McKnight Guitars are coo-coo for Coco

[cigarfan]

Originally Posted by Tim McKnight

After the vinyl sealer dries for 48 hours we pore fill the peg head and body with a super hard epoxy resin. We drizzle (another highly technical term for Dennis) "a little dab will do ya" on the wood:

Then squeegee the excess resin from the surface of the wood:

The drizzling continues on the sides:

Followed by more squeegee work:

Finally the back is the last surface to experience the drizzle:

And squeegee:

All this technical talk ... I have goosebumps!

[Tim McKnight]

Originally Posted by cigarfan

All this technical talk ... I have goosebumps!

Well ... technically speaking ... we call em goosebimples

[pandaroo]

Wow, wow and wow!!

Since your logo is on the fingerboard, so the headstock will be inlay free?

[Tim McKnight]

Originally Posted by pandaroo

Wow, wow and wow!!

Since your logo is on the fingerboard, so the headstock will be inlay free?

Yes pandaroo, you are correct. That is what our client wanted on this build and we aim to please

[Tim McKnight]

After the 2nd coat of epoxy resin grain pore filler dried sufficiently we sanded it with 320 grit in preparation for the final finish:










All surfaces are wiped with a tac-rag to remove any surface dust:










Then we spray a final coat of sealer over the pore filler on the neck:















and over the filler on the body:

[ruby50]

When you sand the filler, do you take it down to bare wood or leave a layer of epoxy on the surface. I have always been curious about why some leave a layer of a fairly dense material that could effect the sound of the instrument.

Ed

[ruby50]

When you sand the filler, do you take it down to bare wood or leave a layer of epoxy? I have always been curious about leaving a layer of fairly dense material on the wood that might effect the sound of the instrument

[Tim McKnight]

Originally Posted by ruby50

When you sand the filler, do you take it down to bare wood or leave a layer of epoxy on the surface. I have always been curious about why some leave a layer of a fairly dense material that could effect the sound of the instrument.

Ed

Hi Ed. That's a great question. My first coat of filler will fill 90% of the open wood pores. I sand the first filler coat level to the surface of the wood using 220 grit and this sanding course does expose some bare wood. The second and final [skim] coat of filler covers any bare wood which was exposed and generally fills the remainder of any open pores in the wood or any new pores that were exposed during sanding. The final filler sanding course, with 320 grit, is basically to mechanically abrade the filler to provide a tooth for the sealer to adhere to with a goal of NOT exposing any bare wood.

The trick to the entire filling process is to NOT apply the filler too thick and to judiciously squeegee ALL excess filler from the surface of the wood. As you eluded to in your question, excess filler build up on the surface of the wood would indeed have a negative impact on the wood's ability to vibrate.

I use a 4" wide auto body "bondo" spreader to apply the filler and squeegee most of the excess off with. As a follow up I use a 12" wide rubber window squeegee to do a final removal of any ridges of filler that may be left over from the edges of the 4" spreader application course.

I apply a LOT of downward force on the application spreader to force the filler into the wood pores. The downward force bends the spreader at a 45* angle to the surface of the wood and hardly leaves any filler standing proud of the surface of the wood. This process isn't like icing a cake to leave a thick layer of icing (filler) on the surface. This is more akin to scraping ice off your car's windows so you can see through the glass.

I hope that makes sense?

[Tim McKnight]

Through the magic of time travel, the finish is almost done. Sorry I didn't show any pics of the finish spraying and sanding process but its really rather boring to see repetitive and redundant photos. I have three more coats of catalyzed urethane lacquer to spray and its at this point that I stop and cut the sound port into the sides. I do it now so that I don't get too much finish build up around the exposed edges of the sound port(s).

[ruby50]

It does make sense. That leaves the question of WHY leave it - why not take it back to raw wood. Does it show off the grain better?

Ed

[FLRon]

Originally Posted by Tim McKnight

Hi Ed. That's a great question. My first coat of filler will fill 90% of the open wood pores. I sand the first filler coat level to the surface of the wood using 220 grit and this sanding course does expose some bare wood. The second and final [skim] coat of filler covers any bare wood which was exposed and generally fills the remainder of any open pores in the wood or any new pores that were exposed during sanding. The final filler sanding course, with 320 grit, is basically to mechanically abrade the filler to provide a tooth for the sealer to adhere to with a goal of NOT exposing any bare wood.

The trick to the entire filling process is to NOT apply the filler too thick and to judiciously squeegee ALL excess filler from the surface of the wood. As you eluded to in your question, excess filler build up on the surface of the wood would indeed have a negative impact on the wood's ability to vibrate.

I use a 4" wide auto body "bondo" spreader to apply the filler and squeegee most of the excess off with. As a follow up I use a 12" wide rubber window squeegee to do a final removal of any ridges of filler that may be left over from the edges of the 4" spreader application course.

I apply a LOT of downward force on the application spreader to force the filler into the wood pores. The downward force bends the spreader at a 45* angle to the surface of the wood and hardly leaves any filler standing proud of the surface of the wood. This process isn't like icing a cake to leave a thick layer of icing (filler) on the surface. This is more akin to scraping ice off your car's windows so you can see through the glass.

I hope that makes sense?

Tim,
I have always wondered about the grit of sandpaper being used on tonewood. To my way of thinking,320 grit paper is extremely rough and would leave deep scratches, which would then require finer grits to sand out the scratches.

My reference points come from my career in the automotive industry. Various components that have been heat treated for example must be hardness tested to ensure they meet the required specifications. Now, I have considerable experience in polishing small test parts that will be placed under a Microvickers machine for the purposes of determining this surface hardness. These surfaces must be polished to a mirror finish and completely scratch free. I usually start with a 320 grit paper but work my way up to 1200 grit paper and finally a buffing pad to achieve the needed results.

In working with tonewoods, why are you not striving for a completely smooth surface finish before applying the lacquer? Or is 320 grit smooth enough because the wood surface will eventually be covered up? Or maybe it’s because you aren’t polishing the wood surface, but rather leveling it in preparation for lacquer? Sorry for so many questions, but I’ve wondered about this for some time.

Love your threads BTW, especially the engineering that goes into what you do. We’re I ever able to have a guitar built, I can’t imagine having anyone but you build it.

[ruby50]

FLRon
It has to do with giving the finish something to hang onto. I got this chart off another forum posted by someone who had taken the tour of the Martin factory and saw it hanging on the wall of the finishing shop:

https://www.flickr.com/photos/ruby16...posted-public/

Click the image to enlarge it

Note it says - do not sand with 320 grit on any body that receives a hand rubbed stain

Ed
Very frustrating - can't figure out how to post a picture

[runamuck]

Originally Posted by ruby50

FLRon
It has to do with giving the finish something to hang onto. I got this chart off another forum posted by someone who had taken the tour of the Martin factory and saw it hanging on the wall of the finishing shop:

https://www.flickr.com/photos/ruby16...posted-public/

Note it says - do not sand with 320 grit on any body that receives a hand rubbed stain

Ed
Very frustrating - can't figure out how to post a picture

I've been making furniture for 35 years and have built a few guitars. But wood is wood.

The thing about sanding and stain is that the finer the grit, the less texture an oil stain has to grab onto: if you sand 1/2 a piece to 120 and the other 1/2 to 220, the 120 will stain darker. That's true for all oil stains but not so much for analine dyes.

As far as adhesion of wood to finish goes, the claim that 320, or 600 grit, for that matter, is too fine, is a myth. 600 grit is unnecessary that's for sure, but 320 on some fine woods, especially if you're using a random orbital, is going to reduce the chance of fine scratches showing than if you were to use 220.

Hope that clarifies things.

[FLRon]

Thanks! That does help to clear things up. So sanding the wood too fine increases the chance that scratches and swirls wil show through the finish.

Thanks for the link ruby50!

[Tim McKnight]

Originally Posted by ruby50

It does make sense. That leaves the question of WHY leave it - why not take it back to raw wood. Does it show off the grain better?

Ed

When you sand the resin filler back to raw wood you expose additional wood pores, defeating what you’ve just accomplished. Additionally, the pore filler I use is almost clear but has a hint of amber. If I sanded back to raw wood in a few spots, those spots would show up as different colored splotches under the finish. Don’t ask how I know that tid bit of information