Sanding turned bowls and platters
[First posted on http://www.woodworkforums.ubeaut.com.au/ and updated, including some comments from forum members (user name in brackets).]
Some comments on sanding … opinions only. There’s always more than one way of skinning a cat and the following is not offered as anything like the one way.
Reason for the page is that I hate sanding and this might be of use to others.
Why sand? To…
1. knock the ridges off left by your tool.
2. remove tear out. NOTE: this takes a lot of work. A few small patches of tear-out 1mm deep means a lot of wood surface has to be removed. Improving your tool technique is the best long term approach to this problem.
3. smooth the wood surface to take a finish.
Parameters:
1. Internal/external bowl and platter sanding.
2. Using a powered 2″ velcro topped disc with foam backing (or a 1″ or 3″).
3. Using a hand-held electric drill. It’s best to use a keyed rather than keyless chuck to stop the chuck loosening off.
1", 2" and 3" pads
General:
1. I’ve used the Vicmarc version of the self-powered rotary sander and found it was too slow for me but it did a nice job and is prob. a good place for beginners to start learning about sanding.
2. Use quality ‘velcro’ paper like SIA or Hermes, or discs from www.ubeaut.com.au
3. You can make your own discs from velcro sheets by hotfooting it to your local muffler place and asking for a length (maybe 200mm) of 2″ muffler pipe. (For 3″ discs find a cap used for steel fence pipe – Cliff).
4. Sharpen the inside of one end with something like a cheap hand-held-drill grinding cone at an included angle of around 30 degrees.
5. This is your punch. The paper goes between the sharp end and a bit of MDF. A solid hammer and a series of blows around the perimeter of the other end completes the assault.
6. I rarely get a clean punch so finish off with scissors. [Another method is to grind the teeth off a hole saw, grind a 15 degree bevel and use it in a pedestal drill to cut through a number of layers of stacked paper - Hughie.]
7. Starting off with coarse grits like 80 and 120 with power sanding takes a bit of care to avoid screwing up that flowing curve you spent hours achieving. So think about point 8 or do as I usually do and use a narrow strip of those grits (c. 25mm) of quality fabric paper on top of a matching piece of Scotchbrite and work by hand. Some people say this is a no no because you build up too much heat and don’t feel it, so alternatively fold your paper in 3 layers and forget the Scotchbrite.
Bear in mind that grits up to 120 are actually shaping your bowl so remember to check for wall width, cracks opening up etc. I have an Ash bowl which came up a treat off the tool but which acquired a hole in the bottom due to over-enthusiastic power sanding.
8. The idea is to orient the drill so its shaft is on the same plane as the equator of the bowl .. if nec. pushing in and compressing that foam backing so the pad conforms to the shape of the bowl. Resist the temptation just to use the edge of the pad.
For timbers with wide growth rings it’s easy to get a ripple effect, with spring growth wood sanding away quicker than late growth. Try reducing the force you place on the pad and again avoid using just the edge.
You can experiment with the disc running with or against the bowl spin direction. I like against but it takes more care.
9. Don’t run your drill too fast. The abrasive then just skips over the wood.
10. Beware of heat build up, cos of 9 or because it’s a dense timber. If there’s a deal of resin in the wood you’ll create ‘plaque’ on the surface, and in dense woods it will likely create cracks or checks.
11. Go up through each grit; don’t skip any. Stop after each grit and brush out the dust from the bowl and from the paper disc you just used. Inspect the bowl. Mild scratches will go out at the next grit. Anything that shows really clearly means you need to back up at least one grit and possibly two and start again. (Brushing out gets rid of any loose grit that will cause trouble next step up, and and at higher grits will also reveal tear-out that your last grit or two missed. … then usually start all over again).
12. If the tear-out is minor you can try this: back up a grit or two, and with the bowl stopped gently power-sand the affected area then inspect. If it’s a small piece, do this with a 1″ pad if you have it or do it by hand with the grain. If you have an index lock, use it to hold the bowl while you stroke. Blend it above and below. You won’t notice it once it’s all done.
So up you go through the grits to whatever level you can stand. 1200 suits me. At some point depending on timber density the paper starts to polish the timber and any indiscretions will show up like dog’s b*lls. You can get to 1200 or 2500 or whatever your obsession is and get the same result, and have to ask yourself do I want to look at this in 12 months time and see the scratches or tear-out again? Cos sure as hell you’ll remember it’s there.
This work can be punishing on the abrasive and it may not last long. When it stops cutting cleanly it causes problems. Easily checked: stroke your finger tip over the centre of the disc, then the side. Clear difference? .. time to ditch it. (Or if it’s a 2″ pad and you do a deal of work with the 1″ pad, cut the centre out for it).
Ubeaut retails a range of quality discs that are convenient and durable and they go up to 1200 grit whereas the velcro sheets only go up to 400 and it’s W&D by hand after then. They’re 75mm std but also available in 2″ size if you ask.
The pad will wear at the perimeter and that can be used to your advantage. The std 2″ disc will overhang it by a smidgen and the unsupported ege can be used to lightly push into an angle, eg. the foot of a bowl, or round-over the rim of a bowl.
So after all that, how to reduce the need for sanding? Searching the WW forum for ‘reduce tear out’ is a start.