> The popular tool of choice to then level out my filler coats appears to be
> a Rotary Orbital Sander (ROS).

> I don't own a ROS, but I do have a decent finishing sheet sander (square
> base).

> Are ROS sanders superior to sheet sanders for this application, and if so,
> why?

We've been sanding down our Osprey with both a Ryobi ROS and an el cheapo Black and Decker 1/4 sheet finishing sander ($15). We've found that they are good at different stuff. Since ROS has no corners, the 1/4 sheet works nice for getting into tight spots or for concentrating on small areas (drips/runs) that need to be brought down. As for the concave areas, they are usually concave in only one direction, so you can get into them with the side of the finishing sander. The ROS removes material much faster and I find the 1/4 sheet a bit easier to control. However, if your glass is laid down flat and your fill coats are basically flat, you will find that you can get the job done much faster and easier with an ROS.

Since the hull of the Osprey was the first fiberglass layup that we'd ever done, we had lots of fun avoiding cutting into the glass since the glass has high spots and the fill coat had low spots. We live and learn and refill and resand and refill and resand. :-) The deck, on the other hand is going together _really_ well with the glass on flat and the fill coats thin with few runs.

If you're trying to save money, you could stick with the 1/4 sheet, but if you buy an ROS, you will find uses for both.

Later,

Tim.