safe and clearance height
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safe and clearance height
Hi,
I always find the safe height / clearance height terminology rather confusing but what it means also seems confused.
In the attached FCStd I have a series of drill holes. The approach to the first one is done at clearance height but in between all others it skims along at safe height.
https://wiki.freecadweb.org/Template:Depths/Heights
The above link shows the space between safe and clearance as "space for clamping".
If I had clamped in that zone I would not have any clamps left !
Am I misusing this or is it as confused at it appears to be?
TIA.
OS: Fedora 31 (Thirty One) (LXDE/LXDE)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.22872 (Git)
Build type: Release
Branch: master
Hash: 7c9e0f3a99d94d87e43df9fda09097d62537bb53
Python version: 3.7.9
Qt version: 5.13.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/United Kingdom (en_GB)
I always find the safe height / clearance height terminology rather confusing but what it means also seems confused.
In the attached FCStd I have a series of drill holes. The approach to the first one is done at clearance height but in between all others it skims along at safe height.
https://wiki.freecadweb.org/Template:Depths/Heights
The above link shows the space between safe and clearance as "space for clamping".
If I had clamped in that zone I would not have any clamps left !
Am I misusing this or is it as confused at it appears to be?
TIA.
OS: Fedora 31 (Thirty One) (LXDE/LXDE)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.22872 (Git)
Build type: Release
Branch: master
Hash: 7c9e0f3a99d94d87e43df9fda09097d62537bb53
Python version: 3.7.9
Qt version: 5.13.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/United Kingdom (en_GB)
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- not-safehieght.png (10.97 KiB) Viewed 3109 times
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- not-safehieght.FCStd
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- sliptonic
- Veteran
- Posts: 3459
- Joined: Tue Oct 25, 2011 10:46 pm
- Location: Columbia, Missouri
- Contact:
Re: safe and clearance height
There are a number of ways of thinking about this but I prefer to think of it this way; Clearance height is the height at which the tool will move between operations. Safe height is the height at which it will move between areas in the same operation.freman wrote: ↑Thu Nov 05, 2020 8:06 pm
I always find the safe height / clearance height terminology rather confusing but what it means also seems confused.
In the attached FCStd I have a series of drill holes. The approach to the first one is done at clearance height but in between all others it skims along at safe height.
https://wiki.freecadweb.org/Template:Depths/Heights
The above link shows the space between safe and clearance as "space for clamping".
If I had clamped in that zone I would not have any clamps left !
Am I misusing this or is it as confused at it appears to be?
TIA.
Your drilling example is a good one. You would not want the drill to retract all the way to clearance height when moving between holes or pecking. That would make an operation with many holes very slow.
You should never position the clamps inside the working envelope of an operation but if you have to, you can always manually set the safe height high enough to clear.
Re: safe and clearance height
Thanks for the reply.You should never position the clamps inside the working envelope of an operation but if you have to, you can always manually set the safe height high enough to clear.
So the documentation on this is incorrect. The space indicated as being safe for clamping is NOT safe for clamping. That at least requires some explication and caveats.
If I need to set safe height equal to clearance height to clear clamps, then the distinction becomes null.
Another problem exposed by this example file is that the drilling operation is descending from clearance to safe at drilling speed , not rapid. Since this is supposed to "safe" space , outside of the stock, what is the point in G1-ing this movement. It should G0 down to safe height then G1 from there. Was this done to avoid a specific geometric problem?
If the "safe space" was traversed as a rapid the case, the objection of not moving to clearance between each hole disappears. A rapid up and rapid down would not be a problem.
I don't know of hand whether this notion of moving between different areas within the same operation makes sense on the other 2.5D tools but I can't see it as meaningful here.
The "you should never" argument does not appropriate. This bar is 800mm long. I require intermediate clamping. I have already had to machine the other pockets with safe=clearance, which is indeed a lot slower than it should be.
What is the reference for how this is done and what these terms mean? Is there a standard method, or was this just the way it was chosen to be done when Path WB was written?
Thanks.
- sliptonic
- Veteran
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- Joined: Tue Oct 25, 2011 10:46 pm
- Location: Columbia, Missouri
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Re: safe and clearance height
The diagram is indicating a cross-sectional depth and is accurate in that sense. The issue is about whether clamps are placed inside an xy area that the op assumes is clear.
If you need to put clamps in an area that Path would otherwise expect to be clear, what else would you suggest? How is Path expected to know that you have a clamp in the working envelope?If I need to set safe height equal to clearance height to clear clamps, then the distinction becomes null.
I'll need to study your file closer,including your post processor. Are you sure this is a Path G1 move to start-depth rather than the beginning of a canned cycle?Another problem exposed by this example file is that the drilling operation is descending from clearance to safe at drilling speed , not rapid. Since this is supposed to "safe" space , outside of the stock, what is the point in G1-ing this movement. It should G0 down to safe height then G1 from there. Was this done to avoid a specific geometric problem?
This too gets into the nuance of canned cycles.If the "safe space" was traversed as a rapid the case, the objection of not moving to clearance between each hole disappears. A rapid up and rapid down would not be a problem.
Again,I'm not sure what you expect us to do. There are real-world situations where intermediate clamps are needed but you haven't told me how we should know about them.I don't know of hand whether this notion of moving between different areas within the same operation makes sense on the other 2.5D tools but I can't see it as meaningful here.
The "you should never" argument does not appropriate. This bar is 800mm long. I require intermediate clamping. I have already had to machine the other pockets with safe=clearance, which is indeed a lot slower than it should be.
Good question. Maybe someone with experience in other cam software can weigh in. Maybe we need to create another kind of object or dressup to indicate a no-go or clamping area but implementing it is going to be a nightmare.What is the reference for how this is done and what these terms mean? Is there a standard method, or was this just the way it was chosen to be done when Path WB was written?
Re: safe and clearance height
No, looking at the unexpanded Gcode before the post processor ( inspect g-code ) the canned cycle starts from clearance on the first hole, there is no move down to safe ht, first. So this is not related to any of the post proc code.I'll need to study your file closer,including your post processor. Are you sure this is a Path G1 move to start-depth rather than the beginning of a canned cycle?
Code: Select all
(bar-fix-Drilling)
(Begin Drilling)
G0 F50.000000 Z21.000000
G90
G99
G83 F1.000000 Q3.000000 R-0.500000 X170.000000 Y-15.000000 Z-20.000000
G80
G0 Z3.000000
G83 F1.000000 Q3.000000 R-0.500000 X320.000000 Y-15.000000 Z-20.000000
There may be a case for this ( though I remain to be convinced ) but my point here was that the doc is incorrect. If this is the thinking behind it, the concept of the "envelope" should be a caveat to the current statement this space is "safe".If you need to put clamps in an area that Path would otherwise expect to be clear, what else would you suggest? How is Path expected to know that you have a clamp in the working envelope?
Assuming that the user can tell what route FC will take and anticipate the envelope is not guaranteed, it not always that obvious. I already have a few lumps missing from my clamps where I got caught out by this unsafe "safe space". One thing I did intend to raise at some point is ordering of "base geometry" being taken into account.Good question. Maybe someone with experience in other cam software can weigh in. Maybe we need to create another kind of object or dressup to indicate a no-go or clamping area but implementing it is going to be a nightmare.
Yes, if someone with trade experience could provide input on existing conventions it would be helpful.
I would have thought where there are separate volumes to be removed , as in this case, retraction to clearance would be preferable. I have not thought it through very much for other tool paths but in principal I would think the same would apply. Pocket and helix are pretty directly analogous, maybe you can come up with a geometry where this does not make sense.
I would think a dressup similar to holding tags could be feasible, if needed. I wasn't sure that there was not already a facility for clamps which I had not discovered yet. I'd seen "fixations" appearing the Gcode comments.
Last edited by freman on Fri Nov 06, 2020 8:53 am, edited 1 time in total.
Re: safe and clearance height
I think too, that the documentation is wrong. If course can clamps be in the way on vertical moves, because they are misaligned, but as we currently don't make any proposals where to place clamps, this can be neglected. Indicating clamps in an image can thus affect only horizontal moves. And I would expect "Space for clamping" to be indeed "Safe space for clamping", i.e. it is safe to make horizontal moves above that height. For anything else it is safe to move above stock.
I think we had talked about this quite some time ago and we talked about the typos - Save vs Safe, and I think there was one more. Perhaps it was missing "Finish Depth".
So I think we should correct this (again?) and include "Finish Depth" as well.
Herbert, I think you are the author and you have the source document?
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Re: safe and clearance height
Hi,
I'm out with my motorhome atm and back at Sunday and can make the changes.
I started allready with the change to "Finish Depth", but want to wait with the upload till it is changed at FC to.
yes, - for both.
I'm out with my motorhome atm and back at Sunday and can make the changes.
I started allready with the change to "Finish Depth", but want to wait with the upload till it is changed at FC to.
Gruß Herbert
Re: safe and clearance height
There are different versions of this file in the wiki:
https://wiki.freecadweb.org/Template:Depths/Heights mentioned in OP and
https://wiki.freecadweb.org/Path_Workbench (Path main page)
https://wiki.freecadweb.org/Path_Pocket_Shape (PathPocket)
The latter two are the same.
https://wiki.freecadweb.org/Template:Depths/Heights mentioned in OP and
https://wiki.freecadweb.org/Path_Workbench (Path main page)
https://wiki.freecadweb.org/Path_Pocket_Shape (PathPocket)
The latter two are the same.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
Re: safe and clearance height
The first is an old one, may be i forget to change the link... It's a label "Start Height" at it, - we have a "Start Depth" at Path WB.
Gruß Herbert
Re: safe and clearance height
Great to see agreement this needs clarification.
Until and unless current behaviour is changed, I think the doc needs to explicitly point out that operations will do rapid moves inside this volume and that careful consideration by the user is needed to avoid collision with clamps.
Honestly, I think the logic of current behaviour is flawed. Unless this is consistent from one pocket to the next I really to not see the point in defining two different heights.
As I suggested above , if drill, pocket and helix ops did rapid retraction from safe to clearance and then back down to the next pocket at safe height, then this would all make a lot more sense and still provide fast practical paths.
This may lead to clearer idea of what these two height are for and hopefully some more clarity in naming. Clearance height seems fine to me but since there is nothing "safe" about safe height there may be place of a better name. Maybe retract height, if the functionality I suggest is adopted.
I think "Space for clamping" still implies it is protected space and that this is what the difference between these two confusing terms is about.Indicating clamps in an image can thus affect only horizontal moves. And I would expect "Space for clamping" to be indeed "Safe space for clamping"
Until and unless current behaviour is changed, I think the doc needs to explicitly point out that operations will do rapid moves inside this volume and that careful consideration by the user is needed to avoid collision with clamps.
Honestly, I think the logic of current behaviour is flawed. Unless this is consistent from one pocket to the next I really to not see the point in defining two different heights.
As I suggested above , if drill, pocket and helix ops did rapid retraction from safe to clearance and then back down to the next pocket at safe height, then this would all make a lot more sense and still provide fast practical paths.
This may lead to clearer idea of what these two height are for and hopefully some more clarity in naming. Clearance height seems fine to me but since there is nothing "safe" about safe height there may be place of a better name. Maybe retract height, if the functionality I suggest is adopted.