Make your move or copy in AutoCAD31 Jan, 2000 By: Bill Fane
Dont you just hate it when the computer does exactly what you ask it to do? Two cases in point are the Move and Copy commands. These two commands are extremely similar. Move is essentially a Copy followed by an Erase of the original objects. Or, you can think of Copy as a Move without erasing the originals. Whatever. Lets study how these commands work normally, and then well cover instances where they do what they are told instead of what you want them to do.
As usual, there is more than one way to start either of these AutoCAD commands. You can type in the full command name or the shortcuts, M and CO, at the Command prompt, or pick them from the Modify pull-down menu, or click on the appropriate buttons on the Modify toolbar. Do you ever get the feeling that we are getting far too many choices in the modern world?
When you issue either
command, AutoCAD replies with the familiar
You can use all of the normal object selection mechanisms, such as picking a single object with a Window or Crossing to select a group, using the default automatic mode for a combination of all three, or entering an L for the last object visible on screen or P to repeat the previous selection set.
You can remove from or add to the set. When you finish your selections, just press <Enter> and AutoCAD moves to the next phase.
AutoCAD now asks you
to supply a
Base point or displacement, which, as the prompt
implies, is the starting point for the move or copy. You face several
choices as to what you do next, so lets follow through each of them.
You can type in an x,y coordinate pair or an x,y,z co-ordinate triplet. The indicated point need not lie on any of the selected objects.
AutoCAD now asks for
Second point of displacement. Here you have a choice.
If you respond with another x,y pair or x,y,z triplet, AutoCAD moves or
copies the selected objects so that the designated base point ends up
coinciding with the indicated second point.
user coordinate system
Note that all moves and copies are relative to the current UCS (user coordinate system) and also allow actions in the current z-direction. You can move an object up one unit from its current location by moving point 0,0,0 to point 0,0,1. Thats all pretty straightforward and obvious, so lets move on.
Back up to the second point of displacement. The first time through, we supplied a specific point. This time, just give a null response, which is a fancy way of saying, Hit <Enter> instead of typing in any numbers. AutoCAD now takes the Base point as a displacement rather than a point.
For example, if you type in a base point of 1,2,3 and then press <Enter> for the second point, AutoCAD moves or copies the selected objects one unit to the right (the positive x-direction), two units upward (the positive y-direction), and three units vertically (the positive z-direction) from their original position. Negative values are also perfectly acceptable. They make things move or copy down and to the left.
However, you dont need to type in the coordinate values. AutoCAD also lets you show it the points by moving the cursor to appropriate locations and then clicking them with the mouse.
This can be one of
the most useful modes because AutoCAD also lets you use running snap
modes. Better yet you can invoke object snap overrides.
So you can move and copy a set of objects from the end of a line to the center of a circle, and so on. Once again, the picked points need not (but can if desired) lie on any of the selected objects.
Here comes the first of those frustrating situations where the computer does exactly what you tell it to do instead of what you really want it to do. When you use an object snap override or a running object snap mode, AutoCAD returns the 3D coordinates of the defined point. You may think you are moving things on the flat, but if the selected end of a line has a z-coordinate that is not equal to zero, the destination for the move wont be in the same plane where you started.
This may not be readily apparent until you suddenly discover that subsequent operations such as Trim, Extend, and Fillet dont work because all the objects arent in the same plane.
Fortunately there is a workaround. If you realize that the target object has an elevation other than zero, you can use point filters.
When AutoCAD asks you to specify a point, enter .xy, then use your object snap. AutoCAD gets the x,y,z coordinates of the point and then filters out the z-coordinate. It holds the x,y values and asks you to enter a z value. Type in 0 (zero) and there you are. Point filters are also available on the middle button or shift-right button pop-up menu.
You must be very careful if you mix point-specification modes. Specifically, you can pick or type in either or both points, but you should never pick the base point and then press <Enter> for a relative move.
The problem arises when you try to pick, then press <Enter>. That is, you use the mouse to pick the base point, but then give a null response (you press <Enter>) for the second point. Unfortunately, AutoCAD does exactly what it is told to do, and does exactly what the documentation says its going to do. It takes the x,y,z coordinates of the picked point as the distances for a relative move or copy. AutoCAD doesnt know or care how you specified those coordinatesit just uses them as received.
For example, start by selecting some objects. Then pick a base point that happens to be located at point 1.37856, 2.63925.
If you just press <Enter> when asked to supply the second point of displacement, AutoCAD moves or copies your selected objects 1.37856 units to the right of and 2.63925 units above their original position. If you define the base point by an object snap onto an object that has a z-coordinate value, additional movement occurs in that direction.
Many are the beginners who issue the plaintive cry, Hey, where did everything go? The answer is displayed by Zoom. Everything is usually up and to the right. Fortunately, Undo or U puts things back.
now for something completely different
The power brakes on a 1937 Rolls-Royce limousine can suffer from something called servo lag.
The power booster, or servo, is a mechanical clutch arrangement driven by the transmission output shaft. The problem is that the car must be moving for the servo to work. The solution is that the foot pedal first applies the rear brakes, then engages the servo. The servo applies the front brakes and helps to further apply the rear ones.
If your car stops normally at reasonable speeds, but rolls forward about six feet before any braking becomes evident at very low speeds, your rear brakes need attention. You are relying entirely on the servo and the front brakes.
This also applies to virtually all Rolls-Royce and Bentley models prior to the early 1960s.