This week we will take a simple look at rotating objects. This one is not as long and thought provoking as last weeks episode………..
The Basics to AutoCAD
Part 5
By now you should be fairly confident in drawing lines, circles and ellipses. You should be able to move them around your model space at will and you should be able to set up your AutoCAD Interface for your ease of finding the icons we need to use. If you are not quite there yet don’t panic, just go back through the tutorials and move to the next one only when you are ready. There is no rush to complete, unless you have a target!
Time To Turn Around……………..
So we have learnt how to draw some objects in constrained positions, i.e. a circle with its centre at 0,0. What we are going to discuss today is rotation, or as AutoCAD likes to call it ROTATE. Below is a diagram that maybe familiar to you from our “co-ordinates” lesson. We will be using this diagram to show how Rotate works.
I will try and keep this as simple as possible, if I can.
Right then, I have drawn four lines, the blue ones, labelled A, B, C and D.
LINE A; from its end point, where the X and Y axis cross, is at an angle of 36˚ from the X-axis in
the positive direction. It is rotated about its end point. AutoCAD by default sets the X-axis as 0˚,
this can be changed but I would suggest it is left well alone.
The red lines indicate the positive directions that all four lines have been rotated around their end
points.
LINE B; from its end point is rotated about that point 160˚.
LINE C; from its end point it is rotated 180˚ + 68˚ = 248˚. The 180˚ comes from LINE C being below the X-axis. The 68˚ comes from the angle, in a positive direction, from that axis. These two values are then added together to give us the 248˚.
LINE D; this is rotated about its end point 180˚ + 145˚ = 325˚. Well we know where the 180˚ comes from, see LINE C. the 145˚ comes from the angle the line is away from the 180˚ point of the X-axis, i.e. 180˚ -35˚ = 145˚.
Ok so we have determined the angles, in the positive direction, at which the four lines have been drawn, by simple math. Now let’s look at the negative direction!
This is basically worked as an opposite of the positive direction because the lines are below the X-axis; look at LINE C and LINE D.
LINE C; is rotated about its end point -35˚.
LINE D; is rotated about its end point -112˚. (180˚ - 68˚ = 112˚).
Read through these two or three times to get a better idea of how the angles work. When we start rotating objects it will become a lot easier to understand, but we must go through the theory part to help you understand.
Let’s rotate it then………
Right then here we go, let’s do it…………
OK open AutoCAD as normal. Hopefully you have set up your interface as instructed in the last tutorial. If you haven’t, then go back and do that now.
First things first, make sure the ORTHO and OSNAP buttons are turned ON.
Now draw a line from left to right across your screen, the length and position is not a concern just yet. Select the ROTATE icon button from your toolbar menu on the left; MODIFY toolbar, 7th icon down, a circle with an arrow on it.
Your cursor turns into a small square. With the cursor, select the line by left clicking on it. If it is selected it should be shown as dotted. Now right click your mouse. Your cursor crosshairs return. By moving the crosshairs close to the left hand end of the line we can select its end point when the little orange box appears. When it does, left click your mouse. We have now told AutoCAD the point about where we want to rotate our line.
If you move your mouse in a circle around the left hand end of the line you will see a representation of the line being rotated into three positions as you go. As we have our ORTHO button on, we are constraining AutoCAD to the X and Y axis directions. So, go down and turn off the ORTHO button by left clicking on it. Now go back and if you still have the line selected move in a circle again around the left hand end we selected. Now the line should be permanently attached to your crosshairs and you should be able to move it round and round and round and round and rou…. I’m getting dizzy now.
OK, left click where ever you want. There is your line rotated about its left hand end point.
To rotate the line from its other end just go through the same procedure but select the right hand end of the line. As a little test, see if you can rotate your line about its centre!
How good was that?
Now let’s do some rotating using some values.
First make sure your ORTHO button is turned off and your OSNAP button is turned on.
Draw a triangle with these line values, (0,0) enter, (45,0) enter, (45,45) enter, (0,0) enter and press enter again. You should have an equilateral triangle on screen. What we are going to do is change one of the existing angles from 45˚ to 30˚.
Select the ROTATE icon from the toolbar and then select the diagonal line with your mouse, right click once selected. Then select the end of the line at the bottom left, when the little orange square appears. The line is now attached to your crosshairs as before.
What we want to do is decrease the angle we have at the moment, which is 45˚, to 30˚. So to do this we just type into the command line -15 and press enter. The software does the rest.
OK, I want you to save this drawing with the file name TRIANGLE1. We will use it again in the next lesson. See those two long lines on the top point of the triangle………..we are going to remove the long bits past where they intersect next time.
Back to today.
So what if I want to draw a line 100 units long at an angle of 57˚?
Well this is what you do. For a start let’s begin with a new drawing. Select the LINE icon and draw a line, with your ORTHO on, left to right, 100 units long. Now select your rotate button, select the line and rotate it from the left hand end 57˚ by typing that value into the command line. That’s the easy way………..
Now the more complicated way, but you will need to learn this as you will, at some stage, find the need to draw a line like this.
This is all done on the command line. First though select your line button, type in (0,0) and press enter. Right now it gets a bit more technical. I will explain each command when we have finished, it won’t hurt I promise…….. Now type in @100<57 and press enter, and enter again. There is your 100 unit line at 57˚.
Now the explanation………. See diagram below………….
Ok so now try drawing some lines with different start points, you don’t always need to use (0,0), select the start points at random. Then enter values of your choosing but one thing you must
know, the angle value can only be to a maximum of 360, as there are only 360˚ in a circle. If you do use a value larger than 360 for the angle AutoCAD will start at 0 and keep going round in a circle until it reaches the value you give it. But between you and me, you will never see a value over 360. Remember you need to always use the @ and < symbols and when you want to finish your line either press enter again or right click your mouse.
How did you get on? Here’s one for you…… now that you have tried with positive numbers, try inputting some negative values for both the distance and angle. Try mixing negative and positive values on the same command.
Well that’s all for this time…… next time we will get back to our drawing that we started a couple of weeks ago.
As usual here is the download that goes with the tutorial;
