What's the secret to achieving the smoothest finish for your bowls?
Among the questions that we receive especially often from
customers here at The ToolPost is that of how the insides and outsides of woodturned bowls can be made smooth.
Many woodturning practitioners who have contacted us have complained of struggling to achieve a
smooth finish, due to there always being "two patches of rough grain". Meanwhile, another individual to have got in touch told us they were "looking for information on how to eliminate torn grain on the inside and
outside of a bowl. I end up with rough grain in some spots."
Well, here at The ToolPost, we would be delighted to help you to clear up this mystery! It is, after all, a far from uncommon problem, although the
solution can vary greatly, depending on the timber, tools and techniques that you are using.
A great finish isn't necessarily impossible
For the purposes of this article, we will presume that you
are using 'dry' timber. It is important to appreciate, however, that you are unlikely to be able to completely eliminate every roughness in the final finish, even if everything goes perfectly. That's why we mostly end
up using abrasives! Of course the world of woodturning does have its experts, whom we all seek to emulate, but we're talking of, and to, we mere mortals here!
The next thing you need to know is that the final
cuts by gouge or scraper need to be made by freshly-sharpened tools, and when we say 'sharp', we mean very sharp. In some timbers, a scraper – however sharp – can be the major culprit causing this ragging, so you should
take extra care to get a good sharp edge or burr on the scraper.
The gouge bevel needs to be rubbing when you use it, and the cut should be maybe 1/32" or 0.5mm, rather than a big, deep ploughing cut. Your use
of the scraper needs to be even gentler – your scraper needs to be producing fine shavings rather than dust, with the latter being a telltale sign that the scraper is not sharp enough.
If the earlier hollowing
of the bowl was done with a heavy hand, you may well find that what you are fighting is sub-surface damage that was caused in the early stages, and which will take some getting rid of using the gentler techniques
Although the scraper is normally drawn from the centre outwards, it may be that to eliminate coarse grain, it is worth trying to cut from the rim towards the base, to determine whether this improves
things with the scraper. Much will depend upon your skill with the scraper, so be very light with your touch!
A heavy scraper of a minimum of 3/8" x 1.1/2" cross-section is called for if you want a decent chance
of achieving the smoothest finish, as this will eliminate the vibration that often causes roughness.
How should your approach to the inside and outside of your bowls differ?
The aforementioned principles
apply equally to the finishing of the insides and outsides of your bowls, although it is unusual to work with a scraper on the outside, unless it is a shear scraper or a Celtic ground gouge used in shear scraping mode.
It is usually sharp tools, used gently for finishing cuts, that make the difference.
Another potential cause of your difficulties with achieving a smooth finish is the timber simply being 'bad' – usually spalted
timber - in which case, you could try soaking the problem areas with sanding sealer, before letting it dry and turning again, or even stabilising it with our special super-thin penetrating CA glue from Starbond.
While there is also scope to use alternative tools to improve your chances of a smooth finish for the insides and outsides of your bowls, we have concentrated in this piece on the basic technique, given that this is the
first thing that must be addressed.
We hope that the above advice will serve you well in your efforts to improve the finish that you achieve on your bowls! Feel free to let us know how you get on by contacting
us through the usual channels, or even popping into our Didcot showroom.