GRBL new post processor with drill cycles G81..G83

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freman
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Re: GRBL new post processor with drill cycles G81..G83

Postby freman » Mon Jul 20, 2020 11:38 pm

Gauthier, I have made small change to get rapid moves in and out of the peck, as is required by the NIST description for G83.

I have used a fixed 3% of the user's peck distance.

https://forum.freecadweb.org/viewtopic. ... ad#p416483

I'm waiting for some comments on whether that is a suitably generic solution for the NIST "backed off a bit" for the downwards rapids.

There's few seconds of video showing it in action.
RatonLaveur
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Re: GRBL new post processor with drill cycles G81..G83

Postby RatonLaveur » Tue Jul 21, 2020 1:33 pm

3% may be a standard, but does it really improve much? it means that 3% of the distance you operate faster (sometimes quite marginally) ? That's overall a rather infinitesimal gain no?

Also, I don't know about NIST, but Haas recommends partial peck, that tends to cut drilling time drastically:
https://www.youtube.com/watch?v=AM6nVgK ... 7&index=36
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freman
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Re: GRBL new post processor with drill cycles G81..G83

Postby freman » Tue Jul 21, 2020 3:28 pm

Thanks for your comment, but I don't think you looked at the code or the vid, or understood the mod.

Say the user picks a Q of 3mm, it drills 3 pulls back to R as a rapid, then rapids back down to Q*0.97 and starts from there at drilling speed down to 2*Q...

This conforms to NIST spec as far as the spec goes and chooses A_BIT=0.03*Q. That is the fluffy bit of the spec which we need to decide for ourselves.

So I gain 98.5% of the travel time at rapid instead of cutting air at tool v_speed.

As your HAAS guy explains, that difference gets huge as you get to more and more pecks.

Now IJK pecks would be cool too , that is even better and would not be too hard to implement.

What I really wanted to know was whether we could use a fixed %age , like 3% or whether there are cases where this one-size-for-all would not work. Or was it not the best guess.

Thanks for the interest. I think you have enough trade experience to comment better now you know what I meant.
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Wsk8
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Re: GRBL new post processor with drill cycles G81..G83

Postby Wsk8 » Tue Jul 21, 2020 5:19 pm

I use an offset of 0,4mm. Why would you need more with a big drill? Why less with a small drill?
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freman
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Re: GRBL new post processor with drill cycles G81..G83

Postby freman » Tue Jul 21, 2020 6:21 pm

Thanks for your input Wsk8. My 3% was just ball park to ensure it did not hit anything at rapid descent speed. Bigger tools tend to work at faster linear speeds so bigger chips and roughness; Q is normally some multiple of tool diam , so I figured a %age of Q was a good starting point.

If you think a set absolute figure for all tools and drilling is better , that's noted. I'm polling for other opinions and advice from those with experience working with different materials.

3% of 3mm is 0.1 mm. Maybe a bit too close if there's some swarf still in the hole.
RatonLaveur
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Re: GRBL new post processor with drill cycles G81..G83

Postby RatonLaveur » Tue Jul 21, 2020 8:48 pm

freman wrote:
Tue Jul 21, 2020 3:28 pm
So I gain 98.5% of the travel time at rapid instead of cutting air at tool v_speed.
I stand corrected and it makes a lot of sense. I apologize for having assumed wrong.
Wsk8 wrote:
Tue Jul 21, 2020 5:19 pm
I use an offset of 0,4mm. Why would you need more with a big drill? Why less with a small drill?
Perhaps the size of the chip and therefore how much it would stay in?
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freman
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Re: GRBL new post processor with drill cycles G81..G83

Postby freman » Wed Jul 22, 2020 7:26 am

Also, I don't know about NIST, but Haas recommends partial peck, that tends to cut drilling time drastically:
https://www.youtube.com/watch?v=AM6nVgK ... 7&index=36
That IJK sounds worth doing but I don't see it in the NIST document I have.

Is that a HAAS extension ? If so, what is FreeCAD policy on such add-ons? I see there already seems to be cases where LinuxCNC takes preference over the standard.

This will need extra inputs in the UI drilling path dlg creating non standard drilling cycles that many controllers will not provide.

I can add this to the GRBL post processor while I'm in there since it looks useful. But there's not much point unless it gets added to the UI as well.
RatonLaveur
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Re: GRBL new post processor with drill cycles G81..G83

Postby RatonLaveur » Wed Jul 22, 2020 11:59 am

Here I don't know really,

Reduced pecking must be also controllable because it depends how long the flutes of the drill bit are. It is necessary to at least bring the flutes back over the surface of the material so they can evacuate chips for example.
GeneFC
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Re: GRBL new post processor with drill cycles G81..G83

Postby GeneFC » Wed Jul 22, 2020 2:08 pm

freman wrote:
Wed Jul 22, 2020 7:26 am
Is that a HAAS extension ?
I believe in most cases Haas machines are in a somewhat different class than GRBL machines. That extension could be quite useful for machines that drill thousands of holes all day, every day. How many GRBL users would see a significant increase in productivity for the same sort of extension? Especially when GRBL does not yet support any type of drilling canned cycles?

There are still lots of improvements that could be made to the Path WB. This one seems pretty far down the list.

Gene
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Re: GRBL new post processor with drill cycles G81..G83

Postby GeneFC » Wed Jul 22, 2020 2:14 pm

RatonLaveur wrote:
Wed Jul 22, 2020 11:59 am
It is necessary to at least bring the flutes back over the surface of the material so they can evacuate chips for example.
Actually there is some thought that this is a bad idea. The drill flutes do a pretty good job of evacuating chips if pulled close to the surface, and pulling the drill bit all the way out of the hole allows some of the junk on the surface to fall back into the hole. It then gets recut when the drill goes back to the working front.

I have seen this in some cases when working with materials like cast iron. Not really a problem for me because I work conservatively.

Gene