Path: Toolpath for operations smaller than tool width.

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reet
Posts: 9
Joined: Sun May 07, 2023 5:26 pm

Path: Toolpath for operations smaller than tool width.

Post by reet »

Hello,
I am new to FreeCAD, and CNC/CAM so please bare with me.

I wanted to build some simple hold downs for the CNC machine, and am struggling a bit to create a toolpath that works optimally for this simple part. The main problem I am encountering is trying to profile and edge that is less than the width of the tool bit. It's the outside edge so there should be no problem to remove the outside of the stock, and only cut in 3mm with a 6.25mm bit.
Screenshot_20230507_104446.png
Screenshot_20230507_104446.png (37.56 KiB) Viewed 1105 times
The only way I have found so far to create this toolpath with a 6.35mm bit is to do a lap around the entire piece with a profile for every 3mm step shown on the right. This adds a fair bit of wasted time when it could just be profiling the right edge, but FreeCAD seems to refuse to make a profile or pocket toolpath for a surface that is less than the width of the bit.

Am I missing something obvious?

FWIW I am using FreeCAD 0.20.2 on Manjaro Linux.
Attachments
stair clamp.FCStd
(158.22 KiB) Downloaded 28 times
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onekk
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Re: Path: Toolpath for operations smaller than tool width.

Post by onekk »

reet wrote: Sun May 07, 2023 6:09 pm ...

Am I missing something obvious?

FWIW I am using FreeCAD 0.20.2 on Manjaro Linux.
Yes probably:

http://forum.freecadweb.org/viewtopic.php?f=3&t=2264

about how to post a correct FreeCAD (FC for short) info.

Sadly there are around many version so it is not clear if you are using as example an AppImage or a distribution compiled version.

This could be the cause as example if someone is trying your file with the AppImage, he could not confirm the behaviour or the other way round.

And this not tell as example against what libraries FC is compiled.

Regards

Carlo D.
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reet
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Joined: Sun May 07, 2023 5:26 pm

Re: Path: Toolpath for operations smaller than tool width.

Post by reet »

Thank you for your response, however detailed specifics of FC version should not be incredibly important here, I'm not reporting a bug, just trying to understand basic functionality of toolpaths in 0.20.2.

Code: Select all

OS: Manjaro Linux (KDE/plasma)
Word size of FreeCAD: 64-bit
Version: 0.20.2.29603 (Git)
Build type: Release
Branch: makepkg
Hash: 930dd9a76203a3260b1e6256c70c1c3cad8c5cb8
Python 3.10.9, Qt 5.15.8, Coin 4.0.1, Vtk 9.2.6, OCC 7.6.3
Locale: English/Canada (en_CA)
Installed mods: 
  * A2plus 0.4.60k
I think I can simplify my question a bit. How does one create a profile or pocket toolpath that cuts into the stock from the outside edge, for a cut that is smaller than the tool bit diameter?
chrisb
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Re: Path: Toolpath for operations smaller than tool width.

Post by chrisb »

Moved to Path forum.
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Re: Path: Toolpath for operations smaller than tool width.

Post by chrisb »

You can use the PathPocket with extensions. Alas, the predefined half of the tool diameter doesn't work. I had to increase it a bit, whhich creates a double tool path. Not sure if this is a bug.
Snip macro screenshot-24f706.png
Snip macro screenshot-24f706.png (12.26 KiB) Viewed 1020 times
I can upload the 0.21 version of the file (incompatible with 0.20).
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reet
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Re: Path: Toolpath for operations smaller than tool width.

Post by reet »

Hi @chrisb, thanks for your reply. I did try with extensions, but unsuccessfully. I have now updated to latest 0.21-weekly, and trying again, I see that I can create the toolpath with extension, I didn't realize it needs a negative number entered here for what I want.

My solution for this part seems a bit hokey. I added the extension to create the toolpath, then offset the toolpath position to move it to where I wanted. Perhaps you have a better solution, please post the file you mentioned, I am interested to look at it.

Code: Select all

OS: Manjaro Linux (KDE/plasma)
Word size of FreeCAD: 64-bit
Version: 0.21.0.33110 (Git) AppImage
Build type: Release
Branch: master
Hash: 18e40941ceb36c52701a7c74ea26043ef3385701
Python 3.11.3, Qt 5.15.8, Coin 4.0.0, Vtk 9.2.2, OCC 7.7.1
Locale: English/Canada (en_CA)
Installed mods: 
  * A2plus 0.4.60k
chrisb
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Re: Path: Toolpath for operations smaller than tool width.

Post by chrisb »

Here is the file. You can see the double line, perhaps an additional boundary dressup can suppress it.
Snip macro screenshot-aa974d.png
Snip macro screenshot-aa974d.png (2.33 KiB) Viewed 950 times
Attachments
stair clamp_cb.FCStd
(114.73 KiB) Downloaded 23 times
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GeneFC
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Re: Path: Toolpath for operations smaller than tool width.

Post by GeneFC »

I played with this file for a while, using a very recent version 0.21. (Good move to update!)

I was able to use the single-edge function of the Profile operation to pattern the steps with minimal extra moves.

The only problem is that each step needs to be set up exactly for the start height and the finish height.

If this is a repetitive job then it is worth setting up. If it is a one-timer I would just go with the full orbit profile and get on with life. 8-)

Gene
bmsaus4ax
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Re: Path: Toolpath for operations smaller than tool width.

Post by bmsaus4ax »

reet wrote: Sun May 07, 2023 6:09 pm Hello,
I am new to FreeCAD, and CNC/CAM so please bare with me.

I wanted to build some simple hold downs for the CNC machine, and am struggling a bit to create a toolpath that works optimally for this simple part. The main problem I am encountering is trying to profile and edge that is less than the width of the tool bit. It's the outside edge so there should be no problem to remove the outside of the stock, and only cut in 3mm with a 6.25mm bit.

FWIW I am using FreeCAD 0.20.2 on Manjaro Linux.
EDIT: posted as Gene also posted. Same solution.

I was able to do the job by using the Profile Op, selecting the top edge of a step, and setting depth and step down to suit
There is no lead in but could be added.

Worked in both Ver 0.20 and Ver 0.21
.

Code: Select all

OS: Ubuntu 20.04.6 LTS (ubuntu:GNOME/ubuntu)
Word size of FreeCAD: 64-bit
Version: 0.20.28993 (Git) AppImage
Build type: Release
Branch: (HEAD detached at 6d92e53)
Hash: 6d92e532bcc31c99a0ab4c153ff00b6414b8f527
Python 3.9.13, Qt 5.12.9, Coin 4.0.0, OCC 7.5.3
Locale: English/Australia (en_AU)
Installed mods: 
  * fcgear 1.0.0
  * Curves 0.4.4
  * Lithophane
  * CurvedShapes 1.0.3

Code: Select all

OS: Ubuntu 20.04.6 LTS (ubuntu:GNOME/ubuntu)
Word size of FreeCAD: 64-bit
Version: 0.21.0.33040 (Git) AppImage
Build type: Release
Branch: master
Hash: 1e830a8800156097ccb3ef6124dced30d4002e76
Python 3.11.3, Qt 5.15.8, Coin 4.0.0, Vtk 9.2.2, OCC 7.7.0
Locale: English/Australia (en_AU)
Installed mods: 
  * fcgear 1.0.0
  * Curves 0.4.4
  * Lithophane
  * CurvedShapes 1.0.3
Attachments
mod_stair clamp.FCStd
(154.4 KiB) Downloaded 24 times
reet
Posts: 9
Joined: Sun May 07, 2023 5:26 pm

Re: Path: Toolpath for operations smaller than tool width.

Post by reet »

chrisb wrote: Sun May 07, 2023 11:27 pm Here is the file. You can see the double line, perhaps an additional boundary dressup can suppress it.
Snip macro screenshot-aa974d.png
Thank you. I see, you are referring to a different option that what I was looking at. I was looking at the "pass extension".

It does only need one pass, but even 2 passes is still better than doing a lap around the entire part like I was doing. You do have the extension formula as "OpToolDiameter * 0.55", however the bit is 6.35mm, and the step is 3mm, so the extension would be a very specific "OpToolDiameter * 0.527559055118", however it doesn't seem to matter how close you get the math, it wants to do 2 passes, I think it's inherent to the pocket operation.

For this particular part, I could use a slot operation with a X axis offset in the placement, but understandably that may not work for every situation.

Thanks again for your help.
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