Methods for producing swirl free finish
rover1
| Posted in Power Tools and Machinery on
I have noticed that I often get swirl marks when using a RO sander but not when using a sheet sander. The wood appears to be smooth until I apply a finish and the swirl marks are then noticable. I use up to 220 grit on many projects on both the RO and sheet sander before applying any type of finish. I thought RO sanders were designed to produce a smoother swirl free finish? I have also noticed my Makita 1/4 sheet sander takes off a finish quicker than either my Makita or Dewalt 5″ RO sanders. I am looking to buy a larger sander (either a 6″ RO or 1/2 sheet sander) and would like to hear your feedback before purchasing. In reality, what type of electric sander produces a more hand sanded appearance; RO or sheet sanders?
Replies
The manual for my Bosch ORS says to contact the wood before turning on the sander, and pull if off before turning it off. Otherwise, it claims that swirls will result.
Just acquired Bosch 1/2-sheet orbital sander (model 1293, I think) from Amazon. Best I ever used. It would have been nice if a dust collection adapter had been included, but its own little dust box provides me with dust I can use for pore filler, an unexpected bonus. As I wrote before: I don't understand the hoopla over ROSs. I can move the sander about randomly with my hands anyway.
Cadiddlehopper
Does that Bosch 1/2 sheet sander have variable speed control?
Edited 12/8/2006 7:00 pm ET by rover1
I make my living doing furniture and cabinet finishing and i have never received a piece from any carpenter or cabinetmaker that they have so called "finish sanded" with ANY form of machine, whether it is the best random orbit out there or not; that does not have many swirl marks and sanding blemishes of all sorts in it. Hand sanding is the ONLY way to insure that you take the substrate to the point where it can be finished blemish free. PERIOD
Deckerman,
I work at making high-end reproductions, and I wouldn't accept or more to the point, my customers wouldn't accept, anything less than a stellar finish. I use a cheap DeWalt RO sander ($89.00 at Lowe's) and it leaves surface that does not show any swirl marks, even in direct sunlight, which highlights any imperfections in a finish. This is the case with any species I've worked with, including maple, which in my experience, is extremely prone to showing swirl marks. The key to this, is to use good quality sandpaper, in a fairly fine grit and moving the sander somewhat slowly over the surface in such a way to thoroughly cover it. Another important point is to not think of the sander as way to "level" joints, or to flatten panels. On unpainted wood, I won't use anything more coarse than 180, but I prefer to start with 220 and finish with 320.
There is no doubt that hand sanding is an excellent way to prepare a surface for finishing, but I can think of a few places that it is inferior to a well done job with a RO sander; face frame joints (or leg to apron joints), veneered patterns, and miter joints. These all present the problem of changes in grain direction, which can be successfully hand sanded, but are far easier with the non-directional RO sander.
Rob Millard
http://www.americanfederalperiod.com
Thanks for your reply RMillard : I agree that the Dewalt RO you mention does an excellent job of sanding, however I stand by what I mentioned about finishing the bare wood with only random orbit sanders. If you take most so called "finish sanded" pieces of work and blow and vacuum ALL the sanding dust from the substrate and THEN wipe the surface with ethyl alcohol liberally as I generally do then you will find most often a myriad of fine scratches that will appear magnified when the coating system is used.These patterns are exaggerated with finer coatings such as lacquer and wax free shellacs.It has been my experience that hand sanding alone will almost eliminate these,however even with the most careful hand sanding, inevitably when the masterpiece is finish coated and examined by the harsh light of a 5oo watt bulb again, low and behold there are some of the little monsters there still. I think a judicious RO sanding up to 220 grit only followed by a hand sanding over the entire surface again ( taken up to max 320 grit ), is the only way to ensure a viable substrate to finish. A note here ( as HowardAcheson states reply 16 ) is that if the substrate is sanded beyond 220 grit the risk of closing the pores and burnishing the wood becomes greater with each successive grit. Occasionally, depending on the wood species, I will sand and prep the surface with up to 320 grit prior to sealing it. When this is done however I ALWAYS blow and vacuum all dust and then wipe the surface with ethyl alcohol to open up the grain and expose any missed areas." if you are not sure if you have the time to do the job properly then don't bother starting it"
Isteed,
I just got back from the shop, where I sanded a piece of maple with just 220 grit paper in the RO sander, I thoroughly cleaned the surface and applied some alcohol. When viewed in normal light I saw no evidence of swirls, nor did I in direct sunlight, and even under 4X magnification there weren't any swirls to be seen. I didn't expect to see any, but I thought I give it a try.
99% of my furniture is topcoated with wax free shellac, so if as you say this accentuates the swirls, I should have been seeing them all along, but they just aren't there.
In the end it is a personal choice how one gets to the finished result, since hand-sanding works for you, and power sanding works for me, we are both right.
I trust the final line in your last post was sort of a tag line, and not directed at me.
Rob Millard
As you say it is a tag line and to to even consider taking it personally it beyond the scope of what forums are intended for... they are a learning only situation...when they even hint at personal attacks..then the whole point of the exercise is lost. If random orbit sanding works for you then I say great - go for it." if you are not sure if you have the time to do the job properly then don't bother starting it"
Edited 12/9/2006 8:56 pm by lsteed
I don't know where you live and what kind of shop you run. I have a very buisy small shop with 2.5 employees and I am pretty well conected in the local cabinetmakers trade. I do not know any shop that hand sands unless it is necessary, such as mouldings. Your statement is extreem and odd to say the least. I RO sand to 220 on stain grade. For paint grade I fill the grain and sand with 220 as well. And my finish quality is nothing short of perfect by cabinetry standards. For high end work where the standards are higher I still sand to 220 but depending on the wood I might use a cabinet scraper. The only time I have sanding marks is if I make a mistake like not sanding thuroughly with intermediate grits. I catch those mistakes by wiping the surface with mineral spirits.Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.
Perhaps there is a misunderstanding here : I am a finisher by trade . When i receive a piece from a carpenter or cabinetmaker I know that I have to finish the sanding process by hand. To do anything else and simply proceed to the finishing process ,by assuming the product is ready to accept a coating system, would be somewhat careless on any finishers part. I am not advocating any production shop to abandon RO sanding- that simply cannot be done today. I am however pointing out that to assume the product is totally ready for a lacquerers touch, with the absence of the final hand sand; would be reckless. That final hand sand can be a simple "with the grain" once-over, with 220 or in some cases up to 320, or it could be a twenty minute redo to fix the poorly sanded products. Every case is different. Production shops are just that- they have to PRODUCE to stay in business. Each and every product is different and the person who attended it is always in a different state of mind and sometimes attention to detail in the sanding process varies. I receive products from individuals whom i totally trust to give me very detail oriented workmanship. BUT I still never proceed to the finishing stage without FIRST checking to see if the product is acceptable to coat. Invariably it isn't and requires at least a few mins final sanding on my part. So I stand by what I said about finishing the product with hand sanding BUT clarify it by repeating what I first said that my statement was from a FINISHERS point of view. Please remember that once the first coats are applied to the substrate, then it is too late to fix any scratches etc that show up at that point... BETTER to err on the side of caution than to adapt a foolish point of view that RO sanding only will give you a totally trustworthy result. The finishers I know who do that tend to have mixed results in their output. I cannot justify a perfect finish over an imperfect substrate by saying to you " WELL THAT'S THE WAY YOU GAVE IT TO ME AND YOU SAID THAT IT WAS READY TO FINISH !!!!"Lorne "if you are not sure if you have the time to do the job properly then don't bother starting it"Edited 12/11/2006 2:09 pm by lsteedEdited 12/11/2006 2:11 pm by lsteed
Edited 12/11/2006 2:13 pm by lsteed
P.S. to my post "Spell checker" is our friend, Mike, my spelling is lousy sometimes too and that's why i have to edit my posts. I just realized they have a spell checking feature here .... I will probably be the first to break it with overuse!" if you are not sure if you have the time to do the job properly then don't bother starting it"
You are correct I did misunderstand you. You have a good work ethic. There are no profesional finishing shops around here that I know of. Either the shop does it them self or they install it and leave it to the GC, which means that the same guys that paint the walls finish the cabinets.
I inspect my work as best as I can for sanding or machine marks. On a built-in or furniture job I will usually use mineral spirits to make it easier, but my booth has adequit lighting to see with out the aid of minerial spirits. On a full kitchen or other large job this is not reasonable, but the sanding is also typically a lot easier because I sand the sheet stock with 220 and the face frames are a flat surface. The doors are the only difficult part. Plus I usually use stains that do not hilight the mistakes.
You are right that before entering the booth everything has to be checked and most mouldings will need hand work.
As for the spell check..... I have to dissable Norton for it to work and it is just not worth the trouble. Besides if I started spelling correctly people my take me seriously. Heh heh.Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.
I agree with you. In the shop I was involved with, the finishers were required to hand sand all "money" surfaces before applying finish.Sanding wood--hard or soft--beyond 220 does little more than burnish the wood making staining difficult. This is particularly true if you are using a pigment stain which sits on the surface and relies on "nooks and crannies" to impart color. Softer more porous woods can be sanded to to 220 but harder less absorbent woods may stain best if only sanded to 150. A number of years ago a large cabinet/custom furniture shop I was involved with did series of adhesion tests with various finishes and sealers. As part of this test we explored adhesion based on sanding grit. We found about the same adhesion up to 180 - 220. Beyond 220 adhesion dropped off due to burnishing of the underlying wood particularly when non-linear machine sanders were used. This was tested on birch panels. We also found that the resulting smoothness of the first coat of finish was not materially affected by the smoothnes of the underlying wood for sandpaper grits between 150 - 220.. The smoothest surface substrate for final finishes was obtained by sanding lightly after the first coat of finish was applied and dry. Which makes the case for a thinned first coat of finish.So our conclusion was that sanding beyond 180-220 was not necessary and could be actually detrimental. But, most important was that there was an appearance affect if the surface was not HAND sanded in the direction of the grain using the highest grit used on the sanding machine. A flat pad sander produced a much flatter surface than a ROS. However, both required final hand sanding with the grain for optimum appearence. If not hand sanded, swirl scratches could show. Final hand sanding using a sanding pad in the direction of the grain is a must. To carry it one step further, sanding at 320-400 grit after the first coat and subsequent coats was the optimum. No improved appearence was noticed by between coat sanding beyond 400 for varnish. 400 was the sweet spot for thinner finishes. Between coat sanding was always done by hand whether for flattening or for adhesion. I think you will find similar thoughts in the popular finishing books but YMMV.Howie.........
No, it does not. When running, it is quite free of vibration. If its speed were changed, I am not sure that would be the case.Cadiddlehopper
My usual practice is to turn the ROS on after placing on the surface, and turn off and let it quit turning before lifting off the surface. Haven't noticed swirl marks with either the 5" or 6" Bosch variable speed ROS, but I have occasionally seen what you are describing in others' work. Typically I'll go over the entire surface with 80 grit 8-12 passes, depending on how hard and how scratched the wood, 6-8 passes with 150 and 6-8 passes with 220. Occasionally I'll make some marks with #2 pencil and see how many passes needed to remove the pencil marks. Just for grins next time I have the 6" beast out I'll try turning it on before placing on the wood and see if I get swirlies.
I too have a 6"Bosch ROS and start with the sander on the wood, then progressively use finer grits, with swirl-free results
Whatever the powered sander, a few minutes of hand sanding or straight line sanding will always improve the finish. Sanders that work in circles, random or not, must of necessity leave cross grain scratches. Good practice avoids excessive swirls but it is not possible for a RO sander to leave no swirls--that how they work.
Random orbit sanders still leave a circular swirly pattern, it is just less noticeable. If you are sanding up to 200 I suspect the swirls you see are from the lower grits. There are several causes for this. Low quality sandpaper, not spending enough time in the intermediate grits, skipping a grit, starting too low, and as others indicated poor technique.
Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.
I think Mike (mudman) is pretty much on target here. I get excellent results from my DeWalt ROS, which is 3 years old. I use high-quality paper, change the paper often (avoid burnishing, keep little pieces of grit from getting involved) and don't push down on the sander. One of the things about paper quality -- the variation in grit size within one stated grit (say 220) can be greater in poorer paper, and even in different grading schemes. I don't have the grading types committed to memory, but I've read a couple of articles that explain how the "average" may be the same, but the range of particles sizes can be quite different.
For the problem you're describing I'll lay my money on possibly starting too low, and then not sanding thoroughly through each step above that.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
I've had exactly the opposite results; the D&B orbital sander I use to have would leave swirl marks if I wasn't extremely careful, but my RO sander has never left a mark. I pay no attention if it is in contact with the wood or not, before starting, so that can't be a factor. I almost never hand sand a flat surface, so I'm not getting rid of them that way.
I believe that most problems with swirls are from using too coarse a grit. I usually start with 220, and follow with 320. I will occasionally use 180. Most of the furniture I build features a combination of veneer and solid wood. I hand plane all flat surfaces ( sometime I will reluctantly use a scraper), and sand the veneer. Just before applying the finish, I will sand all surfaces to 320, going very lightly on the planed surfaces to maintain the texture and to remove any handling marks. This unifies the surfaces, for finishing. The other cause of problems is moving the sander too fast, as this will exaggerate any swirls. I use to move the sander fairly rapidly over the surface, wanting to put this less than exciting task behind me. I noticed that I'd have to go back and concentrate on areas such as pencil marks, in order to sand them away. It hit me that if this were the case with pencil marks, which are imperceptibly thin, I was not doing an adequate job of refining the surface, in those areas that looked clean and well sanded. Now, I move the sander quite slowly, with a 50% over lap between passes. I strive for finishes with high clarity and great depth, and even in direct sunlight I can't see any evidence of swirl marks in my finish.
I think it is a mistake to look at a sander as a stock removal tool. It should only be used to unify and refine an already smooth surface. The amount of material to be removed with a sander should be measured in a very few thousands of an inch.
Rob Millard
Edited 12/7/2006 7:02 am ET by RMillard
Your experience is right on. Orbital sanders leave more noticible pattern. Random orbit sanders leave a less noticable problem. The issue that the poster is having is likely a grit selection/ technique problem.Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.
Here's what I do.
I have two PC 7336 6" RAS, the type that looks like a converted right angle grinder, one with 220g and the other I use from 60g to 120g.
Then I have 3 DW 420s and I keep 120g, 150g and 180g on them.
And I go through the series starting as low as I need and finish w/180g.
The 150g and 180g are Mirka and they do not leave a lot of swirl marks, but if I am worried about the possibility of swirl that I can't see I have Milwaukee 1/3 sheet and a 1/2 sheet sanders that are straight line orbital sanders and they eliminate the probability of swirls.
If you are getting swirl marks after 220g they are probably from a heavier grit that you used before that the 220g grit did not remove.
John
PS: the 6" PCs are very aggressive and are great for flattening large projects.
Edited 12/7/2006 8:03 am ET by pins
I have both a PC-330 orbital and a Bosch 3283DVS random orbital and both will leave swirl marks on Cherry, Hard Maple, Hickory etc. Sometimes you can get away with it on oak but not the others. I only use the monsters on non critical surfaces, All the critical surfaces I avoid using either and resort to hand sanding, Too many times I thought there were no swirls and then you apply the stain and you can spot them. As I mentioned in another thread a couple of high end custom furniture shops in my area do not use either sander on any visible exterior surface, all hand sanding. Another shop uses them, then hand sands and then applys mineral spirits to see if they have removed all the swirls.
Here is something I wrote up for a local woodworking newsletter a few years ago.
Sanding wood--hard or soft--beyond 220 does little more than burnish the wood making staining difficult. This is particularly true if you are using a pigment stain which sits on the surface and relies on "nooks and crannies" to impart color. Softer more porous woods can be sanded to to 220 but harder less absorbent woods may stain best if only sanded to 150.
A number of years ago a shop I was involved with did series of adhesion tests with various finishes and sealers. As part of this test we explored adhesion based on sanding grit. We found about the same adhesion up to 180 - 220. Beyond 220 adhesion dropped off due to burnishing of the underlying wood particularly when non-linear machine sanders were used. This was tested on birch panels. We also found that the resulting smoothness of the first coat of finish was not materially affected by the smoothnes of the underlying wood for sandpaper grits between 150 - 220.. The smoothest surface substrate for final finishes was obtained by sanding lightly after the first coat of finish was applied and dry. Which makes the case for a thinned first coat of finish.
So our conclusion was that sanding beyond 180-220 was not necessary and could be actually detrimental.
But, most important was that there was a big appearance affect if the surface was not HAND sanded in the direction of the grain using the highest grit used on the sanding machine. A flat pad sander produced a much flatter surface than a ROS. However, both required final hand sanding with the grain for optimum appearence. If not hand sanded, swirl scratches would show. Final hand sanding using a sanding pad in the direction of the grain is a must.
To carry it one step further, sanding at 320-400 grit after the first coat and subsequent coats was the optimum. No improved appearence was noticed by between coat sanding beyond 400 for varnish. 400 was the sweet spot for thinner finishes. Between coat sanding was always done by hand whether for flattening or for adhesion.
I think you will find similar thoughts in the popular finishing books but YMMV.
To Isteed, Rover, & Millard also:The sand paper I use almost exclusively is silicon carbide non-loading. Lately I have used Norton's 3X also. I usually stop with 220 or 320 grit. My sanders are plain old orbital quarter- and half-sheet. I clean the paper with one of those crepe rubber chunks occasionally also. I usually finish with oil or tung oil varnish. I have never noticed swirl marks on my finished pieces. I will take a closer look tomorrow in the sunlight and will use a magnifier, too.What type and quality of paper do you use? Could that make a difference? Also, I never sand with anything more coarse than 100 grit if I expect a good finish. Scratches left by anything more coarse take forever to remove with finer paper.Cadiddlehopper
I found that paper that is "loaded" causes more and deeper swirls, and you can reduce them by changing your paper more often than you are now.Hand sanding is the only way to truly rid your work of swirls.Although a finely tuned scraper can clean up really well.
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