I want to address a very strange issue we have had on a few Bullet R2.
It affects around 5% of the machines we have shipped, and mostly goes away after some use, but not always.
It’s been 5 strange weeks trying to get to the bottom of the problem with the doors opening on the R2s. We have had our quality engineer, mechanical engineers, and also the manufacturing engineers work together to try to find the root cause
Things we have looked at include: General tolerances and tolerance stack ups, surface finishes, heat expansion and deformation. Static and dynamic forces on the door.
It has been the strangest mechanical problem to date, and there are still things we don’t understand. However, we do believe that we have a solution.
First of all, the R2 drum is exactly the same as the R1 drum. The door and stainless steel insert on the front plate are also similar in dimensions, even though the R2 insert is held in place with additional screws.
Secondly, the door opening during roasting does not have to be related to the clunking or banging sound that is sometimes heard, these are mostly two separate events.
We have experienced the banging on the R1 in the past, but it would usually go away after the drum is run in, but this time it’s taking a lot longer before it goes away
Door Opening can be caused by:
- Drum not shimmed to the proper distance. (Distance between drum edge and front plate should be around 1mm)
- Drum wall inside edge too sharp or with buurs.
- Drum vane edge too sharp. (The vane that is closest to the front of the drum)
- Drum vane edge too close to the front plate.
- Drum not seasoned enough.
- Freak cases where the beans stack up just right to push the door open.
Fix: If you have done lots of roasting and it only happened once, you can try to soften the inside drum edge, and the front vane edge. Use a fine file to first round the edge, then use fine (600+) sand paper. You want the edge to be rounded and smooth. If it happens on a more regular basis, we will need to replace the drum.
Note: The drums that have this problem are all within spec, so why it happens on some and not others is still a mystery. The location of this vane and the edge quality does play a part, so we will modify this from now on as it solves the problem. Bean size also plays a part.
Clunking or banging:
- Shims on the drum shaft touching the bearing seal and not on the inner ring (inner race). Especially the back shim that is resting on the spring. These shims are stamped, and are not completely flat.
- Drum not seasoned enough.
Fix: Turn the shims as shown in the reference below.
To mitigate this from happening again, we will move the front vanes 2mm backwards, and make sure the shims are turned in the right direction.
The problems with the shims could be because the tool to make them is bending them more than previously. This could be because of the material or a worn tool. We will check this as we want the shims to work in both directions. We might also just make them smaller (OD) so that they will not be able to touch the bearing seal.
If you have any issues, please contact us on support, or the place you bought your Bullet.
Jonas