Trying to pad a sketch drawn in a hole

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jswild
Posts: 12
Joined: Fri Mar 10, 2017 10:13 pm

Trying to pad a sketch drawn in a hole

Post by jswild »

Thanks to NormandC who helped me with my first newbie question. With his help and watching more tutorial videos I've made progress on my design. But now I'm stuck again.

In my design, I have two upright parts with slots in them which are aligned opposite each other across an 8" gap. I want to add a cylinder going through both of these slots and extending 35" to the one side and 1" to the other side. I selected the face of one of the uprights to sketch on, created a circle and aligned it with the center of the circular hole in the upright. But when I try to pad it in two dimensions, 35" in the first direction and 13" in the second direction, it does weird things. Even if I try just to pad in one direction it behaves unexpectedly. I attach the file with the sketch already done, but unpadded. Try to pad it yourself to see what I mean by "weird". This seems a simple thing, but maybe the program does not like sketches which are not actually resting on a base plane?

Another thing I have tried is to create the cylindrical part separately and then import it into this drawing with the idea I could just maneuver it into the slots in my drawing. But "maneuvering" turns out to be a whole black art in itself which seems not to be very well developed in the program yet, so far as I can determine reading other posts and watching tutorials.

Thanks for any suggestions you may have.

Jim

OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.16.6706 (Git)
Build type: Release
Branch: releases/FreeCAD-0-16
Hash: f86a4e411ff7848dea98d7242f43b7774bee8fa0
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17
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GeneFC
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Re: Trying to pad a sketch drawn in a hole

Post by GeneFC »

The problem is that your sketch for the rod is slightly smaller than the slot width in the upright parts. That may make sense from a construction view, but it means that you are trying to create a second completely separate solid inside of the PartDesign workbench.

That is not allowed, since the PartDesign functionality works only with a single solid (In version 0.16).

The Part workbench can be used to add a cylinder as shown in the attached image.

Even simpler is to increase the size of the rod sketch slightly, such as 0.70", so that it overlaps with the existing features. Then the pad will work normally.
Rod_added.jpg
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Gene
jswild
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Re: Trying to pad a sketch drawn in a hole

Post by jswild »

Thanks, Gene.

I've tried again with a 0.7" diameter sketch. I constrained the sketched circle's center to coincide with the center of the slot's semicircular end. But it will not pad. It says "Fusion with support failed", which sounds like my sketch is not touching the surface it was drawn on. This is with a single direction pad. If I try padding in two directions, there is no error message but I am left with the sketched circle as a free-floating ring in space and the rest of the diagram has disappeared altogether.

I had to reference the semicircular arc on the slot as a piece of external geometry, but then I see it as an element of the sketch. That doesn't seem right since then the sketch has two elements, one overlaying part of the other. I tried deleting the arc element (after using it to position the center of the circle), but the padding failed in exactly the same way as described above.

I attach the file again exactly as it is now just before padding.

Jim
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Willem
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Re: Trying to pad a sketch drawn in a hole

Post by Willem »

I should detach the sketch from the face it is assign to by selecting "Reorient sketch" in the pull down Part design menu. In next screen select Detach sketch and say cancel to the last menu. Now you can pad the sketch.
Schermafdruk van 2017-03-13 23-42-45.png
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GeneFC
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Re: Trying to pad a sketch drawn in a hole

Post by GeneFC »

Jim,

I did not keep the original file you posted, but it worked exactly like I said above.

When I tried the new files everything failed miserably. After digging in a bit more I discovered that several of your sketches were not fully constrained. I went ahead and added the missing constraints, without changing any positions.

After fixing all of the sketches everything worked exactly like I said above.

Sketch008 radius of 0.68" fails and Sketch008 radius of 0.7" succeeds.

Fully constrained sketches are not always required, but sometimes they are. If funny things are happening in your design that is one of the very first things to check.

OS: Windows 7
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.16.6706 (Git)
Build type: Release
Branch: releases/FreeCAD-0-16
Hash: f86a4e411ff7848dea98d7242f43b7774bee8fa0
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17


Gene
jswild
Posts: 12
Joined: Fri Mar 10, 2017 10:13 pm

Re: Trying to pad a sketch drawn in a hole

Post by jswild »

Hi Gene;

Thanks for this. As you can see, Willem's suggestion of going through the motions of detaching the sketch also worked.

I've noticed that sometimes my sketches that I want to use for padding or pocketing have been not fully constrained, but they have always worked. I guess I have just been lucky.

Next thing I want to do is to add two half inch dowels sticking out perpendicularly from the one just added. And then each of those new dowels needs a quarter inch dowel 1 inch from its end perpendicular to it.

If I get into trouble with this operation, I'll have to ask for more help.

Thanks for your help,

Jim
jswild
Posts: 12
Joined: Fri Mar 10, 2017 10:13 pm

Re: Trying to pad a sketch drawn in a hole

Post by jswild »

I don't see my reply to Willem, thanking him for his suggestion, which worked. Perhaps I neglected to actually submit it.

Anyway, Thanks Willem, your suggestion worked, though I have no idea why and probably don't understand enough about FreeCAD to understand an explanation.

Cheers,

Jim
chrisb
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Re: Trying to pad a sketch drawn in a hole

Post by chrisb »

If you want to have a parametric connection between the two objects you can use expressions.
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GeneFC
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Re: Trying to pad a sketch drawn in a hole

Post by GeneFC »

jswild wrote: As you can see, Willem's suggestion of going through the motions of detaching the sketch also worked.
Yes, I tried his suggestion, and it does indeed work. However, it does so by creating an independent solid, which is a concept not supported by PartDesign. The end result looks OK at this stage, but you may encounter problems when you try to add more features. (Or it may work just fine. Breaking the rules does not always carry negative consequences.)

There has some recent discussion of this "single solid" limitation with regard to development version 0.17. It appears that the failure to always check for more than one solid may be addressed soon in the development version.

Gene
jswild
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Joined: Fri Mar 10, 2017 10:13 pm

Re: Trying to pad a sketch drawn in a hole

Post by jswild »

Hi Gene;

Well, I've learned a couple of things from your posts. One is that it is best to fully constrain all sketches. So I have rebuilt my project making sure all sketches were fully constrained along the way.

Now I'm at the point where I was when I first posted my question, trying to pad a long cylinder into the slots in the two uprights of my design. I sketch a circle on the face of one of the uprights and constrain its center to be coincident with the center of the arc at the end of my slot. The circle is defined to be 0.7" in diameter and the arc has a diameter of 0.69".

When I try to pad this circle, I get the message "None of the selected sketches/2D objects is valid for padding. Please select a valid sketch or 2D object that is not used by any other feature."

I have tried constraining the circle by using the point coincidence constraint on its center and the center of the arc or measuring in the center of my circle from the upper right corner point of the upright. It doesn't matter how I position the circle, it's always the same error.

I'm sorry to be coming back with essentially the same problem, but at least it's a different error this time :D

I attach the current file I am working with. The only other thing that is different this time is that I have stared renaming the parts of my design.

Thanks for thinking about this.

Jim
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