Ripples When Cutting

[Knight]

Hi All,

Since I have had my machine running, I have noticed a problem with the cut it produces.

First, I have a 100 Watt unit, with Hybrid Servo motors. (same as yours, Techgraphix).

On virtually every cut line, after the head changes direction, the cut results in very tiny ripples or waves. I haven't taken photos yet, but I will and upload them shortly.

I have the Tuning software for the motors, but have not run it yet, simply because I do not want to interrupt the machine now that it is running, unless I know what I should do when I do run the software.

A sort of "leave well enough alone approach".

Second question is in reference to the result I can expect on the edge of the MDF after it is cut.

As I said, I have a 100 Watt tube, which is very new.
When I cut 3mm MDF, it is at 35% Power and 20mm/sec. The edge is nice and red/brown.
However, 6mm MDF, at 45% power and 15mm/sec ends up with a black edge, with a very thin line of red/brown at the beginning of the edge.

I also found that I can cut 12mm MDF at 80% power and 5mm/sec, with a very black edge, but I have decided that it is something I don't need to be doing very often.

Any ideas, anyone? Should I be expecting a red/brown edge on the 6mm as well or am I hoping for more than I can have?

Thanks, Best regards,
Albert

[daniel.macke]

Hello,
On a servo with PID corrector, oscillation are often related to the integral time constant, so the tuning software should be able to solve the problem. Or you can ajust the value "manually" until the waves disappears.
For thick wood, my experience with plywood is that doing several passes with low power and high speed will give better result than one pass with high power and low speed. For example, I would try the 6mm MDF at 35% and 20mm/s, 2 or 3 passes.
Regards.
Daniel

[Techgraphix]

PPI will also reduce the charring. I found that any value between 400 and 1500 gave almost the same result. But you need to apply more power (or less speed) you have to try for yourself.
There is one major difference between steppers and servo's: a stepper makes a step or not. the position is always accurate or you lost a few steps and it's misaligned..
Servo's will always tend to lag behind: but it will always reach the wanted position (unless obstructed).. In the tuning software you can see that. One of the levels is the error-level which is default something of 1000.. that means you will get an error when the position is 1000/4000 x 360 = 90 degrees OFF-position.. When one rotation means 100mm travel, you are allowed to make up to 25mm fault in position!!
But post your photo's first..

Kees

[Knight]

Hi Guys,
Thanks to both Kees and Daniel for your replies.

Certainly I will post some photos.
I will also try some different speeds and power and see what happens.

What I am trying to do overall with my Cutter, is to cut at low power and slow speeds for the longevity of my tube and also because when I cut 3mm, small pieces tend to tilt and catch on the knives below, thus producing a potential problem for the cutting head. Occasionally, the head will snag a piece that has tilted and drag the work piece with it. Job ruined.

The ripples are very noticeable on the 3mm, perhaps because the 6mm is quite black when cut so any ripples might not be seen easily (with my old eyes at least).

However, I will get onto some photos so that you have something visual to work with.

Thanks again for your help.

Regards,
Albert

[SWMS]

I think I might have the same problem as you, although I am using stepper motors.. Post your pics..

[electronrancher]

My new leadshine DM442 stepper drivers had a small oscillation after turning corners when I initially installed them. I used the auto-tune feature (Turn DIP switch 4 ON/OFF/ON) which cured it instantly. So if your stepper drivers have auto-tune, try it. If not, then you need the driver's software tool to adjust the compensation.

NOTE: Changing motors, etc usually requires re-tuning.

[SWMS]

It can be down to oscillation with steppers but I am not sure with servos. You might need to get rid of the vibration.