Surface finish

[JohnHewes]

I cannot get a perfect finish on some burr horse chestnut and hope that someone can help, please.
I have made a couple of shallow bowls and they look really good, until I look very closely at the surface and there are small concentric lines visible. On the second bowl, more like a saucer really, I am experimenting to find a solution, as this is still in the lathe.
I have tried very fine sanding and going back to a 120 grit and starting again, and yesterday I had another go at the surface with a freshly sharpened shear scraper, fast speed and slow feed rate across the surface but the lines are still there.
Any ideas to try, please?

[Les Symonds]

It sounds as though you're doing things properly, do you mind if I ask how much experience you have, just to give us a feel for sort of level you're normally working at?
Have you tried power sanding with a 1" or 2" pad in a drill chuck?
Les

[Paul Hannaby]

Hi John,
Try sharpening the shear scraper again (do so frequently!) and when using it, keep the angle of the edge against the wood such that you are making a slicing cut. Horse chestnut is fairly soft and any aggressive cuts might result in torn grain, particularly where changes in grain direction may be evident (which is what to expect from a burr). It isn't the easiest of woods to finish.
When sanding, go through the grits by not jumping more than 50% of the number each time. i.e. if you start at 120 grit, next would be 180 or coarser, then 270 or coarser etc. In practice, the grits I have are 120, 180, 240, 320, 400, 600 so each jump is less than the maximum.
If the grit you are using hasn't removed the flaws, go coarser until you do get rid of them, then progress through the grits.

[Derek]

Rubbing the bevel to hard can cause what appears to be lines running around a bowl in effect bruising the wood more common when turning softer woods

[Walnut Les]

There are many things that can cause this problem from pressing too hard with the sand paper to sanding at to fast a speed.
A quick fix is power sanding through the grits from 120 180 240 320 400 with fresh sand paper and see if the lines have gone.

It might be something as simple as changing your sand paper if you are using cheap sand paper this can cause this problem.
Using old sand paper or trying to get the most out of already used sand paper also causes this problem. The same as just holding the sand paper up to what you are sanding, the list is endless.

Use fresh sand paper and keep it moving going through the grits without missing any grits pressing lightly but firmly at a slowish speed
should leave no lines. I hope that this helps. Les

[JohnHewes]

Thanks Chaps.
I have had a lathe for about 30 years and had a lesson about 30 years ago! However I didn’t do much until about three years ago when I got a bit addicted and have been spending a lot of my spare time turning, and I have made some stuff which I am happy with, some big bowls and down to babies rattles and spinning tops etc. I recently had a lesson with Mark Hancock, learnt a lot there.
I have tried different types of abrasive, but from your answers perhaps I have been using too high a speed, I thought that would improve it!
I have not tried power sanding although I have some basic kit and will try that soon. Must get the dining room back together first, though!
Thanks again for your helpful comments, and if you have a power sanding set up which you would recommend I would appreciate that too.
Kind regards, John

[Derek]

There are many things that can cause this problem from pressing too hard with the sand paper to sanding at to fast a speed.
A quick fix is power sanding through the grits from 120 180 240 320 400 with fresh sand paper and see if the lines have gone.

It might be something as simple as changing your sand paper if you are using cheap sand paper this can cause this problem.
Using old sand paper or trying to get the most out of already used sand paper also causes this problem. The same as just holding the sand paper up to what you are sanding, the list is endless.

Use fresh sand paper and keep it moving going through the grits without missing any grits pressing lightly but firmly at a slowish speed
should leave no lines. I hope that this helps. Les

What I can't use my 120grit to sand 30 bowls Les and I thought it was now 600 grit

[Walnut Les]

Thanks Chaps.
I have had a lathe for about 30 years and had a lesson about 30 years ago! However I didn’t do much until about three years ago when I got a bit addicted and have been spending a lot of my spare time turning, and I have made some stuff which I am happy with, some big bowls and down to babies rattles and spinning tops etc. I recently had a lesson with Mark Hancock, learnt a lot there.
I have tried different types of abrasive, but from your answers perhaps I have been using too high a speed, I thought that would improve it!
I have not tried power sanding although I have some basic kit and will try that soon. Must get the dining room back together first, though!
Thanks again for your helpful comments, and if you have a power sanding set up which you would recommend I would appreciate that too.
Kind regards, John

I sand at 350 rpm or slower. Most people say that the Simon hope sanding system is the best but any soft Velcro backed 2" sanding arbor that you can put on a drill will do. just don't press too hard and get one with a soft pad on it as that one will do the curve on the inside of a bowl. Les

[Walnut Les]

There are many things that can cause this problem from pressing too hard with the sand paper to sanding at to fast a speed.
A quick fix is power sanding through the grits from 120 180 240 320 400 with fresh sand paper and see if the lines have gone.

It might be something as simple as changing your sand paper if you are using cheap sand paper this can cause this problem.
Using old sand paper or trying to get the most out of already used sand paper also causes this problem. The same as just holding the sand paper up to what you are sanding, the list is endless.

Use fresh sand paper and keep it moving going through the grits without missing any grits pressing lightly but firmly at a slowish speed
should leave no lines. I hope that this helps. Les

What I can't use my 120grit to sand 30 bowls Les and I thought it was now 600 grit

Derek now we both know that you start sanding with 240 grit buddy, but if you did do 30 bowls with one bit of 120 grit you would be now into the micro polishing range. 

[burywoodturners]

What finish areyou applying? If youare applying wax with the lathe running then it could be a build up of wax and not the underlying wood.
Ron

[JohnHewes]

Thanks again, especially the two Les’s, I have now got back into the workshop ( the dining room floor still not finished, though!), and today I have been trying some of your suggestions and experimenting myself. This is a hard piece of burr and not something I have done a lot of yet, but I have got some good results today.
The system that has worked is to use the shear scraper, then a fairly coarse, 80 grit, flap wheel in a mains drill, used at six o’clock and at 90degrees to the circumference of the job, followed by a 240grit flap wheel in the same way. (These are the only grits I have at the moment).
I have a 240 grit red softish mop which I used next.
These worked best with the lathe at about 1500 rpm, any slower and they left a rougher surface. Then I used 240, 360, 400 grit Arberex and it started to really shine.
I finished with a rotary mop and polishing compound from good old Lidl. This produced a surface which is completely line free and even her indoors was impressed. She thought I had waxed it but I hadn’t.

I think a large part of the secret was the six o’clock position, instead of nine o’clock where I was just abrading in line with any tool marks, working across these lines seems to have worked.

I cannot understand why a slower speed should help, particularly if using a drill driven abrasive against the direction of the job, as this increases relative speed between grit and job, doesn’t it?

It’s all relative anyway.

Thanks again Gents, appreciate your help and advice

John

[Walnut Les]

Hi John, your welcome to any help or advice that i can give mate.
Most people sand on a slower speed as when you sand on too high a speed you burn the wood causing heat checks (small cracks in the wood) yew is a terrible wood for this and is best sanded at a much slower speed for this reason.
I have found that most production or profesional turners sand at a higher speed but they start sanding at 240 and finnish sanding at 320 grit at a speed less than 600 rpm where as us hobby turners sand at a slower speed going threw all the grits with out missing any to get a finnish that we are happy with.
A simple rule of thumb is if your burning your fingars when your sanding then your sanding at too high a speed, the cloth backed sand paper will still heat up so you need to make your own jugement on this. I hope that this helps, Les