Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Jeff K on June 28, 2011, 02:44:49 PM
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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
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Can you attach the code.
Hood
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Attached. Thanks, Jeff
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Code seems fine, can you change your xml as well please.
Hood
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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.
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I apologize, but again, I'm new. I don't know what you mean. Can you give me simpler instructions or explanations? Thanks, Jeff
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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.
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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
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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
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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.
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Thanks,
I did turn down the accel, but not the speed. I'm using too fine a threaded rod on Z, so it will be unbearably slow, but I do intend to change it, so I'll give it a try tomorrow at the slow speed as you suggest and change the lead screw later.
My concern for the wild start is safety. I don't have limit switches set up yet, but at least I have an EStop (I stay close to it). Of course, beyond that, I still want to fix it just because it shouldn't be doing it. It's a bit disconcerting. Where the heck is it going? It's like it's looking for a better spot, decides the one I picked is the best, so it comes back and starts where I told it to. A mind of its own. :)
Thanks again,
Jeff
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You need to eliminate the possible causes, so slow it down do the test.
Change the feed rate in the program do the test etc etc.
Once you know what's happening you can figure out why and get as much of the lost speed back as possible.
Z Axis are under much higher load than X or Y, so feed rates have to be a LOT lower.
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Can you attach your xml and I will see if I can replicate the problem here.
Hood
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Incremental mode is shown and the first move is from x&y=0 to the circle. So you may be referencing the axis at the wrong place.
RICH
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Thanks to you all. My problems seem to be fixed, but I'm not sure why. As far as the depth change of the outer circles was concerned, I realized that the Z acceleration should also be lowered as were the X and Y for the G0 repositioning mentioned by ERP. If they were being thrown off, why not the Z. Was my thinking correct? It seemed to work.
Then to the wild start. I finally noticed where the router was going on startup. Each time it headed for machine coordinates that I believe were the tool change position. I found that Auto Tool Changer was checked. Checking Ignore Tooll Change seems to have solved that problem. Again, correct? I see in the GCode an M6 at the start (I've been studying :)). Why was it there in the first place? Was it there because of the Auto Tool Changer. And if M6 is now being ignored, how will I place an M6 where I want it and not have it ignored.
I hope I'm making sense.
I'm sure I'll have more questions, but that's it for now. Again, thanks to all who helped. Your answers to these questions and any comments will be greatly appreciated.
Regards,
Jeff
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I see in the GCode an M6 at the start ....Why was it there in the first place?
Have a look at CamBam settings or post processor since you are telling CamBam that you want to change tools. Ignoring the tool change via Mach settings cancells the
M6 command when Mach runs the program. Note that routers can generate a lot of interference and just turnign it on can create a condition to miss steps in additon to incorrect
velocity or acceleration settings.
RICH