Tabs - again

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K0nrad
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Tabs - again

Post by K0nrad » Sun Sep 04, 2022 7:34 pm

Hi,
I am writing again regarding the way the tabs are generated. Recently, I was designing a simple detail (foot for my device). Detail was intended for milling. The milling was planned in three steps: cutting the central hole, cutting the entire detail along the outer contour and chamfering the upper edge. Chamfer line was inside of the detail (0.5 mm from the contour line). There were three tabs added on the contour line. After generating the gcode, it turned out that the tabs are also on the chamfer path, although chamfer was supposed to be cut separately at a different height (see simulation1.jpg). I added a few more paths (just to see what happens) and tabs appeared on two more. The distance between the last path with tab to the one where the tab was originally located was 1.5 mm - exactly half the diameter of the cutter (see simulation2.jpg). So it seems that the tab is generated in such way that it covers a width equal to the width of the cutter. However, still there is an inaccuracy: when milling is planned outside of the contour line, tab should not cover other areas of the detail. Of course, one can deal with it and generate the correct gcode, but the whole procedure is not very intuitive and - in my opinion - it should be corrected in the next versions of QCADCAM. Gcode should be affected by the tab only for the contour line where the tab was really placed.

Best Regards
Konrad

QCADCAM 3.27.6
Win10
Attachments
simulation1.jpg
simulation1.jpg (321.72 KiB) Viewed 8959 times
simulation2.jpg
simulation2.jpg (465.7 KiB) Viewed 8959 times
stand1.dxf
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Husky
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Re: Tabs - again

Post by Husky » Sun Sep 04, 2022 11:17 pm

Hi Konrad,
K0nrad wrote:
Sun Sep 04, 2022 7:34 pm
After generating the gcode, it turned out that the tabs are also on the chamfer path, although chamfer was supposed to be cut separately at a different height (see simulation1.jpg).
Well, a while ago it was bothering me too but you helped me to find a workaround. Thanks for that! I'm wondering why your own workaround isn't working anymore for you.

https://www.qcad.org/rsforum/viewtopic. ... tab#p36162

Looks good to me ...
Husky-2022.09.04-01.png
Husky-2022.09.04-01.png (27.52 KiB) Viewed 8948 times
K0nrad wrote:
Sun Sep 04, 2022 7:34 pm
Of course, one can deal with it and generate the correct gcode, but the whole procedure is not very intuitive and ...
I agree! It would be nice to have an easier solution to set tabs accurately to a chosen paths. Did you file a Feature request below www.qcad.org/bugtracker ? That would be the right place to ask for it ... :wink:
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CVH
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Re: Tabs - again

Post by CVH » Mon Sep 05, 2022 1:38 am

Husky wrote:
Sun Sep 04, 2022 11:17 pm
I agree! It would be nice to have an easier solution to set tabs accurately to a chosen paths.
Did you file a Feature request below www.qcad.org/bugtracker ? That would be the right place to ask for it ...
Husky wrote:
Sat Jan 15, 2022 9:55 pm
I'll address that in a bugreport.
Husky, you filed a Feature Request on 15.01.2022
https://www.ribbonsoft.com/bugtracker/i ... sk_id=2331

Regards,
CVH
Last edited by CVH on Mon Sep 05, 2022 4:04 am, edited 2 times in total.

CVH
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Re: Tabs - again

Post by CVH » Mon Sep 05, 2022 4:03 am

Some insights:
Bridges will be added at any profile crossing TAB markers above the zFinal of that profile.
- These markers are simply block references on layer 'CADCAM' and the Block 'CamTab' is made up of 2 solid Hatches on layer 0.
- TAB markers have 3 custom properties: "Tab" =1; "Tab Length" & "Tab Thickness".

Profile A may have a zFinal of -18.2 while Profile B its zFinal is -9 and then zFinal of A is not taken into consideration when processing B.
Both profiles sources are in 2D while resulting cutter paths have z values.
As long as QCAM is not aware how thick your piece is ...
... And/or doesn't cross-evaluate all zFinals ...
... It can't know if profiles are stacked in X/Y.

The main solution here is that TABs are made profile depending.
A different solution to this would be an extra marker property that holds the bottom Z value of the TAB.
Given that 'zBottom' is -18.2 all passes of Profile B will never trigger adding bridges.
We could add a profile C and also regenerate profiles when required.

'zBottom' can be sourced in different ways:
- User input on TABs.
- User input of material thickness.
- Lowest zFinal of all profiles.


If we look closer to simulation2.jpg we see that only the 3 outer chamfer paths make bridges.
Indeed, TABs have a certain width.
A tab position is accompanied by a cutting line through the tab position, orthogonal to the shape and extend to both sides by the tool radius.
Any profile shape that intersects with this line will trigger adding bridges.

Again, profile dependency or a 'zBottom' would be a solution.

Regards,
CVH

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K0nrad
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Re: Tabs - again

Post by K0nrad » Mon Sep 05, 2022 11:46 am

Hi Husky,
I remember my own post :oops: but this time the case was slightly different :D.
Regarding the topic: thank you for your all answers. IMHO the simplest solution is to tie the tab to a given line, without any tab width (or more precisely, tie it to a given tool path). The width will be always depended on the cutter diameter. This will allow to create more complex paths, even overlapping one another. It should be on the side of the operator to remember about maintaining (or not) the tab width, during milling.

At least it should be possible to turn off the tab width (or set to zero) to leave it tool dependent only.

Best

Konrad

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K0nrad
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Re: Tabs - again

Post by K0nrad » Mon Sep 05, 2022 12:29 pm

just to show what the fuss is about :D

Regards
Konrad
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