Seeded into the spotless mind of a boatbuilder is the idea of sanding wood. Other than looking good, a smooth finish seems to absorb less epoxy, scientifically unconfirmed, and is easier to glass. These are our conclusions from hours of manual sanding. Lets discuss sanding and sanders.
We have used and own 3+2 types of sanders: belt-sander, orbital sander with a rectangular sole and a random-orbital sander with a circular sole. Lets call these category A sanders. The last two being the Dremel and cordless drill with sanding bits. Let these be category B sanders, as they are not sold as a sanders per se, but can be used as such.
Shape and size: both matter
In general, category A sanders are good for sanding large surface areas. In coparison with category B machines, category A is bulky and does not fit tight spots and crevasses of the boat, for example ill fated corner fillets which have sharp points. You simply wont ram a category A machine in there with efficiency. Thus, there is the element of size when choosing a machine for the job.
Where category A machines part is the shape of the sanding sole. A rectangular base is good for sanding long straight-angle intersections of wood, for example fillets and joints. A round base might leave a less satisfactory result, as it is round and has only one point of contact with a line.
Category B access to corners depends on the bit choise, which is unmeasurably large in the vastness of the internet.
A cross breed of category A and B is the so called mouse sander. I bet these come in forms of orbital- and random-orbital motion, which will be discussed later. The benefit of the mouse sander is that it has both a flat sole and a pointy tip, which benefits flat corners. Acheiving a smooth corner in 3D, a quarter of a semisphere, is problematic with the “mouse” as well. We do not have a mouse sander.
Power and what it incorporates into sanders
We agree that power machines sand faster than we ever could manually, but power incorporates an intrinsic set of threats. When sanding forementioned 3D corners, a lots of power and RPM plus a shaky hand can instead result in a messed up corner and potentially damaged cornering faces. This is especially true if the faces are glassed. Denting the glass is very easy, as a high RPM category B machine can throw a kickback, which is braked by the neighboring surface. To avoid this, one must use a lower RPM or choose a bit which has small grit. In general, corners sould be filleted properly without concideration of later sanding. This saves time and money.
A very spefific problem which might occur with the belt sander is what we would call the “edge eating” effect. It can occur, even with a flat surface, that the edge of the sanding belt eats into the wood when tilted accordingly, leaving an unwanted crevasse into the finish. For example: when using the belt sander for rounding corners and holding the sander cross-faced with the to-be-rounded edge. Again, this can be avoided with practice. Our belt sander is quite powerful, so it must be used with care in any case, since it will eat trough wood quite fast. Sort of similar to the situation where one forgets a fully heated iron onto a shirt for too long.
Power also has its benefits, especially when sanding flat areas. We started our boatbuild out with a couple of 100+ W rectangular sole orbital sanders. Little did we know that the slow progress was not caused by us, but that there simply was too little wattage. When we obtained a 200+ W random orbital sander with a round sole, the difference was significant. So, when usinng a random-or fixed orbit flat sole sander, more power is better. These do not produce the abovementioned “edge eating” and can be used with less care. Again: when sanding flat areas: more power is better. John Welsford has recommended a sander at least 300 W.
Orbital and random orbital motion
The orbital motion of a sander is achieved by an offset rotation axis pintle, which is fixed to the bearing equipped sole. Sort of like an old steam-train wheel, on which the wheel-pushing rod is fixed off center of the train wheel. Random orbital motion is produced by adding an additional degree of freedom to the motion of the sanding sole: namely, it can rotate around its orbital motion base.
Our experience shows that the random orbital sander gives a better surface finish. Since at some random moments, it is sanding cross grain and other random moments it is sanding along grain. One might argue that why is this superior to a fixed-orbit sander. The answer: we do not know. Just experience. So, for sanding large flat areas, by our experience, get a random orbit sander that is at least 300 W.
It tends to be true that the more you pay, the better of a tool you get. This seems to be true for sandpaper as well. Expensive sandpaper uses aluminum-oxide or something similar as the grain material and superior adheshives. Simply put, they last longer. Though through your boat building experience, buying sandpaper is a routine and purchasing a few rolls of cheaper sandpaper must not in principle be concidered a waste. There might be an occasion where you quickly need to hand-sand a surface and just want to rip a piece of sandpaper off the roll.
Aside size, weight, power and all that comes the aspect of how what type of sandpaper your sanding machine needs. Our random orbital sander has a velcro attachment and thus special discs need to be bought. These are more expensive than regular off the roll sandpaper, but have their benefits. Firstly and foremost: ease of use. Take it out the packaing and stick it on. Though we have noticed that the velcro fixed to the sander wears down with use. To our surprise, a replacement sole is difficult to purchase fro mour local on site suppliers, but the internet has yielded. For our fixed orbit sander, we cut proper sheets off a roll and clamp them to the sole of the sander. You can also buy cut-to-size pieces, but they are more expensive and perhaps the extra two minutes you spend on cutting a roll-piece to size is not that painful. The belt sander paper comes in rolls and the only critical aspect here is to remember the size you need and shop accordingly.
Needless to say, the life of a bit of sandpaper depends on what you use it for. Sanding soft, perhaps polymerous surfaces will quickly jam up the grain, due to friction heat and general stickyness, and you’ll effectively not be sanding. So, choose wisely. As they say, start rough and finish off with a smaller grain paper. The smaller the number, the larger the grit, it is an inverse function. 50 grit paper is pretty bad-ass stuff. Whilst a 1000 grit paper might equally well be used to sharpen your chisels or a barbers knife.
Go green: what do do with sanding dust
At first we did not know much about how the world worked, but we learned it in the process. It turns out that sanding dust, I mean wood dust, makes a rather excellent fillet. So, if you want to save money on fillet materials, save up on sanding dust. Use whatever collector bags you have available. To our experience, sanding a whole sheet of plywood will give you, when uncompressed, a third of a bucket of dust. The dust-fillet is hard and not comparably suitable to microballoon fillets if you wish to have a easly sanded finish. But where strenght matters, the dust fillet is a go-go.