools or you click on the number of DOFs.
chrisb
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Re: how to construct symmetrical sketches

Postby chrisb » Wed Jul 11, 2018 4:19 pm

You still have equal dimensions in your sketch, which you should avoid. You asked for it and I explained it already.