manipulating geometric objects

I'm trying to make a trefoil design (http://www.newyorkcarver.com/geometry/Trifoil.htm) per these instructions for a bookcase scroll saw project. It starts with a triangle and then adds circles.

Here are specific starting questions:

1. How to create circles with the centerpoints at the midpoints of the triangle legs

2. How to create a circle with the that is exactly on the 3 vertices of the triangle

thanks

dave

I am not quite sure why you need to draw circles with their centre points at the midpoint of each leg.

The way I constructed this was to first use the Polygon command, and draw a three sided polygon (an equilateral triangle).

Then I used the circle command with the 3P option, to draw the circle through the vertices of the triangle. Then I draw the three circles centred on the vertices because they are the same radius and you do not have to enter the radius again. Then I draw the circumscribing circle, centred on the intersection of the previous circles and with the radius perpendicular to one of the outer circles.

Then by offsetting and trimming and tidying up, you can get the trefoil pattern easily. (It has taken me longer to type the instructions than to draw it)

Eldon,

Thank you very much for your response. Hopefully you can be patient with me and help me with the details. I have tried your response and have these questions. I made the circle around the triangle, but I guessed at the vertices (for the 3 pts). Is there a way to exactly pick the vertices? Then how did you create the next 3 circles at the vertices? Did you create a new circle or copy the one created? Again, thanks for you patience.

Dave

I made the circle around the triangle, but I guessed at the vertices (for the 3 pts). Is there a way to exactly pick the vertices?

You will want to become familiar with object snaps (osnaps). While in command try Shift + Right Mouse.

First you need to use Osnaps, that will snap or grab exact endpoints, centerpoints, midpoints, etc. See the OSNAP button at the bottom of the screen and on most setups you can hold the shift key and press the right mouse button. So if you start the circle command then you can use endpoint and select anywhere on a line to one side of the midpoint.

Next learn to use the command line or watch the Dynamic Input box at your cursor if you are using that. Most commands have options and the circle command has several, one of which is 3Points. So first go to the OSNAP button, pick settings, make sure endpoint is checked, it is ok if others are checked as well. Now start the circle command, type 3p, enter, or select 3p from the dynamic input, now move to each endpoint of the triangle.

Now having said that the image you want to draw was done with instruments and since you have CAD you can take some short cuts. Draw the center circle with the 3p option. Draw the three circles at the vertices of the triangle. Draw the outer circle using the osnap centerpoint and the quadrant to grab the 12 o'clock quadrant of the top circle.

From here you can use the offset command rather than drawing more arcs or circles, but either way works.

IMO, it would be easier to create the 3 inside circles by just using the midpoint between the center of the large circle, and one of the quadrants, then using a polar array.

like this

http://screencast.com/t/7J6DmNob

As you can see, there are many ways of working to get to the same result. Try as many of them as you can, and you will get to your own way of working.

Thanks all for your help. I got it!!

This is one small piece of the puzzle.

Not sure if I attached this right, but this is the bookcase I am trying to make.

Dave