2D Profile in 3D

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_O_blvn
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2D Profile in 3D

Post by _O_blvn »

Trying to get set up to cut some parts on my ShopBot PRSalpha using Vectric Aspire version 11.

The gist of what I've got going on is I'm essentially trying to create something similar to a 2D profile toolpath where the X and the Y travel around the profile of my part but not at a fixed depth.

I have a chair back that is made of two 16.5" long x 7" wide x 1" thick boards. Each board is getting a 4° miter cut along the center seams length and then joined together to create a 172° angle on the inside of the seat back. Needless to say the seat back does not sit flat after it has been glued up.

I've made a jig out of 1.5" mdf to hold the seat back flat on the bed so I can make my profile cut out but I don't necessarily want to cut in to the jig. I've made the jig thick enough to where the lowest point of the seat back (the center seam) is still 1/2" above the machine bed.

My question then is how do I create a toolpath where I'm just doing a profile cut while also allowing for travel in the Z as the bit works its way around the profile and cut all the way through my seat back and not in to my jig.

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adze_cnc
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Re: 2D Profile in 3D

Post by adze_cnc »

The "Project toolpath onto 3D model" (p23d) option of the "Profile Toolpath" will accomplish what you want to do. But, it does take some preparation as p23d needs a 3D model to work with.

The drawback of the p23d option is that the profile toolpath will cut from the surface of the model to the depth specified. So, we can't model only your jig. We need to model the surface of you material on top of the jig.

The attached CRV file gives an example of what would be needed and you could use that but you'd need to change a few things:
  • cutter for the profile toolpath to one that makes sense for your machine
  • I just made a fake jig and used it's measurement so you'll need to measure your own material and jig height (see images below)
I modelled your board and a fake jig to get the measurements needed for the 3D model in VCarve. In the following image the aquamarine is your seat back material. The blue is the fake jig.
 
seat back on jig.png
 
In VCarve I used a triangular tab from the the clipart collection (Pyramid_0.25). I scaled its length and width to match your material (16.5" by 13.9659" as measured in Rhino 3D).

I then changed the component's “Shape Height” to be the difference from the apex of the material to the top of the outside edge of the material (0.4883" in the image above).
 
component.png
 
That gives the top of the material at the surface of the machine. That needs to be lifted to its position on top of the jig. That can be measured from the yellow circled point in the image above to the machine surface (the yellow arrow). That value in my mocked-up example is 2.1595". I changed the pyramid component in VCarve to have that distance as its "Base Height". Of course, for your project you'll need to measure it for yourself.
 
simulation.jpg
 
Steven
Attachments
seat back on jig.crv
(233 KiB) Downloaded 6 times

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adze_cnc
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Re: 2D Profile in 3D

Post by adze_cnc »

One thing to remember (which I forgot) is that the cut at the outside edge will start at 0.48” plus the cutters’ step down value! So you might want to add an initial relief profile cut, that does not use the project to 3D option, to cut down to that 0.48” level.

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adze_cnc
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Re: 2D Profile in 3D

Post by adze_cnc »

Revised file.
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seat back on jig with relief cut.crv
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Rcnewcomb
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Re: 2D Profile in 3D

Post by Rcnewcomb »

I don't believe Cut3D supports "Project toolpath onto 3D model" .

_O_blvn, do you have Cut3D or Vcarve or Aspire?
- Randall Newcomb
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adze_cnc
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Re: 2D Profile in 3D

Post by adze_cnc »

Trying to get set up to cut some parts on my ShopBot PRSalpha using Vectric Aspire version 11.
Perhaps the post is in the wrong forum location.... For that matter modelling things in Aspire might be much easier than using a tab from the clipart. But. as Aspire is not my thing I couldn't be sure.

_O_blvn
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Re: 2D Profile in 3D

Post by _O_blvn »

Thanks for the insight Steven. I have not yet tested the “Project toolpath onto 3D model” feature, but I’ll give it a shot sometime within the next couple of days.

To clarify I am using Aspire version 11 to create my toolpaths and Rhino 7 for modeling.

This is also my first post so my apologies if this topic would be better suited in another forum.

_O_blvn
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Re: 2D Profile in 3D

Post by _O_blvn »

Steven, I'm having a little bit of difficulty determining how to set the heights for my jig and my material. I'm importing my jig and my material in to aspire as .stl files that I exported out of Rhino separately. I am pretty inexperienced with modeling in aspire an am not quite getting my profile toolpath to cut to the appropriate depth which I believe is due to an underlying issue with the way my models are set up in aspire.

Any additional information would be greatly appreciated.

Also, please note that my jig and material have been set up to be cut opposite of how you modeled it, are there any inherent issues with doing that one way vs the other?

Image

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adze_cnc
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Re: 2D Profile in 3D

Post by adze_cnc »

_O_blvn wrote:
Thu Apr 28, 2022 3:10 pm
Also, please note that my jig and material have been set up to be cut opposite of how you modeled it, are there any inherent issues with doing that one way vs the other?
Yeah. I missed the line "where the lowest point of the seat back (the center seam)". Sorry.

I like having the centre seam up because with the jig sloping away the end mill will barely score the jig material. With the jig sloping up the end mill will need to cut into the jig material to get to the bottom of the seat back.

The sloping up jig makes thing a bit more difficult but not impossible. The difficulty, again, lies in the project to 3D wanting to use the 3D model as the starting point for the cut. Great if you are inscribing text in the bottom of a bowl. Not great if you want to do something like this. It would be nice if there was a cut no deeper than the 3D model option for the profile toolpath...

The easiest way is to use a "Profile Toolpath" on your seat back curve with the project to 3D selected and set the depth of cut to zero (0). But... now we are cutting down to the 3D model in one pass. Great if your machine is robust enough to handle it.

I have an idea of how this could be accomplished but I'd have to test it out. My thought is copying and raising the two sloping planes to the level of the highest point on the rim of the seat back. Then using that as the 3D model that the project to 3D option follows. Then cutting to the appropriate depth (the vertical z-axis difference between the orignal sloping planes and the newly raised ones).

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adze_cnc
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Re: 2D Profile in 3D

Post by adze_cnc »

Well, that was tricky. My first thought in the previous post was not quite right.

What I did is:
  • in Rhino using "DupFaceBorder" I extract the profile of the seat halves. Copied this to "sweep" layer
  • drew a line parallel to the XY plane at the lowest point where the two planes of the seat meet (the yellow-circled white line in the image below). The line length is the diameter of profile cut bit (3/8" in my case).
  • I used the "Sweep1" command to create a brim around the seat (layer name "brim"). This is what the "Project to 3D" portion of the Profile toolpath will ride upon.
  • I exported the seat, jig, and brim objects as an STL file. Don't worry about the brim being only a plane Aspire (VCarve in my case) will deal with it.
  • I exported the "sweep" profile and a rectangle representing the overall size of the jig as a DWG file. This will help aligning the 3D and 2D elements in Aspire
  • I imported both the DWG and STL files into VCarve.
  • I created a Profile toolpath using the object in the "sweep" layer as profile. The depth needs to be a bit more than the seat material thickness as the brim is not parallel to the XY plane. I added 1/32" (0.03125).
 
01- seat and jig.jpg
 
02 - sweep rail and cross section.jpg
 
03 - brim.jpg
 
04 - brim seat and jig STL.jpg
 
05 - 2D curves.jpg
Attachments
seat jig.crv
(263 KiB) Downloaded 7 times

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