Engraving an Image With a CNC Router

by:Gewinn     2020-02-23
Most of the projects I do involving CNC routers have 3D results, but the router is also very useful for 2D work!
Here I show a way to carve an image into wood using Rhino, Grasshopper and CNT motion system CNC router.
This method enters a set of lines or paths (in rhino)
The CNC router will cut/engrave and use the information in the image (in grasshopper)
To define the depth of these cuts.
So you can get different results by selecting the cutting bit.
The V-shaped engraving drill will carve thicker lines where the deeper the cut-in material is, so in this tutorial I used a rather typical 60 degree signal cutting drill.
Of course, you need to decide what image you want to engrave first!
Here I am using a still in a recent video project.
This project handles the video as a space volume, so I think the physical version that has part of this video will be a bit neat.
Through trial and error, I found that in the final product, the image with higher contrast will be clearer.
So add a little contrast in photoshop or another image editor of your choice.
As we will see in a few steps, this method samples the brightness of the image to determine the depth of engraving, so the image will also be converted to black and white at this stage.
Use the Background Bitmap command to put the image into the rhino file.
It\'s just a visual aid, but I found it helpful in making design decisions.
At this point, you need to consider the type of line you want to engrave.
This could be anything from a simple parallel line to a spiral to a concentric polygon.
The only thing that is needed is that there is a constant width between one line and the next.
Here I use the \"arraylinear\" command to place 90 horizontal lines on the image, 1/8 apart.
Grasshopper is a program that is very capable of creating parameter designs in Rhino.
If you \'ve ever used another block programming language like Max, it works in a very similar way --
You can enter information or geometry from the rhino file, pass information or geometry through a series of \"blocks\", each block represents a different function or transformation, and output the new geometry back to Rhino
The sketch of my grass grasshopper works as follows: 1.
The curve you draw with Rhino is entered into the sketch. 2.
The digital slider defines the number of subdivisions along this curve, that is, the point at which the image is sampled.
Since my lines are short, I will subdivide them about 213 times (
The exact number is not important). 3.
The \"Divide\" block removes the curve this number of times. 4.
The points that your lines are divided into two data streams-
One is the point deconstruction element, which separates the XYZ information of each point. 5.
At the same time, these points are entered into the image sampler.
Here you can define the required size of the image in the Rhino file-
Use any size of the final product you want.
The image sampler will be sampled at each input point. 5.
The output of the captured image sample-
All we need is a new Z message.
These values are multiplied-1. 6.
The original X and Y data of each point are merged with the new Z information of the point.
Now, the height of each point is defined by the brightness of the image. 7.
Points are regrouped into lines (polylines). 8.
Using the Scale NU block, compress the new line in the Z dimension.
A little bit of math is involved here to find out the correct scaling value
But considering the geometry of the bits you use, you can calculate the maximum cut depth of the path before the online bar starts touching.
Because I use 60 degrees, my line at rhino is.
125 inch apart, I can cut at most.
108 inch of the material.
I\'m actually Fair to be more conservative. 100\". (
Original sample value from-
1 to 1, so the necessary scale factor is. 05)9.
Finally, move the new geometry to the top of the material inventory.
After sending the input geometry through the grasshopper patch, this is what I have left.
The way the lines are presented on the screen, you can even start to see the outline of the image!
At this step, I no longer need flat input lines or other guides I made in the rhino file, so all the extra geometry can be removed.
All we need is a new outline.
To simplify the production process, at this stage I also connected all the lines into a continuous glyph.
In this way, a continuous line can be carved instead of a router carving a line and then having to travel all the way back to the beginning of the next line.
To generate GCode that the router can understand, I used the RhinoCAM software of Mecsoft.
We don\'t need to be too fancy here.
Simple engraving operation is OK.
I am using a very conservative feed price here, but through the experience of the particular section I use, I find that the feed price of 90 inch per minute is very good for the details of soft wood.
I am using a CNT motion router with 4\'x4 \'beds and 11 tool libraries.
This is a router with a very wide range of uses, and in this project I only use a fraction of its features, but I have to explain a small flaw in the machine.
The router measures the length of each tool by selecting the tool and reduces it until it is pressed into the sensor.
With a lot of use, the calibration sensor on this router actually gets a small divot in its center, which means that a small signal cutting bit like the one I\'m using here is not going to be correct
Instead, I manually calibrate the drill bit by jogging it to the top of the material and adjusting the toolpath accordingly.
This router uses a vacuum bed to hold the material in stock, and since I am using a relatively small piece of wood, I have added scrap to the rest of the bed.
This will create a tighter seal and better ensure that the material is kept in one place throughout the cutting process.
Once everything is safe, I start cutting and watch the router work magically!
Whether this particular image can be translated well into a 3D profile is controversial, but the relationship with the original input is definitely clear, so I think this experiment is successful!
To show the profile better, I shot the piece under strong directional lighting, but in the future I might use it as a print block or as a mold for thermoplastic plastic.
I also included some images of past results I got using this method on the CNC router
Carve 30x40 on plywood, fill with wax at the cutting place, and carve 36x36 on plywood.
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