Vrije Universiteit Brussel

Mechanical design notes

by Raphael Furnemont and Hoang-Long Cao We have a cooperation with Fablab at EhB Erasmushogeschool Brussel – gebouw B. Nijverheidskaai 170, 1070 Brussel, Metro Delacroix). This is a prototyping lab with free entrance for all every Wednesday from 13h-21h. More opening hours can be obtained through the responsible Stijn.de.mil@ehb.be and Lieven.standaert@ehb.be or phone +32 2 559 15 11. Their most important machines: Makerbot 3D printers 200*150*100mm, cnc- machining 2500*1500*100mm, PCB-mil A3-format, professional 3D printer 200*200*200mm. Lasercutter 60W 1100*800mm for MDF and Plexi. In case you use the machines for your thesis, you don’t have to pay for the materials or usage of the machines. You have to however inform the responsible of the fact that you work for the Mechatronics Project of MECH department. Starting with one of the machines requires a tutorial which will be checked by the responsible.

3D printer

The 3 printer used is the ultimaker2. Parts that are 3D printed first need to be saved in .stl. Pay attention to the options when saving the parts in stl. For example stl files have their units given in cm by default in Inventor while your drawing generally have their dimensions expressed in mm given a scaling factor of 10. Then the software Cura (https://ultimaker.com/en/products/cura-software) can be used to do the splicing (basically defining how the part is printed). 3D printing gives high freedom for the design but is still limited by several factors (to correctly understand them it is also advised to read tutorials/documentation about 3D printing):
  • Generally very small parts (dimensions of few mm) are quite weak and the printing is generally bad (part not correctly done).
  • Complex part sometimes need support material (this support material is added by Cura during the splicing). The Ultimaker only uses one type of material to print and thus the support needs to be removed manually. As such you have to make sure you can “easily” remove this support material.

Laser cutter

File extension required is .dxf. There are different ways to make .dxf files. One possibility with Autodesk Inventor: make an assembly .iam of your .ipt files. Next, make an .idw file and import your assembly. Next, delete in the model tree (standard on the left) the 'default border' and 'ANSI – Large'. Next, expand the 'save as' menu, press 'save copy as' and chose .dxf. Make sure each new file you create is a file with mm as the standard unit and not inch.


  • For parts fitting together putting the exact same dimensions for both parts generally doesn’t work (a shaft and a bore for example). To ensure that no problem will occur it is advised to reduce the dimensions of the part that has to fit of 0.2mm (thus a shaft of 9.8mm for a bore of 10mm, a square of 9.8x9.8mm inside of a square of 10x10mm, etc…). This is generally sufficient.
  • Always consider how you will assemble the different parts. It happens that some spot cannot be reached during your assembly.
  • Always include all the parts of your design and do not neglect any details. It is not uncommon that the bolts are not included and that there is an interference between them and other parts. It also happens that small details are not considered as important during the design and not even included in the drawings. This generally leads to last minute solutions such as using tape which, even if considered as a common engineering practice to solve problems, is not appreciated by your assistants.
  • It is always interesting to quickly look the previous projects to see how former students designed their robots.

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