Last blogpost!

Long time no post! But in the meantime, a lot has been done. We’ll give you guys a quick summary of what we did in the last few months, what went wrong, how we solved it, and what eventually became the outcome.

In the beginning our plan was to make more prototypes of the small tablet to figure out which material was the best to use. Also, we would adapt the videomapping so it would look better on both the small and the big tablet. Meryam made a new start on the videomapping – two seperate videos instead of one with both the highlighting and the translation, Omar and Samir were struggling to make a mould for the prototypes and Jana went to Amsterdam to buy all the materials for the prototyping, but then a big event happened: the museum wanted something else and our concept was completely changed. We had to start over again.

The new concept was three small (1:1) 3D-printed tablets in front of the audience to touch and three big ones (1:6,25) on the wall, where projections are going to be displayed on. Also there should be some kind of headphones with the audio in Akkadian.

We recieved two new scans from Yale. From there, we needed to test if CNC milling was going to be accurate enough and what we could do to solve it if not.

A sample of one of the big tablets was needed to test with, so we started off by cutting a 100x100mm piece off the STL-file of one tablet. This was done using Meshmixer slicing tool. This sample was carefully picked to represent the entire model. The difficulty here was the high number of constraints. The files we recieved from Yale were enormous in size and put significant strains on our machines. We wished to leave a uniform outline of the tablet facade with no sharp edges or hanging cliffs, but the tablets were not all in great condition, with fragmentation marks cutting deep into the tablet, and also often had odd shapes at places. All this meant a painstaking process where all aspects of the tablet were closely inspected, manipulating orientation, depth and cutting plane for best results.

The samples were to be testmilled from the regular green foam for sale at the PMB, but we already knew that this would not give the proper result for a museum, so a higher quality modelling foam was used. The samples were made in two types of Renshape and an Obomodulan foam. A control sample was made using an ultimaker 2+, using very fine settings.

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The modelling foam samples looked great. The pieces were intended to be milled with a 6mm extra long ballnose mill. This was not available however, so a flat-tip 6mm mill was used and quickly showed that the 6mm mill resulted in too rough of a milling job. A rough milling operation was done with the 6mm mill, to be followed up upon by a 2mm ballnose mill. Highly time consuming, but this yielded a very high quality of details and an amazing finish.

We did find that the dense sample have a bit more character to it than the lighter one. Therefore, the dense Obomodulan material would be the material of choice. Two large plates were ordered in gray, as that would require less or no postprocessing in order to be suitable for the videomapping.

Next, we had to prepare the STL-files of the scans for the milling – they had to be one-faced as they were going to be attached to the wall. The struggle with preparing the files was that the software used for CNC milling, DeskProto, seemed to have a limit of 2GB as a filesize it can open. This was a problem for one of the tablets, which was 2,5GB(!).

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Because the milling had to be very precise, downsamping the file was not an option. So instead, we considered increasing the tolerance level to match that CNC milling machine’s capability. We also looked to make the model hollow, perhaps significantly reducing size. For that last attempt, we used Meshlab to create an inner shell for a hollow model using voxel approximations. The process took many hours but failed to yield a result to our confusion. After all this we found out we accidentally saved the file as an ASCII STL rather than a Binary STL, which is a lot smaller. The problem luckily solved itself! For the rest, the files were up to 1,7GB in size. That did work for our project, but might be a problem when these kinds of resolutions are used for larger objects.

Preparing the material was a tough job, but quite doable with two people workng quite carefully with the bandsaw. It is recommended to have quite a bit of experience with the bandsaw in order to cut this, as it is very difficult steering the very large and heavy plate through the saw. Also, it is VERY expensive, so you don’t want to mess it up.
The milling process was the same as with the samples. A rough milling with a 6mm mill, with the fine work done by a 2mm ballnose. The milling took about a week, but the results were stunning. In the close-up images below you can see the difference in results between the 6mm mill and the 2mm ballnose quite well.

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Of course we also had to think of a way to attach the big, heavy tablets to the wall. Maaike came up with an option (shown as ‘option 1’ in the illustration below), but it seemed as if the center of gravity was going to tilt this way. Incidentally, Meryam visited the Booijmans museum, where she saw some photographs attached to the wall with a metal sliding system. With that in mind we came up with another option (‘option 2’), where the chance of the center of gravity tilting is minimized.

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