Cutter Compensation for Rough / Final Cuts

I am profiling some 12 mm steel plate, side frames for a 5" gauge locomotive.
The profile includes deep wide slots for the bearing blocks, and subtle curves.

The desire is to get acquainted with G41/G42, and G41.1/G42.1.

I am getting "Tool radius not less than arc radius with comp" when I load the file with G42, and a small diameter tool.
After investigating I can see the problem, the error message is correct.

I used CAM to generate the path with a specified cutter diameter, then edited the file to add G42 and tool change aiming to get a roughing pass first.

My question is:
What is the best general approach to achieve roughing cuts, then final cuts?

Keep well,
John (in Sydney Lockdown).

 

Thanks for the comments Andy.

I use CamBam and entered the diameter of the desired tool.
The code produced uses some small radius arcs for the tool paths at internal corners.
Eg: for a fillet of R6, a Dia10 tool moves in and arc of R1.

So, if I attempt a G42 with a tool Dia3 (to get a roughing pass), LC quite rightly complains.
I can sort this out, but it appears I am approaching this the wrong way.

What I did was use a slot drill to mark out the desired profile, then a combination of various tools to manually machine up close to the marked edge.
Hence the need for a systematic roughing pass, then a final to size.

One aspect of the descriptions for G42 is that of gouging.
How many steps does LC calculate in advance for G42 ?
Is it just the current step, or does it allow for the subsequent step to avoid a gouge ?

Keep well,
John.

I didn't put cutter comp into the CAM, I hand-edited the file to add G42 and the change in tool (diameter).

I generated separate files for 16, 14, 13, 12, 11 and 10 mm cutters without G42..
All passes used a (12) 10 mm tool, side cut at full depth, and completed this job.
The minimum design fillet radius was 6 mm.

Your suggestion will be taken on board and trialled on the second plate.
That is essentially what I was trying to do.

Another investigation is whether CamBam can be instructed to code with a selected minimum tool path radius.

John.

Andy, thanks for all the help.
Cutter Compensation in CamBam is a new concept for me, as is interacting with the Tool Table.

I assume it would involve:
- draw work piece with minimum internal fillets suitable for the smallest expected tool,
- revise CamBam PreProcessor to include G42 Dn,
- generate the Gcode, with tool diameter zero,
- edit the Tool Table for tool n, sized to provide a roughing pass,
- load appropriate tool,
- run the Gcode,
- edit the Tool Table for tool n, sized to provide the finishing pass,
- run the Gcode.

Is this close to a workable scheme ?

John.

Andy, I will search on CamBam to see if I can straighten out that end.
I should also explore G41.1 possibilities.
Give me a few days and I will provide details of my current job.

Andy,
The attached photo shows the (nearly) finished results.
The plates are 950 mm long.
All of the pockets and bottom edge profile were done with G42.

CamBam used to define the finished cut line with tool diameter 0 (zero), no cutter compensation.

The code is edited to add G42 with nominated tool number.

Tool Table edited with tool diameter larger than actual loaded tool to achieve a a pass some distance from the final line.
Then re-done with progressively smaller nominated diameters in the Tool Table.

Last pass done with fresh tool correctly sized in the Tool Table.

Along the way learned a lot about the way G42 adjusts the path.
It is not overly smart, but it is understandable, predictable and reliable.

Happy to discuss G42 further with anyone who wants a few simple guidance suggestions.

 

Keep well,
John.