How Setco repaired a damaged Kessler spindle with a cracked shaft in a short time, economically and efficiently.

The industry has started using machining centres in the last 15-20 years and these have really become popular among manufacturing companies using machine tools. This has also led to sudden increase in maintenance activities of these machines. Spindle, being a main accessory of a machine tool, calls for regular maintenance as bearings used in it have specific life. In fact spindles are used in many other cutting machines like grinding, honing, turning centres, PCB drilling and routing, to name a few. But one can safely claim that repairing of machining centre spindles calls for higher skill sets than repairing spindles used for any other application. Machining centre spindles are vulnerable from design point of view as one has to engineer them considering many parameters like feed rates, weight of the spindle, etc.

There are four types of machining centre spindles:

1. Belt driven spindles

2. Gear driven spindles

3. Direct drive spindles, and

4. Built-in motor spindles.

Setco India possesses all kinds of infrastructure and knowledge to rebuild every spindle irrespective of its type or make. Worldwide, machine tool manufacturers produce own spindles. However, there are few independent spindle manufacturers across the globe and Kessler is one of them. Kessler – a German company – is known for quality spindle manufacturing and many European and other machine tool manufacturers buy spindles from Kessler. Recently, Setco received one Kessler spindle for repairs, which is used on a Titan double column milling machine. This was a built-in motor type of spindle, with BT 50 taper and speed 2500 rpm. This spindle was damaged due to an accident and there were cracks in the shaft and hence it was sent for repair.

Problems in this spindle

There was an accident on the machine with tool holder in the spindle taper

Main shaft was cracked inside BT 50 taper, and

Runout problem occurred on the mandrel.

Spindle repair process

On receipt of the spindle, it was taken to the tear down area and then subjected to a thorough inspection, disassembly procedure and everything documented with photographic evidence.

The inspection department checked all the parts to decide upon the optimum method of refurbishment or replacement of parts. In this case, it was clearly evident that the spindle shaft had a major crack and this called for new shaft manufacturing. Generally speaking, it is very difficult to reverse engineer a machining centre spindle shaft. The reason is that it is very difficult to take measurement of internal contour dimensions of the shaft where the draw bar operates. However, in this case, spindle shaft manufacturing was relatively easy as Setco engineers could take all internal dimensions without any deviations.

On making the shaft drawing, the material and manufacturing process was charted out. Setco has enough experience to select appropriate materials and other critical processes like heat treatment and taper grinding. In accordance with international standards, the shaft was produced. The success of manufacturing is realised when the shaft is fitted on the OE spindle without any issues. Moreover, it also depends on how well the draw bar operates. Everything went well with this Kessler spindle shaft manufacturing.

Setco engineers had to change the bearings of this spindle as it is always recommended to replace them once dismantled. These bearings are of ceramic ball angular contact type, FAG make, and it was found that these were available only in France. So by the time the shaft was produced in the machine shop, the bearings were imported and the same arrived on time. Once all the parts were received, skilled Setco technicians and engineers assembled the spindle in the in-house, state-of-the-art, temperature controlled room. As mentioned earlier, the crux of spindle repair success lies in thorough checking. 

The spindle was tested across various parameters such as:

Spindle taper is checked for its blue matching with reference to standard gauge

Spindle run out is checked with the help of mandrel of 350 mm long for run out at the end, which should be less than 0.015 mm, and

Checked spindle for clamping force, which should be 2500 Kgf ±100 kg.

On completion of static testing, the spindle was put through dynamic testing.

The spindle was run for full speed (rpm)

Checked for vibration which should be less than 1 mm/sec, and

Temperature stabilisation.

Thus repaired, the spindle, which was now as good as new, was despatched to the customer and it is working satisfactorily.

Advantages to the customer:

The task was tough. Still Setco India could successfully rebuild the spindle and the same is running without any problem
Had this not been repaired in India, the customer would have had to send this spindle back to the OEM, which could be a time consuming process and costly too, and
Setco India could build this spindle up in 15 days time and probably at 20% of OEM cost.