Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: fenix on July 03, 2012, 07:41:43 PM
-
I am new to this so hopefully the solution is an easy one.
I built my router and have it up and running just fine. I have had success tuning the motors and when I tell it to move a certain distance it does to within .001 inches, which is fine for what I use it for. The issue is that the parts I cut out look like they are right, but are off proportionally by a lot... sometime by more than an inch. I can repeat the part, and while all the parts are the same, they are all wrong by the same amount.
I am using AutoCAD, outputting a dxf to Lazy Cam, creating all of my tool paths and sending it to Mach 3 for cutting. My line of logic is that something is not translating right in one of these steps. I also think this is a software problem and not a machine problem because the parts created are all identical... meaning all sides are completely flush with one another. So repeatability is not a problem, I just need it to reproduce what I drew faithfully.
So if one of you more experienced (not necessarily older) CNC guys out there would be so kind as to point me in the right direction on correcting the error of my ways I would really appreciate it.
Thanks, Dave
-
Hi Dave,
when you cut different parts and they are all wrong by the same amount, it looks to me as it has to do with cutter compensation.
Look if the tooldiameter match the tool you use. look is the G code toolpath with or witout cutter compensation. G42 / G41
If that is ok then be shure scaling is set to 1 . When you import the dxf in Lazy Cam then measure it in Lazy Cam to be shure the size as you expect it.
Alex
-
Hi Dave,
Use your existing system to create the GCode for a square part.
When you load it into Mach check the Program Limits DRO's in the tool path window - do they indicate the correct size of the part ??
When you make the part does it come out to the correct dimensions ??
This will tell you if your problem is with your software or your Mach configuration (steps per unit).
Tweakie.
-
Post your .dxf and the g-code and I'll take a look.
-
Sorry guys,
I have been sick for the past week or so.
I would love to post the g code, but i do not know how to get it out of mach 3 in a manner that I can post it.
All of your replies gave me an ideas though... none of which worked.
Here is what I did... I went into autocad and made a part. I made sure that I was scaled 1:1 before saving as a dxf. The part still did not cut right after going through Lazy Cam, it ended up being 6-3/16" instead of 6" wide. I rechecked the calibration of the axis and they all check out. So, I went and got into v-carve pro and taught myself how to create a part in there and out put it... the damned thing came out at 6-3/16" instead of 6".
So, this tells me that the error is not in AutoCAD, or the Cam program. The axis calibration works out in Mach 3 pro and all of the axis move the designated amount... so where does this leave me??? is there a rogue tool off set that I have missed? How do I set all of Mach 3 pros offsets to a default 0 in a global manner to make sure this is not what is biting me in the butt?
Anyone have any other good ideas?
Thanks for all the help. I have dreamed of having my own CNC machine for more than a decade... I just need to get past this maddening part.
-
Hi Dave,
is your scale set to 1.0 ?
Alex
-
Yeah, I really don't mess with scaling features in mach 3.
-
This would lead me to believe that the part is drawn wrong in AutoCAD.
Or, you're programming for the wrong tool diameter.
-
I would love to post the g code, but i do not know how to get it out of mach 3 in a manner that I can post it.
You can have LC save the code as a file or when in Mach you can click Edit and then save the file.
That said, post both the gcode file and the dxf from ACAD, and we can have a look.
RICH
-
Rich,
Well, duh that makes perfect sense. I have a few things to do this morning, but I will definately get that stuff together and post it later on this afternoon.
-
Rich and everyone,
Sorry for the delay in posting the dfx and the code. Take a look and let me know if there is something amiss.
Thanks
Dave
-
Hi Dave,
If it's any help to you - providing you are using a 0.25" diameter cutter that GCode produces a part exactly 6" wide.
I have a sneaky feeling you may have your axis calibration set incorrectly. ???
Tweakie.
-
Ok...
so I have set the calibration for the tool to move 1". Measuring with a digital caliper, it sure seems to move 1".
Is there a better way to do this?
-
The dxf is no good that you posted. Base on the posted code, the pathing of the file is as shown.So if you cut on the line with a .25" dia cutter
the outside diameter should measure 6". Note that the start point is very far away from drawing 0,0,0,.
You can calculate the steps per unit for each axis or use the axis calibration feature of Mach.
You may want to calibrate based on the longest axis move possible thus inaccuracy wil be less at shorter distances.
Seeming to move without measuring is of no value in CNC work.
RICH
-
Hi Dave,
I am with Tweakie and Rich.
To me it llooks as if the settings are not very accurate. Only a slight lack. But the origin of the part is far away about 1100"
You said accuracy is within 0.001 , but multiply it with 1100 that's the problem. about 1"
Always try to set the origin at a corner or within the part. ( middle) test code by hand the origin is in X = middle Y = lower side
G17G20G0X0Y0
G0Z1
G1Z0.2
G1X1.125F50
Y0.75
X3.125
G3X-3.125Y0.75I-3.125J0
G1X-1.125
Y0
X0
G0Z1
G0X2.2913Y1.5098
G1Z0.2
G3X-2.2913Y1.5098I-2.2913J-0.7598
G1X2.2913
G0Z1
m30
%
Just a thought
Alex
-
Just another thought on this one….
If a 1/16” diameter cutter had been used for this particular toolpath that could explain why the parts are coming out at 6 3/16” wide.
So, with a 1/16” diameter cutter and this toolpath, changing the X & Y Scale DRO’s to 0.9700 should bring the part back to 6” wide.
Just a silly thought.
Tweakie.
-
OOps ... mistake :o
in my last post here.
When the origin is far away like in this case, the size of the part is not affected, only the position is out.
(when she settings are not very accurate)
Alex
-
Fenix....I am also new and learning. When I first started, using a router, my parts were also sized different than programmed. I had not set up the steps of the motors. I am using BobCad and Mach 3.
I used a tape measure, set the move to be 20" and measured the actual move. I then entered the actual move and the program calibrated the adjustment. I had to do this with the X,Y and Z axis.
Good luck.