1. ## CUTTING ARCS

Hi, I would like to be able to draw arcs with my CNC, I have a few wizards that can draw arcs but they always ask for the radius of a circle and that is not exactly what I need.
What I need to do is to cut arcs out of boards of different size:
Ex. Let’s say that I have a board of 72" long by 6"wide and would like to cut an arc of 2" .To be able to reach both ends, I would have to make the radius 36"
Am I missing something with the wizards that I have or is there other ways or wizard to do this?
To mention a few of the wizards that I have: The wizards that comes with Mach3, a registered version of Newfangled solution and a few others.

2. Is this what you want? The arc is a 325" radius. You can draw it in a CAD program, and convert it with LazyCAM or some other CAM program.

3. thank you for the reply, but is there any wizard that one person just insert the length of arc bottom and the rise at midpoint of arc and would do the caculation, has it is I have an Excel sheet that just do this

4. You could always set up Excel to create the g-code.

5. If your control has macro option you can to do that, too at the machine.

6. Originally Posted by ger21
You could always set up Excel to create the g-code.
Thank you for the reply, can you explain me how to do this

7. I don't have Excel installed on this PC, so give me a few days. If I don't get back to you by Monday, remind me.

8. I am lousy with Excel but the formula below will give you the information you need to figure out the radius. You want to use the formula that starts with r=
In that formula c is the length of your board and h is the height of your arc. In your example:

c=72 and h=2

72 x 72 = 5184
4 x 2 x 2 = 16
8 x 2 = 16

5184 + 16 = 5200
5200 / 16 = 325

I hope this helps.

Ed..........

9. Originally Posted by emd68
I am lousy with Excel but the formula below will give you the information you need to figure out the radius. You want to use the formula that starts with r=
In that formula c is the length of your board and h is the height of your arc. In your example:

c=72 and h=2

72 x 72 = 5184
4 x 2 x 2 = 16
8 x 2 = 16

5184 + 16 = 5200
5200 / 16 = 325

I hope this helps.

Ed..........
Thank you for your help, but if you take a look at post #3 you will notice that I already have a sheet in Excel that gives me the radius, my CNC table is only 5 X 10 feet, 325 radius won't fit .
What I looking for is a wizard to spit out the G codes or the way that GER21 mentioned about setting up Excel to create the g-code.

10. I am wondering if you have CAM software?

If you don't, you would do well to find even a cheap CAM software, you will find yourself doing all kinds of custom projects once you have the tools.

Back in the day before having all this nice cheap software, I used to code line by line. If I had a curve I drew it in CAD, and found my points via, the dimensioning tools, or exploded the curve into line segments, then noted the points, and wrote the code according to the x,y of the line segment ends. This is a tedious process to say the least. I can't imagine doing that today, when you can buy any number of CAM programs cheap, and export the g-code into excel or even notepad to insert code specific to your controller.

To be truly useful a wizard would have to let you enter an offset from x0,y0,z0 then let you enter the cord, and offset, as well as the direction to proceed from and to. I like to usually cut in the climb mill direction, to avoid tear out. Also I have found that you can get quite a bit of movement in the material depending on how far apart the parallel arcs of the curve is (a 4" molding blank will move more than a 6" molding blank). I like to secure the board down near the ends of the cut, make a first pass a 1/4" outside the actual cuts, leaving the ends uncut. Then do a final pass at the actual dimension, then cut the ends last or cut them on the miter saw. I have had some molding blanks move near that 1/4 inch, so depending on how long and narrow the arc, you may have to adjust that. I have cut hundreds of hardwood arcs to be ran through a radius molding machine. I have seen lots of movement if the wood is rustic in character, (lots of knots) so for these types of projects it is best to have a CAM program, so you can make fast easy adjustments as needed.

The same rules apply as with cutting a straight board, and I am sure we have all had the experience of getting a board nice and straight, ripping it in half, and ending up with 2 crooked boards.