Getting a datum or reference that actually aligns with the original object?

[GrantRobertson]

This is a basic, "Can it even be done?" question. I have read many posts in the forum as well as the documentation, but all I can find is essentially, "Nope, that doesn't do that."

I am designing a small camper in FreeCAD. I have drawn the trailer. The trailer consists of the frame and the axle (axle, wheels, and fenders). The frame is drawn in its actual location. However, I drew the axle such that the center of the axle was at the Y-axis and then positioned it forward and down, as necessary to place it properly. I did this because the axle's position may change, with respect to the frame, as the design progresses.

[attachment=0]Trailer.png[/attachment]

Now it is time for me to design the camper itself. I am doing it in a separate "Part" so I can more easily hide/show the various major chunks as necessary. I need to design the camper to fit on the frame and around the fenders. I was easily able to create a "Shape Binder" from the top surface of the frame and put that into the "Part" that holds the camper. However, when I create a "Shape Binder" for the fenders, said "Shapes" are located at their original positions, near the Y-axis.

From what I have read, this is the way these "Shape Binders" are supposed to work.

So... Is there some way to get a datum or reference to that fender (or even a copy of it), copied to the correct branch of the model tree, and in the correct location to use as a reference to be able to accurately draw my camper body? (Other than completely redrawing the whole fender in the current location.)

Thanks.

OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.13528 (Git)
Build type: Release
Branch: releases/FreeCAD-0-17
Hash: 5c3f7bf8ec51e2c7187789f7edba71a7aa82a88b
Python version: 2.7.14
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.2.0
Locale: English/UnitedStates (en_US)

[freedman]

I didn't upload your model but here is how to do it. I used body 1 and 2 for ref.
Highlight/select Body2 in the tree where you want the shapebinder, goto body1 and select a face, click on Datum plane. This will give you a Reference Pad and a Datum plane in Body2. You can now work off of the Datum plane in Body2 and the Datum plane is parametric to Body1.

Make it a dependent copy. I know this works but being a dependent copy means there is some risk in Freecad, naming issues.

I throw this out there every once in a while. My new user Tips
https://forum.freecadweb.org/viewtopic.php?f=21&t=29179

[GrantRobertson]

I didn't upload your model but here is how to do it. I used body 1 and 2 for ref.
Highlight/select Body2 in the tree where you want the shapebinder, goto body1 and select a face, click on Datum plane. This will give you a Reference Pad and a Datum plane in Body2. You can now work off of the Datum plane in Body2 and the Datum plane is parametric to Body1.

Make it a dependent copy. I know this works but being a dependent copy means there is some risk in Freecad, naming issues.

I throw this out there every once in a while. My new user Tips
viewtopic.php?f=21&t=29179

1) By "Highlight/select Body2 in the tree where you want the shapebinder" you mean, "When you make a datum plane, it will also create a shape binder, which FreeCAD will use as a reference for the datum plane. That shape binder and the datum plane must be part of the body, in which you plan to use them. Therefore, you must have already created a body and made sure it is the active body. The active body is shown by the light grayish-blue highlight in the model view tree (which is almost indistinguishable from the selection highlight except it does not have an outline and is more grayish). This will be your 'target body'".

2) By "This will give you a Reference Pad and a Datum plane in Body2" I presume you mean, "This will give you a shape binder and a Datum plane in Body2."

3) It doesn't work. The shape binder and the datum plane are still created in the original location of the "source body" (Body 1). The shape binder cannot be moved, and the datum plane, though it can be moved, appears to be useless to me. I would still need to completely redraw the shape.

[chrisb]

Can you please upload your model so we can have a look at it? I'm pretty sure that you did not create the ShapeBinder from the body, but from something inside.

[freedman]

I found this about 2 months ago and have been waiting for someone to notice my posts, tear into it. It does work.

From body2 (hightlighted) select a face on body1, click on Datum instead of shapebinder and the program creates a Reference pad shapebinder and a Datum plane on the pad, if you make them dependent then it's parametric. I will create a basic file with no name changes. Notice the Datum plane Z in Body2 follows the pad Length in Body1.

It gets even better, once the new Reference pad shapebinder datum plane ( I think we need a word for this.. RPSDP) is created, select the newly created datum plane and click on Datum plane in the toolbar to create another plane. Its does not create another plane, it allows you to edit the current plane and put in an offset. This gives you parametric offsets between bodies on all bodies if this process is followed.


Do I win a prize or something.... I like chocolate or beer.


OS: Windows 7
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.14090 (Git)
Build type: Release
Branch: master
Hash: a7c8a4677f480f8733e700c3bd2cabc579e3e061
Python version: 2.7.14
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.2.0
Locale: English/UnitedStates (en_US)

[TheMarkster]

I found this about 2 months ago and have been waiting for someone to notice my posts, tear into it. It does work.

Select a face, click on Datum instead of shapebinder and the program creates a Reference pad shapebinder and a Datum plane on the pad, if you make them dependent then it's parametric. I will create a basic file with no name changes. Notice the Datum plane Z in Body2 follows the pad Length in Body1.

But if you do as Chris said, create the shapebinder with the other body selected, if the other body is moved the shapebinder will go with it.

refpad-shapebinder.gif (882.48 KiB) Viewed 2178 times

[freedman]

I updated my post. The ref. pad datum plane can be parametically offset, how would that be done with a shapebinder?

[freedman]

TheMarkster
Nevermind the offset, I get it. I see what you mean about the difference. Maybe this has a use in a certain design.

[GrantRobertson]

It gets even better, once the new Reference pad shapebinder datum plane ( I think we need a word for this.. RPSDP)

As far as I can tell, you are the only person who refers to these as "Reference Pads." It is merely a Shape Binder with a face in it. Shape Binders can contain an entire body or it can contain individual faces, edges, and points (but not both the body and individual faces, edges, or points because that would be redundant. A single Shape Binder can contain geometry from only a single body but it can contain lots of faces, edges, and points from that body.

When a Shape Binder is automatically created in the process of creating a datum plane from a face, I do not think that Shape Binder is special in any way, other than that the datum plane is "attached" to it. I am pretty sure all of this could be done in individual steps with the exact same result.

I really don't think we need more words for things that already have names.

[freedman]

As far as I can tell, you are the only person who refers to these as "Reference Pads."

I didn't rename them, Freecad named them "Reference Pads.". It would appear they bind only to the Normal off the face where a Shapebinder binds XYZ. I was hoping they had some advanced features but it would seem they are old bones of the program. They do have the advantage of being able to be moved in 2 of 3 axis, that might be useful.