Incorrect Router Repositioning

[Jeff K]

I'm new at this, so I hope someone can help. I'm trying to cut the simplest of cuts and can't imagine what is going wrong. The cuts are two concentric circles. Each cuts perfectly round and to size, but off center. A 3" circle inside a 5" circle winds up with one side of the  3" 1/4" from the 5". Cutting round and to size seems to say the motor travel settings are correct. I also tried pocketing a simple circle. Finishing its first pass, the cutter repositioned off center, lowered, and began its second cut. The cutting path on screen is showing up correctly in each case. Thanks, Jeff

[Hood]

Can you attach the code.
Hood

[Jeff K]

Attached. Thanks, Jeff

[Hood]

Code seems fine, can you change your xml as well please.
Hood

[ERP]

Isn't it likely he's skipping steps during rapids.
i.e. either his acceleration or his max velocity is set too high.
The cut is probably fine because he's probably cutting at a much lower rate than the rapid speed, when the G0 executes to get him to the next pass it skips steps and he ends up with them offset.

[Jeff K]

I apologize, but again, I'm new. I don't know what you mean. Can you give me simpler instructions or explanations? Thanks, Jeff

[ERP]

Try setting the maximum velocities and accelerations to much lower numbers in the motor config.

When GCode runs there are basically two different movement types G1/G2/G3 which move at a specified feed rate and G0 which moves at the machines maximum speed, usually between cuts the GCode uses G0 to reposition the machine. Clearly since you can cut a circle moving at the cutting speed isn't an issue.

I'd start by setting the max speed to whatever cutting speed you are currently using successfully, and the acceleration to something low, if that works you can start looking for what the practical maximums are.

[Jeff K]

Thank you. Lowering acceleration worked like a charm and so far (my testing has been brief) I'm happy with its performance. As you can imagine, I still have a lot to learn.
My next struggle seems to be understanding offsets, coordinates, etc. If there's a simple explanation, I'd appreciate it. I am trying to read the Mach3 manual, but there's a lot to take in.

Again, ERP, I thank you for your time.

 Regards, Jeff

[Jeff K]

Having solved the concentric circle problem, I now have two new questions.

When the cycle starts, the router heads off to the unknown. In CamBam, I set the machining origin to the center of the circles, then in Mach3, positioned my router on the stock, zeroed out all axes, and regenerated the toolpath. The router takes off and can travel about 10" off center, then return to the original spot where I wanted the machining to start. Where am I going wrong?

Second, the router cuts the inner circle correctly, then as it proceeds outward to the larger rings, the depth of cut changes to a higher position each time it goes to the next larger ring, never reaching the -.75" I'm after. The table is pretty flat (for my first build) and the cuts are consistent around the circles, but again, consistently higher each time it moves outward. Thinking it might have something to do with the original problem, I greatly reduced the Z axis acceleration, with no luck. In fact, it seemed to decrease its ability to cut the holding tabs. The Z couldn't rise fast enough to lift over the tabs. Help!

I've attached the GCode. Your help is greatly appreciated. Thanks again,

Jeff

[ERP]

If it's repeatedly higher on each cut I'd still guess that you're losing steps on the ZAxis.
Try turning down the speed and accel on that one axis and see if it improves.
It could be when the down move on the cut occurs, so you might have to reduce the plunge rate in whatever cam software you are using.

I don't know why you get the initial move.