Can anyone help me out here. My issues are with driving a X-carve based CNC router, via Gecko 540, Artcam.....

There are issues somewhere with my Mach3 settings causing excessive rounding from CV mode I presume
On a 90 degree corner in the Gcode the machine is putting a radii on the bend of close to R20 in straight lining the corner
This happens on anything more than Config>StateLook Ahead value of 1
I understand default is 20 and most people run 200.
I've changed the angular CV to 89 in Settings screen and this doesn't make a difference
I've entered G64 into the Gcode to make sure that CV is on
If I turn of CV by unchecking CV Feedrate  (current value of +1), then the program will run with stops in the corner
Speed is set to 8000mm/min and acceleration at 250mm/s/s
I've put G21 into the code to ensure that both the Artcam file, Gcode and Mach3 are in metric. It just seems somehow that the CV adjustment is overly sensitive as it's overcorrecting for a setting somewhere.
I've reloaded a week old Mach3Mill.XML file and double checked it's not a setting I've recently changed by mistake. Was just the same. I just hadn't noticed it before as I'd put radii on corners
I've run out of thoughts on other settings that I could change to make
Screen shot shows the 2 triangles that are part of my test cut program. Bottom Left is cutting inside of the profile and the Top Right is programmed to cut on the outside of a profile

Any ideas anyone?

Thanks in advance Tom

If you increase X and Y axis Acceleration even at the expense of Velocity (which may have to be reduced) then it will reduce corner rounding and overall you should notice little if any increase in job time. It is quite a delicate balancing act to get it just right but give it a try.

Tweakie.


Addition:  Check out Mach3 CV Notes here http://www.machsupport.com/help-learning/product-manuals/

Thanks for your input Tweakie. Most appreciated as I’m new to this CNC game and still on the steep part of the learning curve.

I followed your suggestion and played with the speed and acceleration settings and they definitely do effect the rounding. I changed to 2000mm/s and acceleration of 250mm/s/s.
Rounding was much better but still quite evident. I’m busy researching what acceleration settings are reasonable and used by other. ( FYI This acceleration is about 10”/s/s if you work in imperial) Think I’ll now double the acceleration as this still seems within the range of what I read on the net.

While I can slow the feed rate down to resolve rounding but this approach surprises me for two reasons.

To achieve chip load recommendations to suit materials and cutter sizes I’ve been steadily increasing my feed speeds. Ie for a 6mm single flute cutter in MDF at 20,000 RPM recommendations would be for 4000mm/min (157”/min if you work in imperial) The machine has been happily working at  over this rate for 4mm Depth of cut. If I then changed to a two flute cutter I should be doubling this feed rate. This just isn’t possible if I drop my speed to 2000mm/s max. I expect I’ll need to be reducing my RPM drastically.

What puzzles me as far as my rounding issues goes is that I’m having to keep my look ahead really low to keep rounding reasonable. Ie Still using look ahead value of 5, where 20 is the default and plenty of others use +200 for this value and have reasonable rounding. I seem out of the scale of adjustment for this value. Ie my machines capabilities should be limiting this setting, not my adjustment. This seems strange given that Mach3 is used to run many Heavy Duty CNC routers. These machines should be able to crank up speeds and acceleration until their machines began to struggle rather than Mach 3 deciding on an output with compremised rounding.

I can’t help thinking that I’m out of range for some setting, but I can’t find a setting that would be responsible for this. Its as if the machine is thinking that my feed of mm/minute is actually inches/minute and so if overcorrecting by a factor of 25.4
I’ve checked I’m working in metric unit

Tomorrow I’ll try running an actual cut at lower speeds and ramping acceleration up to 750mm/s/s (30inches/s/s)

Thanks again for your help

To achieve chip load recommendations to suit materials and cutter sizes I’ve been steadily increasing my feed speeds.

An X Carve, and most hobby machines do not have the power to achieve recommended chip loads for most tools.

As for your rounding issue. Make sure both CV Distance and CV Feedrate are both off.
In General Config, make sure "Stop CV on angles" is checked, and set to 89. All other CV options should be off.

If it still rounds your g-code, then can you post the code?
And try setting the angle to 60, or 120, and see if it makes a difference?

I would think that an acceleration of 50"/s/s to 100"/s/s would be needed. Acceleration is more important than speed to prevent corner rounding. The faster you approach a corner, the higher your acceleration needs to be to prevent rounding.

Mike

I cut between 100-150ipm, with an acceleration of 10, and never get corner rounding.