Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: John Watkins on April 13, 2009, 11:37:29 AM

Title: Problem with cutting quality when turning
Post by: John Watkins on April 13, 2009, 11:37:29 AM
Hello everyone.  This is my first post so thanks in advance for helping out the new guy.

I have a problem which I believe I have narrowed down to Mach III mis-interpreting the g-code I give it.  I get a grooved pattern on the preview screen that is exactly duplicated when the part is cut.  No change in feedrate or depth of cut has any affect.  The gouges are always in the exact same place. 

First instinct says that the g-code is based on bad geometry, but this whole curve is only three lines of code, two G02s and one G03.  Any ideas?  I get perfect cuts if I go diagonally or straight.  It only does this on curves and it does the exact same thing if I use all G01s.  Any help is greatly appeciated.

Here's how the curve looks in my CAM software's simulation screen.....

(http://cncguitarparts.com/images/visualturn_screen.jpg)

and here's what it looks like in Mach III.  I would normally just attribute this to imperfect graphics, but the parts are very similar to what's on the screen.

(http://cncguitarparts.com/images/mach_screen.jpg)

Title: Re: Problem with cutting quality when turning
Post by: Hood on April 13, 2009, 01:20:34 PM
Can you attach the code and also the xml for the turn profile you use.
Hood
Title: Re: Problem with cutting quality when turning
Post by: John Watkins on April 13, 2009, 01:31:39 PM
Hood, thanks for replying.  Here's the relevant code;

G18
G2X0.3378Z1.0790K-0.1328I0.4212
G3X0.4566Z1.2939K0.2208I-0.1455

Not sure what you mean by xml for the turn profile.  I created the profile in Rhino, created the tool path in VisualTurn, and posted to Mach III
Title: Re: Problem with cutting quality when turning
Post by: Hood on April 13, 2009, 01:35:05 PM
The xml has all of your settings, if you are using the standard turn profile then it will be found in your Mach3 folder and it will be called Mach3Turn.xml. You will need to copy it to a different location on your drive and then rename it as the forum will only accept a file being posted once. Suggest you rename it JohnWatkins.xml 
 To attach it to the forum use the additional options button on the reply page and browse to the location of the renamed xml.
Hood
Title: Re: Problem with cutting quality when turning
Post by: John Watkins on April 13, 2009, 01:40:16 PM
a picture is worth a thousand words.....

(http://cncguitarparts.com/images/rough_surface.jpg)
Title: Re: Problem with cutting quality when turning
Post by: John Watkins on April 13, 2009, 01:40:54 PM
going to get the xml file now.  thanks again...
Title: Re: Problem with cutting quality when turning
Post by: Hood on April 13, 2009, 01:44:37 PM
Also could you attach the actual G Code file as well please.
Hood
Title: Re: Problem with cutting quality when turning
Post by: John Watkins on April 13, 2009, 01:49:00 PM
trying this again.  not sure what happened.
Title: Re: Problem with cutting quality when turning
Post by: Hood on April 13, 2009, 02:24:07 PM
Dont see any real issues with your profile and code looks good. I am not sure what type of motors and drives you have but you may want to try increasing the pulse width in motot tuning, try it at 3 or even 5.
Hood
Title: Re: Problem with cutting quality when turning
Post by: John Watkins on April 13, 2009, 02:25:33 PM
Going to do that right now.  I'll let you know what happens.  Thanks again for taking the time.  I greatly appreciate it.
Title: Re: Problem with cutting quality when turning
Post by: John Watkins on April 13, 2009, 02:38:36 PM
Same result.  Maybe a little less pronounced.  Any other ideas?  I've gone as far as to move the job around within the travel area to see if it was a blem in one of the screws.  Nothing seems to change it.  One IPM or 40 IPM; same thing.


Here it is with the step and dir pulse set to 5 on both axis.

(http://www.cncguitarparts.com/images/2nd.jpg)
Title: Re: Problem with cutting quality when turning
Post by: Hood on April 13, 2009, 02:43:48 PM
Try setting the active states to high on each axis, it probably wont help but is worth a shot.
 How tight/rigid is the machine/tooling?
 What kind of motors and drives?
Hood
Title: Re: Problem with cutting quality when turning
Post by: John Watkins on April 13, 2009, 02:50:49 PM
How do you get it to travel in the right direction after doing that?

The machine is a harbor freight retrofit using some 90v NEMA 34s and a camtronics control box.  The Z screw is a known-good four-start screw with a very tight polymer anti-backlash nut.  The X-screw is the factory screw held tight with the coupler to the motor.  I suspected the X screw right away, but anything it's doing that would cause this would also show up in a diagonal/taper cut, right?
Title: Re: Problem with cutting quality when turning
Post by: Hood on April 13, 2009, 02:55:25 PM
Homing and Limits, reverse axis.

Your pics show an interrupted cut, is that the shape of the stock you are turning? Was the diagonal on a round or similar to that (if it is as shown in pic :) )

Not familiar with Camtronics stuff, will have a search around in a while.
Hood
Title: Re: Problem with cutting quality when turning
Post by: John Watkins on April 13, 2009, 02:56:27 PM
Here are a couple of pics of the setup.
Title: Re: Problem with cutting quality when turning
Post by: Hood on April 13, 2009, 03:46:58 PM
If you can try a piece that will have the full 360 degrees getting turned.
Hood
Title: Re: Problem with cutting quality when turning
Post by: John Watkins on April 13, 2009, 03:58:12 PM
I have done that in the past with the same result.  I don't mind trying again, but I'm not really able to do it now because all the material for this batch has already been through the milling operations that give you what you see in the pics.  I may have to wait until the weekend to troubleshoot this further because we have a deadline for those parts.  We'll just run them this way and sand them for now, but if anyone has another idea that I could try when I'm able, I'm all ears.

Can't thank you enough for your help.

John
Title: Re: Problem with cutting quality when turning
Post by: marcel beaudry on April 13, 2009, 05:47:43 PM
Hello John

Your setup is very prone to vibration, part is far away from the chuck,tailstock could be shortened.
is the tool at the right height
are the tailstock and the shaft that holds the part center .

Just a tought

Marcel
Title: Re: Problem with cutting quality when turning
Post by: Graham Waterworth on April 13, 2009, 06:14:18 PM
Check that the encoder is not loose on the shaft, you could also try swapping the x & z motor encoders over.

Graham
Title: Re: Problem with cutting quality when turning
Post by: RICH on April 16, 2009, 10:00:36 AM
Hi John,
May be all wet but here are a few things you may want to try.
I echo what Marcel posted.
Try leaving a little more stock to be left in the rough cuts and do more than one finishing cut.
You may also try a different tool tip, one that shears / peals off the wood instead of scraping. Similar to doing the turning manualy on a wood lathe. High clearance and rake, razor sharp, depends on the wood. Also can try doing two at a time by glueing two halfs together with a piece of paper between and splitting them thus you get continuity of the cut around the profile.
Like i said, may be all wet, just some thoughts, been a long time since i did wood turning.
RICH
Title: Re: Problem with cutting quality when turning
Post by: SteinarN on April 16, 2009, 10:28:25 AM
I don't think the setup is weak. The machine is of steel and he is turning wood.

Back to the first post. These imperfections is clearly visible in the Mach3 toolpath. This fact is a strong indication it is nothing wrong with the workpiece setup but that the fault is within Mach3 or its setup or the code or anyting other influencing how Mach3 interprets the G-code.
Title: Re: Problem with cutting quality when turning
Post by: Overloaded on April 16, 2009, 10:39:20 AM
Could it be a VERY coarse "steps per" resolution ?
JAT,
RC
Title: Re: Problem with cutting quality when turning
Post by: marcel beaudry on April 16, 2009, 11:30:04 AM
One thing you can try ,is taking a free cut or a cut of .005 if the profile is still not smooth then he as other problems . As for the machine is made of steel it does not matter
deflection is one of the biggest problem of the machinist world .
Title: Re: Problem with cutting quality when turning
Post by: Hood on April 16, 2009, 11:46:10 AM
I don't think the setup is weak. The machine is of steel and he is turning wood.

Back to the first post. These imperfections is clearly visible in the Mach3 toolpath. This fact is a strong indication it is nothing wrong with the workpiece setup but that the fault is within Mach3 or its setup or the code or anyting other influencing how Mach3 interprets the G-code.
He is turning with interupted cuts which can induce deflection and  resonance, whether that be in the machine, the tool or more likely in this case the stock itself.

The imperfections in the toolpath in Mach are due to the graphics and nothing to do with what will actually cut.

Hood
Title: Re: Problem with cutting quality when turning
Post by: Overloaded on April 16, 2009, 11:56:58 AM
Quote
He is turning with interupted cuts
Hood,
   Exact same results with un-interrupted cuts.
 Reply #15-16

RC
Title: Re: Problem with cutting quality when turning
Post by: Hood on April 16, 2009, 12:06:35 PM
RC
I saw that reply but the OP is going to test again so we will see.
 It would be interesting to see a line drawn on a board with a pen mounted vertically in the toolpost.

Hood
Title: Re: Problem with cutting quality when turning
Post by: Overloaded on April 16, 2009, 12:13:09 PM
Yes..it would.
Also, to do the end of a piece of alu or hard plastic directly in the ghuck. As ridgid as possible.
Thanks,
RC
Title: Re: Problem with cutting quality when turning
Post by: RICH on April 16, 2009, 08:53:36 PM
John,
Could you please post a dxf file of the profle.

Do you realize that that your cutting air with "part" of the finish cut so that your left with marks in the
profile.  I BACKPLOTTED  your code and it is not MACH but your code as created.
See attached.
RICH 
Title: Re: Problem with cutting quality when turning
Post by: RICH on April 16, 2009, 09:52:38 PM
Hi All,
HM......... I just tried that code again and got a different display........  ???  ???
So maybe just ignore reply #27 for now!  :-\

RICH
Title: Re: Problem with cutting quality when turning
Post by: Overloaded on April 16, 2009, 10:07:08 PM
Rich,
 I tried it too and got what you did initially.
What I noticed though, was that even in the area that WAS cut with the finish pass, there are still many grooves/humps.
RC
Title: Re: Problem with cutting quality when turning
Post by: RICH on April 16, 2009, 10:15:35 PM
Hi All,
Can someone else try John's code and see what it looks like in MACHTurn?
SEE ATTACHED as i never came across this one.   ??? So maybe i am not going bonkers!  ;)
RICH
Title: Re: Problem with cutting quality when turning
Post by: RICH on April 16, 2009, 10:21:44 PM
RC,
Maybe " WHAT TAUGHT THOUGHT HE SAW ONLY THOUGHT HE SAW"   ???
Hate to shed doubt!
RICH
Title: Re: Problem with cutting quality when turning
Post by: Overloaded on April 16, 2009, 10:22:11 PM
Rich,
 I can vouch for you.....you're NUTS ! :D
No really... I get exactly as you with RAD. and DIA. settings.
RC :)
Title: Re: Problem with cutting quality when turning
Post by: RICH on April 16, 2009, 10:30:11 PM
HM....
You should try it with the SS Plug in!
I can deal with the "humps and bumps" but if the display is screwy your not sure what
your dealing with without  turning it. I don't even trust my backplotting on this one.

RICH
Title: Re: Problem with cutting quality when turning
Post by: Overloaded on April 16, 2009, 10:48:43 PM
Something else....None of our displays show the zig-zag tool path that John is showing with his rough AND finish passes.
Title: Re: Problem with cutting quality when turning
Post by: RICH on April 16, 2009, 10:49:37 PM
Maybe Graham can comment on the code as there are G18 G17 ?? then also about the G70.
I never used the G70 and my book say's it a Fanuc code??

RICH
Title: Re: Problem with cutting quality when turning
Post by: RICH on April 16, 2009, 10:58:11 PM
RC,
The roughs are straight lines even though they look rather smooth.
When i backplotted the file i got small segments instead of a smooth curve for the finish cut.

Still would like a DXF from John.

What Mach Version are you using? I using 3.042.024 and the standard screen set.
RICH
Title: Re: Problem with cutting quality when turning
Post by: Overloaded on April 16, 2009, 11:10:23 PM
R.020 and std lset
RC