Drilling operation will gouge if retract hight < start depth

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IMback!
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Drilling operation will gouge if retract hight < start depth

Post by IMback! »

I have a drilling operation width a start depth of 14mm (taken from OpStartDepth) and a Safe Hight of 19mm (OpStockZMax + SetupSheet.SafeHeightOffset) the drilling operation has the default retract height of 10mm.

GCODE:

Code: Select all

(Drilling)
(Begin Drilling)
G0 F4.166667 Z24.000000
G90
G98
G81 F4.166667 R10.000000 X10.000000 Y4.000000 Z-0.866025
G80
G0 Z24.000000
My machine uses linuxcnc. As per http://www.linuxcnc.org/docs/2.6/html/g ... ry-motion G81 F4.166667 R10.000000 X10.000000 Y4.000000 Z-0.866025 will rapid into the workpiece. As this is first operation this occurs before the spindle is at speed.

What is the use case of the Retract hight? why is a retract to safe hight not performed instead? if a usecase for the seperate retract height exists i think its default should be OpStockZMax + SetupSheet.SafeHeightOffset.
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sliptonic
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Re: Drilling operation will gouge if retract hight < start depth

Post by sliptonic »

IMback! wrote: Sat Jul 27, 2019 2:07 pm I have a drilling operation width a start depth of 14mm (taken from OpStartDepth) and a Safe Hight of 19mm (OpStockZMax + SetupSheet.SafeHeightOffset) the drilling operation has the default retract height of 10mm.

GCODE:

Code: Select all

(Drilling)
(Begin Drilling)
G0 F4.166667 Z24.000000
G90
G98
G81 F4.166667 R10.000000 X10.000000 Y4.000000 Z-0.866025
G80
G0 Z24.000000
My machine uses linuxcnc. As per http://www.linuxcnc.org/docs/2.6/html/g ... ry-motion G81 F4.166667 R10.000000 X10.000000 Y4.000000 Z-0.866025 will rapid into the workpiece. As this is first operation this occurs before the spindle is at speed.

What is the use case of the Retract hight? why is a retract to safe hight not performed instead? if a usecase for the seperate retract height exists i think its default should be OpStockZMax + SetupSheet.SafeHeightOffset.
In general terms, 'safeheight' is the height at which it's assumed to be safe to move horizontally WITHIN an operation. Safe height should be at least the top of the stock.

'clearance height' is the height at which it's safe to move horizontally BETWEEN operations. Clearance height should be higher than any part of the stock and also higher than any vise or clamp.

retract height is the height the bit will pull back on peck moves to clear chips. This should be at least as high as start depth but might be higher depending on local conditions.

If the hole is at the bottom of a pocket, the start depth would be the floor of the pocket. You wouldn't want to retract to the safe height on every peck.
Russ4262
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Re: Drilling operation will gouge if retract hight < start depth

Post by Russ4262 »

Would it be beneficial to add code that would measure the depth of the hole and set a suggested retract height to at least the top of the hole plus an extra safe allowance?

Russ
IMback!
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Re: Drilling operation will gouge if retract hight < start depth

Post by IMback! »

sliptonic wrote: Sat Jul 27, 2019 7:25 pm retract height is the height the bit will pull back on peck moves to clear chips. This should be at least as high as start depth but might be higher depending on local conditions.
right that would be my expectation, its not however how this works at the moment; it defaults to 10mm. also i do not expect a rapid g0 move below start depth at the beginning of the operation. The retract height generally makes no sense when not pecking.

Russ4262 wrote: Sat Jul 27, 2019 7:48 pm Would it be beneficial to add code that would measure the depth of the hole and set a suggested retract height to at least the top of the hole plus an extra safe allowance?

Russ
I think the retract hight should just default to the safe hight, should be renamed to peck retract and should only be used if the peck is activated.
Last edited by IMback! on Sat Jul 27, 2019 7:59 pm, edited 1 time in total.
chrisb
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Re: Drilling operation will gouge if retract hight < start depth

Post by chrisb »

A use case for retracting not to safe height is this:
To let cooling fluid get to the bottom of a drill hole it is sensible to pull the drill out after having drilled part of the hole.
If it is pulled out all the way it is possible that chips get into the hole.
Going back in again the drill only moves the chips and doesn't drill. If the tool is forced going down, it will break.
Thus it is sensible not to pull the tool out all the way.
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IMback!
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Re: Drilling operation will gouge if retract hight < start depth

Post by IMback! »

chrisb wrote: Sat Jul 27, 2019 10:20 pm A use case for retracting not to safe height is this:
To let cooling fluid get to the bottom of a drill hole it is sensible to pull the drill out after having drilled part of the hole.
If it is pulled out all the way it is possible that chips get into the hole.
Going back in again the drill only moves the chips and doesn't drill. If the tool is forced going down, it will break.
Thus it is sensible not to pull the tool out all the way.
Shure that makes sense with pecking but you cannot have a R value below the operation start depth with a G83 Peck Drilling Cycle in linuxcnc (and fanuc too) as this plane is g0 moved to before the canned cycle starts. To do what you want you need to use g1 movements and not g8x

I have issue with the way the drill operation works when _not_ pecking.Even when pecking on the first hole the tool will rapid into the workpiece with default values! Here is what freecad outputs while pecking G83 F4.166667 Q5.000000 R10.000000 X5.000000 Y5.000000 Z0.000000 note the R10 command, this rapids the tool to 10mm before the canned cycle starts this can be below the operation top and gouge the tool.
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rmu
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Re: Drilling operation will gouge if retract hight < start depth

Post by rmu »

IMback! wrote: Sat Jul 27, 2019 10:30 pm I have issue with the way the drill operation works when _not_ pecking.Even when pecking on the first hole the tool will rapid into the workpiece with default values! Here is what freecad outputs while pecking G83 F4.166667 Q5.000000 R10.000000 X5.000000 Y5.000000 Z0.000000 note the R10 command, this rapids the tool to 10mm before the canned cycle starts this can be below the operation top and gouge the tool.
That one bugs me too. The default value 10 comes from https://github.com/FreeCAD/FreeCAD/blob ... ng.py#L191, maybe the default should be changed to safeheight.
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sliptonic
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Re: Drilling operation will gouge if retract hight < start depth

Post by sliptonic »

IMback! wrote: Sat Jul 27, 2019 10:30 pm
chrisb wrote: Sat Jul 27, 2019 10:20 pm A use case for retracting not to safe height is this:
To let cooling fluid get to the bottom of a drill hole it is sensible to pull the drill out after having drilled part of the hole.
If it is pulled out all the way it is possible that chips get into the hole.
Going back in again the drill only moves the chips and doesn't drill. If the tool is forced going down, it will break.
Thus it is sensible not to pull the tool out all the way.
Shure that makes sense with pecking but you cannot have a R value below the operation start depth with a G83 Peck Drilling Cycle in linuxcnc (and fanuc too) as this plane is g0 moved to before the canned cycle starts. To do what you want you need to use g1 movements and not g8x

I have issue with the way the drill operation works when _not_ pecking.Even when pecking on the first hole the tool will rapid into the workpiece with default values! Here is what freecad outputs while pecking G83 F4.166667 Q5.000000 R10.000000 X5.000000 Y5.000000 Z0.000000 note the R10 command, this rapids the tool to 10mm before the canned cycle starts this can be below the operation top and gouge the tool.
It looks like the default RetractHeight value is hard coded 10 mm. I think I intended the property to be interpreted as a "How high above the start point should the drill retract on each peck" But it's being interpreted as "To what height should the bit retract"

How should we use the property? As an absolute height value or as a distance above start depth?
IMback!
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Re: Drilling operation will gouge if retract hight < start depth

Post by IMback! »

I made a pull request with the behaviour as i expect it here:2386

Retract hight is only used on g83 moves, and defaults to opStartDepth. I was not able to make the field an expression because i have not figured out how applyExpression spinbox.expression and so forth work.

I think however that we should be using g83 moves in incremental mode, in witch case the R parameter of G83 is used relative to current peck depth. This is the moste usefull.
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mlampert
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Re: Drilling operation will gouge if retract hight < start depth

Post by mlampert »

sliptonic wrote: Sun Jul 28, 2019 8:17 pm How should we use the property? As an absolute height value or as a distance above start depth?
I would vote for the distance above start depth - that makes sense to me.
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