How to Achieve a Perfectly Sanded Surface
You may look at this article and think ‘Oh no, another article on sanding!’ or ‘I know how to sand, it’s easy!’, but I’ve seen so much turned work that could have been much better if it had been properly sanded, that I can only conclude that it isn’t as easy as people think. No one likes sanding. It’s the last part of the job before the finish is applied and you get to see the grain ‘pop’ as you wipe the oil over the surface: the part most turners cite as their favourite bit. Sanding is dusty. If you power sand it is very dusty and noisy too. If you hand sand it wears away your finger prints and gets your fingers hot. It is no wonder that turners want to skip through this unpleasantness as quickly as possible and get on to the good part, but (and it’s a big ‘but’) sanding is the last part of the turning process, the part that people will actually see the results of. This means if it’s done badly, that is what people see. Don’t think that applying the finish will hide poor sanding, because it won’t; it will most likely highlight it.
So in my opinion, sanding is one of the most important parts of the turning process. Don’t get me wrong, all of the stuff before sanding needs doing properly and to the best of your ability too, but it is all for nothing if you don’t sand properly.
Where to start?
The abrasive itself, sand paper if you like, has to be the first thing to look at. Your abrasive is a tool, just like your gouges, so buy a good quality tool. Cheap abrasive is, like so many things, false economy. The abrasive I use is known as Rhynogrip, which is an aluminium oxide abrasive with a velcro type backing, so it can be used for hand sanding or on an arbor for power sanding and has all of the required attributes. While it is a premium product, it actually isn’t as expensive as you might think. There are of course other abrasives around, but I believe this is one of, if not the best, on the market.
Good quality abrasive should be
• Fast cutting and efficient without producing unnecessary heat
• Flexible and able to roll and fold into the shapes required by turners
• Long lasting
• Available in a good range of grits
• Versatile, so no matter what you make, you can use the same abrasive: who wants to have different sets of abrasive for different jobs?
Keep it fresh
I have heard a few turners tell me that they save old abrasive and use it as fine finishing paper, suggesting that old 240 grit becomes 320 grit after use. It doesn’t: old 240 grit abrasive is just that, old and worn out. Throw it away and cut a new bit. The effect that these turners are experiencing is actually burnishing, rather than sanding. Fresh abrasive will cut, or more correctly scratch, the surface of the wood: each consecutive grit leaving progressively finer and finer scratches until they are invisible to the naked eye. Old abrasive
doesn’t cut or scratch, it burnishes, which is the same effect that traditional pole-lathe turners would use, picking up a handful of shavings and rubbing them on the work to leave a slightly shiny surface. The definition of burnish is ‘to polish a surface by friction’, so you will make the surface more shiny by burnishing it with old abrasive, but you won’t remove tool marks or the scratches of the previous grit. So if you want to burnish, then go ahead, but sand properly first! Once your abrasive looks worn or at the first sign of it not working properly, having used every part of it, throw it out and cut some more.
The amount of pressure that you apply to the work can have an effect on the quality of finish. The problem is that it is virtually impossible for me to quantify how much pressure you should be applying to the work. Not enough and sanding will take an age and still not achieve the desired results. Too much pressure and you can deform the work and produce too much heat, which is never a good thing for the abrasive or, more importantly, the wood. You do need to apply pressure, but if hand sanding, you shouldn’t hurt or burn your fingers. If power sanding, the drill motor shouldn’t sound like it’s straining; it should run normally.
So if you are sanding but don’t feel like you are getting the result you should, try applying a little more pressure. If you are sanding and burn your fingers or get through drills on a regular basis, you might want to ease back a little.
Top Tip: Avoid heat
Heat is a bad thing when sanding. It shortens the life of your abrasive and can permanently damage the wood, so should be avoided wherever possible. Starting to sand at too high a grit level, will mean that you need to sand for longer than you should. By starting at a lower grit, the sanding will be easier and therefore quicker, meaning that you will produce less heat. A trick I picked up somewhere along the line, is to rotate the abrasive when hand sanding, so that it, and your fingers, never get too hot against the wood. Some woods will handle heat better than others, but some species including yew (Taxus baccata), cherry (Prunus spp.) and many exotics will develop heat cracks in their end grain under excessive sanding. These tiny little cracks cannot be sanded away and can run surprisingly deep; they need to be removed with a sharp tool.
Generally speaking, the advice for gauging turning speed is to run as fast as is safely possible, without vibration or the lathe walking across the workshop floor. For sanding, the speed needs reducing. The exact speed you use will depend on what is available to you on your lathe, but as a guide, if you hand sand at about half the speed that you are turning, and power sand at 500rpm or below, you should be about right. If the lathe is running too fast it doesn’t give the abrasive a chance to work and produces unnecessary heat, which will shorten the life of your abrasive and potentially spoil the work.
Hand vs power sanding
The choice here is entirely yours. For bowl work, power sanding is a good option, quickly smoothing wide, flat or flowing curves. I would just add a word of caution regarding power sanding, that if you aren’t careful, it is very easy to misshape your work. An example of this is on the inside of a bowl with a tight curve, I have experienced a power sanding pad bridge the curve, rather than flexing around it, and spoiling a fluid curve to the bowl. Soft interface pads can help to avoid this, as can choosing the correct sized pad. My advice is to constantly check your progress and make sure you are achieving the results you want. For best results I will often combine hand and power sanding on bowl work. For spindle work or any fine detail work, hand sanding is the only real option.
Power sanding tip
A drill, when used for power sanding, becomes a turning tool, so just like any other tool, try to keep it in against your side and move your body for best control.
Power sanding pads come in a variety of sizes. I would always suggest using the largest size suitable for the work in hand, so for platters with long flowing curves or chopping boards with large flat areas, go for the larger 75mm size. For tighter curves you will get better results with smaller sizes and the addition of a soft interface pad. When hand sanding, I mostly use a rectangle of around 70mm wide, which is easily manipulated around the work, either by folding or rolling as necessary. A larger piece of abrasive is sometimes better however. For example, when sanding my walking canes, I will cut a length of abrasive, around 500mm long, so that I can cover a large area of the work, blending the surface into a smooth and straight taper.
Consider sanding in line with the grain
‘Flat’ woodworkers will always sand in line with the grain on their work, which means that they will rarely sand finer than about 240 grit. As woodturners, we are always working across the grain, whether it be on a bowl or a spindle. That is the primary reason that we sand to such fine grits; to make those cross-grain scratches as small as possible, so that you can’t see them.
On spindle work where you might have a long straight, tapered or curved section, consider sanding
in line with the grain.This isn’t always possible on bowl work. Any relatively wide expanses of wood will show up any flaws in your turning and sanding technique. On areas that are more highly detailed, the eye is drawn to the shapes, rather than any possible scratches, but on these long open stretches, the eye will be drawn to the smooth surface: is that a scratch? Sanding in line with the grain will remove the cross grain scratches and leave an improved surface.
Top Tip: Don’t be too proud
I’m sure everyone has heard turners bragging that they never start sanding below 240 grit; I have even heard 600 grit as a first grit from one turner! I would encourage everyone to have a wide variety of grit sizes at their disposal. Sometimes we all need a little help from 80 grit. It’s all about using the right tool for the job. Often 80 grit would be completely the wrong tool, such as on a highly decorated spindle, or on a softer material, but sometimes it is the right tool, such as on the walking canes that I make. Don’t let pride spoil your work!
What is wet sanding?
Wet sanding is when an oil or wax, or sometimes a mix of the two, is used to lubricate the sanding action. The great benefit of this technique is the reduction in dust. As the lubricant gathers the dust it forms a kind of slurry, which doubles as a grain filler, leaving a very smooth surface. This isn’t a technique that I often use though as the vast majority of my production work leaves the workshop unfinished, to be lacquered or sprayed by the customer. The potential contamination of an oil or wax in the wood could affect the final finish, so I don’t risk it. This technique is also to be avoided on timbers with contrasting colours or spalting, as the slurry can smudge the colours, leaving the work looking dirty.
What grit to stop at?
It really depends on what you are making, the finish that will be applied and the item’s end purpose, as to when to stop sanding. For joinery type work that will be painted, I stop at 180 grit. For spray painted items for display work, I will go to 240 grit. High end items such as bowls, made in indigenous species, that will most likely be oiled, I will go to 400 grit. Work in dense timbers or exotics may go to 600, 800 or even 1200 grit. Harder materials such as alternative ivory, hybrid blanks or horn will then be polished further with an abrasive liquid like burnishing cream, then buffed with a mop loaded with fine abrasive, followed by a soft buffing mop. One professional turner I know mostly makes bowls and chopping boards and tells a story of how he always sanded to 400 grit, until he heard from several customers that his bowls were too good to use. Now he stops at 320 grit, which saves him time, money on abrasive and still pleases his customers!
A win-win situation if ever there was one.
There is little more annoying than believing a job is finished, only to spot a fault later on. To avoid this I will subject the work to natural light, which shows up all sorts of faults that you can easily miss when the item is on the lathe and under standard flourescent workshop lighting. Spotlights set to give a raking light, shone across the work have a similar effect.
Top Tip: Wipe your work
If you were to ask me for one single piece of advice that will improve your sanding, it would be to give the surface of your work a wipe between grits. Whether you wipe with your hand, use a pad of paper towel or
a soft brush, it doesn’t really matter, but do it. This one thing will, I guarantee, improve the finish of your work. As you sand, grits will naturally come away from your abrasive and gather with the dust on the surface of the work. If you blindly keep sanding through the grits, as you progress through the grits you will often pick up a loose grit of the previous coarser grades, which will scratch the surface, leaving a random mark on your work. The only way to remove this is to go back and sand through the grits again. Simply by wiping the surface between grits, it means that each time you sand, you are working on a clean surface, leaving the best possible surface, ready to apply your chosen finish.
Sanding difficult areas
While most work can be accessed easily by simply folding or rolling the abrasive to suit the shape of the work, there are times when special measures need to be taken. For example, the corners of a square bowl are potentially difficult, if not downright dangerous to sand with the lathe spinning. The picture shows a square platter that has been turned. Inside the area defined by the dark pencil ring, it is easy to sand by power or hand, obviously being careful not to encroach on the outer edge or corner area. The corner sections past the marked ring are the danger zones and as such should only really be tackled with the lathe stationary, using a cork block with an abrasive or a power drill with a sanding arbour or a random orbital sander as appropriate. Once sanded, clean up all the edges.
Some boxes have shapes that can be difficult to reach, such as heart-shaped or ginger jar style boxes, where you need to sand around a rim. In these cases, great care needs to be taken: it is not wholly safe to hold the abrasive with your fingers and stick your fingers in the opening hole. You will run the risk of getting caught with the abrasive wrapping around your fingers, which can cause a nasty injury. Using a single finger is always safer than two, but again, sanding with the lathe off may be the safest option, especially on deep undercuts. Other options include using forceps to hold the abrasive, or fastening the abrasive or a velcro ball onto the end of a stick, to work into areas where fingers can’t reach or would be unsafe. Depending on the shape of the item being sanded, you should consider supporting the forceps or sanding stick on the rest while sanding. Remember, if using forceps to sand, never stick your fingers through the finger holes while sanding.
Health and Safety
It goes almost without saying, that while sanding, you need to protect yourself from the dust. I would suggest that the whole turning process produces dust, not just the sanding part, so protection should be worn throughout the process ideally, but when sanding it becomes very apparent. In my workshop, I wear an air fed, full face respirator which protects me from flying shavings and dust. I also have an extractor with a hose that can be positioned close to the source of the dust and an air filter running at all times when I’m in the workshop. The combination of these three protects me as much as possible can from the harmful effects of working with wood. Exposure to dust, over time, can lead to allergic reactions and respiratory problems or worse, which I simply don’t want. Please protect yourself.