I have just completed my first project, a small table for my 2 y.o. daughter, my wife hand painted flowers on it and I was really pleased with the results…until I went to finish it. It has swirl marks from my orbital sander all over (maybe a slight exagerration) the top.
What has caused this? Did I use the ROS on too slow of a setting (I kept it at low for all of the grits up to and including 220). Did I not sand long enough?
How fast do you want your ROS to go…crank it up all the way all the time? How high of grit do you go to before you finish?
The table is veneered oak plywood by the way.
Thanks!
Replies
Maybe don't use a ROS sander at all. Finishing sander or hand sand.
I'm a little confused. Where are the swirl marks? Under the painting or on top of the painting?
The standard sanding schedule is to start with 120 and sand until the surface is flat and shows no defects. The move to 150 and sand until the swirl marks from the 120 are gone, then move to 180 and sand until the 150 marks are gone and then finsih at 220 to remove any remaining marks. Then, and this is the key, hand sand at 220 moving in the direction of the grain. This gives the best preparation for clear coating.
The scratches are under the painting and the stain. If I was to go back and resand it would destroy my wife's painting. Does the speed of the ROS have anything to do with the scratches or does that not matter?
As you found out, the stain is the truth serum for a sanding job. I don't like the ROS for the final sanding--its really hard not to get the swirl marks.
I agree with Gretchen, use a finishing sander like PC 505.
I always finish off with hand sanding using the same grit as the sander. Frankly, for a veneered surface I almost always skip the ROS since its harder to judge when you are sanding too much. One point on using a ROS is that you don't need pressure beyond the weight of the sander. Too much pressure can also lead to swirls.
Also with veneered surfaces you shouldn't have to sand with any thing more coarse than 150, and often you can begin right at 220.
Inspecting before finishing is crucial as well. A low angle raking light helps pick up problems you wouldn't see otherwise.
things I like to practice;
Use the weight of the sander let the tool do the work.
Move slow sand proximally 1'' per second.
I like to sand to 320 grit. Be sure to blow off or wipe of the dust and any grit left from the previous grit.
Finial check in the piece in light at a angle it will show up any imperfections.
Don
rdreid,
Welcome to the wonderful world of " How the hell did I do that...". I'm still discovering new ways to screw up a finish from sanding/scraping/ planing ..too much, too little, etc. Personally, I don't use machines with grits above 150, sanding blocks with cork bases work very well, are less fatiguing and provide better control.
I believe Steve is correct, plywood comes with 180 grit finish and is so thin you really want to avoid going below that grit. As importantly however, checking your plywood carefully before purchase and handling it carefully during the woodworking process is critical....plywood seems to attract dents. I use a thick blanket on the table to protect the parts once I've done the finished sanding.
Thanks...I've become quite well versed in the world of "how the hell did I do that?!?" Thanks for the tips and I think next time I will be able to avoid the mistake.
I agree with Gretchen, but you could learn to use a Jack & smoothing plane proper,then you woun't have to sand as much and you will probly keep your hearing better.
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