[jwhitten]

Howdy,

I've been building my CNC Router (an Ox variant) and I've gotten it all up and running and cut a few things, but I'm having a hard time getting it calibrated correctly. I'm using Mach3 and CamBam and I've done the motor calibration bit over and over and I'm certain it's right, but every time I load a gerber file from CamBam into Mach3, Mach3 renders it at around 10 times the specified size. (It does the same thing with LazyCam too). I'm working in Millimeters ('mm') in all my programs. I have Mach3 units set to 'mm' and all axis calibrated in 'mm'. My CamBam drawing is also set in 'mm' and exported to gerber, presumably in 'mm'. But Mach3 keeps reading it and rendering it as if it's in Centimeters (cm). I have searched all the CNC sites and simply cannot figure out for the life of me what I'm doing wrong. I've looked on Google and have seen a few other people having similar issues but nothing that seems really clear and definitive as to what is happening-- is it supposed to be 'mm' but actually interpreting it as 'cm', for instance? I dunno...

Is there anybody here who could help me figure it out?

Thanks!

John

BTW Just to be clear, this is how I'm doing the calibration. I have the 'motor units' set to 'mm', and verified in the Settings page. Then, on the Settings page, I'm using the auto-compute axis button to calculate the right motor values based on measured travel. When it prompts me for a distance, I enter it in millimeters (such as '10') and expecting it to travel 10 literal millimeters-- NOT centimeters! For more accuracy, I generally do it several times and have it travel further each time, like out to the end of the table in millimeters (e.g., '1,000' millimeters). I also test it backwards to make sure it travels the same distance in both directions.


Here are links to the photo / video stream of my project if anybody's interested:

Photos:https://plus.google.com/u/0/photos/1...81671319135809

Videos: https://www.youtube.com/playlist?lis...-XqtrCqmyk6Sq-

[awerby]

The simplest thing to do would be to enter values in the "steps per unit" box that are a tenth of the values that are in there now.

[ger21]

If you go to Config > Select Native Units, is it set to mm's?

[jwhitten]

>>The simplest thing to do would be to enter values in the "steps per unit" box that are a tenth of the values that are in there now.

That is what I do to cheat. But then all the coordinates show as being off by 10. Which isn't the end of the world, but I'm hoping to figure out what (if anything) I'm doing wrong in the first place and why I can't seem to get it set correctly. Unless there is a "bug" in the program or something, then I can understand that and can live with it.

Thanks for the reply!

John

[jwhitten]

>>if you go to Config > Select Native Units, is it set to mm's?

Hi Gerry,

Yes, it is set to 'MM' in the native units. Do you think it's a "bug" in the Auto-Axis calibration routine? Or am I doing something wrong in setting it up.

John

[bhurts]

Are you using a gerber post processor? I am not clear how or why gerber is involved from reading your post.

Ben

[jwhitten]

>> Are you using a gerber post processor? I am not clear how or why gerber is involved from reading your post.

I'm using Mach3 to drive the machine, which uses gcode as instructions. I use CamBam to generate the gcode to feed to Mach3. I've also used LazyCam with the same results. I don't think the issue is CamBam or LazyCam or the gcode that they generate, it's just that when Mach3 reads in the gcode its off by a factor of 10. I think the issue is however is with Mach3-- I suspect it's something in the axis motor calibration function.

From my original post, here is how I'm performing the motor calibration in Mach3:

I have the 'motor units' set to 'mm', and verified in the Settings page. Then, on the Settings page, I'm using the auto-compute axis button to calculate the right motor values based on measured travel. When it prompts me for a distance, I enter it in millimeters (such as '10') and expecting it to travel 10 literal millimeters-- NOT centimeters! For more accuracy, I generally do it several times and have it travel further each time, like out to the end of the table in millimeters (e.g., '1,000' millimeters). I also test it backwards to make sure it travels the same distance in both directions.


Thanks for the reply!

John

[bhurts]

I appreciate your reply but I am still not clear what "gerber" has to do with your setup. Also is your g-code outputting a g21 at the beginning of the code?

Ben

[bhurts]

Or just to see can you post one of the g-code files?

Ben

[jwhitten]

>> I appreciate your reply but I am still not clear what "gerber" has to do with your setup. Also is your g-code outputting a g21 at the beginning of the code?

Yes, there is a g21 at the beginning of the file. I don't think there is any issue with the gcode file, but I will upload one in the morning.

John

[ger21]

What drives are you using? What microstepping amount? Is this a direct drive belt drive? What is the pitch diameter of the pulley? Or, what type belt, and how many teeth?

[jwhitten]

>> Or just to see can you post one of the g-code files?

Here is a gcode file (Hello.zip - see attachments) that I ran last night. It was generated by CamBam and appears to be correct, I don't see any issues with the gcode itself. Rather, it is Mach3 (IMO) which is where the problem lies.

Here is a snippet from the beginning of the file in plain text so you don't need to download it unless you just want to:

( Made using CamBam - http://www.cambam.co.uk )
( Hello 1/1/2015 11:53:34 PM )
( T3 : 3.0 )
G21 G90 G64 G40
G0 Z3.0
( T3 : 3.0 )
T3 M6
( Pocket2 )
G17
M3 S1000
G0 X12.0 Y22.0
G0 Z1.0
G1 F500.0 Z0.0
G1 F1200.0 Y23.5888 Z-0.1687
G3 X12.5085 Y22.0 Z-0.346 I16.5187 J4.4112
G1 X12.0 Z-0.4
G0 Z3.0
G0 X46.0791 Y17.2

John

[jwhitten]

>> What drives are you using? What microstepping amount? Is this a direct drive belt drive? What is the pitch diameter of the pulley? Or, what type belt, and how many teeth?

Hi Gerry,

I'm using GeckoDrive G213V drivers for the X & Y axis, and a "cheap chinese junk" driver for the Z. (I'll upgrade it to a GeckoDrive as soon as I can afford it).

I don't know what microstepping amount, I'm not sure how to tell, I'm still new at this ;-) (I know what microstepping is, but not how to set it up on the driver). The GeckoDrive drivers are installed in their default configuration with the appropriate current-sizing resistors.

This is a Cog-Belt system, similar to rack & pinion but with a belt. The X & Y axis are driven with the cog belt.

Here are the particulars:

GT3 Aluminum Timing Pulley

GT3 Aluminum Timing Pulley - 20 - OpenBuilds Part Store

GT2 (3mm)
20 Tooth
Aluminum
Up to 6mm/1/4" belt width
6.35mm Bore
2 flanges with hub
Set screws included (1.5mm)
Pulley Diameter 18.3mm ID 6.35mm(bore) H 17.6mm Overall OD 26mm

GT3 Timing Belt

GT3 Timing Belt - By the Foot - OpenBuilds Part Store

Pitch: GT2 (3mm)
Width: 5mm

The Z axis is run from a lead screw, here are the details for it:

8mm Metric Lead Screw / ACME

8mm Metric Lead Screw / ACME - OpenBuilds Part Store

Tr8*8
4 Start
Pitch 2mm
Lead 8mm


EDIT: I should also add that I'm using Nema 23 2-phase stepper motors, 200 steps / revolution, 1.8 degree steps.


John

[mactec54]

jwhitten

I don't think you are doing the calibration quite right, when you enter the say 10mm, the next step it will ask you how far it moved, you then put this number in, (the how far it moved number, is whatever the distance it moved,, it may be 100mm or 200mm or some other odd number, this is the number you enter, then, repeat the process, until it is moving the correct distance, that you can measure,you then need to use a dial indicator, to get the perfect setting for each axes, there are some YouTube video's on how to do this that may help

Your program looks ok

[jwhitten]

>> I don't think you are doing the calibration quite right, when you enter the say 10mm, the next step it will ask you how far it moved, you then put this number in, (the how far it moved number, is whatever the distance it moved,, it may be 100mm or 200mm or some other odd number, this is the number you enter, then, repeat the process, until it is moving the correct distance,

Exactly. That is precisely what I'm doing. Any misunderstanding there is simply a failure on my part to communicate that correctly! ;-) If the machine does not move exactly the correct amount, I enter the measured amount and try again. Over and over using long travels to minimize the potential for measurement error. And then doing it backwards (in reverse) to make sure it travels the same distance in both directions.

I don't have any problems with precision. It moves the same distance forwards and backwards. Just the magnitude of calibration. *I* use millimeters and *it* makes things 10 times too big. *I* use Centimeters and it makes things the right size.

If that's the answer and there is a bug in the setup routine, I'm okay with it. I'll make the adjustments mentally. But I know a lot of people use Mach3 and there must be at least a few that use Millimeters as their native units-- why am I the only one who has noticed this??? Obvious Answer-- I must be doing something wrong in setting it up-- but darned if I can see what it is!

Thanks for the reply!

John

[ger21]

What are your steps/unit in motor tuning?

X and Y should be 33.33
Z should be 250.

[ger21]

Actually, the numbers I just mentioned may be wrong, depending on how you have the microstepping set on your drives. Most Geckos are 1/10, but yours are configurable,

[jwhitten]

>> Actually, the numbers I just mentioned may be wrong, depending on how you have the microstepping set on your drives. Most Geckos are 1/10, but yours are configurable,

Hello Gerry,

Mine are currently set for X & Y: 6.709283937 and Z: 398.8419524 and are "dead nuts" accurate, with the exception that they're off by a factor of 10. When I have them set up this way, I can take the extant dimensions from CamBam, draw a line on the board (workpiece), and draw it precisely in Mach3. The only thing wrong will be the apparent coordinates will be off by a factor of 10. When I adjust the motor settings to account for the magnitude difference, the coordinates LOOK right on the screen, but the motor (axis) moves 10 times bigger than what the line is supposedly set for. The motor calibration values were discovered using the interactive motor calibration function in Mach3 which asks how far to move an axis, moves the axis, and then permits the user to enter the measured amount the axis actually moved. I use long moves to minimize the potential error.

Thanks for your assistance, Gerry, I really appreciate it!

John

John

[ger21]

Just go into motor tuning and change the steps/unit to 10x what they currently are.

[jwhitten]

>> Just go into motor tuning and change the steps/unit to 10x what they currently are.

Yes, but then the coords are off in the display by a factor of Ten.