More About Sanding

      And some more about sanding. Then, a little more about sanding. Finally, just a little more about sanding. June 5, 2006

Question
I'm a cabinetmaker and have a problem when sanding wood doors and veneer panels. We use 100 grit paper, then 150-180 for a nice finish. The problem is that we see those circular scratches like bird's eye marks (whippets) on the wood when stained. How can I get rid of these? (We use an orbital sender for doors.)

Forum Responses
(Cabinetmaking Forum)
From contributor M:
100 is a bit heavy to start with for veneered panels. Most of the time, they're already sanded to 150 or 180 at the factory. So when you hit them with 100, you're actually introducing those sanding swirls and then aren't spending enough time with the successive grits to remove them again.

When you're making your doors, what condition is the wood in when you begin sanding? What was the last grit used in the process of milling the lumber? Again, I suspect that it's your use of 100 paper.

I'd do an experiment beginning with 150, going to 180 and then 220 to see what kind of different results that produces. For your experiment, try wiping down the panel with a little mineral spirits to see what it would look like to have that grit's sanding scratches below a finish. I have a suspicion that your problems may disappear by beginning and ending with higher grits than you are today.



From contributor F:
Try making a final pass with your finest grit using very light pressure on the orbital sander. These types of sanding flaws are generally associated with pressing down too hard on the sander. Care must also be taken when lifting the sander off of the work. You should try to lift the sander straight up and not tilt it. Also, keep the sander at full speed while sanding. If the sander is turned off while touching the work, this will cause marking.


From contributor T:
Try putting the 120 grit in the mix. Don't skip. Maybe just sand the panel with 180 only before the door is assembled. Are you using Porter Cable sanders? If so, scrap them if possible and go to DA sanders. A lot of times, depending on the type of sandpaper you use, blowing the surface off between grits can help get rid of grit from the previous sanding that has lingered behind. Some people finish with a 505 sander. It's a Porter Cable but not a random orbital.


From contributor L:
Contributor M's advice is good. First, if you don't need to be grinding the joints down, you are starting with too coarse of a grit. I usually start with 120 for my grinding of glue and joint leveling. Also, going from 100 to 150 is a no-no. You can't skip grits like that on a stained project. On paint, it is okay. Most veneered plywood is already sanded to 150, but it is a straight sanding as opposed to orbital, so you need to get rid of the straight scratches. Use 150 on pre-sanded veneers.

Also, when you are using an orbital sander, you need to the let the machine do the work. You can't press down real hard to speed up the process - it will only leave deep swirl marks which are harder to get rid of with successive grit sanding. Also, do you have a finishing sander or a regular sander? A finish sander has a smaller swirl pattern (3/32") while a normal sander has a larger pattern (3/16").

I suspect that you are just starting out with too coarse of a grit, but as you can see, it can be many other things, machine and/or operator.



From contributor R:
I concur with all the above responses. In my experience, those marks have been caused by:
1) Too coarse a grit - start with 150.
2) Technique - let the sander do the work. Don't allow your wrist to whip the sander around (like Norm does on New Yankee).
3) Previous sanding debris - clean the surface well between grits. I don't find blowing with air is enough. Run your hand over the surface - your fingers and palm are remarkably sensitive. You may need to vacuum and wipe with a lint-free cloth. This is to ensure that any grit from the previous sanding is removed. Particles from a coarser grit paper can raise he** if trapped under a finer grit.

And as you found out, it doesn't become apparent until you stain. Wiping with mineral spirits or lacquer thinner (only where you're not concerned about it lifting the glue) will generally show these swirls before you commit yourself to staining.



From contributor J:
Before I went out on my own, I worked in a very high end cabinet shop. We're talking Capital Grille, Legal Seafood, etc. It was there I learned that no matter how good a random orbit sander you use, you will always have swirl marks to different degrees. With clear finishes, you can usually get away with 150 or 180 grit. For dark stains, though, we would always go over the panels by hand as a last step. Work up to your 180 grit and then, using a good sanding block with 150 grit, go back and sand out the finer grit scratches by hand. The 150 grit will quickly cut through the finer scratch pattern, and that is fine enough for most cabinet work. For furniture you could always go finer. It's a little more work, but remember - the difference is in the details.


From contributor Y:
I agree with the post above, but I bet you could get rid of most of your problems by cleaning in between grits. I would say that from my experience, that is your most likely culprit.


From contributor K:
I have my random orbital sander hooked up to the dust collector, which seems to help by vacuuming the dust as I sand.


From contributor S:
Sanding wood is one of the basic woodworking tasks everybody should know how to do properly. There is no reason for anybody to be sanding veneer with 100 grit. 100 is used for flattening a rough board or shaping wood. You should only use a 6" DA (works with air) for your first sand with 220 grit, then switch to a finish sander (vibrates usually 1/4 sheet size), also 220. Then lightly block sand in the direction of the grain, again with 220. You should let the weight of the sander do the work and not apply pressure, as you will only overheat the sandpaper and possibly put dents in the work. If you have major scratches in the veneer, you can finger sand them lightly in the direction of the grain. Use 100 grit only on solid wood. It removes way too much material to be safe for veneer and even with solid wood doors, you are actually giving yourself more to sand out than doing any good.

Every shop should have the following sanders and know their proper use and application. You need a sander polisher with a 6” disc, a 6” DA sander, a ½ sheet jitter bug, a ¼ sheet finish sander and sanding blocks. You should stock 80, 100, 120, 150, 180, and 220 and know when to use what grit. Every shop should also have scrapers and know how to use them.



From contributor H:
No one mentioned the quality of sandpaper used. They are not all the same. Sandpaper like Trizac or any paper graded by micron is more consistent than others. Abrasives that are screened for size sometimes contain spikes. Imagine a screen sorting gravel. It will separate 1/4" stones from soil. In that same soil, place a pencil. There is a good chance that that pencil will go through that screen vertically. This is what happens when cheap abrasives are made.

If you want to minimize this, you simply rub two sheets of the same grit paper against each other lightly. This removes the tall trees from the forest. Swirl and sander marks are also subjective. One man's swirl marks, which might be the Grand Canyon to him, could be perfectly normal and acceptable to the rest of us in this biz.



From contributor K:
Just read something that might be worth looking into if you are getting too many swirls. The pad of a random orbit sander should spin freely. If that bearing becomes sticky and doesn't allow the pad to freewheel while sanding, you will get the same results as bearing down too hard on the sander while sanding: more swirls.


From contributor J:
Most professional cabinetmakers never need to touch 220 grit. Nor do we spend very much time with finish sanders. The only reason I use one is because I haven't bought an edge sander yet. If I was building pieces of furniture or jewelry boxes, it would be a very different story. But I am a cabinetmaker, and as such, I need to be realistic in what amount of labor can be done for a given price, and what is really noticeable to most people's eyes. Go to a big box store and open one of their cabinets. Most of the companies they carry don't even bother to sand out the cross grain scratches on the inside rails after they come out of the wide belt. You think their customers notice? Although contributor S is correct in how he sands for his work, don't feel that this is how we all need to sand. And remember - if you do decide to sand out to 220 grit with all these multiple grits and tools, your competition won't, and it's doubtful that anyone would be able to notice the difference.


From contributor F:
My strategy for setting quality standards is 180 degrees to contributor J. I could be wrong, but he seems to be saying that as long as his product quality is as good as on the cabinets displayed in big box stores, he has done all that should be done. Maybe we should give our clients vision tests at the start of a job and then adjust the quality to level to what we think the client will be able to see. "I am sorry sir, but if you would just back up about five feet and then squint a little while crossing your eyes… Yes, just like that! See? Looks great now, doesn't it?"


From contributor Y:
Contributor J makes a good point. 90% of cabinet shops don't sand past 180g in most situations, and there's a reason for it. The extra effort given doesn't produce equal results, so it's not economical. I know guys that run their frames and raised panels through wide belts at 220 and don't touch anything after that. I definitely don't recommend it, but they're successful with it - because most people won't see the difference. If you use a wide belt to get out the initial millmarks, then progress 100 through 180, cleaning in between grits… it is very sufficient. Anything beyond 180 is simply polishing and if you're staining the piece, that can make a problem with absorption. I have to agree with contributor J and, in my opinion, most other cabinetmakers.


From contributor J:
Contributor F, I can see how you may have come to that conclusion from my post, but the point was the quality level of the big box stores, and where they (meaning Masterbrand Cabinets, Kraftmaid, Thomasville, etc.) draw the line on their products. Different sanding for different woodworking. Not where I set my benchmark. My first post describes my sanding technique, which I learned from a shop that does the quality work you see in architectural magazines.

When I first started out, I suggested using 220 grit myself. I may as well have suggested using 1,000,000 grit - that was the reaction I got. I was then reeducated in sanding for cabinetry. And although I'll be the first to admit my quality does not compete with my previous employer, I am still using those same techniques.

My clients would not notice the difference between a door sanded to 150 vs. 220 and I doubt most woodworkers would notice either. But as always, everyone has their own methods and quality level. I have nothing against anyone sanding to 220 and I'm not saying it's wrong, just that it's not profitable, in my opinion, in this business. I may be mistaken, but I do believe most cabinet guys out there would agree.

As for my quality... Well, my clients are happy with it, even from less than five feet away, so I guess it's good enough.



From contributor F:
Actually, I agree with you. It is a proven fact that sanding finer than 180 is a waste of time for wood that will be receiving a film finish. There is some benefit to sanding finer than 180 for oil finishes. I apologize for jumping to a conclusion. After rereading I can see that I completely misunderstood.


From contributor L:
As for higher grit sanding, the finish I use (ML Campbell) won't guarantee their products if you sand beyond 150 grit. I used to sand to 220, but no more. And as for the difference between 150 and 220, I can easily tell. It actually starts to feel smooth and silky at 220; 120 compared to 150 is hard for me to tell.


From contributor S:
While I was still coming along as a woodworker, I worked as a helper to a high end yacht finisher and I have done my fare share of sanding. Some days, if I pressed my index finger and thumb together I could see blood forming at my fingertips because the skin was almost sanded through.

Wood needs to be sanded with the grain in order not so show cross grain scratches. All a swirl mark really is, is a cross grain scratch. Orbital sanders are by no means useful as a finish sander because of this very reason. They makes circles and sand with and against the grain. Orbital sanders are very useful to remove a lot of material in a short time, but you can't leave the work just like that. You need to break up the swirl marks with a vibrating or oscillating sander. After this is done, you need to block sand with the grain to remove the tiny marks left by the oscillating sander.

The best orbital or dual action (meaning it rotates and oscillates the disc) sander is a light DA air powered sander. The reason I say this is because electric sanders are too heavy and their weight causes more material than necessary to be removed and so great care needs to be taken that you don’t sand dents into the work or through-sand the veneer. I use an Ingersoll-Rand palm sander. When you use it, your hand is central to the disc and you can keep the disc flat against the surface easier. With some of the electric sanders, the handle is horizontal and behind the disc, so it is easy to place more weight on the back end of the disk, causing the disk to sand unevenly. The same applies to the 1/4 sheet oscillating sander. I prefer the Porter Cable finish sander – its weight is correct and it’s also well balanced.

When you sand solid wood as opposed to veneer, you can afford to use a heavy grit like 150, but with a high speed DA, you are dancing on thin ice with rocks in your pockets if you sand veneer the same way. Veneers are getting thinner and thinner and plywood is becoming increasingly more flat so the chances of through-sanding with 150 (if you are not careful) is much greater with 150 than it is with 220 and really unnecessary. Most plywood is already smoother than 120 or 150, so by sanding with 100, 120, and 150, you are just adding scratches unnecessarily. Just go after the damaged areas with a finger and 180. Then sand with 220 using the DA to flatten the piece. After this has been done, use an oscillating 1/4 sheet sander to hide the swirl marks where the DA cross sanded and finally sand with the grain with a 1/4 sheet sanding block. You should have no swirl marks, as the first and last grit was the same.

If ML Campbell insists on 150, then switch to 150 to block sand with the grain, but just lightly. As long as you keep the 150 going with the grain, you should have no problems with wiping stain collecting in the cross grain swirls.

Just trust me on this one. All of you guys with the electric DA sanders, put them aside and switch to air-powered sanders. Not only will you get a better finished product, but the sander is lighter and you can actually feel the difference through the sander between sanded and unsanded areas. Those electric sanders are simply too powerful and they cause you to fight with them to control the sanding motion, so sanding is more hard work than it should be.



From the original questioner:
I can see there are many ways to resolve this situation. But one thing is sure - after doing a few tests in the factory, I can say that +- 70% of the sanding problem is behind the sander! Everyone sands his way, but doesn't know the real technique. By letting the orbital sander do its job, no pressure applied, we can see the difference. Removing the dust between each step really helps, too. Then, working with a high quality paper with the right grit between steps will help to get the finish desired. Some say we cannot avoid those swirls, but I don't agree with this. If you look at a door that has just been sanded, sometimes you'll see some swirls at the extremity of the rails, but not everywhere. This proves to me that it has been sanded correctly and not correctly... This means the person is not stable with his technique. I think a good technique lesson to the employee will increase the quality and this should be the first step.

I read in a post that if the customer is a few feet away from the cabinet, he won't see any scratches. But it depends on your quality level! I could say that I won't paint the interior of my cabinets... once the door is on and closed, they won't see it. This makes no sense. Since the competition is high in this business, I think that taking a few more minutes on your job would make the difference for your reputation.



From contributor E:
Many good points. As a cabinetmaker (not a woodworker), I try to match my sanding level to the finish I am applying. To remove yourself from swirl and crossgrain scratches takes proper technique with a pneumatic D.A. sander, quality sandpaper and careful hand sanding. Remember that the sander will leave a finish one level higher than a block of the same grit.

If I desire a 180 finish, I start with a light 120 on the sander, then 150. After this, use a firm 150 hand to remove swirls and then a 180 to finish. Blow off excess between sands and be careful of direction. The grit I need is determined by the wood, stain or finish that I am trying to produce. 220 grit on poplar with a dark cherry stain by Chemcraft is a perfect match for noble mahogany mel by Panolam. If you only sand to 150, it is just a black mess. Get to 220 grit on maple and then try to glaze. You might as well apply to glass after staining and sealing before the glaze.

20 years of finishing has seen a lot of mistakes (and I mean tons), but it also teaches me to try different things and take the time to experiment like I did when I was in high school (I mean with wood). It is amazing how different techniques come from experimenting and can help solve a problem later on. It adds experience.



From contributor G:
The problem you've got is you're using an orbital sander which oscillates. The little circles you are talking about are called oscillations. You have two options. Change your sander or do the final finish by hand. When I went to college back in the dark ages, we were only allowed to finish furniture by hand. Back to basics!

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