Problem- Mach3 Arc Problems

[dynamotive]

Problem 1: I programmed a G3 in the XZ plane (G18), and the mill performed a clockwise arc. In order to get a counter-clockwise arc, I had to program a G2. It seems to me that if you’re facing the front of the mill, the clockwise direction is pretty obvious. Can somebody explain to me why Mach3 seems to think it’s the other way?

Iincidentally, some drawings of how to program incremental arcs (including signs for the center offsets) would be really helpful.

Problem 2: It took me a while to figure out that ‘Incremental IJ Mode’ affects all three planes. You're probably going to say, “Well, of course it does.” Once I figured that out, I realized that the user’s guide says so. However, I was coming from using the old Bridgeport Boss 5 controller, where you can only have absolute IJ mode in the XY plane. The XZ and YZ planes are incremental only. So therefore, when I saw the term ‘Absolute/Incremental IJ mode’, I assumed it only affected the XY plane. I think it should be called ‘Absolute/Incremental IJK Mode’, or even better, ‘Absolute/Incremental Arc Center Mode’.

Problem 3: Mach3 retains absolute/incremental and plane settings until the next run, even if the computer was re-started. You're probably going to say, “Well, of course it does.” However, some machines start up in a standard mode, so you don't have to worry about canceling out whatever weird mode you were using last time. Mach3's General Configuration page has check-boxes for plane and absolute/incremental 'IJ' mode. Sillly me, I thought checking those would make them the default start-up options. Sure, it's a good idea to always completely initialize your setup, but I don't recall noticing in the user's guide a warning that Mach3 retains these settings from run to run.

These are not serious problems, except that you need to figure them out before you can proceed. I assume the objective is to have a short learning curve, not to force people to achieve 'guru' status before they can get on with cutting metal.

[ger21]

Problem 3 first. In your g-code, G90.1 is absolute IJ, G91.1 is incremental IJ. Place this in your file, and it doesn't matter what Mach3 is set to.

Problem 1. A bit hard to explain. Rotations are based on the right hand rule. With your right hand, make a fist, with your thumb sticking out. Point your thumb in the positive axis direction, and the direction your fingers point is the positive rotation for that axis. Positive rotations are counterclockwise. For the XY plane, Z positive is up. Point your thumb up, and you'll see that your fingers point in a counterclockwise location. For G18, rotation is around the Y axis. Y+ is towards the back of your machine. If you point your thumb towards the back of your machine, you'll see that looking from the back, your fingers are pointing counterclockwise (G3). You're looking from the wrong direction. Make sense?

Problem 2. Doesn't really seem to be a problem here. right? Just a terminology issue. I think it's called IJ mode because few people use G18 or G19 arcs.

On a related note. I found a bug in Mach3 recently, when doing G18 arcs. Not sure if it's been fixed in the latest version, but if you notice it, it has been reported and is on the list to get fixed. When doing a G18 arc, I found that the feedrate was limited to the Z axis motor tuning speed. I was trying to cut an arc at 125ipm, and it was only going 55ipm. Which happened to be the max that my Z could go.

[ger21]

Some pics of the right hand rule.
http://images.google.com/images?hl=e...ed=0CCIQsAQwAw

Some of those don't relate. This is a simple one.
http://www2.slac.stanford.edu/vvc/th.../righthand.gif

[dynamotive]

Gerry: thanks for the quick response. Much appreciated.

Originally Posted by ger21 Problem 3 first. In your g-code, G90.1 is absolute IJ, G91.1 is incremental IJ. Place this in your file, and it doesn't matter what Mach3 is set to.

I know that now. Perhaps if I had studied the user's guide more carefully, I would have known it sooner. In any case, I still think it should be called 'IJK' mode, so what it does is more clear. Sometimes terminology is important.

Right hand rule: Ok, now that I know what arc directions are based on, I'm happy. however, I don't see any mention of that in the section on arcs. Odd that the Bridgeport Boss defined XZ CW the opposite way - probably because they thought it made more sense, and they didn't want to bother the operator with the 'right hand rule'.

Incidentally, I have my 'Hillbilly BOB' conversion going, with a control console that pretty much meets my strange requirements - that it not require either a mouse or a keyboard to operate. I got an ELO touch screen on eBay, and made a console for it which mounts on the Boss arm. I used Screen4 to make a control screen that has everything I need to operate, that is, with the addition of an touch-screen entry keypad (programmed with Click-N-Type) which sits in an otherwise empty place on the screen. I can jog either continous or step, with variable step sizes, zero an axis or set it to some value, load programs and see what they're going to do, edit them and run them, override feedrate, with no mouse or keyboard. I have a mouse parked on the top of the console just in case. The screen and keypad still need some optimizing, but it's doing the job for me.