Astonishingly good quality 3D printed spare parts for vintage cars

• What was needed? Replacement worm in the speedometer of a classic car
• Manufacturing method: Selective laser sintering with SLS powder
• Requirements: Long durability, precision, favourable price
• Material: iglidur® i6
• Industry: Automotive industry
• Success through co-operation: High precision, no abrasion, fast and cost-effective production, no lubrication

The application at a glance:
Finding spare parts for vintage cars is usually difficult, if not impossible. It is a familiar problem and especially tough for exotic vehicles and rare models. Dr. Jörg Pühler, the owner of a Stanley 750B built in 1924, was looking for a spare part for the mileage counter in his speedometer.
The original part had been completely ruined due to wear and the work done on the car by the previous owner. The online 3D printing service from igus® The required shaft with screw and gear could be printed cost-effectively and in a short time from the abrasion-resistant SLS-plastic iglidur® i6.

In the Stewart Warner speedometer, the gear on the first intermediate shaft which meshes with the worm on the input shaft was no longer in working order. The pinion was no longer engaging with the worm gear. Due to the work done on the speedometer by the previous owner, it was impossible to determine the correct dimensions. The manufacture of a spare part required several attempts and a material that was stable, enabled high precision and was suitable for continuous use.

With the igus 3D printing service, a fully functioning spare part was made from iglidur i6. Thanks to fast and cost-effective manufacture with the laser sintering method, it was a straightforward matter for the vintage car owner to test several variants of the component in practice. Thanks to the high-performance polymer used with incorporated solid lubricants, the component no longer needs to be lubricated. Even after being in use for more than 2,000 miles, no signs of wear are detectable.

The speedometer of a Stanley 750B vintage car built in 1924 no longer functioned - the mileage counter was defective. The cause of the defect was found by the owner to be the toothed gear that was located on the first intermediate shaft and meshed with the worm on the input shaft. Due to wear, the pinion was no longer engaging with the worm.

The problem was caused by the three-digit day counter: The discs had about 0.2 mm axial play and there was no spring washer to press the discs against each other. Occasionally, a small transmission gear slipped between the discs and jammed the counter. A slightly curved, 0.1mm-thick brass washer fitted at the side eliminated the axial play so that blockage no longer occurred.

After the cause of the defect had been eliminated, it was possible to set about manufacturing a spare part. With the help of the FreeCAD software, Dr. Pühler succeeded in creating a CAD file with a 3D model of the component that was needed The first order through the igus 3D printing service was processed without complication and the finished spare part was received after only a few days.

The material was stable and even the smallest details were reproduced perfectly. The shaft immediately fit into the bearings and the worm gear for the output was precisely fitting. However, it turned out that the original pinion had become so worn that the estimated dimensions of the gear were too small.

Only one parameter in the CAD model had to be changed, after which the second version was quickly sent for printing. The second specimen also ran quite well and passed a short endurance test. As it started to exhibit slight malfunctioning at low revs, however, a third version with an adapted toothed gear module and helix angle had to be made. The third specimen functioned perfectly and engaged correctly.

A big advantage of additive manufacturing is that changes can be implemented quickly and with little effort. The adaptation of the digital model and also the convenient online ordering process and speedy manufacture make it possible to implement adaptations of prototypes and spare parts quickly and cost-effectively.

The difficulty with the manufacture of spare parts by means of 3D printing is often the creation of a suitable 3D model. On the Internet, there are numerous tutorials and free online tools for the creation of CAD models. The igus website® also offers several free CAD configurators for users without prior knowledge, including for gear, bearing and trapezoidal thread nuts. If you don't want to do this work yourself, you can find Support for the design of 3D printed spare parts at open workshops and other repair initiatives.

After the shaft was thoroughly tested on the test rig, it was fitted into the speedometer, which, in turn, was installed in the vintage car again. A significant advantage of iglidur i6 is offered by the solid lubricants incorporated in the plastic, as it is thanks to them that the user doesn't have to lubricate the components - even if the interacting part is made of metal.

After being in use for more than 2,000 miles, the printed worm gear continues to be in good shape without any obvious signs of wear. The slight traces of metal abrasion that can be seen in the picture come from the driving worm gear and were caused in the starting phase of the test, but they did not change noticeably during further use.