finishing question

[bond hinson]

out of all the things in turning thusfar finishing remains the most difficult. Im doing a series of big bowls for someone which were very spalted silver maple. I tried WOP for a finish because the client wanted something very glossy. But the WOP just kept on sinking in and sinking in and would not stay on the surface. I then applied 2 layers of shellac hand sanding in between with 200 and 400 grit as the can suggested- I then applied a layer of poly on top of that but after it has dried a bit I can see all my hand sanding marks all over the finish. I dont know if I'm pressing too hard or what but I can clearly see all the sanding marks. should I just use 600 between coats to even out that gloppy shellac? Should I sand all the way down back to wood and start over? so confused here. WOP has worked great on all other finishes but that rotty wood lovvves to drink... thanks for any advice, happy turnin,
Bond

 

[Bill Boehme]

The sanding marks might be from a previous coarser grit. One thing that is very important is to not skip grits when sanding and also make certain that you sand until all of the scratches from the previous grit have been removed.

There is also a possibility that you are using too much pressure when sanding. Use light pressure and do not use worn out paper. If the paper that you are using does not remove the scratches from the previous coarser grit fairly quickly, then it may be worn out. Also do not let the paper load up with either dust or "corns" (glazed finish nodules).

Too bad about the wipe on polyurethane. It is thin and not a good choice for spalted wood in my opinion. Any kind of glossy finish on spalted wood is going to be a problem, but I think that shellac rubbed in by hand (with the lathe running) would be a good choice for sealing the wood. I don't see a need to sand the shellac, but the shellac should be the dewaxed type or else there might be a problem applying poly over it. If you do sand the shellac, make certain that it is completely cured and wet sand very lightly with 600 grit to prevent gumming the shellac.

WOP builds very slowly and fine scratches may telegraph through the first couple coats. Keep applying at least six coats and do not sand between coats.

 

[MichaelMouse]

There's that old "don't skip grits" business again. Unless you're talking breakfast down south, doesn't mean much. What you want to do is make sure the only scratches are from the current grit, not a prior before you move on to finer. You don't have to have the spectrum of forty grits between 80 and 1800 to get a good surface.

When you begin sanding you have tool marks parallel to the rim down to the bottom. Easiest way to eliminate is to sand across them, which is why most use powered disks. Hand sanding is predominantly round-and-round producing the same pattern, only smaller. It's tedious and inefficient.

Problem arises when you get down to around 300/inch mesh, where sanding across the grain still leaves a visible "grain" against the wood's color and figure background. There you want to sand with the wood grain, by hand, to blend the new scratches into the background. So think more of direction than grit all the way through the process.

As to the spalted wood - especially delignified white parts, you want to use high-test poly at first, not thinned. Or 3# shellac rather than 1#. You want it to sink slower than it cures. Sanding between provides an irregular surface for the necessary mechanical adhesion, but you don't need to go 220 unless you're sanding flat work. Go that 300 or even finer. As long as the entire surface looks dull, it'll stick. Where it's bright and slick - won't. You now have very small scratches which, if you don't wipe off the finish per instructions - can be blended and diminished by flowing the coat. Thinned varnish is nice here, because it remains liquid long enough to lay flat.

You're a Zamboni operator. First you chip down the big scratches, then you lay a good flowing layer that makes what remain almost invisible.

 

[craterdog]

Spalted Maple finish

I've had a similar problem with spalted norfolk island pine. Eventually the wood will stop absorbing the wipe on poly and build the finish you're looking for. When i get close to the final finish, I switch to Minwax spray high gloss poly in the can. I have been able to get a really great finish with 2 or 3 coats, sanding between coats with 400 grit paper. It hasn't required any buffing or remedial work to get out dust nibs because there haven't been any. Maybe this will help you.
Tim Carter

 

[bond hinson]

sorry about the confusion, sanded through the grits100,120,150,180,220,400,600 while on the lathe then took it off the lathe the scratches came about while hand sanding... guess ill take it down with some 400 then move to 600 then reapply with thinned shellac then move to the WOP. I would'nt even put a glossy finish on this but the customer is always right! will letcha know how it goes thanks for the advice

 

[Odie]

sorry about the confusion, sanded through the grits100,120,150,180,220,400,600 while on the lathe then took it off the lathe the scratches came about while hand sanding... guess ill take it down with some 400 then move to 600 then reapply with thinned shellac then move to the WOP. I would'nt even put a glossy finish on this but the customer is always right! will letcha know how it goes thanks for the advice

Bond......

While I don't have any direct experience with the particular methods you are using, your description reminded me of similar issues I've dealt with.

I've found that no matter how well you sand, and to what fine degree of grits, sometimes a sanded surface can initially look very good visually........but, sanding marks can appear AFTER the final finish is applied.

There are two methods I use for dealing with this.

First, some woods......particularly walnut, and a few other dark colored, or dense woods......are susceptible to this "smoke and mirrors" deceptive appearance of a perfect sanded finish, only to find sanding marks after the finish is applied. For "known" problem woods, I finish my sanding on the lathe with a random orbital sander. Usually RO is good to go at a 400gt final sand, but this is only a general observation.......sometimes 600 is required. This usually takes care of the problem, before sanding on the lathe is finished. This option is no longer available after the finish is applied......unless a person waited until the finish is completely dry, then return to the lathe and start sanding a few grits back, and work up the sanded surface again......

Secondly.......If sanding marks become apparent after the finish is applied, they can usually easily be dealt with by using 0000 steel wool while the finish is still wet.......after using the steel wool, wipe off the excess finish and residue, and re-apply the finish. I have a modified mandrel that accepts a wad of 0000 steel wool, and I can do this operation under power with a drill (at a very slow speed). This is the way to go if there is a lot of surface area to cover.

ooc

 

[Bill Boehme]

There's that old "don't skip grits" business again. Unless you're talking breakfast down south.....

Perhaps it is talk about breakfast. How do you like yours? 😀

Not skipping grits is generally good advice for sanding also. However, to be more precise, for the sake of saving time, it is inadvisable to skip grits, but if you do, it is best to not skip more than one (breakfast or sanding). Why? Because you will save yourself a lot of time by not trying to remove 60 grit scratches with 600 grit paper.

If applying an oil finish or a film finish that is rubbed down to a satin sheen then fine scratches are not a big deal since they won't be visible. On the other hand, if applying a polished high gloss finish on a piece of dyed figured maple it seems in my experience that it is almost impossible to remove scratch marks even skipping just one grit without an unacceptable amount of time spent sanding. It is hard enough to avoid seeing scratches without skipping grits.

BTW, I never power sand, but I do sometimes sand with the lathe running with the coarsest grit only and then do all of the rest of the sanding by hand off the lathe. It takes a lot longer, but it is good exercise and I have never seen a power sanding job that I would call satisfactory. From what I have seen, lot of folks including a few professionals seem oblivious to sanding marks.

 

[Odie]

Perhaps it is talk about breakfast. How do you like yours? 😀

Not skipping grits is generally good advice for sanding also. However, to be more precise, for the sake of saving time, it is inadvisable to skip grits, but if you do, it is best to not skip more than one (breakfast or sanding). Why? Because you will save yourself a lot of time by not trying to remove 60 grit scratches with 600 grit paper.

If applying an oil finish or a film finish that is rubbed down to a satin sheen then fine scratches are not a big deal since they won't be visible. On the other hand, if applying a polished high gloss finish on a piece of dyed figured maple it seems in my experience that it is almost impossible to remove scratch marks even skipping just one grit without an unacceptable amount of time spent sanding. It is hard enough to avoid seeing scratches without skipping grits.

BTW, I never power sand, but I do sometimes sand with the lathe running with the coarsest grit only and then do all of the rest of the sanding by hand off the lathe. It takes a lot longer, but it is good exercise and I have never seen a power sanding job that I would call satisfactory. From what I have seen, lot of folks including a few professionals seem oblivious to sanding marks.

Bill......

You are most definitely correct that it's not good advice to skip grits on the lathe. Yeah, it can be done, MM.......but, careful application of "horse sense" will reveal the obvious conclusion that whatever grit you're working on will require you to eliminate the scratches left from whatever the previous grit was........and, if it involves two graduated steps, then it will take much longer to obtain the necessary surface quality than if it were a single graduated step.......

Bill, the trick to power sanding is to do the heavy sanding at the lower grits under power, and switch to hand sanding at some point......but continue to progress through the grits while still spinning the workpiece on the lathe. When you get to the final grit.......THEN, it is time to do some strict hand sanding with power off, with the grain.

I usually switch from power sanding to hand sanding (power on) at 180 or 220/240 grit. Further hand sanding (power on) is continued with 320, 400, and up to 600, if necessary. The highest grit I decide to go with is done in combination with lathe power on.....and with the grain, lathe power off. Not all of the sanded surface requires hand sanding power off, but a decision will have to be made where it's necessary. Generally, just about every bowl needs hand sanding, power off, on the interior of bowls at the center bottom.......the exterior of bowls, not so much.....but, requires a decision whether it's necessary, after inspection.

ooc

 

[Bill Boehme]

Odie, the RO sander at coarser grits sounds like a good plan. The type of power sanding that I think gives terrible results is when done with a drill and two inch Power Lock discs or something similar. I attended a demo at the SWAT symposium where the turnings were very nice, but the sanding ruined the pieces. Some others in the session expressed the same feelings that I had. The small discs left deep scallops all over the piece being demo'ed not to mention that the power sanding rounded over all of the natural edges. Even the kind of small discs with foam padding are a problem with the coarser grits and high sanding speeds.

Rules are meant to be broken and I occasionally have to break my personal "rules" of sanding. This week, I was turning a beautiful piece of highly figured maple and I could not avoid tearing out the grain no matter what I tried. I had to resort to the 80-grit gouge and then the 100, 120, 150, and 180 before going to hand sanding. I generally like to start sanding at 180.

 

[KellyDunn]

Bond, I am a full time production turner in some pretty nasty tropical woods. Here is what I want you to try. When you think you are finished sanding get the work damp. Take maybe an old cotton sock wet then kind of wrung out. Get the work evenly damp. Like dont miss a spot. It will bring up most scratch marks you missed. Then determine which grit to go back to to take care of what you see. I stop at 320 grit. I keep a pad with 220 on one side and 320 on the other. In most cases for me a forward and then reverse with the 320 takes care of it. It only takes a minute or so for the piece to get dry from getting it damp. Please do both forward and reverse with your finish grit. And do that hand sanding. Not under power. Power creates swirls. Forward and reverse really sands the fuzzies down. If you choose to hand sand in the finish process sand in the same direction you did on the lathe. Those concentric lines keep the mind saying all is well. You mix up the direction and folks think you cant sand for squat. I would think that.
Punky wood as has been mentioned is a bear to get the punky part filled. CA glue in the sanding process can help a lot. Its a csae by case thing not an exact science. Unless you want to get into epoxy. But what I suggested will get you light years ahead of the curve you now have.

 

[Gretch Flo]

sanding

Sanding is driving me nuts-good advice here. I think when using discs I may be using too heavy a backing of the sand paper. (Klingspor-cloth backed). It may be too rigid and leave the marks from the edge. I now have 120-150-18-220 wavy, and it helps. However when the sand paper gets worn (and I don't know it) is doesn't clean up the previous sanding marks (or was it 2 grits ago???) and need to get fresh disc. But the edges may have made a deeper groove that wasn;t there 2 grits ago either.
Then is it the problem of the backing pad (have soft , med and firm.)
I too use alot of stressed (spalted, wormy, barked) wood and need to smooth out some tear out in spite of fresh sharpening and lite touches
.Some woods are so easy to sand (such as open grained oak, osage orange, Kentucky coffee tree.) Walnut often is very bothersome, other times not (when really dry when turned. One problem is I sand wettish wood til 300-400, and then return to it when totally dry. Wet wood marks. I have found marks that the only thing I figured out was fingernail mark (I have a bent 3rd finger of right hand'.)
Doing more hand sanding now, but arthritic fingers and the bent finger, especially in small deep bowls, is problematic.
Just rambling, I hate sanding, and yet spend half of my time sanding, hand rubbing, etc,
BTW I am pleased with Lee Vally's Siawool ( made in Gt. Britain.) for finishing the finish -but expensive Gretch

 

[MichaelMouse]

Not skipping grits is generally good advice for sanding also. However, to be more precise, for the sake of saving time, it is inadvisable to skip grits, but if you do, it is best to not skip more than one (breakfast or sanding). Why? Because you will save yourself a lot of time by not trying to remove 60 grit scratches with 600 grit paper.

How many grits are there? The meaningless "don't skip grits" mantra means what? Since they exist, you must use them? Make sure the only scratches on the wood are those from the present grit before moving on. I'm a three and out, personally. 150/240/320 in one back/size, 120/220/320 in another. Using five would be ridiculous.

Couple other points have come up. Wetting between grits is something people do. I do it between 320 and hand sanding, but there are those who need to do it because they've case-hardened the surface with heavy pressure/spent paper, and those who like to do it as a rogue grit removal. You know you need it when you've got that shiny surface with the background scratches. If you don't heat, you can use a dry wipe to get any loose grit off the surface. A few pieces of heavy hidden grit here and there can make some impressive scratches when they're pried loose and carried under 320.

Sanding with the work rotating should never leave burns. Sanding with lathe off and a power disk wants a light touch, and that means control. The flex shaft I use is so much easier to control when static sanding versus a drill. No need to seek support from the work to help weary or arthritic hands. Not sure that the backing on the paper is much of a hindrance, as long as you have control and a bit of give in the velcro backing, but there are a lot of thin-backed papers out there to try. I find they have so much flex in their backing, even on my hard rubber back, that they start making little folds and delaminating from the cloth. If the arthritis bothers, do yourself a double favor and secure the driver of the powered disk while you handle only the piece.

Sanding with the sander supported and the work rotating not only allows for more rapid surface improvement, it allows you to skim those soft spots in your spalted wood, so they don't dish in. A big help because you don't have to treat areas and gum paper with shellac. Static sanding that type wants you to support the disk on the good wood and let it carry into the punk. Sand around, not on the white areas.

 

[Odie]

Odie, the RO sander at coarser grits sounds like a good plan. The type of power sanding that I think gives terrible results is when done with a drill and two inch Power Lock discs or something similar. I

Bill......

The RO (Random Orbital) sanding is done on the final highest grit before applying the finish......not on the coarser grits. There would be no purpose in the value of RO anywhere but the final sanded surface prior to applying the finish. Get a RO sander, use it, and discover this for yourself.

I have been using powerlock discs for 25 years, and if you'll check my album, you won't find a scratch mark anywhere on my finished surfaces. The trick is to learn how to use them. (I suspect many turners give up on powerlocks, because there is a learning curve to them.....They never do discover what you can do with them, before they give up in failure.) Powerlock is aggressive, and used to best advantage, is actually much faster (and less expensive) than the hybrid discs most turners use......I won't go as far as to say powerlocks are better, but the surface quality they are able to achieve is their equal, and certainly faster. The finest finish is the result if used to their potential......and, the thing that is imperative to understand is the potential includes NOT using them on the final sanded surface, which is done by applying sandpaper by hand.

One thing the powerlocks have, and is a distinct advantage, is the ability to install and remove it 50 or 100 times.......the plastic piece that attaches to the back of the powerlocks......just does not wear out. They were developed, and are extensively used in the welding industry for cleaning up weld beads, and longevity is what they are designed around.

ooc

 

[john lucas]

I find that sanding fills the sanding marks with dust and makes them hard to see. I think that's why they hide and don't show up until you get to the finer grits or even put finish on. I keep a soft terry cloth handy and wipe the piece between each grit. At this phase I can see the scratch marks better and determine if I need to hand sand with the grain. Then I go to the next grit. This may not work as good as Kelly's water but it's faster and works most of the time for me. Compressed air also blows the dust out of the scratches and shows them better.
for some reason I have yet to discover some woods will hide the scratches better. I think it has to do with the lighting I'm using as much as anything. I find point source lighting is the best. These are small very bright lights that produce hard shadows. Bare bulbs or small quartz lights work best. You also have to move the light around to change how the shadows fall to be able to discover those hidden scratches.
I don't skip grits. It simply goes faster. You can skip a grit and sand longer with the next higher one until you get all the previous scratches out, or you can go up just one grit and sand for a shorter period of time. When I'm sanding carved surfaces buy hand it is far less stressful to not skip a grit.

 

[Bill Boehme]

Bill......

The RO (Random Orbital) sanding is done on the final highest grit before applying the finish......not on the coarser grits. There would be no purpose in the value of RO anywhere but the final sanded surface prior to applying the finish. Get a RO sander, use it, and discover this for yourself....

OK, I misread the first time. That makes sense. I think that my DeWalt 6" RO sander would be too large to use in the manner that you describe. Anyway, I prefer my Armstrong RO sander 😉. It gives me more precise control sanding off the lathe. Maybe when my joints wear out I will change my mind. While I'm not in a hurry when sanding, I don't believe in wasting time by skipping multiple grits.

I have a bunch of Power Lock discs in various sizes and grits. I used them with a miniature air motor. They are OK, but not the tool of choice for me.

 

[MichaelMouse]

Another thought for sanding off the lathe are the mops. I have this big one on the JET buffer that works a treat, but smaller ones will get you a sanded surface with a glow. Easy on arthritic joints, but it can clear the skin off your knuckles if you get careless.

http://www.woodworkingshop.com/search.aspx?q=mac+mop The BIG guys. 180 finishes like a 320.

http://www.woodworkingshop.com/product/fs92220/ Mediums. Smaller carving details clean up with the truly small.