ROS20VS: the three fitting checks that matter
An exploded sketch separates the shroud and backing pad with four pad screws. A second sketch aligns the damper ring locating bumps to shroud cutouts. A final view contrasts an evenly seated ring with an unacceptable wave.
Remove the pad, not the motor housing
1 is the shroud area; 2 is the backing pad. Hold the pad and remove its four securing screws. The four arrows indicate removal, not a tightening order. Keep the bearing flange cover and locating-pin relationship intact.
Match the ring bumps to the shroud cutouts
1 identifies the locating bumps on the ring underside; 2 identifies the matching shroud cutouts. These are not the backing-pad locating pins. Loosen the two shroud screws only enough for the manual’s approximately 1/4-inch separation.
Check the whole circumference before refitting
The enlarged conceptual section shows 1, the shroud edge, inside 2, the ring groove. Press until this fit continues all the way around, then tighten the shroud screws. A flat ring is acceptable; a bent, rippled or partly seated ring is not.
The sketches show how the ROS20VS pad, shroud and damper ring fit together. Shapes and spacing are simplified, not to scale. Unplug the tool before starting; follow the numbered steps below for the removal and refitting order.
When does the damper ring need replacing?
The ring sits above the backing pad and limits its unloaded rotation when the pad is off the workpiece. A gradual rise in unloaded speed during normal use is a sign of ring wear. It is not an emergency brake, and you should never hold a spinning pad by hand to test it.
Swirl marks alone do not mean the ring has failed. Unplug the sander first and check for damaged abrasive, a distorted backing pad or a disc that will not stay attached. The listed 7,500–12,000 OPM is the orbital frequency, not the pad’s rotational speed; it is not a pass/fail measurement for the ring.
The steps below cover the matching US ROS20VS construction. If your screw count or locating features differ, stop and check the model before dismantling anything further.
Match the replacement before taking the tool apart
Have a compatible replacement ring, a hand screwdriver that fits the actual screw heads, and a small container for the screws. If the backing pad is damaged, it needs its own suitable replacement. A new ring cannot repair a damaged pad.
Start with the ten-digit tool number on the nameplate. US ROS20VSC parts information lists damper ring 2609170071 and tool number 3601C87511. Match the spare-part information to your own nameplate before ordering. The ROS20VS name alone does not establish compatibility across every age or market version.
If you also need a pad, take care with RS033 and RS034: older instructions and current product information reverse their “soft” and “extra-soft” labels. Order by the full part number and confirmed tool compatibility, not just the hardness name. Ask Bosch if the details still conflict. These are backing-pad numbers, not damper-ring numbers.
Remove the pad, then the old ring
- Switch off, wait for all movement to stop, and unplug. Leave the plug disconnected throughout. Peel off the sanding disc to expose the pad screws.
- Hold the backing pad, remove its four retaining screws and lift it off. Put the screws somewhere safe. The sanding disc is the peel-off abrasive; the pad is the support attached by these four screws.
- Pull the old damper ring out of its locating groove. There is no need to dismantle the motor, bearings or electrical parts for this ring change.
- Loosen the two shroud screws enough to separate the shroud about 1/4 inch, or 6 mm. Open it only as far as needed to fit the new ring.
Seat the new ring before refitting the pad
- Find the locating bumps on the ring’s underside and align them with the shroud cutouts. These align the ring and shroud; the pad uses a separate set of locating pins.
- Press the ring into place with your thumbs, working around it until the shroud edge sits fully in the ring’s groove. Check the whole circumference for raised sections, folds or ripples, then tighten the two shroud screws. Reposition an unseated section rather than trying to pull it flat with the screws.
- Fit the pad over the bearing flange cover and align it with the drive-spindle locating pins. Once it sits properly, replace all four screws and tighten them securely. Do not use the screws to drag a misaligned pad into place.
- Clear loose dust from the pad, attach a compatible undamaged sanding disc, and align the dust-extraction holes. Check that the disc lies flat without loose edges.
Do not oil or glue the ring, or leave it out as a workaround.
Check the assembly and try it on scrap
Before reconnecting power, check that all six screws are secured, the ring is not distorted, the pad is undamaged and the abrasive is attached. Clear away the screwdriver and loose parts. Stripped screws, a cracked shroud, damaged locating bumps or a ring that will not sit flat call for repair with the tool unplugged. Do not omit screws or trim the ring to make it fit.
Once everything is assembled, secure a scrap of the same material for a trial. On this tool, place the pad on the work before switching on and avoid excessive pressure. Never power a partly assembled sander to see what happens.
If unusual rubbing, strong vibration or the original speed problem remains, switch off, wait for the pad to stop and unplug. Do not keep swapping parts by guesswork. Even a correctly fitted new ring cannot promise to remove every cause of sanding marks.
Models referenced