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Horizontal Drilling using G81 #4528
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drilling cycles only work in the negative direction. while on most machines this makes sense, I also hit this limitation which was already reported on the forum. https://forum.linuxcnc.org/20-g-code/29162-horizontal-drilling-using-g81
I removed the checks, and it works fine in the other direction. no surprise, math also works with the other sign. Any objections to remove the check?
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grandixximo commentedon Sep 13, 2026
I don't think there are valid objections, the limitation itself stems from a lack of imagination of where a drill bit could be mounted, and at most you'd be "drilling" away from your part, which is safe and fairly easy to fix.
rene-dev commentedon Sep 13, 2026
https://github.com/rene-dev/linuxcnc/tree/horizontaldrill
grandixximo commentedon Sep 14, 2026
On second thought, reading the patch, your warning is accurate. A swapped R/Z no longer errors, it rapids to R and cuts the other way, so my "safe and fairly easy to fix" claim was wrong.
How about keeping the check as an INI option instead of removing it:
[RS274NGC] ALLOW_REVERSE_CANNED_CYCLES, default 0 so existing machines keep the typo protection, 1 for machines that drill horizontally. Horizontal drilling works, nobody loses the guardrail silently on upgrade.alex-pres commentedon Sep 16, 2026
+1 to keep check for most machines , it is easy to make error when typing G81 to MDI window.
andypugh commentedon Sep 16, 2026
If you forget the negative sign, in most cases you will just drill away from the work, no harm done.
alex-pres commentedon Sep 16, 2026
when R is less than Z we will get rapid move to R through stock.
if that is incorrect, drill shards will fly near your head, that is what I personally tested )
Not with G81, though, but having additional safety here is clear win. I believe that is rare case when this check must be bypassed.
rene-dev commentedon Sep 16, 2026
ok, I will add a ini parameter.
grandixximo commentedon Oct 12, 2026
@rene-dev still on this? It's been on the back of my mind, forgot to mention it Sunday...
rene-dev commentedon Oct 12, 2026
Its still on my list, but im currently stuck in ui code.