Cutter Compensation for Rough / Final Cuts

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05 Jul 2021 00:47 #213730 by electrosteam
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).

 

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05 Jul 2021 22:30 #213797 by andypugh
You might be doing radius compensation both in the CAM and in the controller. (ie. twice). If you needed to tell the CAM the tool diamtere then it will already have offset the paths.

One option might be to tell the CAM to use G41, and then you can edit the numbers.

Which CAM?

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06 Jul 2021 02:06 #213817 by electrosteam
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.

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06 Jul 2021 14:32 #213860 by andypugh
What is your input shape? The profile must be a shape that the selected cutter can touch all of for G42 to work.
If the shape is suitable, but then CamBam creates an offset profile with sharp corners because it is adding an offset to the G-code then the resulting path will not be compatible with G42.

So, I think that you probably have to turn off cutter comp in the CAM. Though it is possible to use both, for example using 6mm cutter in the CAM and a 1mm dia then 0mm dia in the G42 for an actual 6mm tool.

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07 Jul 2021 00:40 - 07 Jul 2021 07:16 #213926 by electrosteam
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.
Last edit: 07 Jul 2021 07:16 by electrosteam. Reason: Correction to tool diameter

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07 Jul 2021 07:46 #213946 by andypugh
You mentioned that you told CamBam what the tool diameter was.
If it isn't doing cutter-comp in the CAM then it doesn't need to know.

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08 Jul 2021 05:12 - 08 Jul 2021 05:27 #214007 by electrosteam
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.
Last edit: 08 Jul 2021 05:27 by electrosteam. Reason: add tool diameter zero at generation, add tool loading,

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08 Jul 2021 10:24 #214019 by andypugh
I only used CamBam briefly. When I did use it I let CamBam do the cutter diameter comp. (ie, CamBam offsets the G-code path according to the cutter diameter you give it)
I am not clear whether CamBam has the option to use G42 instead. With some CAm systems I have used there is a choice between compensation-in-CAM (generally the default) and compensation-in-the-controller (ie G42)

I am actually pretty confused about what you are doing now, what CamBam is doing, and what you want to do.

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09 Jul 2021 01:02 #214056 by electrosteam
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.

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04 Sep 2021 03:04 #219571 by electrosteam
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.
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