Limiting depth of cut for a surface

Here's the place for discussion related to CAM/CNC and the development of the Path module.
ian.rees
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Limiting depth of cut for a surface

Postby ian.rees » Tue Mar 14, 2017 3:15 am

Hi folks,

Apologies if this is a dumb question or answered elsewhere - I've still not made it through the whole "new era" thread (but looks cool so far!).

My aim is to rough out a banjo neck with a CNC router (actually a mill that's adapted to this purpose). I'm wondering what the best way is to limit the depth of cut, while cutting a surface. For example:
Screen Shot 2017-03-14 at 1.24.59 PM.png
Screen Shot 2017-03-14 at 1.24.59 PM.png (34.52 KiB) Viewed 244 times


The toolpath I'm getting seems to be just going straight down to the final depth. What I'd like is to mill the first N mm down, surfacing any of the shape that extends in to that volume, then do the next N mm, etc. Is this possible with Path in it's current state?

If not, does anyone have thoughts on what that functionality should look like? -Ian-
vk3uao
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Re: Limiting depth of cut for a surface

Postby vk3uao » Tue Mar 14, 2017 4:00 am

I use the 'Step Down' field, but I only use pocketing and profile cuts. I'm not sure if the same options apply with you are surfacing a part? Apologies if this isn't any help!

Image
ian.rees
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Re: Limiting depth of cut for a surface

Postby ian.rees » Tue Mar 14, 2017 4:23 am

Thanks vk3uao! That doesn't seem to work with the surfacing tool, but perhaps that isn't the tool I should be using to start with? Will play with it more this evening. -Ian-
GeneFC
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Re: Limiting depth of cut for a surface

Postby GeneFC » Tue Mar 14, 2017 3:08 pm

I don't have an answer for FreeCAD, but a trick I use frequently in this type of situation is to fake the z-setting in the CNC program. (I use linuxcnc.)

It is certainly not the most elegant solution, and it is not production-worthy, but it works just fine for one-off parts.

Gene
herbk
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Re: Limiting depth of cut for a surface

Postby herbk » Tue Mar 14, 2017 8:03 pm

Hi Ian,
3D surfacing is not realy usefull in that time.
On dropcutter you got only 1 path along the contour of your object, stepdown has no effekt and setting a stepp over is not possible to.
For the stepp over an other problem is there to: The stepp over is bigger as the tool diameter, so there is left some material between each toolpath.
door_2.jpeg
door_2.jpeg (269.38 KiB) Viewed 183 times
Gruß Herbert
ian.rees
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Re: Limiting depth of cut for a surface

Postby ian.rees » Wed Mar 15, 2017 9:37 pm

Thanks for the info!

Is the plan for the "stepdown" parameter to work with the surfacing methods? If so, I could take a stab at implementing it. -Ian-
chrisb
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Re: Limiting depth of cut for a surface

Postby chrisb » Wed Mar 15, 2017 11:38 pm

ian.rees wrote:Is the plan for the "stepdown" parameter to work with the surfacing methods? If so, I could take a stab at implementing it. -Ian-
From my side: go for it, please!
sliptonic
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Re: Limiting depth of cut for a surface

Postby sliptonic » Thu Mar 16, 2017 4:05 am

ian.rees wrote:Thanks for the info!

Is the plan for the "stepdown" parameter to work with the surfacing methods? If so, I could take a stab at implementing it. -Ian-


The surfacing operation, which uses opencamlib, can certainly be improved. Anything you do in this area is much appreciated! Studying the HeeksCNC code might be very helpful here.

There might also be new possibilities using realthunder's PathArea. I don't think it would work so well for finish operations but roughing operations might be very feasible.
herbk
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Re: Limiting depth of cut for a surface

Postby herbk » Thu Mar 16, 2017 8:06 am

Hi Ian,
if you want to work an 3d surfacing, please let me put in a few thoughts. My skills in programming are to bad to jump in. I try'd to find out how to change the "stepp over" on 3D Surfacing, after a few days of searching i found a parameter in the PathSurface.py file to change it, but don't find a way that it's result in a "input field" on the gui.

But first: i think we agree in mind that a 3 Axis system never can produce a real good 3D surface. So we talking about going as close at possible... :)

3D surfacing should can change the direction it works and have the passibility to set step down and step over.

3D surfacing allways makes a path of the whole part, without considering the dimensions of the raw material, thats to much i think.
(Allways not considering the dimensions of the raw material is not the best idea, but that's an other thing... ;) )

The most stepps to do on a "3D part" can be done with existing operations. Only "not flat" lying areas needing a different way to get a path.
So, would it not be better to reduce the "3D Surfacing" operation to the area where it is realy needed for? And create a "3D whole part" operation which combines the existing (and well working) operations we have with the reduced 3D surfacing?
My skills in programming are to bad to jump in. I try'd to find out how to change the "stepp over" on 3D Surfacing, after a few days of searching i found a parameter in the PathSurface.py file to change it, but don't find a way that it's result in a "input field" on the gui.

Here as an example a part (it's only a example, i don't need to make it realy) hat i want to mill out of, the red, translucent, box is the peace of the raw material.
3d_part.png
3d_part.png (57.51 KiB) Viewed 107 times


All steps, excepting the selected surface, i can do with existing operations
3d_part_2.png
3d_part_2.png (55.01 KiB) Viewed 107 times

3d_part_3.png
3d_part_3.png (79.66 KiB) Viewed 107 times


The only things i'm missing, is the considering the dimensions of the raw material, so i have to set the hights on every path manual and a 3D Surfacing operation for the "not flat area"...
Attachments
3d_test_1_mPf.fcstd
(15.64 KiB) Downloaded 2 times
Gruß Herbert