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automated French polish?
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Author:  wbergman [ Sun Aug 24, 2014 6:06 pm ]
Post subject:  automated French polish?
Is there any machine to apply French polish? For example, has anyone programmed a CNC to run the pad, so all you do is drip occasional shellac onto the pad? I see a lot of postings about the physical pain caused to the hand and arm by French polish.
Author:  Josh H [ Sun Aug 24, 2014 7:00 pm ]
Post subject:  Re: automated French polish?
I'm not a French polish guy, but I've watched some people who are. There is so much going on with the French polish process that I don't think you could ever have it done by machine and receive the same quality result as someone who has mastered the process. I have stayed away from it because of the time and arm wear involved. I'm known a number of builders who in a short amount of time ended up with arm and shoulder problems as a result of French polishing. On the other hand I know builders who have done it for years and are fine. Technique I'm sure has a lot to do with it.
Author:  patch [ Sun Aug 24, 2014 8:07 pm ]
Post subject:  Re: automated French polish?
i'm french polishing one right now. i can't imagine ever being able to program a cnc to do the work but they are building houses with 3d printers so who knows. this is my forth and so far no shoulder or arm problems yet. i do think part of the technique is being relaxed and not tensing up your body while you polish. something i learned years ago after getting carpal tunnel while playing guitar and gigging lots.
Author:  Frank Ford [ Sun Aug 24, 2014 9:22 pm ]
Post subject:  Re: automated French polish?
wbergman wrote:
Is there any machine to apply French polish? For example, has anyone programmed a CNC to run the pad, so all you do is drip occasional shellac onto the pad? I see a lot of postings about the physical pain caused to the hand and arm by French polish.


Not going to hold my breath waiting for that fantasy to come to a workshop near me!

Pretty much the whole deal with French polishing is continually observing and adjusting the way the materials are behaving. As to the injuries, well, I have this to say about that:

I'm an old guy, and I have a pretty good memory. NEVER is how often I recall having heard about repetitive stress injuries when was young. My mother was a legal stenographer and clocked 100 words/minute (corrected) on manual typewriters. She never talked about "keyboarding" stress injuries on the job. I have a friend my age who is a lifelong dental assistant and she tells me that the younger techs all get repetitive stress injuries and go on disability instead of continuing to clean teeth. I asked her about her early career, and she said, "No, I didn't get the injuries - only the young ones get them - I'm too old to get hurt cleaning teeth." Now that made me curious so I demanded an explanation. She said it was simple - the schools quit teaching how to handle tools without stress, and it saved some money do avoid that class.

I had a friend who worked at a guitar factory installing frets in the traditional manner, and he got quite good at hammering frets. But, he and the others on the line all got repetitive stress symptoms because they weren't trained in how to handle a hammer. When I saw him working on a fret job, I could see the stress in his grip, all the way up his arm to about his right earlobe! No wonder he hurt.

Manual training was a part of the regular school curriculum back in the days of skilled labor in factories, and I'm sure there were lots of French polishers who had long careers without joint injuries from the job. Learning to relax while working is critical for handcraft. To ignore that simple fact is to set yourself up for, well, you know, pain in the long run.

Me, I have enough joint pain from inherited osteoarthritis, so I'm acutely aware of my movements, but I can still do French polishing without hurting myself. Admittedly, I don't don't do that kind of thing for full workdays, so I am showing a bit of the reckless courage of the noncombatant. But, I believe there's some truth in what I say.
Author:  meddlingfool [ Sun Aug 24, 2014 9:51 pm ]
Post subject:  Re: automated French polish?
I watched a vid with David Wren in it, and he was doing FP in a different way, which I believe he learned from one of the DeJonges.

Instead of teeny little circles, he was going back and forth in long stripes, more like painting with a brush. Much less tension in that method I bet.
Author:  Lonnie J Barber [ Sun Aug 24, 2014 10:52 pm ]
Post subject:  Re: automated French polish?
I'm with Frank as I'm an old guy also. I hung drywall for 25 yrs. driving hundreds of thousands if not millions of nails. Once I had a bout of tunnel Carpel. But recovered and never was bothered again. Learning to relax is an art form. But if you don't relax there is no way you can do your best job.


Sent from my iPhone using Tapatalk
Author:  RusRob [ Mon Aug 25, 2014 12:40 am ]
Post subject:  Re: automated French polish?
I don't think you will see a machine do FP until they perfect artificial intelligence. I have done a fair amount of French Polishing and it isn't something that you can just rub on and end up with a perfect finish. It requires a lot of feeling how the finish is going on and adjustment to the amount of shellac vs alcohol vs oil to achieve the correct amount of drag, the level of gloss and the smoothness of the finish. Throughout the entire process you are constantly adjusting to the tactile feel and visual cues which is something I don't think any present day machine can do.

I was taught back in the late 60's by someone that I considered to be one of the best French Polishers I have ever met and she taught me the same way she was taught. One of the first things she said to me was you have to be relaxed and comfortable or it would show up in the finish. She also taught me to never keep repeating the same pattern. So if you start out doing circles the next application should be in figure eights and the next one should be overlapping straight lines. I have found that to be the best method for me and I think that is also helps to keep you relaxed as well. If you are relaxed then you are not straining any muscles and therefor you won't end up with strain related problems.

If you are wanting to automate it why not just spray it on and sand it smooth and buff it out? That is not considered French Polishing but it does achieve the same end results. You could even automate a robotic arm to do it.

But then you would loose the romantic idea of a hand applied French Polish finish. idunno

Bob
Author:  Michael.N. [ Mon Aug 25, 2014 6:05 am ]
Post subject:  Re: automated French polish?
Learn to brush the stuff on.
Actually what I do now is almost a hybrid version, brushing and then a very quick French Polishing with the pad. It's simple and fuss free. You do need skill with the brush though. Don't think for one moment that it is any easier than French Polishing. It isn't. It cuts down the working time significantly but the waiting time (hardness) is extended by a couple of weeks.
This is one I did a few years ago. No polishing agents or buffing, finished straight from the rag.

Image
Author:  Pmaj7 [ Mon Aug 25, 2014 10:14 am ]
Post subject:  Re: automated French polish?
Michael.N. wrote:
Learn to brush the stuff on.
Actually what I do now is almost a hybrid version, brushing and then a very quick French Polishing with the pad.


Michael, is there a thread with your process? So, you're saying that it gets just as hard as a regular French process, just takes a few weeks longer to cure?
Author:  WendyW [ Mon Aug 25, 2014 10:41 am ]
Post subject:  Re: automated French polish?
Michael, I'd like to see your process as well.

I have French polished 3. Interestingly, the first came out beautiful and caused me no problems. I think I was more relaxed at the time. There was a few years gap between it and the next 2, which never looked as good. And I developed terrible thumb joint problems from the process. I had to have injections in the joint and eventually it got better, but always can be triggered by certain positions that I avoid. I am extremely reluctant to French polish again.
Author:  jfmckenna [ Mon Aug 25, 2014 10:51 am ]
Post subject:  Re: automated French polish?
I brush on the first three coats and sand it back flat before using the FP technique. It saves a lot of time and as far as I can tell it's not hurting the process at all. As was mentioned there is too much finesse involved to be able to make a machine within any reasonable price range capable of doing a good FP. If in the future our robot overlords are programmed, or learn to, enjoy guitar music then I'm sure they will build a luthier capable of making a fine FP finish :)
Author:  Michael.N. [ Mon Aug 25, 2014 12:07 pm ]
Post subject:  Re: automated French polish?
pat macaluso wrote:
Michael.N. wrote:
Learn to brush the stuff on.
Actually what I do now is almost a hybrid version, brushing and then a very quick French Polishing with the pad.


Michael, is there a thread with your process? So, you're saying that it gets just as hard as a regular French process, just takes a few weeks longer to cure?


There's not really a lot to say about the process. You just have to become proficient at using a Spirit varnish and a brush.
I use my own slight variation of the 1704 varnish recipe (easily found with a search engine). It uses Seedlac, which is fine if you are after a lot of colour in the varnish. If not you will have to substitute one of the more refined grades of shellac and add more alcohol. You want to end up with a very watery varnish. I don't know the exact cut but I doubt that it's any more than a 1 lb cut. I use the Spike Oil as a brushing agent/retarder although I'm sure the stuff from Shellac.net can also be used. Don't use too much of this, it will just lengthen the hardening process considerably. I use a touch over half the given amount. I use Gum Benzoin in the varnish, this and the Spike Oil gives you an incredibly heady mix. Smells divine!
Brush on in a methodical and confident manner. Use slightly overlapping strokes. Do a single 'band', going across the Back and then move. You can't stay in one place doing multiple strokes like you can with paint or Oil varnish. It flashes off too quickly. You might get 3 or possibly 4 strokes on the same 'band'. That's all. If you make a mistake or miss an area, leave it. Do not be tempted to go back and 'repair' it. Small mistakes are of no consequence. They get covered in the subsequent coats. You can try storing the varnish in the fridge to give yourself a bit more working time. When you become proficient with the brush this shouldn't be necessary.
Sides are a little harder to do. I always go across the grain on the Back but with the grain on the Sides.
I use around 18 coats, which does seem an awful lot but this is thin varnish. Each coat should take no more than a few minutes each to apply. It's fast, it has to be. I put all the coats on in the space of 3 days, 9 am to 9 pm. You can spread it over 4 days but no longer. Too long between coats and there is a danger of witness lines. You wouldn't think it possible but I've seen witness lines on a few occasions - until I started to work to the 3 day limit.
After the last coat is applied the whole thing is soft, very soft. Even 4 or 5 days later you can literally peel the whole layer off with a fingernail. This is where you must be very patient. Leave it, minimum 3 weeks but preferably 4.
I then rub down (wet) with 800G. If your brushing hasn't gone so well start with 600G. 800 is the only abrasive that I use. After that I switch to the French Polishing pad, glazing polish thin. It's all done in very straight lines, no circles. Just a few lines done quickly. Again, a Back should take just a minute or so. Very quick. Do 8 or so of these sessions over a couple of days. Just enough to fill in and eliminate all the scratches left by the 800G. The straight lines will leave a touch of texture from the cloth. That's what I want, enough to take the away the hard glass like finish. If you are after the glass look then skip the french polishing pad stage altogether and go through the grits, right through to the polishing paste/buffer.
I then leave the instrument a further 2 weeks. With pore filling the total time isn't that far off 2 months. Lengthy yet the total working time is probably less than half that of a full French Polish. I estimate that it's no more than 4 hours, including pore filling.
Practice on a few boards first. Always a good idea, although brushing on Shellac is very rarely fatal.
Author:  Stuart Gort [ Mon Aug 25, 2014 1:16 pm ]
Post subject:  Re: automated French polish?
Haha....there are plenty of nc based finishing processes out there in guitar land but I seriously doubt one would ever be developed for french polish.

By the time you're able and ready to finish 100 guitars a day I believe you'd be well past the notion of old world finishes. Not that there's anything wrong with french polish. It's just that the method seems to fit into the "handmade" notion of things. It's incongruous, and perhaps even antithetical, to think of doing an artisan finish with a machine.
Author:  Greg B [ Mon Aug 25, 2014 1:36 pm ]
Post subject:  Re: automated French polish?
Strange as it seems, FP was a production finish at one time. A few years back I was restoring an old carved mahogany back bar, and some old timer happened to walk by. He poked his head in the door and said, "I haven't seen anyone doing that for a long time!" It turns out he had worked in a production furniture shop doing FP as a young man. I got some good tips that day!

It should be pointed out that FP can be done very quickly, at least as a furniture finish. People used large pads and worked quickly. We are sort of biased by the nitpicking nature of guitar finishing.

I'm pretty sure that I've seen a picture in an old magazine of someone doing french polish by machine. IIRC it was sort of like an ROS crossed with one those dish soap dispensers. I couldn't find offhand anything on the net, though there are at least a couple patents for automated french polishing machines. A more careful search of archived microfilm periodicals would probably bring it up.

Obviously, the main use would have been things like tabletops. This would have been about the time NC lacquer was catching on, rendering FP obsolete for most production uses.
Author:  Parser [ Tue Aug 26, 2014 11:11 am ]
Post subject:  Re: automated French polish?
I'm sure you could do it with a robot, but I'm also sure it wouldn't be cheap. I am around a lot of R&D robotics applications here at work and the technology is definitely there...whether it is cost effective to do something like this is another question...and is probably the reason that most production shops don't use FP finishes.
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