CNC Issue

T

Tony Zinzola

AzB Silver Member
Silver Member
I'm using Bobcad v21 and Mach3. Whenever I cut circles, they don't seem to be perfect circles. The photo below may be hard to see, but to me they look like squares with rounded edges, creating a near circle.

The cutter is square to the table, I have checked that several times. I've also tried dividing the circle into many pieces and I'm still getting the same thing.

Are there any settings in Mach3 or Bobcad I'm missing?

circle.jpg
 
Cnc

I think John ment are you using a G2 or G3 command to cut the circle.
I just drew a .024 radius cirlce in Bobcad and then converted it to g code for my techno machine.
G0X0.Y0.Z0.1
X0.24
G1Z-0.024F3.
G2I-0.24J0.F10.0
G0Z0.1
X0. Y0.

Line 3 is the actual circle, that's the "J" he's talking about.
If your code looks like that, then it's your machine/controller. I had a similar problem with a maxnc driver set.
 
I just did the same thing and this is what I got:

N1 G00 X0. Y0. Z0.1
N2 X-0.0375 Y0.237
N3 G01 Z-0.125F5
N4 G03 I0.0375 J-0.237F6
N5 G00 Z0.1

This is still relatively new to me, so I can see it's different, but I'm not entirely shore what I should be looking for.
 
Cnc

Well I've never claimed to be a CNC guru, but your code looks good.
You are just starting the circle at a different spot, and cutting in a different direction, either clock wise or counter clock wise. Doesn't matter.
What seems to be happening to me is that the x and y steppers aren't in synch. How and why I have no idea. I do know that circles are a really good test of a machine/driver board combination. Even the ultra high end machines don't cut dead nut's circles. Way above my pay grade.
Who is making the drivers on Lee's machine, I'm sure he's using good stuff, so maybe a tweak will get it humming again.
 
Tony Zinzola said:
I just did the same thing and this is what I got:

N1 G00 X0. Y0. Z0.1
N2 X-0.0375 Y0.237
N3 G01 Z-0.125F5
N4 G03 I0.0375 J-0.237F6
N5 G00 Z0.1

This is still relatively new to me, so I can see it's different, but I'm not entirely shore what I should be looking for.
Click to expand...
That circle is GOOD. Something is going on in your controller. Hopefully it's just improperly configured software.
 
I want you to go to the center of your hole go down to the depth you want and G12/G13 Circular Pocket Milling

G12 and G13 are G-Codes in the part program that specify a circular pocket be milled. G12 causes the pocket to be milled in a clockwise direction while G13 mills counterclockwise. The radius of the circle is typically specified with an "I" command. For example "G12I5" specifies a pocket with a radius of 5 be cut in the clockwise direction. The cutter should be positioned to the center of the circular pocket using a move in a prior block or an X and Y command in the same block. The tool will return to center when the pocket is finished.


If your tools DIA. is not in your cutter comp then subtract 1/2 of it from I
 
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You might try setting for a "climb" cut. For the circle it should be clockwise. Also, check to make sure your table isn't binding, or possibly very loose. It looks to me like the "Square" is following the grain in the wood. JMHO
 
wildbill9ball said:
I want you to go to the center of your hole go down to the depth you want and G12/G13 Circular Pocket Milling

G12 and G13 are G-Codes in the part program that specify a circular pocket be milled. G12 causes the pocket to be milled in a clockwise direction while G13 mills counterclockwise. The radius of the circle is typically specified with an "I" command. For example "G12I5" specifies a pocket with a radius of 5 be cut in the clockwise direction. The cutter should be positioned to the center of the circular pocket using a move in a prior block or an X and Y command in the same block. The tool will return to center when the pocket is finished.


If your tools DIA. is not in your cutter comp then subtract 1/2 of it from I
Click to expand...

That was a piece (not a pocket) that I had a picture of. It was just sitting on a wooden table. I'll try your command though, to make sure that the pocket is cutting round. I'm pretty sure it is. I did a bunch of round pockets yesterday and they all appeared round.
 
Ok, I cut the pocket with the G12 command and it didn't look perfectly round. I also cut a another piece out, making sure I was cutting clockwise and it was the same as the one this morning.
 
Switch To G13 And See If That Gives You A Round Pocket .

If Not There Is A Problem In The Machine (THE LEAD SCREW )They Should Have Wear Compensation In X And Y And They Are Out Of Adj.

G12 clockwise IS CONVENTAL MILLING
G13 CONTERCLOCKWISE SOULD GIVE A BETTER FINISH
 
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If the code is correct......look at your back lash comp. When the cutter is reaching different quadrants of the circle the screw is changing the direction it is turning....if there is slop there will be a problem.


<~~~just something else to think about........
 
If the code is correct......look at your back lash comp. When the cutter is reaching different quadrants of the circle the screw is changing the direction it is turning....if there is slop there will be a problem.


<~~~just something else to think about........







RIGHT that is what I was saying by compensation in the machine if you put a mag base on your table and set a indicator on the spindle and move the table .001 in one direction and then -.001 in the opposite direction it will tell you if that is the problem
 
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Tony,

Check both your lead screw mounts. It looks to me like one or both of your screws are moving lengthwise when they change direction. It is basically the same thing as backlash, but not in the nut.

Royce Bunnell
www.obcues.com
 
I am not sure how your machine/ controller works. But on hardinge lathe, they have a parameter for controlling backlash. With a indicator held somewhere , you should be able to move a very small amount, and tell the control to go to the zero or where it was. Then move the other direction.
What they do is have a record of how much clearance there is. Then the macine knows that when changeing diection, how much the count is off to get to zero.
If your machine has been working fine before and this is a fairly new problem , I would 1st be looking at the obvious things like, are the screws that hold the lead screw in place are still tight, etc. Check that the stepper pulley are not loose, etc.

Neil
 
I spent a long time on the phone with John Roker tonight and it looks like everything is working. He showed me how to calibrate the machine. The numbers that were used before were the ones given to me when I bought it.

I'll see how it's working tomorrow evening when I Have more time to play.
 
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