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Surface prep
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=45137		 Page 1 of 2
Author:  JSDenvir [ Fri Feb 13, 2015 6:19 pm ]
Post subject:  Surface prep
I'm finding that as my French polishing gets better, it's showing just how badly my surface prep sucks. Any tips, hints or techniques?

Thanks in advance

Steve
Author:  DannyV [ Fri Feb 13, 2015 6:23 pm ]
Post subject:  Re: Surface prep
Naptha and your close up glasses. :) Best I've got. I'd like to hear better also. Doesn't matter what the finish, it's always a pain to deal with once you start finishing.
Author:  Josh H [ Fri Feb 13, 2015 6:29 pm ]
Post subject:  Re: Surface prep
Are you talking about scratches or unevenness? Or maybe both?

Really good light has helped me with seeing scratches. I usually try and view the guitar in a variety of different lights at ever angle possible. I also do most of my final sanding with a block and sandpaper sanding with the grain (up to 220). I use Naptha as well.

In order to get an even surface I switched to hand sanding with a hard block. Using an ROS sander only will sand the different woods unevenly (binding, purfling, rosette, etc.). I now use an ROS sander and a hard block for final surface prep. I'll start at 120 with the ROS and then go back over the surface with some 120 on a block to make sure everything is even. Then 150 and 220. It doesn't take long and ensures a nice evening surface for finishing. Maybe a really hard sanding pad on an ROS sander would work, but mind don't have that.
Author:  tysam [ Fri Feb 13, 2015 7:01 pm ]
Post subject:  Re: Surface prep
Sunlight and naptha..... old eyes here as well. I find that lights I have tried using don't seem to highlight the sanding scratches like natural light does. I try and get the guitar outside to view it. Also, I now go to 400 on my final sand and take a lot more time on my pore filling. That seems to be an easy thing for me to try and rush through.
Author:  JSDenvir [ Fri Feb 13, 2015 8:55 pm ]
Post subject:  Re: Surface prep
DannyV wrote:
I'd like to hear better also.


Thanks Danny, cracked me up.

Steve
Author:  unkabob [ Fri Feb 13, 2015 9:21 pm ]
Post subject:  Re: Surface prep
Nobody has said anything about wetting the surface with water to raise the grain. I wet the surface at least twice for each grit.
I use sandpaper glued to blue Styrofoam for hand sanding.

Just my thoughts.

Bob :ugeek:
Author:  Colin North [ Sat Feb 14, 2015 1:53 am ]
Post subject:  Re: Surface prep
I'm still struggling at the same thing. Natural light at a low angle (all angles really) is best, but halogen at night if you have to, reveal with Naphtha, cork glued to wooden backing block for sandpaper (to 320).
I raise the grain twice (damp cloth) normally at around 180 twice, then once at 240, once at 320.
Oh, and I wear magnifiers., or use a large magnifying glass.
Author:  TimAllen [ Sat Feb 14, 2015 2:27 am ]
Post subject:  Re: Surface prep
I also have problems with this. It's getting better but I have a ways to go.

I've traced some of the problems I have to the fact that my sanding tends to create very slight hollows that retain scratches from previous grades. A few things I've learned to reduce this:

1. Don't use a ROS, using a sanding block. (There are people really skilled with a ROS that can use it. Not me, not yet.)
2. Make sure the sanding block is really flat.
3. Sand without pressing hard.
4. Replace the sandpaper frequently to get an even, controlled cut.

I also find that finishing reveals tiny gaps next to inlays and purfling. To reduce this I:

1. Assume that there is a gap and preemptively fill with CA.
2. Look closely for telltale sanding dust in tiny gaps next to inlays and purfling, then fill them.

A final problem is that I don't see scratches and gaps before finishing because I don't want to see them; I'm sick of prep and want to move ahead to finishing. To reduce this I:

1. Don't decide to move ahead to finishing after several hours of prep. I wait till the next day when I can make the decision with less bias.
2. Adopt the expectation that the first few coats of FP are mainly to help identify the areas still needing finish prep.
Author:  klooker [ Sat Feb 14, 2015 7:29 am ]
Post subject:  Re: Surface prep
TimAllen wrote:
...

A final problem is that I don't see scratches and gaps before finishing because I don't want to see them; I'm sick of prep and want to move ahead to finishing. To reduce this I:

1. Don't decide to move ahead to finishing after several hours of prep. I wait till the next day when I can make the decision with less bias.
2. Adopt the expectation that the first few coats of FP are mainly to help identify the areas still needing finish prep.


This really hits home for me. Thanks Tim [:Y:]

Kevin Looker
Author:  Hesh [ Sat Feb 14, 2015 7:31 am ]
Post subject:  Re: Surface prep
Not all ROS are created equally...

In the past when I was using two different professional finishers both of them took me aside and asked me how I was doing my final prep sanding. When, as is my way.... I asked them why they both told me that my stuff was a joy to finish because unlike many guitars that they were receiving mine did not need any final sanding and the pore filling could begin at once. One time when I dropped off a few one finisher just started slathering on the West Systems right in front of me to demonstrate his confidence in my final prep work.

Now before you think Hesh is tooting his own horn is a shameless self-promotional rant.... :D what I am doing is tooting the horn of my beloved Festool 5" ROS. That thing does a wonderful job, has superb dust collection, has a truly random pattern that seems to work much better than the other usual suspect ROS's that I've used prior.

My routine is using the ROS with 120 and then 220 and then I called it good. Very easy. Difficult areas are sanded by hand with a thick felt block from LMI.

By the way both professional finishers told me stories of the nightmares that people send them with black purfling lines that don't meet up, deep scratches often in the back plates from running the backs though thickness sanders and then not seeing or addressing these "lines" before sending to the finisher. In fact both finishers related to me that the worst part of their jobs at times was having to do the final prep for some builders who seem to see a pro finisher as an apprentice of sorts that you throw all of your crap work at.... They were not pleased...

Anyway a Festool ROS was one of the best tools that I ever bought in terms of the value received, quality of the work produced, and superb dust collection.

Highly recommended!

PS: Remember to shove a towel in the sound hole when using a ROS on a box, it quiets it down a great deal.
Author:  Fred Tellier [ Sat Feb 14, 2015 9:14 am ]
Post subject:  Re: Surface prep
+1 for the Festool RO, I resisted purchasing one do to price but when I finally opened my wallet and got one I will say they are worth the price.

Fred
Author:  david farmer [ Sat Feb 14, 2015 10:21 am ]
Post subject:  Re: Surface prep
If you have the air, Dynabrades are the chump too. I think pressure is the most overlooked problem. Too much pressure is the same as using a soft pad. If you push or flex into depressions early on, the following grits keep missing them later. It's counter intuitive but the coarsest grits should get the lightest pressure.
Author:  Michaeldc [ Sat Feb 14, 2015 10:34 am ]
Post subject:  Re: Surface prep
One note on the Festool RO with Festool vac... Don't run the vacuum at full chat. You can end up with sanding swirl. I'm usually a proponent of more is better. Not in this case. It also takes more effort to move the sander over the surface with the vacuum cranked to 11.

M
Author:  SteveSmith [ Sat Feb 14, 2015 11:02 am ]
Post subject:  Re: Surface prep
Steve, I have the same problem. It seems like the more I learn about finishing, the more I find that I need to do better.

r.e. ROS's: IMO going to a high-quality ROS makes a big difference. I went to a Mirka 5" because the standard configuration ROS's really aggravated my carpel tunnel. I considered Dynabrade but don't have the space for a a large compressor. In my experience, the ROS random pattern is much improved if you don't put a lot of pressure on it. Basically, I just let the sander do the work although that can strain my patience a bit.

Some other thoughts that may or may not be useful:
- Since I almost always do my sanding on my downdraft table I keep an old T-shirt there and wipe the sandpaper quite often, helps to keep it from clogging. Mostly I do this when hand sanding, not so much on the ROS.
- I use a wide variety of sanding blocks made out of various materials. My favorites are made of wood, drafting erasers, and felt blocks. Sizes range from 1/4" x 3/4" to 3" x 4".
- I use good sandpaper (3M gold for hand sanding or Mirka for ROS) and change it as soon as I think it isn't cutting well. Costs a little extra but seems to work faster and do a better job.
- I have two 100 W 5K LEDs just above the downdraft table. Not quite as good as sunlight but helps find the scratches fairly easily. I'm thinking of increasing the wattage on those. When it's daylight I just walk over to the window.
Author:  JSDenvir [ Sat Feb 14, 2015 11:25 am ]
Post subject:  Re: Surface prep
Thanks for all the tips. And here's one in return that I got from Patrick Hodgins. For hard sanding blocks, Patrick buys cheap flip flops at the dollar store. They're easy to cut into any shape you want, and they're just a little stiffer than the sanding block that comes with Micromesh pads.

And for you Festool advocates, is there a model you recommend?
Author:  Hesh [ Sat Feb 14, 2015 12:00 pm ]
Post subject:  Re: Surface prep
Steve my friend this is what I have:

Image

I see that it's gone up in price about $30 since I bought mine but sometimes good stuff costs more.

I bought the Festool dust extractor too, the CT-22 HEPA I believe and that thing is great as well. It pulls 132ish CFM and actually does it unlike may over rated tools that list specs under the best of conditions and/or make em up.... This vac works just as well with my Performax 10 - 20 as my 1,100 CFM General. I know it's difficult to believe but I see no difference in the paper not gumming up or excess dust with either machine.

While I'm at it I also have a Festool cordless drill that I bought about 10 years ago and the original batteries still work although I'm planning on replacing and upgrading them this year. This drill is my work drill in our business shop and gets used with every guitar I repair since I also use it as a string winder/unwinder.

Great stuff and I'm sold on Festool - the best tool purchases I have ever made, so far.... :)

One more word about the Festool ROS. A vac is not required and the thing comes with a bag and bag holder. I've used it without the vac and the dust collection is exceptional and I see no difference from when I have the vac connected. I'll second the idea of turning down the vac as well, I do this too and my belief is that this sander does indeed benefit from just steering the thing and not pressing at all.
Author:  klooker [ Sat Feb 14, 2015 1:45 pm ]
Post subject:  Re: Surface prep
The little 5" has only a 2mm orbit which is probably one reason why you get nice results for final sanding. The Festools also run very smooth & I think they still have a 30 day money back guarantee.

Kevin Looker
Author:  Ben-Had [ Sat Feb 14, 2015 5:17 pm ]
Post subject:  Re: Surface prep
Not sure how it compares to the Festol but my finishing mentor worked in the finishing dept. at the Martin Factory for 35 years (was the supervisor there for years) and he recommended to me the Porter Cable 330 (USA made, not the current one). It also has a 2mm orbit. I bought one used and a new pad and my finishing has taken a giant leap forward.
Author:  Fred Tellier [ Sat Feb 14, 2015 7:02 pm ]
Post subject:  Re: Surface prep
Steve I also have the 5" 125 EQ
http://www.leevalley.com/en/festool/page.aspx?p=68468&cat=5,68343

Fred
Author:  Goodin [ Sat Feb 14, 2015 11:29 pm ]
Post subject:  Re: Surface prep
I have the Festool 125 EQ as well. Works great. Still need to get the Festool vac, just can't swallow forking over $600ish for a vac, excuse me, dust collector ;).

Not much new to add but here are my techniques and tips:
120 grit off the thickness sander with good clean paper, checking that there are no deep lines.
Sand up to desired grit with combo of ROS and hand sanding, raking low angle light with high power focused led light, water raise grain between grit.
apply first coat of sealer (shellac, vinyl, oil varnish, or whatever is necessary for finish schedule) to bring out remaining scratches
Apply second coat of sealer, get out anymore scratches. repeat until all scratches are gone.

I am getting good enough at sanding where I usually don't have to get out any scratches after applying first coat of sealer. Sanding is one of the true arts of guitar building (bending sides by hand on a hot pipe is the other). Continuous improvement through experience.

Oh, use the gold paper! It works so much better than the usual hardware store paper. Doesnt load up as easy, more effective, and last longer. More expensive but worth it.
Author:  J De Rocher [ Sun Feb 15, 2015 2:17 am ]
Post subject:  Re: Surface prep
Base on posts above, I'm unclear on what different people have in mind when they refer to a hard block. To me, that would be a material with no flex or give like a block of wood or one of those hard rubber blocks that are flat on one side and convex on the other. It sounds like materials such as erasers, felt, cork, and styrofoam may be considered to be hard blocks too. I just want to be sure I understand correctly when someone suggests using a hard block for sanding.

Maybe some day I'll get the courage to try an ROS.
Author:  Hesh [ Sun Feb 15, 2015 8:53 am ]
Post subject:  Re: Surface prep
J yeah a hard block can be many things and they can have some flex and should too in them as well. We use very dense rubber that comes in sheets and is about 1/2 - 3/4" thick or felt of the same thicknesses. You want the block to conform to surfaces that are not flat with minimal pressure on the block.
Author:  B. Howard [ Sun Feb 15, 2015 9:17 am ]
Post subject:  Re: Surface prep
I do all my final prep by hand with a wood block lined with 1/4" cork. The one I use the most is only 1" X 2" in size. Guitars are small and the surfaces are not flat, I find an ROS to be overkill for them. Even when I built large things like cabinets and furniture I only used mechanical sanders for construction sanding. All my prep has always been by hand. e would stop with the ROS at 120 and then hand sand again with 120 and then 180 and possibly 220 depending on the wood and the type of finish going on it. I only use silicon carbide papers that are coated for anti loading. Garnet papers are to inconsistent and often have poor bonded grains that will come off the paper and work themselves into your surface. ALOX tends to load up and burnish softer woods like spruce.

As for inspection, it's easier when hand sanding. Without all that vibration going on the sanding dust will settle into missed marks and scratches and highlight them for you. You can also hear the paper cutting the surface and it's sound will change when it is making a complete (or almost complete) cut. I have a light on an adjustable arm at my sanding area and always have it positioned so that the light is raking across the surface to catch anything I may have missed. I clean with alcohol at the very end and use it to make my final inspection. Prep is the key to a good finish.
Author:  Terence Kennedy [ Sun Feb 15, 2015 9:35 am ]
Post subject:  Re: Surface prep
Ben-Had wrote:
Not sure how it compares to the Festol but my finishing mentor worked in the finishing dept. at the Martin Factory for 35 years (was the supervisor there for years) and he recommended to me the Porter Cable 330 (USA made, not the current one). It also has a 2mm orbit. I bought one used and a new pad and my finishing has taken a giant leap forward.


I couldn't agree more. Addam Stark loves the 330 and got me using it. It's great for sanding the contours of the heel and headstock neck transition as well as flat surfaces. Those are areas where challenging scratches really seem to hang out for me.

I've always used Naptha and every light angle I can think of. I consistently think I have it perfect and find the next morning there is stuff I missed.
Author:  Clay S. [ Sun Feb 15, 2015 10:47 am ]
Post subject:  Re: Surface prep
Blowing off the sand paper and work piece frequently helps economize on materials and improves their performance. Using "micron" abrasives that have uniformly sized particles can avoid some of the problems associated with CAMI papers (a few deep scratches caused by poorly graded grit, (P graded papers are somewhere in between)).
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