BF20 Vario plastic gear replacement with metal gear

I own a BF20 Vario mill and have—like many others—problems with the plastic gear that transfers the momentum from the motor into the switched gearbox. every 20-40 hours of operation, the spindle starts rotating unevenly because the gear wears out. In my experience this vibration has for example led to the opening of the drill chuck that holds drill-tools and the like. Furthermore, the machine runs much louder than with a new gear.

I bought 3 plastic replacement gears, and I am now feeling that the last one starts to wear out. Since I sometimes also do CNC work with this machine I need a reliable spindle drive. I started out to find replacement gears made of metal, but couldn't find any.

The original gears are like this:

20 teeth brass gear

drill diameter 10mm

keyway 4mm

37 teeth plastic gear

drill diameter 15mm

keyway 5mm

I measured the axial distance to be about 37 mm, the gear ratio is 1.85.

These gears appear to be imerial with a diametral pitch of DP=20, but I am not certain of it - also because I have not found any reports on the Internet that somebody found standard imperial gear parts for replacement.

I have found metric Module 1 gears that at least have the same axial distance. They have slightly different transmission ratios, so I have decided to buy the two sets that match the ratio best. The gears also have slanted teeth but the teeth are a bit finer.

Here is the type numbers and where you can find them online. Not the cheapest, but if the whole operation works they are definietely worth the price. Make sure to get pairs of left and right rising teeth, otherwise they will not fit together!

Mädler has an online shop for Europe where you can find these parts - they usually ship within days.

1         21435000            Stirnzahnrad aus 11SMnPb30 mit einseitiger Nabe Modul 1,0                13,10 €

1         21434000            Stirnzahnrad aus 11SMnPb30 mit einseitiger Nabe Modul 1,0                17,25 €

1         21423000            Stirnzahnrad aus 11SMnPb30 mit einseitiger Nabe Modul 1,0                14,85 €

1         21422000            Stirnzahnrad aus 11SMnPb30 mit einseitiger Nabe Modul 1,0                14,27 €

The two sets I bouhgt are:

20 teeth to 50 teeth resulting in a gear ratio of 2.5, or

30 teeth to 40 teeth resulting in a gear ratio of 1.33.

The pairs have an axial distance of 37.25mm which should be possible to adjust by tightening up the motor box of the machine to the gearbox. Maybe I have to rework some of the holes a little bit...

One set will make the spindle spin a little faster with less torque, the other one slower with more torque. The gears have arrived and look very well made. I have orderd some square HSS metal to cut the keyways on my Sieg C2 Lathe (see this YouTube Video on how I am planning to do it).

The next challange is to bore the holes to fit the shafts and manufacture the keyways. I will get back to you here as soon as I have further news.