Need Help! Milling at an angle instead of 90 degrees

1. ## Milling at an angle instead of 90 degrees

Hi,
I bought the following milling machine a few years ago and finally got it working, sort of.
I have a 1979 Bridgeport BOSS Series 1 CNC Mill.
The mill has a 1997 Upgrade that is called Artisan or CNC Pro. Artisan is the software and hardware to drive the stepper motors.
I am using a free program called Draftsight to draw 2D of the part I want to make
I am using another free program called CamBam to add the depth of cut per pass and final depth of cut
CamBam also generates the Fanuc G-Code.

Lets say I want to mill a Rectangle in a piece of wood:
Instead of making a rectangle with 90 degree angles it will cut some of the corners
at an angle of a few degrees off of 90, like maybe 87 degrees.

I dont know much about cnc machining yet, but I determined that when the cutter gets to the corner
of the rectangle it uses X, Y, I and J coordinates. It looks like these moves are causing the cutter to travel a little arc as it
goes around each corner.
I tried removing the I, and J steps in the G code and then it started cutting the rectangle
square and not at an angle like before. The rectangle isn't the size its supposed to be but the angles are now square.

I was trying different things to see if I could get an idea of what is going on, so I tried to plot the gcode commands on a piece of graph paper for cutting a circle. It looks like Artisan uses three 120 degree arcs to make the circle. Is this normal? Is it more common for the g code to use four 90 degree arcs rather that three 120 degree arcs?

Another thing I noticed is that the Artisan software came with a few G code programs for simple shapes. I looked at the G code that it has for a rectangle. I noticed that it does the rectangle without using the I and J coordinates. Is it possible that the Artisan software can't handle I and J coordinates when doing linear moves?

Another thing I have found is that it cuts circles just fine and it uses I and J when it does circles.

I am thinking that I havent described things very well, but I am hoping somebody can give me some advice on how I might proceed. This is the first post I have ever done on a machining forum.

Thanks
Rob

2. ## Re: Milling at an angle instead of 90 degrees

The reason the CAM draws arcs around the corners is because it is compensating for the tool radius. You could draw a rectangle that is wider than your part by the radius of the tool, and have CAM run the toolpath on that outline, but you'd see the machine would run a lot slower because it has to stop at each corner.

It's possible your CAM is set for absolute I, J, instead of incremental I, J; or vise versa. Switch it around and see if it helps.

3. ## Re: Milling at an angle instead of 90 degrees

I am using a program called Cam Bam, to generate the Fanuc g code, that my mill software is supposed to want.

I'm not very familiar with Cam Bam yet, but so far I don't see anywhere where I can reverse the I J from absolute to incremental or incremental to absolute.

Rob

4. ## Re: Milling at an angle instead of 90 degrees

Should be a settings or configuration setting somewhere. I use a FANUC post-processor in my CAM (OneCNC XR4 Mill Expert) to output to my machine. I believe some controllers can be set up for either, but if it's not coordinated with your CAM you'll run into some funky issues...

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