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| sanding scratches won't go away http://luthiersforum.com/forum/viewtopic.php?f=10101&t=39529 |
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| Author: | Tai Fu [ Wed Feb 27, 2013 9:54 pm ] |
| Post subject: | sanding scratches won't go away |
I have been noticing a very odd problem. I let the finish cure for about a month or so, and then sand with 2400 and 3600 micro mesh, and buff with medium and fine Menzerna. The problem is even after buffing with medium menzerna the scratch that came from the micromesh, some of them appearing to be somewhat deep won't go away. The buffing wheel polishes up the finish very well but from a certain angle you can see the scratches. I am really tempted to buff harder but from experience it burns the finish when I do that. I have also noticed that the scratches became more apparent when I wipe the finish with naphtha to remove the oil... so the question is, was the menzerna leaving a coating of wax on the finish that made it look as though the guitar was polished, and what can I do to remove those sanding scratches once and for all? It was less of a problem with polyester repair jobs because I just buff at 1500 rpm (rather than 1000) and press HARD, and all scratches goes away on fine. |
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| Author: | grumpy [ Thu Feb 28, 2013 5:34 am ] |
| Post subject: | Re: sanding scratches won't go away |
The 3600 micromesh is still too coarse; you need to go finer. Micromesh's rating system causes a lot of confusion, as it's not the same scale as most of us think of(the CAMI scale), and with the P scale thrown-in, it gets even more confusing. But basically, the 3600 MM(micromesh) is only about 1200 grit(CAMI), and with most finishes, you want to go to at least 1500 grit(4000 MM), and with many finishes, 2000 or 2500(CAMI)(6000/8000 MM) is the better ending grit. Here, print this chart, and hang it in your shop. It may not be the most precise chart, but it's a good start to understanding abrasives. Attachment: grit-chart.jpg
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| Author: | bluescreek [ Thu Feb 28, 2013 7:16 am ] |
| Post subject: | Re: sanding scratches won't go away |
Also do not sand with the grain when working on a finish. |
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| Author: | violinvic [ Thu Feb 28, 2013 7:25 am ] |
| Post subject: | Re: sanding scratches won't go away |
Try sanding all the way up to 12000 and then use microgloss polish. It is a lot of work, but then no additional buffing is needed. |
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| Author: | Robbie_McD [ Thu Feb 28, 2013 7:37 am ] |
| Post subject: | Re: sanding scratches won't go away |
Very timely, thanks for the chart Mario! |
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| Author: | bluescreek [ Thu Feb 28, 2013 7:53 am ] |
| Post subject: | Re: sanding scratches won't go away |
mario do you use a block ? I like to use a soft cork pad. I find my fingers can make marks |
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| Author: | B. Howard [ Thu Feb 28, 2013 8:16 am ] |
| Post subject: | Re: sanding scratches won't go away |
Are you sure you are transitioning through the grits completely and removing all the scratches left by the previous grit? |
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| Author: | Colin North [ Thu Feb 28, 2013 8:28 am ] |
| Post subject: | Re: sanding scratches won't go away |
Robbie_McD wrote: Very timely, thanks for the chart Mario! +1 |
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| Author: | John Coloccia [ Thu Feb 28, 2013 8:34 am ] |
| Post subject: | Re: sanding scratches won't go away |
bluescreek wrote: mario do you use a block ? I like to use a soft cork pad. I find my fingers can make marks My favorite finish sanding blocks lately are erasers. The pink ones are great because they come in different sizes, but this one is my favorite: http://www.staples.com/Staedtler-Mars-P ... uct_274795 Eventually I transition to a cork block on flat areas, but this works great for the initial pass to quickly. BTW, that Staedtler-Mars erase with some micromesh wrapped around it is MAGIC on frets! I had to laugh when I saw StewMac's fret erasers. |
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| Author: | Colin North [ Thu Feb 28, 2013 8:52 am ] |
| Post subject: | Re: sanding scratches won't go away |
bluescreek wrote: Also do not sand with the grain when working on a finish. John, I seem to remember reading advice to sand diagonally with each consecutive grit, different way each time you go up a grade. I was wondering if this is what you do? If not, how do you do it, and what grit do you start with? |
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| Author: | Tai Fu [ Thu Feb 28, 2013 9:31 am ] |
| Post subject: | Re: sanding scratches won't go away |
So it would help if I start sanding at 4000 micromesh grit? I find when I start with a coarser grit like 1500 the sanding scratch was so deep that no matter how diligent I was in going to the next grit, and so on, it feels like the scratch just keeps coming back and wouldn't go away. Also once you sanded up to a point the finish starts sucking on the paper, making it very hard to move. I went with 3600 grit just because I started with that when I was polishing up a Kamaka ukelele (it wasn't polished at the factory) and it worked... the buffing wheel seems to have absolutely no power in rubbing out scratches. |
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| Author: | Pmaj7 [ Thu Feb 28, 2013 10:31 am ] |
| Post subject: | Re: sanding scratches won't go away |
Tai Fu wrote: start sanding at 4000 micromesh grit? END with 4000 (or higher) Tai Fu wrote: Also once you sanded up to a point the finish starts sucking on the paper, making it very hard to move. Are you 'wet' sanding? I always wet sand with mm. (except I have some mm for ROS that I use dry) |
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| Author: | Tai Fu [ Thu Feb 28, 2013 10:43 am ] |
| Post subject: | Re: sanding scratches won't go away |
pat macaluso wrote: Tai Fu wrote: start sanding at 4000 micromesh grit? END with 4000 (or higher) Tai Fu wrote: Also once you sanded up to a point the finish starts sucking on the paper, making it very hard to move. Are you 'wet' sanding? I always wet sand with mm. (except I have some mm for ROS that I use dry) Of course I have been wet sanding, although MM can work dry it clogs rather quickly. I won't use any other brand of sandpaper for finishing after using MM simply because other brands are really rough and stiff compared to MM. |
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| Author: | Jeffrey L. Suits [ Thu Feb 28, 2013 3:48 pm ] |
| Post subject: | Buflex |
Get sample kits from Eagle: http://www.eagleabrasives.com/buflex.html |
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| Author: | grumpy [ Thu Feb 28, 2013 4:36 pm ] |
| Post subject: | Re: sanding scratches won't go away |
Tai, study that chart... MM "1500" is really 320 grit, and that's what I use to sand the WOOD, before sealing, even.... The 2400 you said you started with is really closer to 800 grit, which is still relatively coarse(rough) if you don't have a deft hand with it. Since you seem married to the MM, start at 3200, and end at 6000, and all will be golden for you. Sand in opposite directions as you go up through the grits, so that you can tell when you've completely removed the scratches from the previous grit. Do NOT move to the next grit up until you've removed ALL the scratches from the previous one. Always end with sanding with the grain. This way, if any of the finest scratches still remain, they will tend to disappear with the grain lines. Always use a block; I like the pink erasers, too. Get the big a$$ ones at joke shops(they usually say "for BIG mistakes" on them <bg>) , and cut them into various shapes. I also use smaller white erasers for detail sanding; they're softer, and allow a bit better feel. When you buff, again, start opposite the final sanding, which means you'll begin buffing perpendicular to the grain(assuming you're going to buff with only two compounds), and again, complete the final buffing with the grain. Let's all recite, out loud, the guitar finisher's lament: "We need to find the sumbeech who decided that guitars would have perfectly level and glossy finishes, dig him up, and kill him. Again!" |
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| Author: | Rod True [ Thu Feb 28, 2013 5:39 pm ] |
| Post subject: | sanding scratches won't go away |
grumpy wrote: ... Let's all recite, out loud, the guitar finisher's lament: "We need to find the sumbeech who decided that guitars would have perfectly level and glossy finishes, dig him up, and kill him. Again!" Amen!! |
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| Author: | Tai Fu [ Thu Feb 28, 2013 8:46 pm ] |
| Post subject: | Re: sanding scratches won't go away |
Rod True wrote: grumpy wrote: ... Let's all recite, out loud, the guitar finisher's lament: "We need to find the sumbeech who decided that guitars would have perfectly level and glossy finishes, dig him up, and kill him. Again!" Amen!! I agree with that, but a large majority of customers don't... and the old saying is customers are always right. I mean a lot of Martins/Taylors are this way, but having worked on some OLD guitars, I much rather have a guitar that sounds good with a rougher finish than a shiny guitar that sounds like poop. FP is so much easier... plus customers who specs FP don't generally care about a really glossy finish because you won't get a plasticy shiny finish with FP. |
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| Author: | grumpy [ Fri Mar 01, 2013 12:23 am ] |
| Post subject: | Re: sanding scratches won't go away |
What's any of that got to do with the sanding scratch issue you're having, Tai? |
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| Author: | Tai Fu [ Fri Mar 01, 2013 12:28 am ] |
| Post subject: | Re: sanding scratches won't go away |
grumpy wrote: What's any of that got to do with the sanding scratch issue you're having, Tai? I was answering the statement above where they said something about people demanding glossy finish on guitars. |
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| Author: | WilliamS [ Fri Mar 01, 2013 9:17 pm ] |
| Post subject: | Re: sanding scratches won't go away |
[/quote] FP is so much easier... plus customers who specs FP don't generally care about a really glossy finish because you won't get a plasticy shiny finish with FP.[/quote] I don't know about that. I'd expect a well done FP finish to be quite glossy. While my FP certainly doesn't look plasticy it does look about as glossy/shiny as I (or I'd expect most anyone else) could want it. |
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| Author: | Robbie_McD [ Wed Mar 13, 2013 7:04 am ] |
| Post subject: | Re: sanding scratches won't go away |
grumpy wrote: start at 3200, and end at 6000, and all will be golden![/b] Tai, did you sort out your issue? This post was very timely as I had just ordered some MM pads. I let my EM6000 cure for 5 days and hit it with the MicroMesh 3200 to 6000 as Mario suggested, (wet-sand with water and a drop of dish-soap) and all is certainly golden. Definitely my easiest and best hand-rubbed gloss ever - hand-polished with the Meguiars Mirror Glaze 17 then 10 after the MM- no scratches on a dark blue electric build. Rob |
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| Author: | Tai Fu [ Wed Mar 13, 2013 7:20 am ] |
| Post subject: | Re: sanding scratches won't go away |
I don't know, it worked well when I polished up a Kamaka uke by ending with 3200 grit. I think I should have ended with a finer grit, I was just foolish in thinking that medium menzerna can polish out scratches. I have not had any finishing work at the moment so I have not been able to try things out. The lacquer requires at least a month to cure otherwise it gets all soft. |
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| Author: | Robbie_McD [ Wed Mar 13, 2013 8:01 am ] |
| Post subject: | Re: sanding scratches won't go away |
Agreed - I have essentially divorced my buffing setup - Mezerna medium does nothing for me but waste my time.... However, I might try the Lee Valley bars as suggested by Pat H.... |
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