
Originally Posted by
wazkelly
Hi Buddy, all good questions to ask.
Suggest you carry out a close inspection all over both the body and neck first to identify any machine marks that run across the timber grain as these will require a different approach before doing what you think would be normal sanding.
Let's start with the neck....being made from rock maple these don't usually require much effort at all and would suggest a light sanding with 120 grit along the back where your hand rests whilst playing to knock down any splintery bits. If planning to stain body & neck the same colour, best not to sand the neck too much otherwise it gets difficult to match colours as the maple grain is very tight and too much sanding ends up polishing the surface which can repel attempts to soak up enough stain. As the headstock is already pre-shaped you may find some machine marks in the various curves and if you want it looking smooth and showing off the grain these will need to be sanded out otherwise stain will end up accentuating that more than the grain underneath.
Sanding a body..... I always use a cork block starting with 80 grit and do a fairly robust sand on top & bottom, sanding with the grain. This helps to knock down irregularities and begin to smooth down both surfaces. On the sides, and particularly curves around upper and lower horns leading to the neck pocket you will notice what looks like fine saw tooth marks left behind from when the body was cut but machine. End grain of the timber tends to show this more than side-on and to get rid of them the natural approach seems to be sand across these marks. You could try that but it takes a lot of time & effort however a better approach is to sand in the direction of the machine marks first until they are gone, and then revert back to sanding in the direction of the grain or aspect of that part of the body. For example, near where bottom strap button would be located is where most of the end grain will be visible and you will be sanding across the grain, usually at 90 degrees and this is how it's done all the way around side edges.
If using 80 grit is taking too much off or getting nervous about it step up to 120 grit. Out of 7 builds I have done 2 with binding and it copes OK with solid 120 & 180 grit sanding.
Generally I would recommend going as hard as you can on all surfaces with 120 grit trying to use that grade alone to get it as smooth as you possibly can, then maybe a light to medium session with 180, then stop and evaluate where things are at. If planning to do a stain finish, I have found this to be the best starting point. After 240 grit it feels very nice and smooth, but too smooth as surfaces become over polished and repel efforts to evenly soak up stain.
It is easy to obsess over getting a super smooth surface before applying any finish and that would be true for applying a solid spray finish but stains require a different approach as outlined above.
Stained finishes can end up looking as smooth as glass, it just requires more & more layers of top coats to flatten things out.
Hope this provides some clarity for you.
Cheers, Waz
EDIT: Forgot to mention when to add grain filler.....just after you have done your best with 120 grit as that seems to allow more of the filler to do it's job. To make sure some of it stays put and acts as a contrasting grain popper you may need to just lightly sand back with 180 to 240, but don't go nuts with either grit as you can strip lots off or end up over polishing.