Finish sanding

[Dominic]

A question for Trevor or others in the know,

In the build book in the finishing section Trevor mentions using micro-mesh for initial leveling of the surface dry and that LMI have it. Is this the stuff, they call it microfinishing abrasives. http://www.lmii.com/CartTwo/thirdproduc ... +Abrasives

or is it this stuff http://www.lmii.com/CartTwo/thirdproduc ... cro%2DMesh

I don't like wet sanding, it makes me nervous not being able to see what is happening and I want to keep my finishes as thin as possible. But even good paper 'pills up' after a little use although the 3M gold free-cut stuff is pretty good. Once I have the surface level I use festool Platin pads dry on my sander up to 2000 grit and I get pretty good finish with these.

So I just want to sort out the initial leveling and I'll have a pretty efficient process.
Cheers
Dom

[kiwigeo]

or is it this stuff http://www.lmii.com/CartTwo/thirdproduc ... cro%2DMesh

This is the stuff.

[simso]

That only goes to 1200 by the looks of it, I think my micro sand paper goes to 12000 grit, and that still leaves abrasive circular marks in the lacquer

[kiwigeo]

That only goes to 1200 by the looks of it, I think my micro sand paper goes to 12000 grit, and that still leaves abrasive circular marks in the lacquer

The stuff in the LMI link goes to 12000 grit

[J.F. Custom]

Dom,

You can also get it here -

http://www.carbatec.com.au/micro-mesh-f ... ack_c20899

If you want to try it sooner than an overseas purchase would allow. But they only carry the small (50 x 50mm) set of dual sided foam/sponge squares. From memory, the grits in this pack start at #1500 and go through to #12000.

Just saw the LMII pricing so it is evidently much cheaper there - provided it is in with another order so you are not paying international freight for the one item. Nevertheless, don't be put off Micro Mesh price wise in comparison to regular sandpaper - it washes up easily and lasts a long time.

However, note that "Micro-Mesh" is a finishing product - as self-evident from the grits. It's not what I would have suggested was suited to your "initial leveling" request.

Jeremy.

[simso]

Cool, I clicked the first link, and it just identified 1200 grit, thought that was a bit average for micro mesh, didnt notice the second link, and thats identical to my stuff.

Follow up with a buffing pad fitted to a power buffer and some meguiars. Beautiful.....

[Dominic]

Dom,



However, note that "Micro-Mesh" is a finishing product - as self-evident from the grits. It's not what I would have suggested was suited to your "initial leveling" request.

Jeremy.

Thats why i thought the first link would be better, something around 600. I got a pack of the micromesh and think mine starts at 1500 which I would think would take some work to level a surface. Great for frets and stuff.

But its not mesh. i used to use this stuff to make surfboards which actually was mesh and dust would go through the holes. I imagined something like this would be good for leveling because the 'pills' would have somewhere to go and not scratch the surface.

If I keep the surface wiped down and keep wiping the sanding block on a bit of carpet every 30 seconds or so I can use the 3M gold with not too much effort.

And from 1000 up I use the platin disks on my festool sander so I don't need the higher grits. I just finished two classical guitars and carefully sanded like this to 2000 and they look good enough to leave like this. Nice flat sheen, makes it easier to see the wood.

Anyway, thanks for your hints guys.
Dom

[Allen]

When you guys start talking grit numbers like 1,200 or 12,000 just remember that grading systems are different between many brands, and even within a brand there can and often is a marked difference in the scratch pattern that is achieve with what you think is the same grit. Also a big difference in scratch pattern between wet and dry, as well as by hand and random orbital. Then you can add a soft interface pad and you again change the mix.

I believe you are getting confused by numbers that have absolutely no correlation to each other.

Most common grading system uses the "P" designation, and is the one I'm sure that most of you are familiar with. When it comes to that grading system the finest product I've ever seen listed in a sandpaper is P3500 and that's pretty much finer than what you could abrade with the pad of your finger. It's also obscenely expensive. We only use that for the most fussy of surfaces prior to buffing. Those are the super hard clear coats we need to bring European luxury cars back to spec. Never in a million years would you use them on something like lacquer.

For lacquer going to P2000 would be the absolute finest you would ever need to go. I never take mine finer than P1500, and that's only if I can't find a sheet of P1200 around.

[Dominic]

From what I understand, the difference between P ratings and micron ratings is that micron ratings have more consistent grain sizes and leave fewer scratches. It is a more refined product at least according to the blurbs.

It is also my understanding that using a particular grit disc on a random orbit sander will leave less deep scratches than if the same disc is used by hand. It effectively increases the P rating.


But as I have mentioned, I am asking about products suitable for dry sanding to level a finish off the gun. Something around what P600 wet and dry would give which was what made me think the micro-finishing papers from LMI might be worth a go.

Allen, as the pro finisher around here, do you use wet sanding for initial levelling on your guitars and ukes? And what products do you use?

Cheers
Dom

[Allen]

First level sand is alway dry. I use P320 usually but if none on hand then P400. The P320 is less likely to ball up.

Never finer because you can't level with anything finer. Those grits just refine what is already there.

Reason you dry sand is that you can see the low spots very easily. They are still shiny. Impossible to see when you wet sand. You also do not go any finer after the level sanding, as it's not going to make any difference to your finish. And you took great care in knowing how many coats of lacquer you put on, the approximate film build and how much you took off to level it out. Sanding more only increases the risk of cutting through.

Doesn't really matter much on what brand your sandpaper is, lacquer is always going to ball up on you. The ultra expensive stuff might last longer but then it's bloody expensive. The Gold and Grey papers are a little bit better than most, but not by much and a fair bit less expensive than Abranet, Micromesh etc.

One trick is to use a medium density rubber/foam sanding block (not to hard, or too soft) and a really light touch. Keep snapping the paper across your hand to knock off any hard nubs building up. I even flake off really stubborn ones with my finger nail until the paper reaches a point where you just can't take another swipe over the lacquer before it loads up. Then it's time for the bin. I cut my sandpaper into 4 squares per sheet. One square will do a uke most times. For a guitar it may go up to 3 squares.

It really should not be difficult or time consuming to get a smooth surface on the lacquer. It comes down to making sure that when it's time to spray, that surface is as perfect as possible. Then it's left to your spraying technique and how you've mixed your product. When that first spray session is done and cured, it really should be just a light level sand to take out any texture. We are not talking divots and orange peel. If you've got that then you missed the class on prep and spraying.

The second spray session (and should be final) sanding is done starting with P800 wet. I know that there isn't anything to worry about levelling, because that was taken care of in all my pore filling and first spray session. I'm just taking any slight texture out of the finish. Then I go over quickly with P1000 and P1200. These grades only refine the scratches of the previous grit, so it's a really quick going over. With the wet paper those same squares will have done several instruments.

No matter what, if it's gloss you are going for, you have to hit the surface with some sort of buff. I can take P1200 scratches out in one go either by hand or with the buff. Doing it by hand gets old really quick though. I can't see any point in wasting time and materials that aren't going to make a lick of difference to how long it's going to take to buff, or the finish that I can achieve.

Buffing compound has been Autoglym 03B and 02B. When they run out I'll be switching to Mothers heavy duty cut. Better finish quicker with the Mothers Brand. You will find these in most Automotive finishing suppliers. I use a mini pistol buff with a 75mm white foam pad made by Farecla.

[simso]

P3500 and that's pretty much finer than what you could abrade with the pad of your finger. It's also obscenely expensive. We only use that for the most fussy of surfaces prior to buffing. Those are the super hard clear coats we need to bring European luxury cars back to spec. Never in a million years would you use them on something like lacquer.

For info, the finest grade you need to wet sand a car is 1500, then buff. My old man was a spray painter by trade, Ive painted at least 30 odd cars for mates. 3500 would frustrate the crap out of you to try and sand a car with.

However I like to micro mesh guitars all the way up to the finest grit and then buff

[Kim]

However I like to micro mesh guitars all the way up to the finest grit and then buff

If we are talking lacquer finish on a guitar then I am not understanding why that would be necessary. The truth is that as long as the surface is 'flat' @ P800 wet sanded, then the scratch pattern is going to buff out with medium cutting compound anyhow. By the time you then move to fine cut through to swirl remover, the surface should be as clear and glossy as it ever will be bar a coat of polish. I love using micro mesh on all kinds of stuff but to use it on nitro seems a lot of extra time, effort and money just to grind all that elbow grease away with cutting compound by the end of it.

Will add that I take both acrylic and nitro to P1200 wet before buffing just to be sure to be sure.

Cheers

Kim

[simso]

Its just one of those things for me kim, buffing = heat, heat = possible damage and burning, so for me minimise heat by micro meshing and then light buff. Both methods work fine, one method merely reduces the risk of burning through the lacquer whilst buffing..

[Kim]

Fair enough Steve, good point and yet another example of how there are not so many 'best' or 'better' ways to get to where we're going in this craft only different sceneries along the pathways to journeys end.....wow...how celubrical is that grasshopper... must have been a flashback

Cheers

Kim

[simso]

One of the things I find kim, because I have to turn busted instruments around quickly for stores, is theres really not enough time for the lacquer to cure,

example,

I have a acoustic in at the moment thats been dropped, its burst the side and crushed the back along the bottom, I have 5 working days to have it repaired lacquered and back in the store, now thats just a rod Ive built for my own back, but it means when it comes to the lacquer it wont take a lot of heat before it will peel away, so micro mesh really fine, light buff and out the door she goes. That being said its only an hour or two of work but its spread over a few days.