Transitions between regions

Here's the place for discussion related to CAM/CNC and the development of the Path module.

How should freecad perform region transisitons?

At clearance height.
2
33%
At safe height.
4
67%
At the height of a new property, which defaults to clarence height.
0
No votes
At the height of a new property, which defaults to safe height.
0
No votes
 
Total votes: 6
IMback!
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Transitions between regions

Postby IMback! » Sat Aug 03, 2019 12:43 am

Hi, i have a question\ poll for path users here.

First Some terminology:
  • Area transition: a rapid transition between two points within the same feature to be machined (think within one pocket)
  • Region transition: a rapid transition between two features to be machined by a single freecad operation (think from one pocket to the next within one operation)
  • Operation transition: transitions between different freecad operations
In freecad, we have 2 heights for transitions, Safe height and clearance height. currently they are used in this manner:
  • Area transition: mostly clearance height, but sometimes Safe height
  • Region transition: clearance height
  • Operation transition: clearance height
Edit: the above list was wrong.

It is my option that transitioning between regions at something below clarence hight is useful, as seen Exhibit A, when machining features into existing pockets, that are deep, long retracts when switching between regions can be avoided. In PR 2386 i changed the height of the Region transition in the drill operation to Safe height, which proved to be unpopular.

I therefore would like to ask the users of freecad how transitions between regions should be accomplished (poll)
Attachments
Screenshot_20190802_124130.png
Exhibit A
Screenshot_20190802_124130.png (12.9 KiB) Viewed 578 times
Last edited by IMback! on Sat Aug 03, 2019 10:09 am, edited 1 time in total.
herbk
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Re: Transitions between regions

Postby herbk » Sat Aug 03, 2019 8:13 am

Hi,
i voted for "at save height" because it saves a little bit time to "clarence height".

The options to "new property" coukd be dangerus by a users mistake...
Gruß Herbert
chrisb
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Re: Transitions between regions

Postby chrisb » Sat Aug 03, 2019 8:13 am

I would like to continue the discussion from 2386 here in the forum because it is easier to include images and videos.
I should say first that I am not a professional machinist.

I would like to add some observations and thoughts to the discussion:

1. What a great video from sliptonic. Great idea and shown very very convincing. And it took doubts out of the discussion.

2. There is a simple explanation why canned cycles are great for old machines: They are short of memory. A canned cycle on my machine needs one line for its definition and can then be reused at different positions with just another line.

3. I can't believe that there are really two inherently different industry standards.

4. When I code the GCodes manually I use rapid moves down to 1mm above the material.

5. I am not familiar with the English notions beyond their usage in FreeCAD, but from this image in the wiki ... Image

... it seems clear to me that for rapid horizontal moves clearance height is used, and that safe height is used to be safe that the tool hits the material at milling speed. For drilling operations this means that all movements below safe height are vertical moves. I am quite, but not absolutely, sure that no horizontal moves should be made at safe height either.

6. In sliptonic's video all milling is done in one operation, right? Then there is (currently) no possibility to reduce the height of the horizontal moves, they always have to go all the way up.

7. If we don't want to retract all the way while being in one pocket (and as mentioned above, that's how I would do it manually) then we need two operations. And here we come to an interesting question: How do we get from one pocket to the next at the appropriate height? I see two possibilities:
a) We add another parameter to the job. It would be very appropriate to have there a job-clearance-height, which is above all clamps and can be used between operations.
b) We add a retract height at the end of an operation. That's perhaps what clearance height was originally designed for.
IMback!
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Re: Transitions between regions

Postby IMback! » Sat Aug 03, 2019 10:08 am

Hi Chrisb thanks for your input. Im not a professional mechanist either, i'm just a mechanical engineer, working mostly in the theoretical space. So my experience with machine programming is limited mostly to my hobby, and hevaly influenced by how things are done in the siemens plm suite.
2. There is a simple explanation why canned cycles are great for old machines: They are short of memory. A canned cycle on my machine needs one line for its definition and can then be reused at different positions with just another line.
This is true, but not how it works currently in freecad, as we emit g81/g82/g83 with all parameters and g80 for every hole, so its only barely using less bytes for the pure gcode, except for when using g83.

7. If we don't want to retract all the way while being in one pocket (and as mentioned above, that's how I would do it manually) then we need two operations. And here we come to an interesting question: How do we get from one pocket to the next at the appropriate height? I see two possibilities:
a) We add another parameter to the job. It would be very appropriate to have there a job-clearance-height, which is above all clamps and can be used between operations.
b) We add a retract height at the end of an operation. That's perhaps what clearance height was originally designed for.
So your suggestion would be to have a new property for Operation transition, while always rapiding at clarence within the operation, and you would have this default to where clearance height is now?
IMback!
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Re: Transitions between regions

Postby IMback! » Sat Aug 03, 2019 12:06 pm

chrisb wrote:
Sat Aug 03, 2019 8:13 am
5. I am not familiar with the English notions beyond their usage in FreeCAD, but from this image in the wiki ... Image

English is also not my first language, but i take issue with this image, as it implies that g0 can be used to rapid dowards all the way to the stock top. This is, in my opinion a bad idea for 2 reasons:

  • It assumes that the stock is touched off perfectly and is not higher then setup in freecad by even one tenth of a mm
  • Even if the stock is touched off perfectly, the tool will be touching the stock after the g0 move. In linuxcnc and maybe other gcode interpreters g0 can be used while the spindle is not yet at the speed commanded by the S parameter. Only g1 waits for the spindle-at-speed signal. Depending how long the vfd takes to get going the tool may touch the stock before starting to spin at all.
GeneFC
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Re: Transitions between regions

Postby GeneFC » Sat Aug 03, 2019 12:50 pm

IMback! wrote:
Sat Aug 03, 2019 12:06 pm
This is, in my opinion a bad idea for 2 reasons:
As I have said many times on the Github page, go ahead and choose your clearance height, safe height, and retract height to suit your concerns. That is why they are adjustable.

Just don't try to keep me "safe" by telling me what I can or cannot do. I always pay attention to clearance issues and take care as needed.

Gene
IMback!
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Re: Transitions between regions

Postby IMback! » Sat Aug 03, 2019 1:29 pm

Gene: no thats not the issue. the issue is to not rapid to the stock, i would have to lie to freecad about how high my stock is... this is different to changing clearance or safe height. The fixture operation for instance rapids to stock top.
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sliptonic
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Re: Transitions between regions

Postby sliptonic » Sat Aug 03, 2019 2:24 pm

IMback! wrote:
Sat Aug 03, 2019 12:06 pm

English is also not my first language, but i take issue with this image, as it implies that g0 can be used to rapid dowards all the way to the stock top. This is, in my opinion a bad idea for 2 reasons:

  • It assumes that the stock is touched off perfectly and is not higher then setup in freecad by even one tenth of a mm
  • Even if the stock is touched off perfectly, the tool will be touching the stock after the g0 move. In linuxcnc and maybe other gcode interpreters g0 can be used while the spindle is not yet at the speed commanded by the S parameter. Only g1 waits for the spindle-at-speed signal. Depending how long the vfd takes to get going the tool may touch the stock before starting to spin at all.
Just because the user might touch-off incorrectly doesn't mean we should change the meaning or behavior of the system when it comes to using the data. If you tell the system that the top of stock is at a particular height, the system should be able to move at rapid speed above that. The system shouldn't be second-guessing the data it's given.
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sliptonic
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Re: Transitions between regions

Postby sliptonic » Sat Aug 03, 2019 2:29 pm

The chart is good for general understanding but for those who care about trivia or just like being extra picky: :lol:

it's ALWAYS possible to move at G0 speed away from the material. ( Z+ in most cases.)

In some canned cycles, the system will also move at G0 speed toward the work. For example in pecking cycle, the system moves at G0 downward through the already-cleared part of the peck before starting the next feed section.
IMback!
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Re: Transitions between regions

Postby IMback! » Sat Aug 03, 2019 3:01 pm

sliptonic wrote:
Sat Aug 03, 2019 2:24 pm
Just because the user might touch-off incorrectly doesn't mean we should change the meaning or behavior of the system when it comes to using the data.
I believe we should, the gecode generator should be somewhat defensive and not assume that the stock is touched off to extremely high precision, this is why other applications have an engage height.

also even when the stock is touched off perfectly, that is to at least 0.01mm precision, rapiding to the stock with g0 will cause issues because the tool may not be spinning yet! the fixture operation, among others, dose this!