safe and clearance height

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freman
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Re: safe and clearance height

Post by freman »

Herbk, I realise English is not your native tongue but you have consistently referred to "save height" instead of safe height ( it should be safe as in Sicherheit not gesichert). Please pay attention in any changes you make.

I'm not sure that the principal use of this height is anything to do with tool changes, even if it can be used that way. Maybe best to wait until the discussion gets a bit further before doing much editing. "Safe for clamping" should be removed since it is wrong any way.
i don't see the name "save height" as a problem, because it's possible for everyone to make this height save...
The way this works is that this is a user input. But it does NOT result in a safe zone. The user then needs to check what FC produces as an automatic routing between holes and see whether it is safe or know FC well enough to anticipate what routing it will produce.

If the agreed meaning and function of this height level is for horizontal rapids between holes, then the name should probably better reflect that. That is a valid an useful feature, which is fine if it is clear.

Since the difference and meaning clearance height vs safe height is not at all apparent , there is probable good cause to change the name to something clearer.

If wsk8's idea of "keep tool down" is adopted, it could be labelled "keep down height". ( suggestion ).
chrisb
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Re: safe and clearance height

Post by chrisb »

herbk wrote: Sun Nov 15, 2020 8:17 am I will change it to "space for toolchange" asap...
Please wait a bit more before you make any changes until we have found more consense (especially as I think that space for tool change is not at all what it means).

Perhaps the image could be improved by moving the horizontal line from Safe height further down. It can usually be quite near above the surface, while space for clamping is much higher.

Can the image be converted to an SVG? Then others could edit it as well.
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herbk
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Re: safe and clearance height

Post by herbk »

Hi Chris,

yes to all... :)
The Pic is made with LibreOffice, so i can export it to .svg.
Biggest problem is to find it, because it's not at the laptop i'm working with now. But i'm still have it, - i'm sure.
Gruß Herbert
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freman
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Re: safe and clearance height

Post by freman »

I mentioned being able to edit the base geometry list to determine the ordering of drilling a list of holes. That is related to the problem of avoiding clamps inside the "safe zone". I explained in full here with a FCStd and screenshot.

https://forum.freecadweb.org/viewtopic.php?f=15&t=51900
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freman
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Re: safe and clearance height

Post by freman »

Please take a look at the attached file.

Earlier I ran backjob and noticed that the Pocket ops are doing just what I would expect : rapid down from clearance (22mm) to safe ht (3mm), then cutting speed downwards. Retraction between holes it fully up to clearance ht.

This is sensible and agrees with the existing doc that the space between these two heights is safe for clamping.

Clearly this was what was the intended behaviour at some stage and drilling ops seem to have gone down a different route at some point.
Attachments
SBR20-cutout-75.FCStd
(271.16 KiB) Downloaded 75 times
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lrak
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Re: safe and clearance height

Post by lrak »

The problem is the names - they should be changed to protect the innocent. And the default values as well?

Safe height should be call retract-height.
Clearance height should be called Clamp height - or clamp-clearance-height.

The most common clamp height + bolt head ends up at 34mm - so the default probably should be 35mm.

I could see another variable - tool-change-height.

Getting the names right is important.
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GeneFC
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Re: safe and clearance height

Post by GeneFC »

lrak wrote: Sun Sep 25, 2022 10:31 pm Safe height should be call retract-height.
Clearance height should be called Clamp height - or clamp-clearance-height.

The most common clamp height + bolt head ends up at 34mm - so the default probably should be 35mm.
Names will always be a problem, especially with translations.

"Common" is very local to your installation. I do not believe there is a different default that would be any better than the current one. 34 mm certainly does not work for me.

These things are part of the setup sheet. Any serious user should have his or her own values for defaults already loaded.

Gene
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freman
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Re: safe and clearance height

Post by freman »

Thanks to Irak for picking up this discussion. It is important and it's a shame it just fizzled out.

IMO chrisb's comment here should be starting point of all further discussion:

https://forum.freecadweb.org/viewtopic. ... 30#p447298

Clamp clearance height would be more explicit and it seems that this was the original intention but if the behaviour was consistent Clearance Height would probably suffice. It maybe part of work-piece we need to avoid hitting, not the clamps. This is Chris' height #3:
3) Height above the clamps. Used to avoid any crashes
The problem comes with "Safe Height" which is anything but safe. This, IMO, needs renaming to reflect what it does. Unfortunately this is not even consistently applied. As I pointed out in my previous comment drilling seems to have taken on a different use of "safe height" than that used by pocket ops. This obviously needs to be used consistently across all Path WB operations. Once we know what it does, we can find suitable name and documentation diagrams can be corrected show how to use it.

Pocket ops retract to "Clearance Height" between each pocket and use "Safe Height" in the sense of Chris' height #1:
1) Height where vertical rapid-down-moves end and motion changes to working speed. This is used so that the tools enter at decent speed into the material
Drilling seems to use "Safe Height" as in the sense of Chris' height #2:
2) Minimum height at which I can move horizontally. This is used e.g. for moves above the surface between clamps and can be used for two adjacent pockets or for drilling operations for several holes if no clamps obstruct the paths between them.
My bold.

It seems that current FreeCAD functionality requires at least these three heights. .
As I previously stated, it seems that wsk8's "keep tool down" mod could be used to maintain access to current drilling behaviour while removing the inconsistent use of height conventions provided it is off by default. Both pocket and drilling ops would apply ht #3 and ht #1 , and "keep tool down" would provide a manual over-ride to apply ht #2 between holes and pockets in the same operation.

Making use of BaseGeometry order would allow the user more control in avoiding clamps too:
https://forum.freecadweb.org/viewtopic.php?f=15&t=51900
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lrak
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Re: safe and clearance height

Post by lrak »

OK - safe height is NOT retract height. That height is set on the operation tab. Safe height is some part of FreeCAD - and not respected when drilling.
Trying to change this to clear a clamp.

The "safe height" is not respected - it moves at retract height.

Code: Select all

(Begin Drilling)
G0 F0.000000 Z35.000000
G90
G98
G0 F0.000000 X8.750000 Y7.100000
G0 F0.000000 Z3.000000
G73 F4.166667 Q4.500000 R3.000000 X8.750000 Y7.100000 Z-11.838402
G0 F0.000000 X68.750000 Y7.100000
G0 F0.000000 Z3.000000
G73 F4.166667 Q4.500000 R3.000000 X68.750000 Y7.100000 Z-11.838402
G80
G0 F0.000000 Z38.000000
G0 Z35.000000
So the retract height is different than safe_height - supposed to be how far it retracts as it peck-drills. If you want to move at safe height - you need to add a G0 Z(safe_height) - in between the G73 or G83 followed by a second G0 back to retract height. You don't want to change retract or it will slowly retract all the way up to the clearance height at every peck.

So "safe-height" is not "retract height" - and seems to be ignored when it matters?

,,.
Screenshot_20221120_173427.png
Screenshot_20221120_173427.png (40.95 KiB) Viewed 1088 times



The names are very important - most of this starts in English, and if not properly named will cause errors in translations as well.

What I said above still holds - if we look at gcode - G73 peck drilling - the R stands for retract height - (sometimes called canned cycle plane) this has been in use for many decades.

Also - still focused on Names - if I define a end mill - Path is using wrong names there as well:

Cutting edge height - SHOULD be called 'length of cut' as it is in the tool catalogs. (it isn't a height).
Length - SHOULD be called Over-all-Length as it is in the tool catalogs (sometime OAL)..

Missing terms:
Number of flutes - this will matter later..
radius - all end-mills have some edge radius even if we pretend they don't - this will matter as FreeCAD-path advances.
Neck length - the relieved bit beyond the flutes.. Also - Neck diameter.

http://www.mitsubishicarbide.net/conten ... ology.html
I would rather have questions that cannot be answered,
than answers that cannot be questioned’
Richard Feynman.
Giulio Buccini
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Re: safe and clearance height

Post by Giulio Buccini »

I do not want to enter into the running discussion about names.

Just an on-the-fly thought about avoiding crashes against clamps:
since the clamps are usually located around the border of the stock, what about a tool-movement strategy that favours moves toward the center of the piece to be machined, and then moves toward the border to reach the starting point of the operation?

I know, this would make machining a piece a little bit slower, but it could enabled/disabled with a check button.
--------------------------------------------------------------------
P.S.
Other softwares (i.e. Fusion 360) offers the possibility to model your clamps in 3D and then add them to your drawing. After that is done, there is an option to create path avoiding those clamps.

Even if the above approach seems the better on paper, I think it is quite useless: I usually do not know in advance where I will place my clamps during the actual machining.
It depends from many factors:

1. maybe I placed a second fixture close to the actual one, so there is no clamping space available on that side as I planned before;
2. maybe I used long clamps elsewhere so I have to use shorter ones in a new configuration;
3. maybe I'm using remaining material (with an irregular shape) from previous machinings, so the clamps have to be repositioned;
4. and so on...
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