Sanding --> dirty finish

[GrahamRounce]

Hi again...
I've currently reached the stage of sanding, preparatory to Plastic Coating (which, thanks Derek, seems to work great).

I started at 100 grit, then 240, 320, 400, 600, 1000, 1200 (!), mixing glass, aluminium, wet & dry (used dry) types as they came to hand. On the walnut that makes the surface smooth as silk. On a pale wood, though, (tulipwood), it's nice & smooth but the dark-coloured finer grit sticks in the grain after 1000 & makes it look grimy & horrible.
Should I have stuck with glasspaper only? Would that still leave an infestation, only light-coloured?
Now I've gone back to 240, trying to make it look clean again, not fully successfully.
No doubt the same thing happened to the walnut, only it didn't show so much.

Who'd have thunk there was so much to learn?
Any comments/advice please?
Thanks,
Graham

 

[DaveL]

Graham,

Are you sanding something with the walnut and tulipwood together? I find that the sanding dust from the dark wood will discolour the light one, I use an air line to blow the dust off, it mostly works. :roll:

 

[Ironballs]

There's a school of thought that suggest you don't go beyond 320 or perhaps 400 grit on bare wood prior to applying the finish. You're into diminishing returns final finish wise and potentially with some finishes making it hard for the finish to attach itself to your wood.

I've never gone beyond 400 grit on bare wood

 

[Lord Nibbo]

The answer is to use a final scrape with a card scraper.

 

[yetloh]

I and others I know have made the mistake of using finishing paper on bare wood big mistake. the anti bind material in the paper can leave a horrible grey stain on pale timbers. The dark blue fabric backed stuff that comes in a roll (forget the name) can do the same. I now stick to stuff like garnet paper or abranet for bare wood and don't go beyond 320 or 400 as there seems to be no advantage in going any finer.

Jim

 

[Sgian Dubh]

I now stick to stuff like garnet paper or abranet for bare wood and don't go beyond 320 or 400 as there seems to be no advantage in going any finer.

Jim

If you are applying a film forming finsh such as shellac, varnish or any of the lacquers there is no advantage going beyond 220 grit even on fine textured diffuse porous woods like cherry or maple. Open pored woods like oaks, ash, elm, etc, don't benefit with sanding beyond 180 grit really-- the open pores are bigger than the abrasive grit if you go to 220, 240, grit and beyond.

In fact there are disadvantages to sanding too smoothly prior to applying film forming polishes. If the wood is too smooth it effectively becomes burnished and doesn't provide a good key which is needed, particularly for some polishes to adhere to. There are well documented cross-hatch adhesion tests that demonstrate the greater prevalance of film adhesion failure when applied to wood sanded very finely.

Another factor to consider is that a film forming polish will level out and hides the striations left behind by abrasive grits in the 150-180 grit and above range. It's a bit like hiding a fine cut diamond in plain view by dumping it in a glass of water.

The previous notes don't really apply if you are following up sanding with a thin, lightly applied in the wood finish like pure tung oil or boiled linseed oil, or even a few wiped on coats of what are sold as Danish oil or teak oil. From what I've been able to piece together over the last couple or three decades, Danish oil type formulations are generally made of generous amounts of tung oil (or linseed oil), a lot of white spirits and some resins (possibly alkyd, but who knows for sure because the makers keep it all a secret), perhaps some metallic dryers; the resins and the oil cause a film to build. In other words they are essentially a sort of soft long oil varnish that is easy to apply with a rag. Slainte.

 

[GrahamRounce]

Thanks to all for the advice. It was getting very boring sanding with grits 400 & over anyway - I won't be sorry to leave those in the drawer.

As for the scraper.... as it happens, I just got a plane from Ray Iles (which I'm very pleased with), together with a new blade, and the old original blade was enclosed with it. I guess that might be ideal for scraper-making?

Graham

 

[Ironballs]

Depends what the blade was. Scrapers are pretty cheap, even when buying a decent Clifton one

 

[Sgian Dubh]

Graham, in an earlier post you said

started at 100 grit, then 240, 320,...

You were actually missing a few grits in the sequence. In general, and if your initial wood preparation using cutting tools (such as planes and scrapers) is good, you should be able to start your final sanding at 150 grit, but sometimes you'll need to start with 120 grit abrasives.

Anyway, don't skip grades to ensure that the sanding process is as fast and efficient as possible. If you find you have to start at 120 grit to remove the last vestiges of cutting tool marks, follow this with 150 grit, then 180 grit and finish at a 220 grit for fine textured woods.

You should check that the striations left by the coarsest paper you start with are consistent over the whole surface of the piece and that all little nicks and tool marks are removed. Follow up with the next finer grade and check that all the coarser striations from the previous grade are replaced with the finer grade striations, and then move to the next finer grade, and so on.

You can go straight from 100 grit to 240 grit as you described, but it takes longer to get the wood all to show an even pattern of 240 grit striations than working your way through the intermediate grades to this grade. Slainte.

 

[Derek Willis.]

A wipe over with a rubber soaked in Methylated Spirit should romve the stains.
Derek.

 

[miles_hot]

interestingly when looking at Ancient Kauri wood from New Zealand they receomend going to some pretty fine grits prior to finishing...

Miles

 

[CHJ]

interestingly when looking at Ancient Kauri wood from New Zealand they receomend going to some pretty fine grits prior to finishing...

Miles

Ancient Kauri is somewhat in a league of it's own regarding finishing, the pieces I have worked have virtually no visible pores and no hope of hiding any abrasive scratches, in some ways a person may be excused from thinking it was moulded plastic.

Where I may well stop at 240 grit for the majority of my turnings there is no way you would get away with it on Ancient Kauri.
Nearest common english wood for surface appearance would be cherry, again a wood renowned for showing scratches, although it's much harder and denser than the kauri I have used.

 

[miles_hot]

interestingly when looking at Ancient Kauri wood from New Zealand they receomend going to some pretty fine grits prior to finishing...

Miles

Ancient Kauri is somewhat in a league of it's own regarding finishing, the pieces I have worked have virtually no visible pores and no hope of hiding any abrasive scratches, in some ways a person may be excused from thinking it was moulded plastic.

Where I may well stop at 240 grit for the majority of my turnings there is no way you would get away with it on Ancient Kauri.
Nearest common english wood for surface appearance would be cherry, again a wood renowned for showing scratches, although it's much harder and denser than the kauri I have used.

Interesting as I have just manged to secure a couple of lumps of cherry (see a thread to be started soon) and buoght a 7" bit of Ancient Kauri however I am holding onto that until I am good enough to do it justic - the wood looks quite plain but I love the thought that it is soooo old

I hadn't realised that the Cherry (though wet) might be able to act as a practice for the Kauri.

Miles

 

[CHJ]

The kauri I had was gifted to me direct from the supplier in NZ and was rather bland in appearance but with micro texturing when finished, the timber can however have very distinctive and spectacular figuring but it then commands a price premium

The Cherry will be a lot harder in texture but the surface finishing will be similar as regards eliminating visible scratches.

 

[miles_hot]

The kauri I had was gifted to me direct from the supplier in NZ and was rather bland in appearance but with micro texturing when finished, the timber can however have very distinctive and spectacular figuring but it then commands a price premium

The Cherry will be a lot harder in texture but the surface finishing will be similar as regards eliminating visible scratches.

When you say micro texturing - what sort of thing are you talking about - something you apply; very high grit level sanding or something that is intrinsic to that bit of wood?

Miles

 

[CHJ]

what sort of thing are you talking about - something you apply; very high grit level sanding or something that is intrinsic to that bit of wood?

Miles

Terminology might have been a bit misleading there, perhaps micro patterning might be better, the wood I have is very close grained, indicating slow growth, in areas the growth rings exhibit a herringbone like shimmy that is not obvious viewed from a distance but have a multiplicity of pattern results in the round when viewed up close.

 

[miles_hot]

Ah CHJ I understand - this is something in the wood which can be seen at higher grits rather than something you do to it...

Thanks for the clarification

Miles