Hi,

This is my first post on the forum so i hope I have put it in the correct place!

I have been struggling with the attached set of programs. The show the outline of a guitar body with 4 symmetrical tabs at its extents. When the 'outline' code (attached) is machined the body it creates should fit into some MDF blocks that are mounted to the bed and then trimmed down using the 'location' code also attached. 

When machined the body fits exactly one way round but when flipped won't which i guess shows asymmetry. The CAD model has been checked and i have printed a full size outline to double check which all measures up perfectly symetrical.

The code looks symmetrical on the mach 3 toolpath screen, & i have also overlaid the 'outline' code with the same path but machined from the other side  and these join up on the toolpath screen.

Can anyone suggest where this inaccuracy could be coming from? The inaccuracy is in the region of 1-2mm & it is cut the same every time whether cutting through 5mm of wood or just marking the surface of the MDF bed.

I have also attached the xml i am using.

Any help is greatly appreciated!

Could be inaccuracies in your machine.
Gantry or bridge type router ?
Out of square ?
Backlash in any axis ?
Can you post the DXF ?(it's probably OK)
More details about the machine would help.
Russ

Hi russ,

Thanks for the input. The machine is basically as follows just slightly larger.

http://www.worldofcnc.com/3-axis-a3-ballscrew-assembled-cnc-router-package-p-1318.html

I have had good sucess machining other items acccuratly.

I don't have any allowance for backlash, and don't know how to measure if this is a problem can you suggestr soemthing?

A dxf of the outline is attached

Thanks very much

Luke.

The DXF is symmetrical.
Backlash is probably not the problem, it would be minor.
If it shows up with light cuts, it's probably not tool deflection.
I would double check for squareness.
With a precision square or similar to what you have already done.
Mill out a perfect square block, measure it, mill a matching square pocket, then flip the male part and see how it fits in the pocket.
It will show any misalignment.
You can also clamp a good square on the table, indicate one edge true to an axis, then check the other side with the indicator.
Russ

Hi Russ,

I have checked for squareness and machined a block that flipped perfectly.

It is probably also worth mentioning that this has happened across two very similar machines (from the same manufacturer) Running virtually identical mach 3 settings (only the bed dims are slightly diffrent in softlimits)

Could it be something to do with the mach 3 to controller box interface?

Luke.

If the machine is square and the files are correct, you might verify that you are not loosing any steps during machining by checking that the axis' return precisely to a known REF point after the file runs. If all is good there (likely so as it is repeatable between 2 machines) then I would look more closely at the 2 cut files. Some here can back plot your .tap's or you can post the other DXF so we can check for any anomalies.
Russ

Hi Russ,

I don't believe that any steps are being lost as no matter how i try and cut the location feature (contours or pockets) they line up after having returned home... is that correct or could this still not be showing up?

I have atatched the DXF that would be used to generate the code for the location features.

Thanks.

It could be that the CV function in MACH3 is altering your code just a squeak. You r ACCEL rate may be a bit to slow and mach3 cannot create the precise contour needed while in CV mode.

Try cutting it in exact stop mode to verify.

(;-) TP

Hi Luke,
The DXF's look to be fine (other than they show up one twice as large as the other, and very large dimensions)

Noticed also that both of the .tap files have the exact same coords at the outer flats of the tabs indicating there is no offset to allow for the cutter dia.

Not sure where to look now.

Hi TP & Russ,

I have tried to verify the cut running in exact stop but still following exactly the same path!

Is it worth playing with the acceleration and velocity settings beyond this?

Also looked at a PDF about cv mode and my CV dist tolerance is 180units is this high would it have any effect?



Any other ideas?