Need Help!- plasma cutting question

[ironarbor]

I am plasma cutting 330 in/min, as you can see the letters have square edges but they are cutting round, is there a cv setting wrong, or if anyone can tell me what to do or set differently I would appreciate it
Thanks

[Torchhead]

You get sharp corners from torque (which begets acceleration). You have servos and high ratio gear reduction so you should be able to crank your torque up in motor tuning. If you still continue to have bad corners then you may have some backlash in the system. Whatever your backlash is in the gear box is multiplied by the pinion gear setup ratio.

If you are cutting thin material use the smallest tip and current setting combo (by the charts) that you can so you can cut at slower speeds. It's easier (quicker) to accelerate from 0 to 120 IPM versus 0 to 333 IPM.

Your acceleraion and deceleration in motor tuning determines a lot as to how far away from the actual toolpath your cutter will deviate. The software tries not the make moves that violate the settings and could cause a servo fault.

The amount of mass you have to move with a given torque predicts the acceleration curves. If you have a big heavy gantry then you need lots of torque to make it stop instantly and accelerate in another direction.

I don't know what size gantry (weight you have to move) or the servo motor torque ratings or if it's dual drive (two motors). All those things effect the perfomance of your table and predict the acceleration you can acheive and ultimately the tightness of your turns.

TOM Caudle
www.CandCNC.com

[Larken]

I think mach starts rounding corners more the faster you go. It has to to keep up its feed rate or banging would occur.

Exact stop mode gives square corvers but can't run that on a plasma .

There are settings to reduce rounding, but i'm not sure where.

[jimcolt]

I have to agree with Tom.....use a smaller nozzle orifice and cut at a slower speed. If you are using a Hypertherm Powermax unit....the FineCut consumables are designed for slower speeds, lower power and more intricate cutting. I would suggest getting your speed to a maximum of 120 IPM....make sure your torch to work distance is correct (too high will also round corners).

Jim Colt

"I am plasma cutting 330 in/min, as you can see the letters have square edges but they are cutting round, is there a cv setting wrong, or if anyone can tell me what to do or set differently I would appreciate it
Thanks"

[Larken]

I think he's talking about the actual motion

This is from the Mach3 CV settings PDF file
http://www.machsupport.com/docs/Mach3_CVSettings_v2.pdf

-Motion Mode (Constant Velocity OR Exact Stop) Constant Velocity “CV” – This mode attempts to maintain a constant velocity during ALL angular or arc moves while obeying the acceleration parameter. This is not possible during some moves...such as single axis moves that change direction (i.e. Motion must stop at some point during these moves). On moves where constant velocity can be maintained, the corners will be rounded depending on how high the acceleration is set combined with the CV Distance Tolerance (see below) . Higher accelerations and smaller CV Distance Tolerance values will result in tighter corners and lower following errors. Exact Stop – This mode accelerates and decelerates to each “point” in the gcode. Mach-3 only sees one move at a time and usually machines run somewhat rough and very slowly in this mode. Exact stop should only be used where a machine must not round any corners (inside or outside). However, remember that most CAM software will output many tiny G01 moves to form arcs. In exact stop mode this type of movement will leave very bad surface finishes and can be hard on tooling and machine components.