[Lozzie]

Greetings!

My name is brother Paul, I am a novice woodworker, currently living in a small hut at Mount Athos in Greece. Together with a friend we are trying to work out the production of small scale copies of manual sculptures made by us.

We use a small CNC machine bought from China, it's a YOO CNC or LY CNC model 6040, with an active surface of 600x400mm. We live off grid and have a photovoltaic system of 5kw and since our products are all small we thought this size will be just enough.
We scanned our first project with an industrial scanner and have a quite good resolution STL file, which then i processed in Artcam 2018. The original file is 10 inches high (26cm) while the copy you can see below is 5.9 inches (15cm).

Being a novice everything is new to me but with God's help i gained quite some production knowledge in a short time span.
I still have many things to learn obviously but the main scope of this topic is to try to find if my CNC machine is of bad quality or if it is just a matter of correct setup of parameters and fine tuning.

My main problem is that i can achieve decent quality only with very small feed rate, much lower than the ones in the Tool Database of Artcam. As soon as I speed things up a little, I lose accuracy and the project becomes altered with lots of jagged lines, as you can see below.
Is the loss of quality a limitation of the CNC machine, a problem with the Gcode generated by Artcam or a thing of Mach3?

[Lozzie]

This is the lower quality cut, made with 1mm ball nose and higher feedrate than the one above.

[Lozzie]

I forgot to add, the small cross which has 77mm, was made with the 0,5mm diameter ball nose end mill while the bigger one, 150mm, was made with the 1mm end mill.

[Lozzie]

Since all the images i've posted have been resized, i'm attaching this ZIP file so you can see the details in the larger photos.

[peteeng]

Hi Lozz - Can be all of what you mention. Since the machine cuts well slow lets assume we can speed it up. Looking at the cutting data firstly with such a small bit I'd be running it flat out maybe. Does the spindle go to 24000rpm? Increase your tolerance to 0.01mm and look at your plunge rate. I'm not sure if this is the max feed rate for the Z or only on plunges? Can you set max feeds per axis in the controller? If so what are they? Looking at the "crop" image the rough bits are when the tool goes up and down. ie its something to do with the z axis motion.

The g code from artcam will be OK. The controller will change the tool trajectory depending on velocities and curvature and the axes settings. At 10,000rpm a 0.5mm dia tools surface speed is 15.7m/min this is very slow and tools will run up to 300m/min easily before overheating. Looking at the cut ie the chip thickness per tooth assuming it has 2 teeth its 0.050mm per tooth. This is very fine cut for timber. This means you have to speed up the feed to get a bigger chip. But you may not be able to do this. Trying for a 0.1mm chip at 10k rpm means the feed is 2000mm/min or 33.3mm/sec. Can the machine do this?

I presume you want to speed it up to make them faster So 1) check out the controller settings for the z axis and note them here. There will be a velocity max and a acceleration max setting. 2) we shall start at the z axis and sort that first 3) also if there are undercuts in the vertical areas the machine cannot follow the code so may jitter. If artcam has an undercut analysis or draft analysis run it on the stl and check for undercuts. That's enough to digest for now. Peter

edit - and check that everything mechanical is snug and not loose. Especially on the z axis...

[awerby]

I've found that with detailed carvings, the feed rate I set is pretty irrelevant. Since the toolpath consists of lots of tiny combined movements in Z plus X or Y, the controller will be slowed down a lot more than the nominal feedrate would indicate. If it comes to a straight stretch, then it will suddenly go much faster. If you provide your machine with a faster motion-control system, it will speed things up generally, but you can always expect a series of very short moves to take more time than long straight ones.