I purchased a Bosch bench drill for our workshop – a PBD 40. The data sheet looks good, and I bought this tool second-hand, but I had some reservations before purchasing it:
You often read that the accuracy leaves something to be desired, especially when drilling small diameters in metal. It was clear to me from the outset that if I bought this model, I would immediately convert the internal bearings to something more precise.
That’s why buying second-hand made sense; I didn’t want to be restricted in my actions by a warranty period and preferred to invest the money I saved on the purchase in the conversion. Alternative bench drills, e.g., from Scheppach* or Parkside, don’t really offer much more, and I can’t imagine that they are any more accurate. That’s why I opted for Bosch, even if it’s “only” Bosch Green (for private use, not commercial).
Upgrade
First of all: There was a really interesting and useful thread in the official Bosch forums about which bearings are suitable and how to convert the whole thing.
Unfortunately, it seems to have been deleted in the meantime; at least, I can’t find it anymore. If I come across the content in the future, I will add it here, but unfortunately that seems unlikely. Things can disappear so quickly!
The precision bearings used were these two from Kugellager-Express.
Disassembly and reassembly is quite easy to do. Simply remove all visible screws until you have taken the gearbox apart. Be careful with the cables and plugs, as these are often quite short.
The most difficult part is removing the pressed-in bearing in the aluminum housing; even with an internal puller, it took me several attempts. Photos:
Conclusion
The observations made by the original posters of this conversion were not exaggerated: the concentricity and drilling precision have really improved considerably, even with the original drill chuck, which is often described as “poor”!
There is virtually no noticeable play anymore. Anyone who owns a PBD 40 and is dissatisfied with its precision should carry out this conversion; I am very satisfied.