Need a little help with AutoCAD

Discussion in 'Archived Threads 2001-2004' started by Travis Cain, Mar 15, 2003.

  1. Travis Cain

    Travis Cain Stunt Coordinator

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    Hey guys.. I'm already into the thought process of building a dual Tempest sub.. So, I thought since it'll be a while until I actually build it, I'd see if I could model it up in CAD..

    I've figured out most of the basics.. Enough to suit my needs, anyway, except one thing..

    [​IMG]

    I am trying to do the cutouts for driver mounting using the circle command, but rather than seeing it as a cutout of the main panel, it still sees it as being a solid object circle.. How do I tell cad that it's a cutout, rather than just a circle shaped piece of material?

    I'm using AutoCAD 2004, by the way.. I imagine the technique would be the same as in previous versions though..
     
  2. RichardHOS

    RichardHOS Second Unit

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    Are you doing the modeling in 3D or 2D? I'm not that familiar with 2004, but I would assume things haven't changed that much since 2002/MDT6. Give me a little more information on what you've done so far, and I'm sure I can help.
     
  3. Travis Cain

    Travis Cain Stunt Coordinator

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    OK.. I'm using 3D.. So far, nothing hard.. Starting from scratch with no template..

    First, I go to Format, then Thickness and set it to 0.75 (For 3/4" MDF)

    Then I go to Draw, Solids, Box

    Enter in the box dimensions (24",57.75",3/4") which gives me the panel shown in the pic.

    Then I use the circle command twice, once for each cutout with the center point being 12,41.3125 and 12,17.1875 with radius of 6.9375 to give me the 13 7/8" cutouts needed for Tempest..

    It all looks great in wireframe mode, but as soon as I attach a texture and render, it thinks those circles are solid too, rather than material removed from the original panel..
     
  4. RichardHOS

    RichardHOS Second Unit

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    OK, sounds like your circles are just 2D circles overlayed on a 3D box. Assuming things in 2004 are working on the same dumb solids engine Autodesk has used for years, do the following:

    enter the command "extrude"
    select both circles
    for height enter .75

    enter the command "subtract"
    select the box and then enter
    select the circles and then enter

    If that doesn't work, then the height should have been -.75 instead of positive .75


    Now, for a bit more explanation. When working with dumb solids (boxes, cyclinder, cones, spheres, etc.) in AutoCAD, you use what are called "boolean" operations to make complex shapes. Boolean operations are subtract, intersect, and union.

    Union means adding one solid to another separate solid, creating a new solid that contains all the volume of the original two. If you placed a cylinder on top of a box, and used the union command to join them, you would have one solid that was a box with a cylinder sticking out of it. Pretty obvious, huh?

    Subtract means just that... subtracting one solid from another. Instead of using the "circle" and "extrude" commands to create a solid cylinder, you could have just used the "cylinder" command to create the cylinder in one step. Same result, same solid, just two ways of going about it. Subtracting a cylinder from a box leaves a hole in the box. Agan, pretty obvious once you get the idea of how boolean works. I think of creating holes in this manner as creating a drill bit the right size (using "cylinder") and then drilling the hole (using "subtract").

    Intersect is a bit more complicated. It creates a new solid that contains only the volume that was orginally contained within, or shared between, both solids. Intersecting a box and a cylinder that passes through it will leave the intersection of the two... which is the portion of the cylinder which was "inside" the box. You can sometimes create complex shapes this way, but usually add and subtract can do all you need.

    Now that you understand the basics of ACAD solids, you might realize there is an easier way to model a sub enclosure than just building each "side" of the enclosure and putting them together. This easier way would be to create one solid, a box, that was the total exterior dimensions of the enclosure. Then create a second solid box that was the interior dimensions (1.5 inch less on each of the three axes... 2 x .75 MDF thickness). Use the "move" command to align the two boxes where they should be relative to one another (easy way is use "move", snap on the corner of one, and then snap on the corner of the other... then use "move" again and enter in the displacement in the correct directions to account for the .75 thickness... something like ".75,.75,.75").

    In this way, you create all sides of the enclosure with just a few commands. Create a couple of cylinders the correct size for driver and port cutouts, subtract them (being careful to make sure they don't penetrate both sides of the enclosure), and walla.

    Hope that helps. Of course, this is kind of an antiquated way of solid modeling. Newer techniques involve what is called "parametric" or "feature-based" modeling (there's a subtle difference), and is in some ways easier and in others more difficult. To be honest, I'm not sure if AutoCAD 2004 is capable of parametric modeling or not, but I'm pretty sure it can still function in the way I've described.

    If you have more questions... shoot away. I constantly get calls from friends with ACAD questions, so I'm kind of used to explaining things. [​IMG]
     
  5. Geno

    Geno Supporting Actor

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    n/m
    suggestion covered
     
  6. Travis Cain

    Travis Cain Stunt Coordinator

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    Thank you much for the help and explaination.. That's exactly what I needed.. I was having trouble at first but once I managed to select the panel for the object to subtract from without selecting the cylinders too, it worked.. It can be a pain sometimes to select an object without selecting others that are positioned within it..

    BTW.. I chose to model each panel individually rather than the solid box so that way I can make drawings of each piece w/ dimensions and fit them all together as they will be when it's time to build.. I plan on modeling all the bracing, etc, into it as well..

    Once again, thanks.. [​IMG]
     
  7. RichardHOS

    RichardHOS Second Unit

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    A little tip about selecting objects...

    When you drag a selection box from right to left (doesn't matter if you drag up and left or down and left), it's a dotted line box and is called a "crossing box". This type of selection box selects any objects within the box and any objects which are "crossed" by the box, even if they are only partially inside.

    When you drag a selection box from left to right, it's a solid line box and is a "window box". This type of selection box selection only objects that fall entirely within the window-box area. Objects that are partially inside are not selected.

    A little practice will tell you when to use which type. Some things are easier to select by grabbing only an edge of it (crossing box), and sometimes it's easier to select one object entangled in a mess of other things by using a very precise window box.

    Also, if you have a command in progress (like erase, or subtract) and you have selected more items than you wanted to select, you can enter the command "remove" right in the middle of the other command to de-select the objects you don't want. If you then want to toggle back to adding obbjects, enter the command "add" and you go back to adding selections.

    For example, you might enter this command sequence:

    "Union"
    select a bunch of objects... oops, you got too many
    "remove"
    de-select a few of them... oops, you de-selected one you shouldn't have
    "add"
    select that one again that you de-selected on accident
    then enter to finish the "union" command

    BTW, when I say "enter command" I'm referring to actually typing in that command (a habit of mine). Though, all of the commands I've mentioned (union, subtract, intersection, torus, cylinder, box, sphere, etc.) can be found in the menus... somewhere.
     
  8. RichardHOS

    RichardHOS Second Unit

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    And I understand why you modeled the panels separately. Sometimes I do the same.
     
  9. Travis Cain

    Travis Cain Stunt Coordinator

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    It's coming along nicely now, thanks to you.. [​IMG]

    [​IMG]
     
  10. Travis Cain

    Travis Cain Stunt Coordinator

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    Just thought I'd show how much progress I've been able to make with your help..

    [​IMG]
    Not done with all the bracing yet, but gettin pretty darn close.. The goal is a Dual Tempest, 4 PR-15 Adire Alignment.. [​IMG]
     
  11. RichardHOS

    RichardHOS Second Unit

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    Looks pretty nice. Also looks like 2004/MDT6 have better wood grain material textures for rendering than those I'm stuck with in 2000i/MDT5.

    Maybe I need to go download some more materials for the library. [​IMG]
     
  12. Geno

    Geno Supporting Actor

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    Travis, wow, I cant even get Autocad to have textures. well I import to 3ds max though. try messing with the fillet command for the edges. I have acad 2002 and it rounds the corners and edges of my boxes very well. Nice job btw.

    PS to try to rid your renders of the "lines" that make up the circle cutouts, try the SURFTAB1 and SURFTAB2 commands. I think default is 6, i raise mine to 50+ depending. It changes the amount of planes that make up a surface. so a low # will make a circle look like a stop sign and a high # will be a circle, got me?
     

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