Sanding/ finishing question

[Chris152]

This is a problem I found in another of my threads - sanding lines appearing in the finished bowl. I've done some photos of the stages of sanding and finishing a scrap bit of beech, 4" x 4". By the end of it, tiny lines are still visible in spite of my best efforts! The photos look odd because I've lit them to expose any sanding lines.
These are the steps I took having started at 120 grit and worked through to 320).
320 grit on lathe:

320 by hand following grain:

400 on lathe:

40 with the grain:

I then used 600 and 1000 nyweb lightly on the lathe and then each by hand with the grain. I then applied shellac sanding sealer:

I denibbed with the 1000 nyweb:

Sanding lines had returned, so I used nyweb 1000 with the grain:

The lines seemed to have disappeared so I applied soft wax:

Some lines are back!!!

Is this just what photographers call pixel-peeping? Looking for faults and not the whole picture? Or would you expect better? Here's the final bit of wood, under normal lighting:

ANY thoughts much appreciated.

Thanks

C

 

[CHJ]

The images suggest to me that you are not removing the scratches from the previous grit created with the lathe revolving before moving on. (the scratches are concentric)

The edges of your wood sample appear to be rounded, this to me is an indication of applying too much pressure (thus causing you to destroy the edges.)

You should need minimum pressure on the abrasive, just holding it against the rotating surface should see a dust stream coming off if the abrasive is cutting.

Do not spin the wood too fast, if you do so the facets of the abrasive just bounce along the surface without having chance to cut effectively.


This is a piece of Yew, notorious for showing scratches sanded to 320 grit and sealed with cellulose sanding sealer, (subsequently buffed to polish)
there are very few indications of sanding scratches.

 

[Chris152]

The edges of your wood sample appear to be rounded, this to me is an indication of applying too much pressure (thus causing you to destroy the edges.)

You should need minimum pressure on the abrasive, just holding it against the rotating surface should see a dust stream coming off if the abrasive is cutting.

Do not spin the wood too fast, if you do so the facets of the abrasive just bounce along the surface without having chance to cut effectively.

I saw your reply at just the right time Chas - I was on the point of finishing the underside of a bowl using Cedar of Lebanon. I spent whole other level sanding by hand down to 600 grit, and I'm sure I was placing too much pressure on the abrasive as you suggest (though the dips in the corners of the test piece were turned like that initially - I only really paid attention to the more central area). I think it's made a real difference, hardly any sign of the concentric sanding lines now. That said, this CoL seems very soft and even with 320 grit abrasive it was easy to put scratch marks in when following the grain by hand.

The only marks that bother me now (this is a new one!) are the swirly ones that the wax has made when I applied it (you can just about make some out in the first photo below). I tried not to wait for it to start to dry too much but maybe it did. Also, I'm applying and buffing it with white paper kitchen towel - is that a bad idea?
Overall, much improved I think - I really appreciate your reply.

 

[CHJ]

Swirly marks from wax application sounds like you are applying too much wax.

Remember that the wax finish only needs to be microns thick as a protection, apply just enough paste wax to feel a slight tackiness to surface, should not really be visible only as a dulling of surface when first applied.

Cedar is one of the most difficult to get a scratch free surface on with sanding, it also bruises easy from tool pressure, if you have to sand heavily to remove tool marks you are on a road to ever diminishing finish quality with differing wood densities in the growth rings coming into play.

As for your ever finer sanding grits, remember that a lot of woods don't benifit from trying to polish the wood as far as appearance is concerned.
A lot of cabinet makers do not sand below a grit level that matches the wood texture, say 240-320 grit.

With turned items the visual scratches caused by sanding are due to the fact that sanding with the lathe rotating results in 50% cross grain action on faceplate work and near 100% cross grain in spindle work.
A spindle turned item that has visible scratches showing at say 240 grit while rotating will invariably have no visible scratches to the naked eye if lightly sanded by hand along the grain with the same grit and the lathe stationary.

Scratches are still there but the eye can't resolve them from the grain structure of the wood.

But of course these are just my take on what you are experiencing, others will have differing ideas and their own preferred ways of achieving a satisfactory outcome.

 

[Chris152]

Swirly marks from wax application sounds like you are applying too much wax.

Remember that the wax finish only needs to be microns thick as a protection, apply just enough paste wax to feel a slight tackiness to surface, should not really be visible only as a dulling of surface when first applied.

There's every chance that's the issue Chas. Turning's stopped for the day so I can make dinner etc. but I'll work on the inside of this one tomorrow and try a thinner application of wax. Today/ this thread has been incredibly helpful, slowing down and looking more closely at what I'm doing with the help of a mentor has really moved things along for me. Thank you.