CNC router occasionally makes jarring noise and home jumps when it does this. Help!!

[kingcreaky]

The way i think of it is, the Acceleration and Velocity settings in Mach act like your speed limiter, they over-ride whatever settings the CAM software specifies in the job.

Its also critical (although I cannot explain why) to ensure the Acceleration and Velocity settings are the same for both your Y axis and X axis. (Z can be different) Otherwise (I found) it effects 90deg corners. Where (I think) the machine is still decelerating (moving) when the next move starts

Personally (others will disagree, I set the accelleration very low (often 100), and the velocity to a comfortable speed for the machine as Im far more interested in quality, than speed) I also find having acceleration set so low helps when jogging your machine manually into a start position and also makes a nice smooth start and stop to each move.

As mentioned above, Mach is your speed limit. So if you have set your velocity to 6000mm/min in mach, and your tool to 8000mm/min in vectric (or your cam software) mach wont let the machine exceed 6000.

The machine jogs (ie with the arrow keys, at the maximum speed stated in mach)
The machine moves (between cuts, at whatever speed the Gcode outputted by your cam software) -- but limited by mach.

The above is just my opinion.

[Jonathan]

You're noticing the variable corner rounding effect because the acceleration is too low. You should be aiming for around 1000mm/s^2 for the acceleration - certainly at least 500... otherwise in some circumstances your parts wont be as accurate.

[Neale]

Isn't there also a gcode parameter which affects accuracy at corners? You can either specify stop/start for maximum accuracy but lose feed rate at corners, or give a maximum error value so that Mach or LinuxCNC can approximate the corner to maintain cutting speed. Coupled with a max acceleration figure, it can all start getting a bit complicated.

[JAZZCNC]

Matt just going to make some things a bit clearer for sake of others not picking on you here mate but it's not clear and your Soooooo wrong on some it. .

The way i think of it is, the Acceleration and Velocity settings in Mach act like your speed limiter, they over-ride whatever settings the CAM software specifies in the job.

As mentioned above, Mach is your speed limit. So if you have set your velocity to 6000mm/min in mach, and your tool to 8000mm/min in vectric (or your cam software) mach wont let the machine exceed 6000.

The machine jogs (ie with the arrow keys, at the maximum speed stated in mach)
The machine moves (between cuts, at whatever speed the Gcode outputted by your cam software) -- but limited by mach.

This is true but I'll make it clearer because it does apply here.

In the G-code this will only apply to the G1 moves which have F### feed rate parameter but all G0 moves will be at the Velocity setting in motor tuning. So if your over tuned on velocity then you will still lose position if G0 moves are in the g-code even if you lower the feedrate in Cam software.!

Its also critical (although I cannot explain why) to ensure the Acceleration and Velocity settings are the same for both your Y axis and X axis. (Z can be different) Otherwise (I found) it effects 90deg corners. Where (I think) the machine is still decelerating (moving) when the next move starts

Personally (others will disagree, I set the accelleration very low (often 100), and the velocity to a comfortable speed for the machine as Im far more interested in quality, than speed) I also find having acceleration set so low helps when jogging your machine manually into a start position and also makes a nice smooth start and stop to each move.

This is the bit your Sooooo wrong about matt... .Lol

It's not critical and perfectly fine to have differant setting for each axis, Mach will only go fast has the slowest axis anyway when moving 2 axis at same time. Try it.!! . . Double the Speed of Y axis velocity (if machine can do it) and home the machine and jog away good distance and Type G1 X0 Y0 F ( Feed value abobe X axis velocity or same has Y axis velocity) in the MDI box.

Like Jonathan pointed out most if not all of trouble is coming from having the Accel far far to low.
Molasses moves faster than that so MAch's gets tired of waitng and Knobs off to the pub for a quicky but has few too many so when it gets back it's forgot where it was upto and thinks bollocks to it i'll just carry on from here and that's why your getting square circles.!!. . . . Mach pissed.!! . .Lol . . . . Ok well maybe being bit silly but the point is your messed up on tuning.!

You really want to be within 500-800 just for normal use and 1000 and above this if doing mostly 3D type work.
Just remember the golden rule that you can't have High Accel and High Velocity you need a balance and you won't go wrong.

[Jonathan]

In LinuxCNC you can specify a tolerance on the G64 command, so the controller sacrifices constant speed to maintain the toolpath within the specified tolerance. e.g. put 'G64 P0.05' at the begining of the G-code and the path will not deviate by more than the P from the true value.

It's not critical and perfectly fine to have differant setting for each axis, Mach will only go fast has the slowest axis anyway when moving 2 axis at same time. Try it.!! . . Double the Speed of Y axis velocity (if machine can do it) and home the machine and jog away good distance and Type G1 X0 Y0 F ( Feed value abobe X axis velocity or same has Y axis velocity) in the MDI box.

You've raised a mildly interesting point there, which I think is worth expanding to show why what you've observed occurs. The velocity of each axis cannot exceed the values in the motor tuning, however the speed of the machine (i.e. the feedrate) can, unless the machine is only moving in one axis. This occurs because when two axes are moving at given velocities, the resultant feedrate is the vector sum of these velocities. One way to visualise it is as a right angled triangle, where (for example) the velocities of X and Y are the sides adjacent to the right angle - the length of the hypotenuse will equal the feedrate.

Example 1:
Suppose you set your maximum velocity settings for X and Y both to 1000mm/min, home the machine (so it's at 0,0) then enter 'G0 X100 Y100'. Mach will move both X and Y as fast as it can (as it's a G0 move), so the feedrate you actually get is ., assuming the machine can accelerate to that feedrate within the specified distance.

The practical upshot of this is you can specify a feedrate higher than the velocity setting, and get that feedrate in some circumstances.

Example 2:
Same as example 1, except we enter 'G1 X100 Y200 F1100'.
The required speed is 1100mm/min, so the following must hold: ., where X and Y are the X and Y axis velocities.
The Y axis must travel twice as fast as X to go in the correct direction (as 200/100=2), so we have .
We also have the condition .,due to the motor tuning settings.
From (2), ., so substitute that into 1:
.
.
.
Whence,
.

(You can also solve this graphically quite easily - which may be more intuitive.)

So the X and Y velocities do not exceed 1000mm/min, yet the machine can in this example cut at 1100mm/min.

In reality, it's probably not a good idea to use this 'feedrate bonus' as it makes the feedrate a function of the direction in which the machine is travelling, so unless you're cutting a single straight line the feedrate you actually get will vary (continuously if an arc move).

[JAZZCNC]

From (2), ., so substitute that into 1:
.
.
.
Whence,
.

I see you like your new toy. . . . Lol . . .(Shame Nobody got F'#$ing clue what your saying. .)

[Clive S]

I see you like your new toy. . . . Lol . . .(Shame Nobody got F'#$ing clue what your saying. .)

Dean: its a recipe for a sponge cake anybody can see that ..Clive

[GEOFFREY]

I see you like your new toy. . . . Lol . . .(Shame Nobody got F'#$ing clue what your saying. .)

Hey Jazz, I was under the impression that you were into latex!!! G.

[JAZZCNC]

Hey Jazz, I was under the impression that you were into latex!!! G.

Nah but I do have a pallet of Latex I can sell you.???. . . .Gloves. . . .( Also Nitrile and Vinyl if that's your fetish. . Lol)

[itsmillertime]

Nah but I do have a pallet of Latex I can sell you.???. . . .Gloves. . . .( Also Nitrile and Vinyl if that's your fetish. . Lol)

OMG lol What did I just walk back into?

I wanted to update you on my progress with getting this jumping/ noise issue out of the way. Well... I figured that you guys Jazz I think mentioned it first that I was expecting too much and the speeds were too high with the rapid and cutting settings.

Well, Lo and behold after trying lots of different tuning combinations. I discovered setting the speeds too low also made for some horrible sounds. But I came across a another post with some supplier recommended settings. That were indeed a lot slower than what I had been gave.



These settings were actually found to be the best for my 6040 machine. And they are

steps velocity accel' step dir
X 320 2000 200 10 5
Y 320 2000 200 10 5
Z 320 800 150 10 5


My old settings that made the occasional noise and stalled the motors were

steps velocity accel' step dir
X 320 3000 200 3 1
Y 320 3000 200 3 1
Z 320 800 200 3 1


It sounds loads better now and doesn't fly about making my table shake slightly with the speed of movement of the gantry.

I have re-cut a few test pieces and haven't had the horrible sound or any missed steps.... yet ;-) Never say never eh!


I just want to say a really big thanks to all you guys for all of your invaluable advice I really do appreciate it and would have been stuck without all your help. cheers guys

Andy :-)