Official Luthiers Forum!

Owned and operated by Lance Kragenbrink
It is currently Tue Mar 19, 2024 1:45 am


All times are UTC - 5 hours


Forum rules


Be nice, no cussin and enjoy!




Post new topic Reply to topic  [ 31 posts ]  Go to page Previous  1, 2
Author Message
PostPosted: Thu Sep 05, 2019 9:28 am 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Mon Jan 28, 2008 5:21 am
Posts: 4837
Location: Central PA
First name: john
Last Name: hall
City: Hegins
State: pa
Zip/Postal Code: 17938
Country: usa
Focus: Build
Status: Professional
actually with robotics in martin the finish in man hours was drop about 40% finish is about 1/2 the time of making a guitar. I can do a finish in about 6 to 8 man hrs that is from prep sanding to final buff. the first few guitars tool me a lot of time . Once I got the proper equipment and experience your time will drop. this is for Nitro gloss
but it still takes about 4 weeks to do for allowing cure time. In martin and large production shops many have clean rooms and evironmental rooms to aid in curing from weeks to days.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it


Top
 Profile  
 
PostPosted: Thu Sep 05, 2019 5:28 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Wed Feb 15, 2006 7:37 am
Posts: 4775
Woodie G wrote:
Pros tend to be very good at consistent application of material, getting a perfect wet coat every time. This wet coat is of predictable thickness, and if the solids ratio of the thinned finish is known, it is a straightforward process to calculate the required number of wet coats to build to a specific final dry film thickness.

When I started spraying, one of the early exercises was making up two dozen 3mm x 15" x 5" meranti marine plywood test panels with scrap spruce handles attached and filled with epoxy pore filler (scrap ply from a boat-building project - nothing went to waste). I sprayed these panels in vertical orientation with thinned instrument lacquer of known mix ratio, then measure the wet film thickness on each panel using a wet mil gauge (see link below). A few panels were intentionally sprayed very wet, and a few done using a double-coat method that builds finish very quickly. The applied film thickness was the measurement of the last wet tooth plus 0.5 mil (0.001").

Mohawk Classic Instrument Lacquer (solids content): 13% by volume

Thinning: 70/30 by volume (solids 9.1% after thinning)

Wet film thickness (desired): 4.5 mil max (yields .41 mil dry film thickness per wet coat)

Desired dry film thickness after 21 day drying cycle: 0.0035" top; 0.004" sides/back/neck

Number of wet coats to be applied: 8 to top; 9 to back, sides, and neck (sealer coat adds remaining thickness)

Sanding removes between 0.5 and 0.75 mil, so final thickness after sanding and buffing is targeted at .003" top and .004" sides/back/neck.

https://www.amazon.com/82-479-Film-Gaug ... B01BM7MU02


Thanks, Woodie. Do you know that a 4.5 mil coat leaves .41 mil dry from measuring your test sprays?

I ordered the gauge before even finishing your post. :)


Sent from my iPhone using Tapatalk


Top
 Profile  
 
PostPosted: Thu Sep 05, 2019 8:15 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Wed Feb 20, 2008 7:15 pm
Posts: 7214
First name: Ed
Last Name: Bond
City: Vancouver
Country: Canada
Focus: Build
Status: Professional
Those electric film thickness testers underneath that guage seem like the bomb...I was considering one at 2k$...



These users thanked the author meddlingfool for the post: Cal Maier (Thu Sep 05, 2019 10:58 pm)
Top
 Profile  
 
PostPosted: Fri Sep 06, 2019 7:14 am 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Sun Mar 30, 2008 8:20 am
Posts: 5920
The best finishing advice I would give to my fellow hobby builders is to "learn to enjoy the work". Finishing takes time, and if you look at it as a chore and try to speed the process, inevitably you will make a mistake in the application or sanding /buffing out.
Good prep work is essential - trying to fill irregularities in the wood with finish is a fool's errand. Being familiar with a finish and it's application requires experience using it. Most finishes have a learning curve and jumping from one finish to another may not allow you to over come it. Finding the process that works for your particular situation and temperament may be something only you can do.
What works for me is to use nitrocellulose lacquer formulated for stringed instruments (piano lacquer is not (a piano is a percussion instrument organologically)). An advantage of this finish is that you can leave it in an all metal spray gun for a week without needing to clean the gun. Spraying the finish only takes a few minutes, but cleaning the gun can take much more time.
I use low cost spray equipment and get the best results by spraying bodies by laying them flat, so I use hot melt glue to glue small blocks of wood in the previously taped off bridge and fingerboard extension area to act as "stand offs". This allows me to spray a full wet coat on the top and a lighter coat on the sides, allow it to flash off, flip the body over and spray a full wet coat on the back and another light coat on the sides, and then allow it to dry. By spraying heavy coats of finish the material has time to flow out better so the limitations of cheap spray equipment (and personal technique oops_sign ) are somewhat overcome. I tried spraying guitars by hanging them, but found that even using a double coat method I would inevitably get a run somewhere on the piece. Besides being a buzzkill it became a time sink and made sanding between coats necessary.
I have also learned to not rush the finish and only do the sanding and buffing after the finish is completely cured and when I am in the mood to do it in a relaxed manner. Sanding finishes is a lot more enjoyable with a cool drink and tunes on the radio and all the time in the world to do it.
Without a major investment in equipment and experience the amateur luthier is going to require more time to create a finish as good or better than the factories do, so again - learn to enjoy the ride. pizza


Top
 Profile  
 
PostPosted: Fri Sep 06, 2019 7:41 am 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Fri Jul 10, 2009 4:44 am
Posts: 5396
First name: colin
Last Name: north
Country: Scotland.
Focus: Build
Status: Semi-pro
Clay S. wrote:
The best finishing advice I would give to my fellow hobby builders is to "learn to enjoy the work". Finishing takes time, and if you look at it as a chore and try to speed the process, inevitably you will make a mistake in the application or sanding /buffing out.
Good prep work is essential - trying to fill irregularities in the wood with finish is a fool's errand. Being familiar with a finish and it's application requires experience using it. Most finishes have a learning curve and jumping from one finish to another may not allow you to over come it. Finding the process that works for your particular situation and temperament may be something only you can do.
What works for me is to use nitrocellulose lacquer formulated for stringed instruments (piano lacquer is not (a piano is a percussion instrument organologically)). An advantage of this finish is that you can leave it in an all metal spray gun for a week without needing to clean the gun. Spraying the finish only takes a few minutes, but cleaning the gun can take much more time.
I use low cost spray equipment and get the best results by spraying bodies by laying them flat, so I use hot melt glue to glue small blocks of wood in the previously taped off bridge and fingerboard extension area to act as "stand offs". This allows me to spray a full wet coat on the top and a lighter coat on the sides, allow it to flash off, flip the body over and spray a full wet coat on the back and another light coat on the sides, and then allow it to dry. By spraying heavy coats of finish the material has time to flow out better so the limitations of cheap spray equipment (and personal technique oops_sign ) are somewhat overcome. I tried spraying guitars by hanging them, but found that even using a double coat method I would inevitably get a run somewhere on the piece. Besides being a buzzkill it became a time sink and made sanding between coats necessary.
I have also learned to not rush the finish and only do the sanding and buffing after the finish is completely cured and when I am in the mood to do it in a relaxed manner. Sanding finishes is a lot more enjoyable with a cool drink and tunes on the radio and all the time in the world to do it.
Without a major investment in equipment and experience the amateur luthier is going to require more time to create a finish as good or better than the factories do, so again - learn to enjoy the ride. pizza

That all sounds like good common sense to me, sticking with one finish.
My "spray booth" is horizontal and on wheels so I can get around it in a limited space. The body is on a stick which goes into a section of plastic pipe, so I can rotate it as it flashes off, it helps with heavy coats.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.


Top
 Profile  
 
PostPosted: Fri Sep 06, 2019 8:56 am 
Offline
Koa
Koa
User avatar

Joined: Sat Jan 19, 2013 7:33 am
Posts: 1831
First name: Willard
Last Name: Guthrie
City: Cumberland
State: Maryland 21502
Zip/Postal Code: 21502
Country: United State
Focus: Repair
Status: Semi-pro
Dry film thickness is the wet film thickness times % solids in the final applied finish...the variable is film thickness, and that is something that just takes practice. On our bridge rout-downs, film thickness (feeler gauge on bare wood bridge patch) has been between 0.004" and 0.005", so assuming some sealer penetration, it looks like we get 0.003"-0.004" dry film...that seems acceptable.

Some good quality stainless shim stock in thousandths increments (18-8 stainless is durable and not too expensive) and consistent routing pattern stock (MDF is amazingly consistent in thickness, but we still check it on all edges) makes this check easier - especially for trim routers without good micro-adjust on depth. A sheet of 0.004" sets us to just kiss the surface at setup, then pull the shim stock for a depth just over 0.004"...scrape to get any last bit of sealer that went deeper. This approach only works for new guitars with undistorted tops - repair work requires a different approach to avoid unnecessary or excess removal of top wood.

An electronic film thickness gauge would be very useful, although a rout-down on a test panel and feeler gauge measurement seems adequate for hobbyist or small shop use. I'm not sure how accurate electronic film thickness measurements on woods like spruce, redwood, and cedar may be, but fingertips do a pretty decent job of detecting very small differences in thickness of adjacent surfaces (e.g., buffed surface and surface of feeler gauge).

_________________
We have become a civilization that elevates idiots, prostitutes, and clowns. Am I still to defend it? Yes, for its principles. Yes, for what it was. Yes, for what it still may be.

-Mark Helprin, The Oceans and the Stars: A Sea Story, A War Story, A Love Story (A Novel)


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 31 posts ]  Go to page Previous  1, 2

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 28 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group
phpBB customization services by 2by2host.com