Hi, I am a new bee.  If I posted this post in the wrong place, please let me know and direct me ...

I was attempting to draw a spiral using the MACH3 software (latest version) and two G201 stepper motor driver  with G901 multipliers.

When the cnc draws the spiral, at low speed, I get even spirals.  When the speed (velocity/acceleration) changes, the spiral becomes flat-edged at the X and Y axis because it all of a sudden jurks the arm ... When I repeat the same run again, it repeates the same pattern exactly - with the error (so, I am thinking it is not missing a step.  Is that assumption correct?)

Pleas ehelp.

Dan

Hi, Dan

It could be a number of thing's, Post your dxf & G-code file's, Use the REPLY & Additional Option's button.

If the Flat's are at 3, 6, 9 & 12 O-Clock, It's probably a backlash Issue (slop in your axises) that needs correction.

Chip

Dan - when you say a spiral, do you mean a circle - i.e. a G2 (or G3) command on the MDI window. As Chip says. this is possibly backlash.

You do not say, however, what you machine is, or how the axis are controlled. Is this a milling machine, or a router, are the axis controlled by a threaded rod, or a toothed belt, or what.

You must first set up the steps per unit correctly, which you probably have done. Your motors should then be tuned to give you the best speed for reliability performance, and then your machine should be checked for backlash.

Once you have done that, you can draw a circle - the big problem with a circle is that the direction of each axis changes at least once, and more than likely twice, and it is when your machine changes direction that problems occur.

Gentlemen, thank you for taking the time to address my question.

What I am using is a CNC router (from K2CNC) which I am using to dispense glue on a board in a spiral manner.

I was able to correct the problem.  It turned out that the speed was very hign and the acceleration low (set to 45 ...) When I increased it to 80, 90 and then 100, it worked.

Now, I have another problem, the G code I am using was written by this guy I no longer have the contact info for.  I believe it was written using Master Cam (code listed below).  The code was generated using a tool-size of 1.5 (with the assumption that the successive spirals - of dispensed glue - have a bleed of 1.5 inches, so that the successive spirals do not touch each other).  The problem, however, is the "bleed" varies depending on the flow-rate, the height from which the glue is dropped, the viscosity, etc. 

In short, what I need is code that I can run with different tool size (gap between successive spirals).  How do I modify the G code and have versions for tool-sizes of .75, 1.0, 1.125, 1.25 and 1.5?  I do not have the software to generate G code, what can I do?

I much appreciate your help. G-code is below:


%
O0000(14SPIRAL)
(DATE=DD-MM-YY - 24-03-09 TIME=HH:MM - 13:45)
(MCX FILE - T)
(NC FILE - C:\DOCUMENTS AND SETTINGS\DAGNEA\DESKTOP\14SPIRAL.NC)
(MATERIAL - ALUMINUM INCH - 2024)
( T244 |  1-1/2 FLAT ENDMILL | H244 )

(A is for Valve position -- 0=closed 1=fully open)
(F is for feed/speed, its modal command/persist until changed)
(G1 linear move with F requirement)
(G0 is rapid move at max speed)

N106 G1 G90 G54 X5.151 Y3.5397 A0 F400
F1200
G0 A.15
N112 G2 X6.25 Y0. R6.25 
N114 X-6.25 R6.25
N116 X5.151 Y3.5397 R6.25 A.2
N118 X6.1875 Y0. R6.5625 A.6
N120 X-5.4375 R5.8125
N122 X4.6875 R5.0625
N124 X-3.9375 R4.3125
N126 X3.1875 R3.5625
N128 X-2.4375 R2.8125 F1075
N130 X1.6875 R2.0625 A.5 F1000
N132 X-.9375 R1.3125 A.4 F800
N134 X.1875 R.5625 A.3 F550
G1 A0 F100
N144 M30
%


Dan

Tried using the circle pocket wizards?
  Setting the toolsize to what you want and having the % stepover set to 100 should give you the abilty to make the code do exactly what you want.
Hood

Hi, thank you for your replay. 

I am afraid I am not familiar with "the circle pocket wizard".  I am totally new to this.  Will you please guide me as to how to do this and what to use ...

Thank you.

Dan

Click on the wizard button as shown below, open the circular pocket wizard, enter your dimensions especially paying attention to the stepover and tool size to give you the spiral width then press Post code button and you will see the result. As you will see the last full revolution will close in as it coes round so you may need to edit that last few lines of motion out of the code.
Hood

Thank you so much, Hood.  This is a great help!

I just generated the G-code; I am trying to understand all the params, reverse the direction (it now goes from in to out).  I trully appreciate it.  If you know where I can get a legend for the params and/or some documentation, it would be great.

THank you!

Dan

There is no documentation , its all fairly straightforward, if you dont understand what a setting is for then try it and generate the code and you will probably see what it does by looking at the toolpath display. If you double click on the toolpath  display it will give you and isometric view, double click again and it goes back to  plan. Hold down right mouse when in the toolpath window and you can drag the image, hold left you can rotate, shift and left held down it will zoom as you move etc etc , these may help you see more clearly what a changed setting is doing.
Hood

I tried it, it does.  Thank you so much for taking the time.

Dan