dkp619

Preventing "stripping" from sanding with an orbital sander?

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Hello. Thanks for any help in advance as this is driving me nuts! :)

Using my orbital sander I seem to get sanding "stripes" from the leading/trailing sides of the sander. These are showing up through the finish regardless of what grit I sand up to.

To answer some questions ahead of time. Yes I am sanding with the grain (though it happens if I don't too), I'm following the 1 inch per 1 sec rule and it seems to happen if I over lap sand or not (obviously I get more "stripes" the more I overlap). The wood I am working with is maple.

In the picture attached the lines I am talking about are the black lines (4 of them) running north to south. The line are not "black" in real life it's just how the picture came out. They're just visible is the best way to describe them.

Thanks again

post-8201-0-31896500-1354671544_thumb.jp

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I'm afraid I don't see what you are talking about.... could you draw arrows pointing to the black lines in photoshop, or some other image editing software?

- EG

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I don't know how to do that unfortunately. But if you click on the pic to make it larger, in the background there is a lamppost across the street. That pole lines up perfectly with one of the lines... Thanks

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It looks like you've applied a stain to this piece. Is this correct? Any unevenness in sanding (and if I had to guess I'd say that either the sander is imbalanced or you were unconsciously pushing harder on one side) will change how the wood absorbs finish. If your first coat is any sort of pigment (stain, dye, tomato juice, etc...) then you'll get what you describe. The solution is always start with at least one coat of a clear finish before going to pigments. Sanding sealer, Charles Neil's blotch control, thinned out shellac, etc...take your pick. The important thing is that thirstier parts of the wood are going to drink up a massive slurp of whatever your first coat is. Best that that be something clear, then you can bring in whatever pigment you wish. The only exception to this is when you're trying to accentuate figured wood. i.e. Popping the grain in tiger maple.

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I think Rob is right on with his analysis. It looks like the wood is blotching. This is normal... so you're probably not doing anything wrong to cause this to happen; however, there are steps you can take to avoid it. As Rob mentions, applying shellac as your 1st coat will help considerably. I have not used Charles Neil's blotch control, but every person I speak to who has used it says it works much better then shellac.

Please let us know how you make out.

Scott

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Thanks guys for the feedback but that's not the issue. I have done this staining before on maple multiple times (and I do use a thinned out shellac). It's not blotching just a poor Iphone pic, I can see these sanding "stripes" before the shellac or stain. I wrongly assumed they wouldn't show through the stain..... As far as pressing down on the sander, that being a cardinal sin, lol, I didn't do it. Now I am using a fairly "cheap" Ryobi so maybe it is a bit unbalanced and it is my first time with a random orbital (all previous times I've used a palm sander but it left small scratches that I hated) . All I know it's it driving me nuts. I had tried many times, for many hours and everything I could think of to get rid of them before taking the chance and moving ahead with the staining. Is there a specific technique for the orbital I should be using maybe?

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I encountered some issues you are talking about when I first started using a random orbital sander. I am sure it is different for every sander, but I have a Dewalt 5" random orbital sander.

I found out that I was putting too much pressure on the sander itself. If you are seeing the lines regardless of grit then two things need to happen. Once you get to 120 or so (<120 will have lines no matter what, because the sander is moving cross grain), don't move to the next grit until your lines are gone, or very faint. If you move to a higher grit with the wood still blemished, you just increase the work load of the higher, finer grit.

Second, you need to evaluate your grip on the sander. I changed my grip on the sander. I used to hold the sander on the top (so the top of the sander was pressed to my palm). This leads to unintentional pressure. I found that if I hold the sander on the sides (pressed between my thumb and index, or middle finger) and just let the sander "float" on the wood, I avoided lines I could see.

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Kind of looks to me like the effect of burning through the finish or sanding off some of the finish. However, I'm assuming you did the sanding before you finished and the streaking showed up afterward. It almost looks to me like some of the wood pores got clogged in the sanding process so the finish/stain went on unevenly. Perhaps a good wiping with mineral spirits or some other light compound after you sand and prior to finishing might be in order.

I'll admit to kind of grasping on this one but there's definitely causing different rates/qualities of absorption in what I'm seeing.

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Only worry about sanding with the grain when hand sanding. When I break dance with my orbital I sand the entire surface in one direction and then turn perpendicular on my next pass. I always go with the grain on my final pass before going to the next grit. Sounds like you're doing everything else right.

Also, I always back up a grit and hand sand before finish.

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This might be a stretch but are you using really cheap sandpaper? Grit is not consistent.

that, and dust your project between any grit. if there are some sandpaper particles left on your project form the previous grit, you will drag them along and scratch your project accordingly.

what i do is i rarely go below 100 with the orbital. if there are big planer marks or something i try to remove them with a scraper before.

then, you want to wet your project with water with a damp cloth to raise the grain and to "un-compress" the fibers.

when the wood is dry, you can hit it with a 80 by hand, then move to 100 with the orbital, up to the grit you want.

but, this is how we learn it, once your are done with the orbital sanding, you go back to hand sanding for the last grit. if you obital sand to 220 for example, you go back to 220 by hand and sand with the grain.

some teachers even recommand you go 1 grit lower by hand, so you'd go back to 180 by hand. you still saved time and elbow grease even if you go back like that.

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i had this exact same problem refinishing a maple coffee table. I too was using a Ryobi orbital. It was an easy fix though, just needed to hand sand it and problem solved as mentioned.

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