Relief based on a drawing

27/03/2012 Posted by Claus

Coat of arms carved out of white marble on a CNC machining center by Jürgen Schmidt



finished relief coat-of-arms carved on CNC

This marble relief was quite difficult and time consuming to produce because we only had a hand painted picture to start with. The first hurdle was that the original hand drawing was slightly bigger than A3 format. We only had an A4 scanner and we did not know anyone with an A3 or even bigger scanner. So we ended up scanning separate images and then used photo editing software to join them together.

After we took the first hurdle we realized that there is still a long way before we can put the marble onto the CNC machine to start cutting. The next step was to find a way to change the image from 2D to 3D. There are a number of software packages around for the image conversion to 3D. Most of them work in the same way and require that the image is in 8bpp grayscale which allows for 256 different shades of gray. Each shade represents a different height where black is 0 and white is the max height you specify.

We used the 3D conversion software which came with the CNC machines laser scanner from Scantech. The 3D software also calculated the toolpath for the CNC machine in a simple G-Code format. That’s all we need to run the CNC machine but luckily the 3D software has a very good simulation and we saw straight away that the images needs to be edited in a certain way so you have a nice and smooth flow of one level of gray to the next. After many trials and errors I ended up to redraw by hand a great part of the scanned image to get the gray levels right for all the details.

The relief was carved on the CNC machine with only two different diamond tools. The electroplated 16×30 milling finger bit was used to roughly cut the marble to shape. The WIDIA conic mill 3mm diameter tip has cut the final shape.

I ran the first CNC program to do the rough cut in the afternoon and started the the second CNC program for the finish cut before we went home to save time as we needed the CNC machine during the day for the normal granite countertops. Surprisingly everything was okay when we came in the morning.

Needless to say we were quite happy with the result.

first attempt of the grayscale image of coat-of-arms
first attempt of the grayscale image
edited grayscale image of coat-of-arms
edited grayscale image
simulated rough finish of the marble relief
simulated rough finish

simulated finished marble relief
simulated finish

the original scanned image of coat-of-arms
the original image of coat-of-arms
finished relief coat-of-arms carved on CNC
finished marble coat-of-arms

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