Bug? Trying to put a hole in a revolved surface.

Experienced CAD user, new CorelCAD user.

I'm trying to draw a pulley.

I start with two parallel lines, with an arc connecting the top of the lines. I then use

Solids-Draw-Revolve

with the axis of revolution being the bottom of the lines. Ta-da, something that looks like a pulley. I can twist and rotate (Rollview) and it looks exactly like what I expect.

Now I want to put a hole in middle of the pulley (because pulleys run on shafts).

Circle - Extrude.

Solids - Solid Editing - Subtract.

Doesn't work. When I try to specify the entity to subtract FROM, CorelCAD never finds anything.

I think I know what I'm doing, as I can put a hole in a cube.

Rectangle - Extrude.

Circle - Extrude.

Solids - Solid Editing - Subtract.

works fine.

But there's something about the "solid" made by revolving ...

Any thoughts appreciated.

0 Klaus Vossen over 9 years ago

Hi Alan,

did you verify the 1st object (combination of lines/arcs, revolved) is a solid? You can use the Properties palette for that. With the shape selected, have a look at the top of the properties palette - it will give you the type of shape you have selected.

Please attach the sample DWG file so that others on this forum can have a look at the shapes you've created and can help.

Thanks,
Klaus.
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0 alan-bc over 9 years ago in reply to Klaus Vossen

Figured it out.

The issue was as you suggested, that the 3D "thing" was not a solid, merely a bunch of surfaces.

Turns out I had to "join" the 2D plines and arc, and then revolve that resulting single entity. That created a 3D solid that could then be subtracted.

This makes sense in hindsight, but took a bit of a flash of inspiration to figure it out.

I think the real problem is the lack of documentation with the package. There's no explanation of WHY you do something; the online help just explains HOW.

That is, once I knew I had to join the plines, the help told me how. But nothing anywhere told me I had to join them.

One would think that there would at least be a PDF document somewhere ...
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0 cj7hawk over 9 years ago in reply to alan-bc

Another easy to make mistake with revolve is that the object must be closed - eg, when using PLINES, use C to "close" them at the end, rather than just joining to the start ( or if you do join to the start, still use "C" to close ) - Joining all the PLINES together without gaps will achieve the same goal too.

This will ensure that you have an object that can be a 3D solid, rather than a 3D surface.

This isn't a CorelCAD issue - it's just how AutoCAD does it and CorelCAD tries to work in the same way for compatibility.

Regards
David
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0 alan-bc over 9 years ago in reply to cj7hawk

Thank you for this!

Yes, I eventually figured it out. The problem is that I am NOT an AutoCAD user, I've been using a COMPLETELY different CAD system(2D only), so I am starting from scratch AND doing so without a whole lot of tutorial assistance. Sadly, the online help is more along the lines of "reminders" about what a command does, meaning you had to know how to do something in the first place.

I'm about to break down and buy the Inside CorelCAD ebook, as the sample pages do seem to show that it would be useful. Annoyingly, it's now free with a CorelCAD purchase, but was not when I bought the program a month ago. Oh well.

Your post does raise a question though. Can I simply follow some of the zillion AutoCAD tutorials and gain useful CorelCAD knowledge as a result?

And if so, what version of AutoCAD should I be looking for?

Thanks again.

Alan
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0 cj7hawk over 9 years ago

I know what you're going through - I made the same mistakes for the same reason - :)

Learning curve.... ;)

Generally I check the holes too now - SOmetimes it's possible to create a kind of "semi solid" or hollow solid - And sometimes 3D operations work on these... But if you look inside under hidden line ( after saving and reloading ) you'll spot it if this happens - Once you know the trick though, it rarely catches you out - :)

David
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