OOZNest CNC jerk values

psychotik2k3

Re: [OOZNest WorkBee](screw driven)

@catalin_ro said in OOZNest WorkBee, screw driven:

After a lot of tests done with G2/G3, based on issues discovered while trying to machine a rather small Aluminum item, the maximum jerk should be limited to 300mm/min for X, Y and U. So change in config.g the line for M566 to:

M566 X300 Y300 Z12 U300

Hi @Catalin_RO Sorry to dig up such an old post but when i found this maybe you have the answer for me:

i have an OX CNC powered but duet 2 wifi clone and i'm quite happy with it i have mostly 0.1 to 0.3 max tolerance when milling aluminium which considering that the ox is far for rigid (especially the x grantry in torsion when plunging).

but every time i try to mill circles they are not exactly round, and it don't come from the material as i do have the same problem with a test milled with acetal.

when i check my circles, the diagonals radius are always 0.6mm bigger compared to the X or Y radius.

I just checked and my jerks (don't knwo why i have these values probably from the configurator) are set to

M566 X500 Y500 Z500               ; Set maximum instantaneous speed changes (mm/min)

would that explain my circles no so round ?

oh and i just checked on the gcode generated as i use ramps for plunging i have both succession of G1 and G2 used, here is an eaxmple for one depth (got 5 other layers like this one)

; MOVEMENT_RAMP
G1 X55.535 Y28.094 Z1.984 F400
G1 X55.158 Y27.84 Z1.968
G1 X54.776 Y27.593 Z1.952
G1 X54.391 Y27.352 Z1.937
G1 X54.001 Y27.119 Z1.921
G1 X53.607 Y26.891 Z1.905
G1 X53.21 Y26.671 Z1.889
G1 X52.808 Y26.457 Z1.873
G1 X52.404 Y26.251 Z1.857
G1 X51.995 Y26.051 Z1.841
G1 X51.584 Y25.858 Z1.825
G1 X51.169 Y25.673 Z1.81
G1 X50.751 Y25.494 Z1.794
G1 X50.33 Y25.323 Z1.778
G1 X49.906 Y25.159 Z1.762
G1 X49.479 Y25.002 Z1.746
G1 X49.05 Y24.853 Z1.73
G1 X48.618 Y24.71 Z1.714
G1 X48.184 Y24.576 Z1.698
G1 X47.748 Y24.449 Z1.683
G1 X47.309 Y24.329 Z1.667
G1 X46.869 Y24.217 Z1.651
G1 X46.426 Y24.112 Z1.635
G1 X45.982 Y24.015 Z1.619
G1 X45.537 Y23.925 Z1.603
G1 X45.09 Y23.844 Z1.587
G1 X44.641 Y23.769 Z1.571
G1 X44.191 Y23.703 Z1.556
G1 X43.741 Y23.644 Z1.54
G1 X43.289 Y23.593 Z1.524
G1 X42.837 Y23.55 Z1.508
G1 X42.383 Y23.514 Z1.492
G1 X41.93 Y23.487 Z1.476
G1 X41.476 Y23.467 Z1.46
G1 X41.021 Y23.454 Z1.444
G1 X40.567 Y23.45 Z1.429
G1 X40.112 Y23.453 Z1.413
G1 X39.658 Y23.464 Z1.397
G1 X39.204 Y23.483 Z1.381
G1 X38.75 Y23.51 Z1.365
G1 X38.297 Y23.544 Z1.349
G1 X37.844 Y23.587 Z1.333
G1 X37.392 Y23.637 Z1.317
G1 X36.941 Y23.694 Z1.302
G1 X36.492 Y23.76 Z1.286
G1 X36.043 Y23.833 Z1.27
G1 X35.596 Y23.913 Z1.254
G1 X35.15 Y24.002 Z1.238
G1 X34.706 Y24.098 Z1.222
G1 X34.263 Y24.201 Z1.206
G1 X33.822 Y24.313 Z1.19
G1 X33.383 Y24.431 Z1.175
G1 X32.947 Y24.557 Z1.159
G1 X32.512 Y24.691 Z1.143
G1 X32.08 Y24.832 Z1.127
G1 X31.651 Y24.98 Z1.111
G1 X31.224 Y25.136 Z1.095
G1 X30.799 Y25.299 Z1.079
G1 X30.378 Y25.47 Z1.063
G1 X29.959 Y25.647 Z1.048
G1 X29.544 Y25.832 Z1.032
G1 X29.132 Y26.023 Z1.016
G1 X28.723 Y26.222 Z1
; MOVEMENT_FINISH_CUTTING
G2 X14.521 Y55.31 I11.811 J23.778 F825
G2 X16.04 Y56.55 I1.519 J-0.31
G1 X65.03
G2 X66.548 Y55.31 J-1.55
G2 X28.723 Y26.222 I-26.014 J-5.31

thanks

Catalin_RO

Hi @psychotik2k3,

If you dig further into that old thread, you will see that the jerk could be increased over time. Right now I still have it set to 400mm/min for X and Y, much lower for Z and 4th axis. But this parameter is used only when changing the movement direction on each axis. When machining/printing circles the jerk speed should normally not be used, or it shouldn't really matter, as the circles come up on each axis as a very natural movement, especially if the circle is large.

Have you considered looking for possible backlash sources? From my own experience that is the most overlooked cause for such problems. And it must be checked in all components.

I had my own ShapeOko clone above 5 years ago, but bought as a complete kit from an UK company. The delivered parts where of very good quality and I could get very precise results on Aluminum even if it was using belts and my milling motor was a beefy Proxxon weighing almost 3kg.

I also have access to a low cost Chinese engraving laser, with a flimsy frame and small steppers. That one exhibits problems similar to yours and we have tracked it down to the pulleys on the steppers. Somehow they are not perfectly mating with the belts and introduce some backlash, no matter the feed rate.

Even the 0.1..0.3 tolerance on your milled Aluminum parts indicate more of a mechanical issue. Even with my old ShapeOko clone I could get under 0.05mm precision. With my WorkBee I had to spend quite some time to properly determine the best steps/mm values as it is much easier to manufacture a close to perfect belt than to machine a leadscrew. Now I have to do the same for the upgrade - QueenBee (btw, pretty rigid with the 800W spindle).

So, if I were you, I would start milling small squares, like 50mm*50mm, and check their size, edges and corners. And that should be done at least in 9 places so you can check all extremities and central areas of the axes. if you have around also a decent machinist square, you can also insure indirectly that the machine is perfectly squared. The backlash should also be visible when machining squares, usually by not having perfect 90° corners or straight edges.

The Z-axis lack of rigidity may have two components. One is a rotation around the X axis due to the flimsiness (can't call it otherwise!) of the V-slot in that setup, and another one is rotation around the X axis plate (grab the spindle perpendicularly to the X axis, from the front, and try rotating it CW and CCW - you might find some wobble). The rotation around the X axis make impossible to machine thick items with perfectly vertical edges and tend to easily brake small end-mills (had my share of broken end-mills with the WorkBee), but it can be ignored for thin items (3-4mm thick!). The rotation around the X axis plate, though, produces a lot interesting artifacts, including some backlash-like. Also, this rotation around the X axis plate produces thick pieces that are smaller at the top than at the bottom on the X axis.

So, do some tests on acetal, better if 10-15mm thick, and check for all angles and sizes. From there a lot of things can be understood and it will be easier to find the problem. Check the resulting pieces after machining in each position of the OX. When you find a problem, just stop and ask as it would be a pity to waste the material and the time.

psychotik2k3

@catalin_ro thanks, if the shipping costs where not that high i would go to teh queenbee pro, because it got interesting solutions about the rigidity on the X/Z axis.

On my side the flex is on torsion around the X axis, i mitigate a little by bolting both 2060 together but it's not enough.

i'll check on the z gantry around the Y axis as you mentionned to see if i have some.

0.05mm tolerance ? woaw, and i was quite happy with my 0.1mm.

i have to check if it changed or not but my machine is squared.
I had to replace the pulley because yes i had huge backlash because of that. But once again all parts came from ooznest, and if i have to redo them then i would probabley go to original gates belt and pulley to be sure.

i will try some pieces and yes i do have a smal square to check

thanks for the informations.