Squiggles left by ROS?

[Bruno Frontera dela Cruz]

I have a Porter Cable 390 5" ROS that is always leaving squiggles behind that remain in the surface ready to make my hours of sanding look like crap. I realize that this could be 100% operator error but I figured I would post here just to see.

This happens under most grits but gets deep enough where I never can sand it out...when I drop down in grit enough for significant material removal I just create the defect again. I have tried light pressure, hard pressure, med pressure and they all leave these marks.

I am using Norton3x paper starting with 80 grit going up through 220 grit. Oh, and I brush, vacuum and wipe between each grit change and I brush often during each grit.

My main machine question is, could there be too much vibration in the z-axis causing the broken abrasives to be pounded into the surface?

Thx

[Todd Burch]

Are you starting with semi-rough lumber? 80 grit is WAY too coarse for dressed lumber or ply.

All ROSers leave squiggles, but the theory is they get so fine you don't notice them.

Tell more about your stock, your full sanding schedule and your finish.

[Bill White]

Are ya letting the sander do the work, or are ya mashing the crap outa the machine. One of the members of our WWing club was having the same prob. Come to find out, he was all but standing on the ros expecting the added pressure to speed the process. After I abused him (verbally), all is well.
Bill

[Howard Acheson]

The first two responses have dealt with the most likely issues and solutions. If you are using wood that has been through a planer, you should be starting your sanding with 120 grit and working up to no more than 180 grit for hardwoods and 220 grit for softwood. The final step is hand sanding in the direction of the grain with the last grit used. Sand with each grit until you have removed the sanding marks from the preceding grit.

Let the sander do the work. Don't apply a lot of down pressure on the sanding machine. Too much down-pressure can lead to burnishing of the wood surface which will lead to finish problems if you plan to stain. You should only be controlling the position of the sander, not the aggressiveness. Keep your movements smooth and sort of "swoop" down to the wood and "swoop" off the wood when you start and stop your sanding.

A final note, be very careful sanding todays thin veneered plywood. It's very easy to sand through the veneer. Plywood is factory sanded to about 180 grit and any sanding should be at 180 grit or higher. It's best to delay your sanding until you have a coat or two of your finish applied. Then sand with 320 grit by hand. This way you are sanding the finish, not the wood and minimize or eliminate the possibility of sand through.

[Tom Ewell]

Linear pace in moving the sander can also affect the swirl pattern, move too fast and the swirls become elongated, less random and more noticeable.

[Bruno Frontera dela Cruz]

I seem to notice it most the harder the wood species. No issue on poplar, some issues with walnut, and big issues on oak. I normally start with 120 or so if I milled the lumber but in this case I am dealing with a huge red oak slab from Scott Smith. Reversing Grain and knots are all over the place so hand planing with my gear was out so I started a bit coarser with the 80 grit.

Even when I start finer, the squiggles are there, they seem to form from the initial grit..

Oh and, no I don't put any weight on the machine, just enough to control it.

Thx

[Steve Jenkins]

make sure the pad is clean. If it is psa clean the glue residue off with lacquer thinner or goof off. Little balls of glue can cause this. If it's felt, blow it off really well and same for hook and loop to be sure there are no wood chips under the paper.

[Kevin Bourque]

I stopped using ROS's a few years back because of all those damn squiggly lines everywhere. I always ended up doing the final sanding with a conventional sander anyway.

Anybody want to buy a lightly used ROS?:D

[Bruno Frontera dela Cruz]

Conventional as in by hand?


I stopped using ROS's a few years back because of all those damn squiggly lines everywhere. I always ended up doing the final sanding with a conventional sander anyway.

Anybody want to buy a lightly used ROS?:D

[Don Jarvie]

Start with 150. Unless you need to take of a lot of material or have some dips in the wood 150 is the place to start.

[Kevin Bourque]

No, as in 1/4sheet power sanders

[Zach Callum]

All power sanders will leave little swirls or squiggles behind, this would also include 1/4, 1/3, and 1/2 sheet sanders.

[Rick Fisher]

Pushing on the sander causes it for me, I hand sand after using an ROS .. SIA makes a Velcro sponge with replaceable paper, love it ..

[Mike Wilkins]

No one seems to have mentioned one important step that all finishing experts say is very important during the sanding phase: did you clean off the wood between grits???? Failure to do so can result in a piece of grit from the prior sanding step getting left on the work surface, creating havoc with the next grit. Carefully wipe/brush/blow all the debris from the wood before you start sanding with the next grit. Even more important with porous woods such as oak. Hope this helps.

[Prashun Patel]

Squiggles and scratches are almost always caused for me by pressing too hard and are usually caused by the coarser grits. The reason is that the initial grits require a lot of work. They pressure me into wanting to press harder to make it go faster. It's best to change paper quickly and use a light touch. Norton 3x is great paper and should last longer than most. Still, switch sooner than you think is right.

What's yr next grit after 80? I sometimes skip to 120, and if the sanding has been aggressive @ 80, or there are some dense areas like end grain or knots, the scratches really won't come out with 120. You have drop to 100 and go grit by grit. As I go higher, it appears to be less critical to use every single grit. But for rough stock prep I find it essential and less frustrating.

Know too that when you press hard, you slow the rotation, which contributes to swirls.

[Tom Ewell]

You're right Mike, I tend to forget mention of that basic step, just do it automatically even with dust extraction on the sanders.

[Todd Burch]

Mike and Tom - read closer - one person did mention this already:


...Oh, and I brush, vacuum and wipe between each grit change and I brush often during each grit.

[scott vroom]

Are you starting with semi-rough lumber? 80 grit is WAY too coarse for dressed lumber or ply.

I dunno if I agree with that....I use 80 grit regularly to smooth the inevitable small lip where rail meets stile on my cabinets. I follow up with 120 then 180 and have no visable squiggles. Knocking that lip down with 100 grit just takes too much time and effort.

[Todd Burch]

I dunno if I agree with that....I use 80 grit regularly to smooth the inevitable small lip where rail meets stile on my cabinets. I follow up with 120 then 180 and have no visable squiggles. Knocking that lip down with 100 grit just takes too much time and effort.

Well, you have a point there Scott. I assumed he was sanding flat stock, not fixing bad joinery.

[Patrick McCarthy]

I dunno if I agree with that....I use 80 grit regularly to smooth the inevitable small lip where rail meets stile on my cabinets. I follow up with 120 then 180 and have no visable squiggles. Knocking that lip down with 100 grit just takes too much time and effort.

Scott, that is why God invented handplanes!

[scott vroom]

Scott, that is why God invented handplanes!

Or, that's why God created 80 grit.