Uneven cut

[Jonni Toobad]

Hi, I have a problem with my machine and hope you can help. I am running Mach 3 along side V Carve. When my router cuts a shape it leaves an uneven / wavy finish like it is stepping as opposed to running smoothly. The waves are in the same place every pass so it leaves even ridges along the cuts so I figure it's not a random thing.
Does anyone have any ideas as to what the problem is and how I can get a smooth cut?
Thanks, John

[Tenson]

If you use the keyboard to manually move the machine around, does it still leave wobbly cuts or are they clean? This will rule out Mach3 and the machine, leaving just bad G-code.

[irving2008]

Is the issue occuring on both x and Y axes?

[JAZZCNC]

Hi John,

This could be one of a few things.?
1: It could be a lose coupling which is slipping ever so slightly.
2: Missed steps either most likely thru over tuning.
3: Electrical issue's either thru lose or faulty wiring or interference noise/bad earthing etc (possible bad drive thou unlikely)

First stop is check couplings etc, use witness marks if possible to easily see any slippage.
Check for lose wires etc.

Then and probably the cause of the problem look to the motor tuning, esp the acceleration.

If you could give more info on the system it will help greatly. Things like.!
Drives model and micro stepping used.
screw pitch
voltage running
BOB model
Mach motor tuning settings: . . .velocity setting, acceleration, steps per, step pulse, dir pulse.
Shielded cables or not.?
Is Star grounding being used.?

Does it look to be just in 1 axis direction or more than one.? If so which.?
Is the wavy stepping a side ways consistent step over or wavy in and out.? up or down.? Pics would help.

[Jonathan]

I think you're describing the machine cutting curves with straight line approximations, so for instance if you cut a circle it will come out as an n-sided polygon? If you could post the g-code we can immediately see if this is the problem.
I had that happen once with V-carve when I accidently changed a setting it decided to export the toolpath at a really poor resolution, so used several straight lines instead of arcs. I think it was the toolpath tolerance setting, so in V-carve try going to 'Edit' then 'Options' and change the toolpath tolerances to a very small number, say 0.001, then try again. Clicking 'Restore ALL Original Settings' may also work.

[Jonni Toobad]

Is the issue occuring on both x and Y axes?
Hi, thanks for getting back so quickly to my problem. I have moved the machine with the key board and found that I get a very even cut on ther x axis but I get a very even but wavy cut on the y axis. This is the same if I move it in the xy (diagonal) too.
thanks, John

[irving2008]

How wavy is wavy? If the 'wavy' is cyclical then what is the pitch of the wavy-ness and how does that relate to the mechanics of the axes e.g. the pitch of the thread?

[Jonni Toobad]

Hi, yes the wavy cut does coincide with the pitch of the thread and if I run a diagonal cut the waves are twice as far apart along the length of the cut. Thanks, John

[irving2008]

then you probably have either a bent screw or a dodgy ballnut...

If your X and Y screws are the same pitch then swap the x and y nuts (being careful not to lose any balls). If the problem moves, its the nut, if it stays put, replace the screw...

[JAZZCNC]

What kind of machine is this.? How well built is it or rather what material is it built from.?

Some pics of the problem and machine would really help.!

[JAZZCNC]

then you probably have either a bent screw or a dodgy ballnut...

If your X and Y screws are the same pitch then swap the x and y nuts (being careful not to lose any balls). If the problem moves, its the nut, if it stays put, replace the screw...

Ermm I wouldn't do that really, it's not a conclusive test for a worn nut and any wear could easily be masked due to differences in the screws.
If the nuts worn enough to cause that much wazy-ness then it will be quite obvious and easy to feel or see without going to that much trouble. A bent ball-screw would show more has a vibration and wouldn't really show has a consistent uniform wave.

If It's mechanical issue it's more probably going to be a floating ball-screw due to lose or worn fixed end bearings or some other lose assembly or component.

Like I say some pics and possible file your having problem with would help.

[Jonni Toobad]

That all makes sence. Thanks for your help, John