Soviet hand drill repair

Pre Story

My father bought the thing at the flea market sometime. The price of 5 rubles (Ц. 5Р.) is incorporated in the handle, because at that time in the Soviet Union there was the planned economy and you could get a pack of butter for the same price in the big whole country.


The drill always did its job. It is particularly suitable for small jobs and you can dose the torque manually. Only at some point the drill got stuck somewhere and my father exerted too much momentum on the big bevel gear until a few plastic teeth sheared off, rendering the thing useless. The old bevel gear consisted of two parts: The front side with the teeth was made of a plastic casting and the back side was made of some kind of metal, which was somehow connected to the plastic (unfortunately no photo). So a new bevel gear was needed.


First, the teeth of the bevel gear had to be counted. There are 60 teeth. The driven bevel gear has 15 teeth, so there is a ratio of 1:4. In addition, all dimensions, such as the height of the teeth, their width and the bore diameter of the bevel gear had to be measured with a caliper gauge. The problem: the teeth are not simply arranged in a straight line, and their “focal point” is somewhere in the air. They are also wider at the outermost diameter than at the inner diameter of the bevel gear. So the geometry is a real challenge and you can’t just build the thing with a CAD program if you’re not a professional.
But what to do? Fortunately, I happened to come across a solidworks tutorial on the internet. It shows how to create configurable standard parts using the solidworks (SW) design library. And that worked well!


Open Solidworks, open any assembly and throw out all the parts. Somehow it didn’t work out any other way for me. Then, on the right side of the screen, open the construction library and shimmy through the tree. Toolbox, ISO, power transmission, gears, degree bevel gear (driving).


For me, the ISO standard matched well with my Soviet part. Then the “Degree bevel gear (driving)” must be dragged and dropped into the assembly window. Now the “Configure component” dialog opens on the left. The module, the number of teeth, the pressure angle, etc. can be set. Here you have to experiment, have the bevel gear with the green check mark built again and again and measure it. (Tip: If you click on a component edge, the bottom info bar of SW conveniently shows the measured length directly).


However, you cannot specify all dimensions and geometry properties in the configurator. And here’s where it gets a little tricky. If the tooth geometry of the blank created fits so far, the rest must now be added manually. I used the function “Attachment/Base rotated” to build a created sketch as a body of rotation to the blank (see screenshot). Again, I had to measure the old bevel gear over and over again.


Once you are satisfied with the part, you need to export it to *.STL format for 3D printing. And off we go to the Fab Lab Siegen! Here Fabian helped me out, showed me the 3D printers and started the printing. Thanks a lot! 😊


The first print was unsuccessful (of course). In 3D printing, for example, the holes are always slightly smaller compared to the model. The teeth were also too small, so that they could not engage deeply enough with the opposing teeth. These teeth also sheared off during initial attempts. In addition, the bracket for the crank was a bit too thin and is therefore broken off.

Gears printed

Drill machine open

But now it was possible to measure the printed bevel gear and improve the dimensions in SW and finally start a second attempt. However, the second time it went better than expected and the bevel gear installed beautifully. The hand drill runs very smoothly and if any problems should occur in a few years, I’ll just print out the bevel gear again 😉 .



Project: 3D Copy Shop A Wooden Codel Was Created from a Plaster Face Cast

A Contribution from Eri

  • A photo series was created from a plaster face mask.
  • A point cloud from the photo series was created with Linux/Colmap.
  • The points were cleaned up and processed with Meshlab
  • The milling paths were generated with Pycam.
  • The toolpath files were created with a tool developed in-house.

simplified so that the GCode can be run with the Fablab CNC software as well as NCcad.

  • The workpiece: a 1 1⁄2 year old, dried piece of end-grain wood, pre-drilled for “spaxing” onto the sacrificial plate.
  • Cutter: 6 mm cylinder for “roughing” and 6 mm spherical head for “finishing”.

About The Manufacturing Process

The feed rate for milling could be increased significantly. The cutter length was not sufficiently taken into account during the creation. This is how the saying of the day came about: “One more delivery is possible”. Before any collisions occurred, it was stopped. After remodelling and x-times finishing (Proxxon), the following emerged:


This project was kindly supported by the University of Siegen. Many thanks for this, especially to Daniel for his collaboration and Helga for text drafting and layout.

Only a very slow Linux notebook (Ubu 19.04) is available on site. (possibly faster with SSD or cloud computing ??)
Network access for updates planned.
Friday afternoons are aggravating and not so well suited for such projects with public traffic and the limited time of the staff.
Other spax screws are missing or have not been found.
The cutter selection is limited.
Unsolved : Chatter marks.

The Creation of a Bow Handle

A contribution by Philipp Dasbach

The Problem

In archery, the repeatability of the entire shooting process is
crucial for a good result. I myself have owned an Olympic recurve bow with sights (aiming device) and stabilization system (weights for balancing, for smoother aiming) for several years.

Characteristic of this type of bow are the curved or backward bent ends of the bow, from where the English term “recurve” comes.
Unlike other shooting sports, where, for example, is shot over the rear sight and front sight, the sight of the recurve bow has only the front sight. Thus, the body posture and the stopping point of the bow (anchor point) form the second reference point of the recurve bow to define the direction in which the arrow flies. That is, even if the front sight always points to the gold (center of the target), but the bow is slightly different in your hand than it was when you shot it before, the arrow will hit somewhere else.

Therefore, many archers customize the grip of their bow with grip tape or modeling clay to craft a grip that is perfect and stable in their own hand. Since I was not satisfied with the grip of my bow, I decided to design my own grip, which also looks professional due to 3D printing.

The Recurve Bow

Attempts to apply known knowledge

Before I designed the grip according to my ideas, I first wanted to copy the original grip of my bow, so that I could make the adjustments that seemed reasonable from this basis.

Due to my mechanical engineering studies at the University of Siegen, I am familiar with the use of CAD software and have confidently approached the design. However, two things caused me an unexpected amount of problems.

First, it took me a long time to design the many interlocking fillets of the handle. These fillets are very difficult to reproduce with software solutions from the mechanical engineering sector, since they usually have defined geometries. This took me some time, but also forced me to learn new features and capabilities of CAD software.

The second issue that cost me a few tries in 3D printing is the measurability of the hard-to-define geometries.
Since the handle has only a very narrow, straight edge, it was very difficult to measure the position of the hole, bevels and radii. However, it is important for the attachment of the grip piece to the sheet that the geometry of the grip piece corresponds exactly to the geometry of the receptacle provided for it on the sheet. Since I could only roughly estimate many dimensions, I had to approach the correct geometry step by step through trial and error.

During this trial and error, I was able to learn a lot about 3D printing from the staff and makers in the Fab Lab. Above all, they helped me find the ideal slicer settings for my part and the right material. In addition, the Fab Lab works with different CAD programs, all of which have their strengths for different problems.


After four attempts I had copied the original grip of my bow sufficiently well and started with attempts to adapt the grip geometry to my hand. In the process, I tried a total of five different versions.

First, I made changes that seemed logical to myself to stabilize certain areas of the hand to prevent it from slipping back and forth. On the other hand, I combined this with geometries of grips from different manufacturers to arrive at my individual and optimal grip.

Currently, I have mounted a version of the grip on my bow, in which I have rounded some disturbing edges of the original grip and minimize the back-and-forth slipping by changing the angle of the contact surface.

Arch with mounted handle on bracket

Satisfied, but surely there’s more?!

I definitely achieved my goal of getting a better grip than the old one. Whether I have already found the ideal solution, I do not know, because there are still some geometries that I could try.

In the meantime, I uploaded the latest version of the grip to Thingiverse and hope to run into an archer who also uses my grip. Overall, I have to say that through the exchange in the Fab Lab I got ideas and tips that I would never have come up with on my own.

Handle piece, mounted on bow

Copyright Pictures: Philipp Dasbach

Zeit.Raum – Making Siegen come alive

The interdisciplinary research project ZEIT.RAUM Siegen is being carried out in close cooperation with citizens and aims to make the city of Siegen experience and understand its space and history in a collaborative way using innovative technology. ZEIT.RAUM is designed to facilitate collaboration and exchange between all interested parties – from academics and students to schoolchildren and amateur historians – about the city’s history, present and future. This opens up new forms of knowledge generation and transfer.

The project consists of two interlinked components: A touchable table-sized city model for interaction, produced using various digital fabrication processes and exhibited in the Siegerland Museum. Built-in sensors enable an interactive experience of the city and its history, which also stimulates individual memories. The second central element of the project is the Stadtwiki, a collaborative digital platform on Siegen’s city history, which is being developed by and for citizens. In addition to collecting information, it also serves as a forum to discuss the meaning of the data collected. Places of remembrance are identified, processed and reflected upon. All components of the project should be designed in such a way that they are easily accessible, understandable and easy to use for all interested parties.

One of the first test prints for the interactive city model

The role of the Fab Lab

We at Fab Lab are also involved in the project on several levels, especially in the creation of the interactive city model. The existing virtual 3D model of the city of Siegen, which was created by Prof. Jarosch, serves as the data basis for this. The topography is milled out of a large plate in the Lab. Which material is best suited for this is currently being tested. The true-to-the-original buildings of the city installed on it, on the other hand, are printed with the 3D printers in the Fab Lab. The sensor technology that will later be installed in the city model, which should be as user-friendly as possible, is also being developed in our lab. Several students are also involved in the project, working on individual components of the project within the framework of qualification theses.

Paper prototype for the interaction concept of the city model

Current developments

Currently, students are working on the design of the interaction concept and have, among other things, created a paper prototype of the city model. Likewise, the first prototypes for the city model have already been successfully printed and the sensor technology extensively tested. The model is printed with conductive filament so that the sensors can later be built directly into the city model. As part of this initial technical work, a developer board (see cover picture) was also created on which the following were installed: Arduino-Leonardo, Raspberry Pi 2, CAP1188-Breakout, 3D-printed touch sensor and 3D-printed matrix.

Test of the sensor technology to be installed in the city model

During one of our last project meetings, a first model of the Nikolaikirche – probably the best known landmark of the city of Siegen – was already printed. It took our Ultimaker a whole three hours to make the 1:9000 scale model.
Here you can see the result:


Other project partners

In addition to the Fab Lab, the University of Siegen also involves the Chair of Didactics of History headed by Prof. Dr. Bärbel Kuhn, the Chair of Practical Geodesy and Geoinformation headed by Prof. Dr. Monika Jarosch and the Chair of Computer Supported Group Work headed by Prof. Dr. Volkmar Pipek. The realisation was made possible by the support of the university and the Friends and Patrons of the Siegerlandmuseum, who see the project as an investment in the future of the Siegerlandmuseum. The Siegerland Museum is to be strengthened by ZEIT.RAUM in its role for cooperative and inclusive historical work in and with the region.

We will of course keep you informed about further developments of the project in and around the Lab.