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Mach Discussion => General Mach Discussion => Topic started by: AlexanderJamesGuitars on February 04, 2016, 05:35:46 PM

Title: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: AlexanderJamesGuitars on February 04, 2016, 05:35:46 PM
Hey everyone.

I have some toolpaths where I cut out a guitar neck. While doing any straight cuts, my CNC router runs great. When I get into doing the heel or volute carve on the guitar neck, the CNC is going through A LOT of little code to make the moves and it can start to shudder / jitter pretty bad. It shakes the whole CNC.

I am running those paths at 50 IPM but Mach 3 only says it makes it to 10-15 IPM for all those lines.

I don't know anything about CV mode but could it be that? Or would it be my post processor for Mastercam X4?


Any help would be greatly appreciated.
Thanks.
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: robertspark on February 04, 2016, 05:53:31 PM
Can you post your XML file

You will need to call it something unique like Alexander James guitars... Or it won't upload.

Can you paste a bit of the code when this is happening to have a look at?

What is your setup... Parallel port, motion controller (which one), are your drives microstepping, at what resolution?

Give as much info as you can... No one ever says you have provided too much info
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: fixittt on February 04, 2016, 05:57:30 PM
Make sure you are set to constant velocity and not exact stop, see pic for CV setting.

Exact stop mode will make the machine stop at the end of each line and give you what you are describing.

Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: robertspark on February 04, 2016, 06:00:36 PM
...you can also prefix your gcode with g64 in your post processor...
http://machmotion.com/cnc-info/g-code.html/
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: AlexanderJamesGuitars on February 04, 2016, 06:12:00 PM
I am using an Ethernet Smooth Stepper.
My drives are microstepping at 1/13 (I think that is how you write it), or 4000 pulse/rev

I have uploaded my XML.
Here is a sample of the guitar neck volute toolpath that I get a lot of shuddering on:

N100 G17 G20 G90 G40 G80 G64 G49 G0 M05
N102 G8 P1
N104 G90 M5 Z0
N106 G52 X0. Y0. Z0.
N108 G43 H5 Z.25
N110 T5 M6
N112 G0 G90 G54 X7.3898 Y9.0113
N114 S13000 M3
N116 Z.1
N118 G1 Z-1. F50.
N120 X7.4171 Y9.0341 F100.
N122 X7.4443 Y9.0571
N124 X7.4713 Y9.0801
N126 X7.4981 Y9.1031
N128 X7.5249 Y9.1261
N130 X7.5515 Y9.1489
N132 X7.5781 Y9.1715
N134 X7.6047 Y9.1939
N136 X7.6312 Y9.2159
N138 X7.6577 Y9.2375
N140 X7.6842 Y9.2586
N142 X7.7108 Y9.2793
N144 X7.7373 Y9.2993
N146 X7.7638 Y9.3188
N148 X7.7903 Y9.3375
N150 X7.8168 Y9.3556
N152 X7.8434 Y9.3729
N154 X7.8699 Y9.3894
N156 X7.8964 Y9.405
N158 X7.9228 Y9.4198
N160 X7.9492 Y9.4336
N162 X7.9756 Y9.4465
N164 X8.0019 Y9.4585
N166 X8.0282 Y9.4696
N168 X8.0544 Y9.4797
N170 X8.0806 Y9.4888
N172 X8.1068 Y9.4971
N174 X8.133 Y9.5044
N176 X8.1593 Y9.5108
N178 X8.1858 Y9.5162
N180 X8.2125 Y9.5209
N182 X8.2396 Y9.5246
N184 X8.2671 Y9.5274
N186 X8.2953 Y9.5294
N188 X8.3241 Y9.5304
N190 X8.3313
N192 X8.3387 Y9.5303
N194 X8.3463 Y9.5302
N196 X8.3542 Y9.5301
N198 X8.3624 Y9.5299
N200 X8.3707 Y9.5297
N202 X8.3793 Y9.5294
N204 X8.3881 Y9.529
N206 X8.397 Y9.5286
N208 X8.4062 Y9.5282
N210 X8.4156 Y9.5278
N212 X8.4252 Y9.5272
N214 X8.435 Y9.5267
N216 X8.4449 Y9.5261
N218 X8.4551 Y9.5255
N220 X8.4654 Y9.5249
N222 X8.4758 Y9.5243
N224 X8.4865 Y9.5236
N226 X8.4973 Y9.523
N228 X8.5082 Y9.5223
N230 X8.5193 Y9.5216
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: RICH on February 04, 2016, 07:56:49 PM
Are you using steppers or servos?

RICH
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: AlexanderJamesGuitars on February 05, 2016, 09:43:48 AM
I am using closed loop stepper motors.

Here is an ebay link:

http://www.ebay.ca/itm/Leadshine-Closed-Loop-stepper-Drive-motor-HBS507-573HBM20-1000-3PH-2NM-57mm-NEW-/121559936057?hash=item1c4d896c39:g:dxoAAOSwVL1V-OrR (http://www.ebay.ca/itm/Leadshine-Closed-Loop-stepper-Drive-motor-HBS507-573HBM20-1000-3PH-2NM-57mm-NEW-/121559936057?hash=item1c4d896c39:g:dxoAAOSwVL1V-OrR)
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: robertspark on February 05, 2016, 05:28:16 PM
Hello,

Sorry, I have only just got a chance to look at your XML file

Can I ask what leadscrews are you using and what microstep resolution are you running?

Do you REALLY need a step resolution of 0.049 thou per step?

I don't know your setup or how much or little you know, so please bear with me..... (not trying to be a smart A$%%^ or something).

Motor torque diminishes with increased microstepping.

Basically if your drives are set on full step resolution you will get your motors rated torque, however the torque diminishes via the following equation

T actual = Torque Rated x Sine of (90 / microstep setting)

Hence if you are running say 16microsteps.... you get about 9.8% of your motors rated torque...

The rule of thumb is generally microstepping up to about 8 is fine (~20% of the rated torque).

___________________________

I suspect as your drives are closed loop what is happening is your machine is loosing steps as it lacks the holding / stepping torque (because of a high microstep setting) and in turn your drives are trying to automatically correct and jumping

Note..... I've never used close loop drives so its just a guess (only you know your machine, and setup as to why it is configured as it is!)

______________________________

Question.... how are you controlling your router, spindle / mill?

You seem to have disabled M3/M4 controlling output1 on the ports & pins >>> spindle setup tab

And you are not using step & direct / PWM for the spindle but have a defined output 1

____________________________

Although its not your problem..... it may be worthwhile increasing your lookahead to 200 lines on the general configuration tab

Have a look in the FAQ's on the Warp9 site.... if you run out of data at any point this is likely to be your problem.... it comes up quite a bit on the SS forum on the Warp9 site.

Rob

Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: Tweakie.CNC on February 06, 2016, 02:48:24 AM
Quote
Motor torque diminishes with increased microstepping.

Basically if your drives are set on full step resolution you will get your motors rated torque, however the torque diminishes via the following equation

T actual = Torque Rated x Sine of (90 / microstep setting)

Hence if you are running say 16microsteps.... you get about 9.8% of your motors rated torque...

Hi Rob,

Once, this info was correct but it is now many years out of date and still the myth continues to be perpetuated.

The manufacturer's of the various stepper driver chips (eg. Allegro/Toshiba/etc.) are well aware of the stepper motor characteristics and design their circuitry accordingly. Basically their chips are ‘smart’, using a form of back emf to proportionally increase the current through the energised windings to balance the available torque in relation to a micro-step position and shaft loading.
It’s a few years now since I carried out comparative angular deflection testing between a number of different manufacturer’s chips and I can confirm that the test stepper motor’s rotational shaft deflection, under a controlled load, (which is basically, holding torque) was within a knat’s whisker between whole step positions and micro-step positions.

Tweakie.
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: robertspark on February 06, 2016, 03:11:10 AM
Here is another way to look at my steps comment.....

Looking at your G-code, your x and y movements are in the range of 0.0001"   or 0.1 thou

Which to me is really impressive....

so if your step resolution is ~0.049, you are getting two steps for every commanded movement

Hence half'ing your microstep resolution will align your steps to your commanded motion. (and improving your stepper motor torque)

You also need to consider backlash (you cannot really eliminate it.... just reduce it to the point that it does not affect what you are doing..... in order for a ballscrew (nut or anything) to slide over a leadscrew, it requires tolerance to provide slip and movement.... hence you always have some small amount of backlash)

0.1 thou of movement is impressive, and I know nothing about what you're machining or your required surface finish or detailing, but what does 1 thou of cutting accuracy do for you (0.0254mm).... have you tried it, is it noticeable?   it will again 1/2 your microstep resolution and increase your available stepper motor torque.

I think at that sort of resolution of cut I would also be considering if there is any movement in spindle, guide rails etc

Only you know your machine and I am by no means an expert, only you know your machine and these are just things to consider.

___________________________________________________

(Tweakie, thanks very much for the guidance, I'll take note and stop myself perpetuating the myth..... I think it makes a little difference, I went from 50uStep resolution to 10uStep on my plasma and the torque improve dramatically (AM882H drives) .... I considered the step resolution of what I was asking the machine to really do..... with a blunt instrument (plasma cutter) and the finish I was getting and my backlash).



Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: RICH on February 06, 2016, 07:36:06 AM
Something to try, would be to use exact stop for the posted code.
Air run the code.

Reduce velocity values for each axis in steps of 20% each time you run it and see if the problem stops.
If not, then start reducing the accel values by 20% at the lower velocity setting. See if the problem stops.
If not, then your motors ( actualy it could be a combination drive / motor / settings ) may be the problem and it has to do with acceleration. To make small combination moves you need almost instantaneous accel ...decell.  
Fortunately if your problem is repeatable you can play around and try to find what is causing it.

FWIW:
I had problems with my mill and it drove me bonkers. Wasn't skipping in the traditional sense, ( couldn't hear a skip at those silly 0.0001" moves), could not tell exactly when,  it was random in the 1000's of lines of code and never had a problem with 2D machining.  Put dwell in the code and could never duplicate it at different locations and like you the code was for very small moves ( had external DRO's to compare Mach to actual location).

Adjusted the machine to reduce / MINIMIZE the torque required to move all axes and still MINIMIZE the backlash.Adjustment done such that I could measure the required torque to just move the axes and also see what the backlash was. In the end the required torque to just move the axis was reduced from around
80 / 90 in oz to about 15 in oz and for 350 in oz motors that's a great improvement.
Things improved.....so i changed the steppers to 500 in oz and have not had a problem since.

In general a lot more torque was available which provides for improved acceleration ( you higher up on the curve for given motor rpm.....actual in or closer to max power on the curve.

Just some thoughts and have fun playing around,

BTW.....One can do all the advanced calculations etc. they want using computer programs but
when the day ends good old fashion test, measure, try is sometimes required.

RICH

Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: stirling on February 06, 2016, 09:12:59 AM
I am using an Ethernet Smooth Stepper.

I might be wrong here but I seem to remember something about (some/all ?) external controllers suffering from buffer underflow when dealing with lots of extremely short lines.

Certainly in the snippet you posted, the code starts with lines in the order of 1/100ths of an inch long but towards the end it drops to lines a few thou long. (see pic).
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: stirling on February 06, 2016, 09:34:46 AM
Re: the great micro-stepping/torque myth/truth debate - crikey this one runs doesn't it? -  ;D

How about a PRAGMATIC approach?

Micro-stepping a) increases resolution (up to a point) and b) reduces resonance.

Re: a) - more than 10 is pointless. The argument goes something like this: A stepper has a full step accuracy of +/-5% or a 10% swing. That means it's accurate to within 0.18 degrees. That just happens to be the resolution of factor 10 microstepping. So, how can you increase resolution beyond the accuracy its capable of? - answer: you can't it doesn't make sense.

Re: b) - We're running full step or perhaps low micro-stepping and we get resonance. That resonance builds up and results in a stall. Stall happens when torque is zero. We increase micro-stepping. It no longer stalls. Which therefore has the most torque?
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: AlexanderJamesGuitars on February 06, 2016, 09:59:34 AM
Hey everyone.

So, this is all a lot for me to take in because I would not consider myself professional at CNC but here is what I have gathered.

1. Try halving my micro stepping and see if it produces a smoother result
2. Play with reducing velocity and acceleration to produce a smoother result



I also wanted to try to give more back story. The shuddering during this toolpath is definitely repeatable, it is not random.
When really trying to hear and see the shudder, I have been running the CNC dry (just running the toolpath in the air, not cutting anything).
I used to have 125 oz in. steppers on the machine and I do remember the shuddering while running this toolpath then.
The closed loop steppers (linked to in a previous post by me) are new and this is my first time running them through movement tests.


I will try 1 and 2 up there ^ but please let me know if you have any other possible solutions or you need any more information from me.
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: robertspark on February 06, 2016, 10:12:30 AM
Stirling, thanks for that, I learn't something with (a) [never considered].

(b)... can you not tune out with digital programmable drives?   (Leadshine AM882)

Say I'm using 1/2 stepping on a plasma z (because I've not got the right leadscrew... yes!) ... 2mm / 200 steps / 2 micro steps... 0.005mm / step

Or if I'm using a better l leadscrew (10mm pitch).... 10 / 200 / 2 = 0.025mm per step .... or would I be better with 4 u Step resolution or some other custom number?

Something I've never known... can you set a stepper drive with a microstep resolution of 5 (odd number multiples).

Thanks for the time & guidance.

__________________________________________________________________________________

Back to the OP & helping

With regards to the external motion controllers and buffer under flow..... would increasing the lookahead not help and also changing the SS velocity update frequency too?

Lookahead is presently set at 100 lines, and the velocity update frequency 1kHz..... although you'd need to reduce the update frequency to increase the ESS buffer  (or reduce your step frequency update too.....  which is 128kHz..... hence halving the ustep resolution will allow for the ESS step frequency update to also be reduced to 64kHz)

Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: ger21 on February 06, 2016, 11:11:19 AM
He said he's using closed loop stepper drives, so doesn't that throw all the microstepping issues out the window? You're dealing with an encoder, and probably can't adjust the microstepping to the motor, as it's probably related to the encoder count.

Jerky motion can be caused by a combination of lookahead and the various CV settings. First thing you should do is turn off all of the CV options, both on the Settings page and in General Config. But make sure CV mode itself is turned ON.

Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: BR549 on February 06, 2016, 11:17:12 AM
I think you have the old problem of a marginal table with a bit of loose motion and NOT a heavy weight frame Which gives you little damping effects AND running microsegmented code that Mach3 does not handle well. Have you bumped up your look ahead to at least 200 ??  Do you have any setting set in the CV mode.  

The problem starts for mach3 not being able to handle CV in microsegmented code very well so it ends up running as exact stop. Then the banging starts as the frame not being a rigid structure cannot dampin the resonance properly. Mach3 has a bang bang planner and that does not help matters with fast tables.

SO you end up with shake rattle and roll. AN Scurve planner would smooth thing s out a lot.

(;-) TP
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: AlexanderJamesGuitars on February 06, 2016, 01:43:17 PM
Hey everyone.

Here is what I have come up with:

Just right now, I noticed every time the toolpath would start up, the CV MODE would turn off and I was originally not noticing this.
The start of my code looked like this:

N100 G17 G20 G90 G40 G80 G64 G49 G0 M05
N102 G8 P1
N104 G90 M5 Z0
N106 G52 X0. Y0. Z0.
N108 G43 H5 Z.25
N110 T5 M6
N112 G0 G90 G54 X7.3898 Y9.0113
N114 S13000 M3
N116 Z.1
N118 G1 Z-1. F50.

ETC...

I then wrote in a G64 (as previously recommended) and noticed this turned on CV MODE.
The NEW code:

N100 G17 G20 G90 G40 G80 G64 G49 G0 M05
N102 G8 P1
N104 G90 M5 Z0
N106 G52 X0. Y0. Z0.
N108 G43 H5 Z.25
N110 T5 M6
N112 G64 G0 G90 G54 X7.3898 Y9.0113
N114 S13000 M3
N116 Z.1
N118 G1 Z-1. F50.

Here is what happened:

Almost all of the shuddering went away, and I started having a smooth, curve like motion come out of the CNC toolpath. The toolpath was running A LOT better. There is only a small amount of shuddering of very rapid small moves from front to back (backlash?), but it is barely noticeable.

I timed the toolpath for efficiency:
200 lines lookahead

At 3mins 48 secs, CV MODE on, 9890/9890 lines finished
At 3mins 48 secs, EXACT STOP on, 2366/9890 lines finished (very shuddering and jerky motion)




Now this seems to have solved my issue but I am left with a couple questions:

1. What should I have turned on in relation to CV MODE (other than CV MODE)?
2. Do I need 4000 pulse/rev for microstepping or is there a better amount to use to optimize my system?
3. Is there any other things (settings, etc) you folks can think of to help make my system run smoother?
4. Why does my GCODE turn off CV MODE?
5. Should I always have CV MODE on?
6. How can I program Mastercam to always input a G64 into my GCODE?

Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: BR549 on February 06, 2016, 02:22:09 PM
IF you noticed on the first line it did include teh G64 (CVmode) BUT it then turned it off with G8 (exact Stop)

(;-) TP
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: robertspark on February 06, 2016, 02:44:30 PM
is G8 a valid code with Mach3?

http://machmotion.com/cnc-info/g-code.html
http://machmotion.com/documentation/Software/Mach3/Mach3%20GCode%20Language%20Reference.pdf
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: BR549 on February 06, 2016, 03:16:55 PM
Don't believe everything you read about Mach3    :o 8)
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: robertspark on February 06, 2016, 03:19:37 PM
Hahaha.... Yeah I'm very very quickly learning that.... Everything I read seems to be turning out to be wrong...

Aghhh.... I hope someone will keep their eye on the manuals for m4 and keep them current and useful
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: RICH on February 06, 2016, 03:20:08 PM
So need to pencil in another G code on to the cheat sheet!  :D

RICH
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: RICH on February 06, 2016, 03:21:14 PM
Maybe we should put the G8 command on the "Did You Know This" thread.......

RICH
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: RICH on February 06, 2016, 03:23:15 PM
Oh, BTW,
That's why they keep Terry around.....he knows where the poop is!  >:D

RICH
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: robertspark on February 06, 2016, 03:26:20 PM
I think I've learnt more from him in the last few weeks than I have reading stuff... <><><>removes hat
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: Overloaded on February 06, 2016, 04:06:17 PM
From the Mach4 manual Rob posted:

"G09 – Exact Stop: G09 is a non modal exact stop. Machine accelerations cause
corners to be slightly rounded; when a true sharp corner is required G09 should be
used. Although similar to G61 in function, G09 is not modal while G61 is."

Is this the equivalent of G08 in Mach3 ?

(bowing w/hat removed as well)
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: Overloaded on February 06, 2016, 04:15:39 PM
http://www.machsupport.com/forum/index.php/topic,25975.msg183136.html#msg183136

"Right now, G8 is equal to G61 (exact stop) and G9 is equal to G64 (cancel exact stop).

Same as Mach3."

???
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: BR549 on February 06, 2016, 04:28:02 PM
AH GEE Do I gotta give up teh magic monkey dust again  >:D

In mach3 G8 and G9 are the same as G61 G64.

In Mach4 G9 changes to a one time Exact stop move and I hope that G8 is not there any more.

now for the next lesson when it is late at night and you can't sleep simply bring up teh MDI line and start from G0 and keep going up till you reach G1000. IF you see it does not error (;-) then it must do something, THEN you figure out exactly what it does do (;-) You MAY find some things that carried over from teh original EMC code.

Same with #vars (;-)  I created a serach program in CB that prowled all teh Variables up to 30,000 to see what might show up. Then compared the OLD EMC code with Mach3s code references to see what might be lurking there.

Same with Mach3's CB editor. You would be surprised what works based on Visal Basic calls  and is NOT in teh Mach3 CB manual.
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: Overloaded on February 06, 2016, 04:39:53 PM
Flippin' n' a floppin' .... gotcha   ;)

(i'll take an ounce of that there monkie dust, put it on mu account  ;D )
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: BR549 on February 06, 2016, 04:44:31 PM
In this case teh User was using a Fanuc post cause Fanuc uses teh G8 P0 and P1 to turn off/on exact stop.

And someone is getting very Quick with Mach3 searches (;-) Old QuickSearch McGraw

NOW you know, (;-) TP
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: Overloaded on February 06, 2016, 04:50:42 PM
Well, that dust is a workin'. You're reading my mind !
My next ? was regarding the "P*" I see in various searched examples.


From a search   ...    http://www.csun.edu/~hws86622/CNC_Mtrl/G_Code.html
G08 Ramping function at block transition / Look ahead "off"
G09 No ramping function at block transition / Look ahead "on"

Sometimes searching gets confusing.
Best to go directly to the Monkey Dust Man".

Thanks again Terry,
Russ
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: BR549 on February 06, 2016, 04:50:52 PM
In this case teh User was using a Fanuc post cause Fanuc uses teh G8 P0 and P1 to turn off/on exact stop.

And someone is getting very Quick with Mach3 searches (;-) Old QuickSearch McGraw

I also have a copy of ALL teh old Yahoo Messages even from teh Master5 days. There are MANYMANY thousands of pages of messages from that era of Mach3  Art did a LOT of explaining back then and it is ALL in teh archives.  Another late night best reader (;-).  Art is quite teh story teller (;-)

I would do the same for this site but don't have a clue as to how to get them all.

One day they are going to disappear and it would be a shame NOT to have a copy.  

NOW you know, (;-) TP
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: stirling on February 07, 2016, 05:18:01 AM
Now this seems to have solved my issue but I am left with a couple questions:

1. What should I have turned on in relation to CV MODE (other than CV MODE)?
2. Do I need 4000 pulse/rev for microstepping or is there a better amount to use to optimize my system?
3. Is there any other things (settings, etc) you folks can think of to help make my system run smoother?
4. Why does my GCODE turn off CV MODE?
5. Should I always have CV MODE on?
6. How can I program Mastercam to always input a G64 into my GCODE?


1. Nothing if you can help it. All the CV settings cripple CV to one extent or another.
2. Unlikely - 2000 p/rev would be more normal. (caveat - I know zip about those fancy dandy servo type drives).
3. I'd be looking at why your CAM produces so many lines of code. It seems excessive to me. Are you for example converting arcs to lines unnecessarily? Also take another look at the pic I posted, why have the lines suddenly changed from around 3 hundredths to 7 thousandths for no apparant reason?
4. I think this one's been done...
5. Pretty much - unless you have good reason for turning it off - and then you'd want to look at 1. again first.
6. Looks like it does already - you need to stop it sticking the G8 in afterwards.
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: ART on February 07, 2016, 07:03:25 AM
>>3. I'd be looking at why your CAM produces so many lines of code. It seems excessive to me. Are you for example converting arcs to lines unnecessarily? Also take another look at the pic I posted, why have the lines suddenly changed from around 3 hundredths to 7 thousandths for no apparant reason?

    This was the root of your trouble. CV was the cure in this case, but M3 ( and all controllers) have a problem with very small
segmented motion at times. Its a question of predictability. Even if in CV mode, a trajectory planner has to computer various
equations on accel, velocity and time on each segment as part of the process. Tell ArtCam (or what your using) to put out in
lower resolution and it gets much smoother.

        CV of course must be used in this type of file, but it works best with larger segments, it always has. Ignore the microstepping
stuff ( my advice), I use as high a micro-step as I can, balanced with speed, if I need more speed Ill lower the micro-stepping,
but in general , and in almost all cases, the higher the micro-stepping, the smoother the motion.. 
      Higher micro-stepping also allows using higher frequencies to control with , and the higher the kernal base frequency,
the smoother the motion as well. For steppers, micro-stepping is pretty much unavoidable for performance..

Nice to hear you've smoothed out. :)
Art


Art
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: BR549 on February 07, 2016, 11:21:17 AM
HIYA ART , You do know you just contradicted you r own advise to only run as high a kernal speed as you need to make the speed you are running (;-).

Now they are going to try as high as a kernal speed as they can get teh PC to run (;-)

Just a thought, (;-) TP
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: robertspark on February 07, 2016, 12:21:49 PM
The original poster is using a smooth stepper... Set the kernal speed at 25khz and leave well alone is the advice given on the warp9 forum.

Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: AlexanderJamesGuitars on February 07, 2016, 12:42:26 PM
3. I'd be looking at why your CAM produces so many lines of code. It seems excessive to me. Are you for example converting arcs to lines unnecessarily? Also take another look at the pic I posted, why have the lines suddenly changed from around 3 hundredths to 7 thousandths for no apparant reason?


I create all of my geometry in Mastercam X4 and it also writes the GCODE as well. It seems to put out BOTH the G64 and G8 codes. I don't understand why it is doing this. It is saying; use CV MODE, then turn off CV MODE.

I also have no clue why Mastercam is producing so many lines of code. Could it be that my geometry in Mastercam X4 is fine but my post processor in Mastercam is what is writing the excessive amount of code lines?

Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: ART on February 07, 2016, 12:59:50 PM
The reason Darwin was advised to be run as low as you can use is because Darwin and mach3 used CPU time and space in your system. At 25Khz, it used about
25% of your CPU speed, ( hidden from you, your true cpu speed was 0 - 75%), at 100Khz, you have 0% left.. so I always advised keeping it low,
to increase true CPU capability.
  In actual fact the best smothness is at 100khz, but no computers could really handle 100khz, but my system ran very happily
at 45Khz, so I rarely used less. However, take a hypothetcial system at 1000 steps per inch at 0 uSteps, at 25Khz he would get  25
inches per second at a set smoothness, increase microstep to 10 , he now has 10,000 steps per inch, but only 2.5inches per second. If he then bumps
to 250,000 as the core speed, he gets the same original 25IPS, but at a much smoother motion, and a higher resolution... one of the benefits
of an external controller.

Just saying...
:)

Art
.
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: BR549 on February 07, 2016, 01:00:12 PM
It is because it is using a Fanuc Post not a mach3 post ??  Micro segmented code IS normal for 3d machining it is the nature of the beast to be able to carve great detail and surface features. It is just some controllers handle it better than others. Being able to use very high accel rates in Z helps it run faster as well. A slow Z slows down the entire process.

(;-) TP

Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: ger21 on February 07, 2016, 02:40:21 PM
There may be a tolerance setting in MasterCAM that determines segment length in g-code.
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: stirling on February 08, 2016, 06:02:52 AM
I create all of my geometry in Mastercam X4 and it also writes the GCODE as well. It seems to put out BOTH the G64 and G8 codes. I don't understand why it is doing this. It is saying; use CV MODE, then turn off CV MODE.

I don't use Mastercam but my guess would be that if you post your post file someone here will be able to take out the offending G8 line.

I also have no clue why Mastercam is producing so many lines of code. Could it be that my geometry in Mastercam X4 is fine but my post processor in Mastercam is what is writing the excessive amount of code lines?

Could be either or a combination of both I suppose. Regards the sudden change though, my guess would be your CAD geometry is suspect. Did you create it from scratch or did it start out life as a .dxf profile? That said though - if it's cutting ok now (with the G8 removed) - why worry.
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: BR549 on February 08, 2016, 10:34:41 AM
HIYA Ian remember this is a 3d profile Cutting file not a flat 2.5d. It is really hard to get away from micro segmented lines and still have great detail in teh carving. 

AND YES if it works good now NO problems.

(;-) TP
Title: Re: CNC router shudder and jerky / jitter doing 3D toolpaths
Post by: stirling on February 08, 2016, 11:01:29 AM
Hi Terry - I don't think this IS 3D though. Check out the code he posted. There's no Z going on.

Whatever though - what I'm getting at is there's no reason (that I can see at least) why the lines SUDDENLY change length dramatically. Check out the pic I posted again, There's NO detail there that would require it. Maybe I'm wrong - just thinking.

Anyway - as we've both now said - it's working so it doesn't really matter.