Official Luthiers Forum!

I'm working on the final sanding of my adi spruce top. I'm a little lost on how this seemingly simple task should be done. I've went up from 100 to 320 grit with those 3M sandblaster sanding sponges but when I hold the guitar up to the light at just the right angle I can see light scratches left from where I sanded with lower grits (80-120 I think). These will be visible under the finish right? How should I go about removing them? I'm of course worried about taking the top too thin. Should I drop down to 100 grit or start with 180 grit and just sand till the scratches can't be seen? I'm not even sure how much time should be spent between grits. Any advice would be greatly appreciated.

_________________
Jeremy Douglas

Jeremy buddy you sand with one grit long enough to remove the sanding marks from the previous more course grit.

I sand initially with 120 and then move to 240 for the final sanding. You might want to nix the sanding sponges in favor of just tri-folding a quality sandpaper and using it flat with the flat of your hand. Tri-folded paper has some structure but will easily do the curves on the sides.

I never sand beyond 240 for final sanding. You are done when you can't see any sanding marks.

Hope this helps.

_________________
Ann Arbor Guitars

you have to work through progresivly finer grits. if you start with 100, then go to 120, 150, 180, 220, 250. if you skip one, you may leave scratches from the coarser grits.

take the off cuts from the top and practice on them till your confident to tackle the top.

I always use a hard block under my sandpaper when sanding softwoods. Using an ROS can help too as it moves faster and has no set sanding pattern.

_________________
My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Don't listen to Rod - he's messy and a slob........

_________________
Ann Arbor Guitars

get back to your cave you troll

_________________
My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

The sanding sponge may be part of the problem in getting rid of all the scratches. (Also, sponges will cause the rosette sometimes to stand proud of the top surface a little and it won't really show up til the finish is done. ) I use a small mahogany block about 3" x 4" and just fold the sandpaper around it. Its perfectly flat on the sanding side and the edges are slightly rounded to prevent accidentally gouging anything.

I would go back to 120 or 150 fre-cut and sand methodically back and forth with the grain. Glide the block onto the edge and finish the stroke as you're going off the other end. Check after a while and see if all the scratches look uniform. Then go to 180 or 220 and do the same. I would then, not that you have to though, wipe the top with a clean white cloth dampened with a little distilled water to raise the grain. Just slightly damp is all you need...not wet. Wait an hour or so to dry and lightly use the 220 again. After you think you're close wipe down the top with Naptha and a paper towel to remove sanding dust etc. and you can see while its still wet with Naptha if you have any deep scratches. Unless they're really deep they probably won't show but the wetting with Naptha will tell you that.

FWIW, I never go past 220 when using lacquer and when french polishing I usually stop at 180 as not to choke the wood and make it too difficult for the finish to adhere.

_________________
"We might not be big but we sure are slow"

aaww man, I can't believe everyone's down on my sponges I guess I'll go with my rubber sanding block and fre-cut sandpaper, it just seemed cumbersome compared to the sponges I thought. I do have an scrap top I might practice on.

btw, how does final sanding and the finish come into play with setting the neck? It seems these processes would change the neck to top geometry. Is it insignificant?

Thanks everyone for the help, Jeremy

_________________
Jeremy Douglas

Final sanding and the finish should not affect the set of the neck. The finish thickness should be between 0.003"-0.008". I always set the neck once the body has been final sanded.

_________________
My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson