Finish pass

Discussions around the CAM Add-On of QCAD.

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lagnat
Junior Member
Posts: 24
Joined: Mon Dec 07, 2020 4:58 pm

Finish pass

Post by lagnat » Sat Dec 19, 2020 5:48 pm

I'm new to CAM so my terminology might be wrong but I am looking for a feature that allows me to specify a margin to add onto outside or inside milling operations, and then doing a final pass at full depth without the margin to cleanup tool marks.

I was able to "trick" QCad into doing this for me by lying about the tool diameter for the milling passes. I added a few thou to the specification of the tool diameter, which made QCad cut the part a little fat and the I added another toolpath at full depth with the proper diameter for the cutter. I suspect this is a feature request but thought I'd ask in case I missed something.

CVH
Premier Member
Posts: 3416
Joined: Wed Sep 27, 2017 4:17 pm

Re: Finish pass

Post by CVH » Mon Dec 28, 2020 4:54 am

Hi,
Leaving something to cut in a gentle and more controlled way, that is what a finishing pass is all about ...
And that start with a larger offset for roughing.
How this is addressed in real world may vary.

An undercut is only the beginning:
https://www.cnccookbook.com/milling-fin ... -lesson-7/

A final cut may even 'overcut'!
Test this!

In a simple setup we usually use a different tool setup:
- a larger offset or an overrated cutting radius for roughing
- Minimum chiprate for finishing (never to low!)
- Never with a rather dull cutter, but not with the newest one either
- Higher Feedrate for finishing, even higher Speed (rpm)
- Lower step-over for finishing pockets
Or one might use a different tool all together.

Direction is also important depending the stiffness of your setup:
https://www.cnccookbook.com/climb-milli ... l-milling/

Diversify side or surface milling.
Diversify size : https://www.cnccookbook.com/micromachin ... g-machine/
Diversify tool type, material ... use the correct tool.
Use a tool calculator.

So, your approach isn't wrong but there is more than an offset to consider.
Under QCAM and even for the same tool, use another tool setup to start with, use another and dedicated CAM path.

Regards,
CVH

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