GCode for curve incorrect.

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MAX THE MILLER
CNC Expert
CNC Expert
Posts: 144
Joined: Tue 23 Aug , 2011 18:25 pm
Hardware/Software: Denford Triac PC. VR Milling 5.51.0.616

GCode for curve incorrect.

Post by MAX THE MILLER » Thu 22 Feb , 2024 21:30 pm

The attached .DWG file is imported into QT2DD and used to produce a .LCM drawing. The Cam Wizard is then used to create a .FNL file containing the GCode for producing the part.

If a simulation is then run in QT2DD the RH turning tool cuts the curve nearest the chuck correctly. Next I would expect the LH turning tool to cut the curve furthest from the chuck, the billet being sufficiently long to prevent the tool exceeding movement limits on account of its proximity to the chuck jaws.

What actually happens is that the parting/grooving tool cuts a series of steps approximating a curve which is then smoothed out by the parting/grooving tool following a curved path. However the curve is convex rather than concave.

I haven't tried to machine the part for real, so I don't know whether it's a problem with the GCode or the simulation.

Either way can the problem be fixed please?

Thanks, Max.
Attachments
Recess.DWG
(77.54 KiB) Downloaded 39 times
RH TOOL.jpg
RH TOOL.jpg (78.57 KiB) Viewed 372 times
PARTING TOOL.jpg
PARTING TOOL.jpg (76.87 KiB) Viewed 372 times
FINAL SHAPE.jpg
FINAL SHAPE.jpg (73.45 KiB) Viewed 372 times

MAX THE MILLER
CNC Expert
CNC Expert
Posts: 144
Joined: Tue 23 Aug , 2011 18:25 pm
Hardware/Software: Denford Triac PC. VR Milling 5.51.0.616

Re: GCode for curve incorrect.

Post by MAX THE MILLER » Thu 07 Mar , 2024 18:52 pm

I've been doing a bit more work on this and it seems that curves machined in what I'll call the South East quadrant of a circle aren't machined correctly, the GCode produced by QT2DD design being incorrect.

There is no .MML file for a Denford Mirac supplied with QT2DD, so I've been using the file Turn270PRO_recommended_Tooling.MML. It turns out the RH Turning Tool isn't enabled in this file. Enabling it caused the RH Turning Tool to be brought into use to finish turning the curve, but it's still machined as a convex rather than concave shape.

This can easily be remedied by changing the appropriate G02 Circular Interpolation CW instruction to a G03 Circular Interpolation CCW instruction. This is fine for simulation, but not for cutting on a real machine as there's far too much material remaining after rough profile cutting to be removed in a single cut.

The rough profile cutting for this curve is done by the groove/parting tool making a number of side by side plunging cuts on the X axis. These cuts aren't deep enough though and QT2DD is obviously calculating the X values in the G01 Linear Interpolation instructions incorrectly.

I reckon that by editing the G01 instructions to decrease value of the X parameters (diameter turning) I'll get a better approximation to the finished curve, after which the RH Turning Tool can be used to finish off.

I shouldn't have to do this though. QT2DD should do it for me........!!!
Attachments
RHT.jpg
RHT.jpg (77.24 KiB) Viewed 234 times
VRT.jpg
VRT.jpg (30.6 KiB) Viewed 234 times

MAX THE MILLER
CNC Expert
CNC Expert
Posts: 144
Joined: Tue 23 Aug , 2011 18:25 pm
Hardware/Software: Denford Triac PC. VR Milling 5.51.0.616

Re: GCode for curve incorrect.

Post by MAX THE MILLER » Wed 13 Mar , 2024 16:11 pm

This is a file importation problem.

If the .LCM drawing is produced from scratch the GCode is correct although IMHO there is rather a lot of material left to be removed by the LH turning tool when making the final cut on the curve remote from the chuck.

If I import the .DWG file and use that to generate a .LCM file the GCode is incorrect and no final cut is made. The .DWG drawing is a single polyline.

The two .LCM drawings look to be the same, but there is obviously some difference.

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