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Endgrain - cannot sand clean

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GrahamRounce

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Hi - can anyone tell me the answer to these marks that won't sand away on the lathe?
20210227_154046.jpg

I've set the lathe to super-speed and used grits between and 600. The worst of it has slooooowly gone, but I can't get rid of it completely.
I've found in the past that a LOT of hard work sanding by hand will eventually get pretty close, but, again, not fully.
By the feel of these areas, I think that perhaps reversing the direction of the lathe might help, but I can't do that.
Thank-you,
Graham
 

marcros

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I would think that it is torn grain, and goes deeper than you would expect.
 

marcros

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My turning ability is fairly basic, but I think that I would try and take a very light pass with a very sharp tool. I am not going to advise on which tool to use, I know what I would use but I don't know whether it is correct. Whatever it is though, very sharp- couple of passes and resharpen sharp.
 

Phil Pascoe

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It's rather like pro snooker players chalking their cues - they do it before the shot not after they've missed it. When you are approaching the final cuts, stop and grind the the tool - don't wait for tears then try to rectify them. There's no point leaving it til the very last cut, the damage will have already been done - get your retaliation in first. Some woods are bad for this marking - ash is one.
 

Sachakins

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The only ways to deal with it now are:

1, go back to your first grit and don't move up till the marks gone, moving up to next grit to early will always be near impossible to remove with later finer grit.

2, use a newly sharpened tool and try shear scraping, then sand again.

If you clean with spirit after each grit, this will show any marks immediately, so you have and indication if you've sanded enough.

It's the first sanding with the lowest grit that does the removal. Also after sanding each grit, then sand across the piece before moving on, this helps remove radial marks caused by sanding.

As an aside, are you sanding at a low speed, sanding at too high a speed only causes the abrasives to skip across the grain rather than cut the grain.

Also a good tip is to use light pressure, the same on all grits. (See Mike Waldt video on YouTube about sanding)
 

BEE13

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I agree it looks like tearout although it could be that the wood is bruised maybe by rubbing the bevel a bit too much or too hard.

I'd give my favourite small gouge a really sharp edge and reshape that area very carefully. You only need to remove less than 1mm thickness so the shape shouldn't noticeably change.

Brian
 

gregmcateer

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Hmmm, had that happen loads!
Usually a sharp edge a GENTLE, MEASURED cut should remove it, our at least some of it.
If it's gone out of round as it's relaxed, it could be a pig to use a tool on it and just lead to frustration.
Onto sanding - slow speed. It seems frustrating, but worth it. Use 80g if you have to - no sense heating it all up with 120 or higher and still not solving problem.
If you've got no flexible sanding Arnie, (prowered or not), then wrap the abrasive round e.g. a dense sponge, so your fingers aren't dipping in and out of the low point.
And if your lathe had got reverse, use it on either search grit, or each alternate grit.
Basically, patience. (And I speak as a very impatient turner, who's used a lot of abrasive!!).
Good luck and let us know what you find works and see the result. 👍
 

Owd Jockey

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Hi Graham, Sachakins point " 1, go back to your first grit and don't move up till the marks gone, moving up to next grit to early will always be near impossible to remove with later finer grit. " was the first lesson I learnt about sanding. Taking a final very sharp cut can work, but a slight slip could make matters worse.
 

Phil Pascoe

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Taking a final very sharp cut can work, but a slight slip could make matters worse.
This is why these marks arise - very sharp light cuts should be taken a few cuts BEFORE the final cut, that's where the slight ripping of the grain occurs. Everyone is offering sound advice on how to attempt to remove the marks, but the time is better spent avoiding them in the first place.
 

Danieljw

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The Mark's are grain tear out, either from a snatch or a blunt gouge.
Re cut with a sharp tool, or keep sanding for another hour :)
 

GrahamRounce

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Thanks again.
The reason I cranked up the lathe speed is... I can put a sanding disc on the lathe, a round piece of wood with say about 200 grit paper double-sided sticky'd on.

Sanding endgrain with it, either a flat piece or turning the piece to make a curve, always gives a perfect surface!

I'm kind of puzzled by why fast-moving sandpaper and relatively still wood is fine, but the opposite isn't!?
 

Danieljw

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Friction!
For the most part.
Slower surface action with little pressure on the surface will always cut quicker.
Most people press far to hard when sanding by hand or machine,
The abrasive has limited depth, there is no point in trying to push it further.
 

OldWood

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I'm surprised from my understanding of the sanding process that no one has picked up on the OP's comment about 'lathe..super speed'. That, in my opinion, is where this is going wrong - sanding does not occur at high speed as the grit just bounces on the surface and does not cut, and if it does the temperature rise due to the high speed weakens the bond of the grit to the backing sheet and it flakes off. My books always tell me never to sand at greater than 500 rpm.

Now I am quite happy to be told by those with greater knowledge than I that my books are wrong, but these are the ones that are normally recommended when in the beginner stage and that for me was some 15 years ago.
Rob
 

Danieljw

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That would be friction then?
Hence, slow and soft....
 
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