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Why / How did I end up with one entity ?

I'm designing a desk for my welding shop as a learning exercise to get to know BricsCAD. When I tried to design the top, something unexpected happened.

See attached drawing that has been stripped down to only the necessary layers. Note the UCS.

The Top layer shows a square tube steel base that needs a plywood top.
The Strange layer shows the steel base with the plywood top addition.

As soon as I put a rectangle on the base and extrude it 1/2" for the plywood, the entire steel base plus the top becomes one entity.
I've done this several times and I've seen the entity described as a Region, but not in this example. Everything still says Solid Face.

Why did adding the box to the base cause everything to become one entity?



  • The DmExtrudeMode system variable controls the default (Auto) behavior of DmExtrude. The value of this variable is saved in the registry and therefore depends on the user profile you start BricsCAD in. In a Mechanical user profile, new extrusions are unified with touching existing solids. In a BIM user profile a separate solid is created. When defining the extrusion height you can tap the Ctrl-key to cycle the various options of DmExtrude: create, subtract, unite, ... The tips widget at the bottom of the screen (and the command prompt) indicate the currently selected option.
    Choose Settings in the Settings menu or type settings at the command prompt to open the Settings dialog, then type dmextrudemode to look up the variable.

  • @Louis Verdonck

    Thank you for the lead. My setting in V18 3D Modeling was 0.

    That also explains a problem I was having working through a 3D example in the "Inside BricsCAD" book by Ralph Grabowski.

  • Remember you can use the SLICE command to split solids.

  • @Louis Verdonck

    I tried using Explode and it didn't work so I nuked the layer and started over again. I'll look up Slice.
    Eventually I'll stumble into all the corners of the product.

    Thank you for the heads up.

    I've attached the completed drawing of my shop desk. If I were to dimension it I could cut the steel and weld it up, but only because I would understand the shortcuts I used in the drawing process. I couldn't give it to a third party.

    I used solid 1" square steel for the drawing, but would use 1" thin wall (1/16") square tubing in actuality. The wall thickness and the welding techniques used for an actual build matter and are not reflected in the drawing. As wall thickness increases, so does the need to take it into consideration at the drawing level.

    I'm going to redraw the desk using hollowed out solids of 1/16" wall thickness that takes real world materials and technique into account just to see what gotchas I'll run into.

  • I had a look at your model and I noticed the solids overlap at the corners.
    Drawers are solid boxes, Use the Body/Shell option of the SolidEdit command to remove the top face and assign a thickness to the bottom and sides.

  • Only some of the solids overlap - the corners. That's due to the technique used to shape the corners and then weld them.

    It's referred to as coping the joint instead of a miter. To cope a joint, the ends of one element are partially cut away so the other element can occupy that space. Coping is stronger than a miter because it uses more weld metal to join the elements. Notice that the interior of the Top layer steel structures are cut to size and are butt joined instead of coped. My use of overlapping solids where appropriate is an attempt to show the length of material needed for a coped joint without doing all the work to actually display a coped joint. When cutting steel, length is obviously very important.

    You're very observant. What you noticed is why the drawing isn't suitable for building purposes to anyone but me because I know what I was thinking when I drew it. Even I won't build from it because the shoddy drawing will cause me to make mistakes in cutting and shaping and alter the intended dimensions of the finished product. I've had first hand experience of taking short cuts and know it rarely works. It's why I'm looking for a CAD product more sophisticated then the relic I'm using that doesn't have the smarts to do what I want done. It's also because I'm an Engineer and thereby a perfectionist by training where being 1/16" off is not tolerated.

    Since this is for my welding shop, I'm going to use plastic milk crates sold by Amazon and old plastic cases used for soda bottles with the interior plastic skeleton hollowed out. I purchase these from the local beer & soda distributor for 50 cents each. I didn't bother with any detail on these because all I needed was a place holder and a box suffices. The width of the left pedestal is slightly larger than the right because the cases have different dimensions.

    I used solidedit to do exactly as you describe during one of the exercises in Ralph's book.

  • @Louis Verdonck

    I've attached an updated version of my drawing that could be used to build from if I dimensioned the drawing. The design assumes that the top is bolted to the pedestals so the desk can be somewhat disassembled.

    Note the coped joints. A mitered joint is not affected by wall thickness, but a coped joint is very sensitive to wall thickness. If, for example, the wall thickness went from 1/16th to 1/4", the vertical members of the pedestals would need to be shortened the difference to keep the desk height the same.

    I assume a LISP routine could be written to apply a cope to a standard member, including taking wall thickness into consideration.

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