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Cut Quality Issues

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Joined: Mon Jan 02, 2017 11:18 am

Cut Quality Issues

Postby Jtucker7000 » Sun Jan 08, 2017 8:35 pm

I'm new to the Forum, and Plasma cutting too for that mater so I apologize in advance if I'm posting incorrectly or in the wrong place. I have issues with cut quality and would love some suggestions. To start with I have a really old Plasmacam Table Model 98z and I've retrofitted it with the following Parts.
gecko320x drives
CUI encoders
350oz IN servos for X and Y (automation Technologies Inc)
60 amp Power Supply
The z axis is a linear Slide from ebay with a stepper motor
Gecko G 210x drive
Proma THC SD
Feather Touch Ohmic Sensor
C11 Breakout Board
Software: Mach4, CamBam
Mach4 Settings
Traverse Mode: Feed
Motion Mode: Constant Velocity
Distance Mode: Absolute
Arc Center Mode: Incremental

all these parts were a guess based on what others have done, I've had no previous experience with CNC and I'm amazed that I've managed to make any of this work. I spent hours tuning the drives and feel they are tuned by ear to the best of my ability. In Mach4 I set the steps through trial and error and Dimensionally parts are correct the Texas star I've attached should be 4" and is 3.988. In Mach 4 Motor Tuning I'm using 300 for velocity and 25 for acceleration and I typically cut at 70 IPM for 14 guage. I've attached some examples of the cut quality. I have 2 main issues, first I don't know what to call it but the cut seems to shake or stutter. Second I use a tangent lead in of .25" but it almost always seems to over cut and leave a dimple at the starting point. I've tried making minor methodical adjustments to mach or the pid loops but find there is too many variables for me to narrow down the issue. I'm hoping there is an obvious solution from someone with more experience. I just don't know If this is caused by mechanical slop, servo tuning, electrical noise,something simple in software, or maybe a computer issue. Also if it matters In cambam I usually convert everything to polylines.

thanks in advance,

Cut Quality.jpg

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PlasmaCam 98z retrofit to Mach4 & Proma THC
Hypertherm Powermax45
Mach 4, CamBam, Inkscape

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Re: Cut Quality Issues

Postby acourtjester » Sun Jan 08, 2017 10:40 pm

One thing that will help you better visualize the problem and save metal is to attach an ink pen to your torch or replace it with one paper is cheaper the metal.
just set up a simple post processor no need for anything more then setting the surface and then setting the touch height so the pen will mark the paper. Your first image shows straight lines but for 14 Ga you should be moving much faster like 250 IPM. I do see dimples but not bad.
The star is much worse have you looked at the drawing in Inkscape to see how many nodes are showing too many nodes are not good. Also are you saving the file in SVG not DXF that can make a difference too. The cut should be what you draw 4" should be 4" cut your steps per inch is off. I don't know if Mach 4 has a procedure for doing axis calibrations like Mach 3 does. It is very easy to do it with that, do it about 3 times in a row and move the axis longer and longer travel each time until you go almost the full travel of the axis. Your lead in needs to be only longer then the kerf width, SheetCam will flag if it cannot fit the lead in inside of the drawing.
I'm sure many will help to get your table dialed in.
DIY 4X4 Plasma/Router Table
CandCNC DTHC-IV & Feather Touch
Hypertherm PM65 Machine Torch
Drag Knife and Scribe
Miller Mig welder
13" metal lathe
Small Mill
Everlast PM 256 tig

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