Christian - Apparently my method is more accurately called Spirit Varnishing - see this:
Reportedly some professional French Polishers use this method then sand back and use a cloth pad for a final coat:
https://www.woodshopnews.com/columns-blogs/cut-through-the-myths-involved-in-french-polishing
Eucy
Reportedly some professional French Polishers use this method then sand back and use a cloth pad for a final coat:
https://www.woodshopnews.com/columns-blogs/cut-through-the-myths-involved-in-french-polishing
Eucy
Eucy.
Interesting videos, he mentions using shellac crystals, and not to use readily made bottles from the shop, as you do not know how long they have been on the shelf.
He describes how it goes off with time and never dries properly, staying sticky.
This is the problem I had 10 years ago, so I never used shellac again.
It's nice to finally know where I went wrong.
Although being slightly sticky might help reduce some panel or exciter self noise ?
Mabe I should have used his scraper method on my 5mm XPS panels, instead of the roller ?
For a much lighter panel.
he used very little epoxy even for 2 or 3 coats.
it's something to think about.
Steve.
Interesting videos, he mentions using shellac crystals, and not to use readily made bottles from the shop, as you do not know how long they have been on the shelf.
He describes how it goes off with time and never dries properly, staying sticky.
This is the problem I had 10 years ago, so I never used shellac again.
It's nice to finally know where I went wrong.
Although being slightly sticky might help reduce some panel or exciter self noise ?
Mabe I should have used his scraper method on my 5mm XPS panels, instead of the roller ?
For a much lighter panel.
he used very little epoxy even for 2 or 3 coats.
it's something to think about.
Steve.
Steve - I use the dry flakes for the same reason - and I wouldn't seek a sticky surface
I suggest trying my simple method as per #5860 on some scrap material as a start
Cheers
Eucy
Ency.
I was more interested in the use of the epoxy, and applying a very thin coat to my 5mm xps panels.
I'm not sure which is best for a good sound, the thin light coat or the thicker coat .
I have decided not to use a fibreglass mesh as this would increase the weight of the panel and may make the panel too stiff ?
I prefer the epoxy to the pva for this job , as the pva tends to stretch, whereas the epoxy will break rather than stretch.
But that's another project.
Steve.
I was more interested in the use of the epoxy, and applying a very thin coat to my 5mm xps panels.
I'm not sure which is best for a good sound, the thin light coat or the thicker coat .
I have decided not to use a fibreglass mesh as this would increase the weight of the panel and may make the panel too stiff ?
I prefer the epoxy to the pva for this job , as the pva tends to stretch, whereas the epoxy will break rather than stretch.
But that's another project.
Steve.
Hello Eucy
Thank you for your 2 clear and detailed posts.
I understand your approach. I was a bit suspicious too with the idea to add a material like pumice in such an application.
As it is the first time I exchange in English about this type of techniques, i didn't know the vocabulary. So I understand that "spirit varnish" is what I have been doing for years since I made my first trials in my father's workshop.
It is interesting to see the epoxy used as grain filler. I don't know if it is explain in the next video (or in this one but I didn't catch it) why not used on the sound board : is it a matter of sound quality or of finishing... on the neck it is a matter of aspect.
Close to that I remember I found a paper speaking of the role the porous surface in such application. Something to search again...
Christian
+ @Eucyblues99 , @Veleric
Interesting remark Steve; I was surprised in the previous post about your balsa + FG Eric too see "how fast" the weight increased from the light balsa to the final material (ratio of 3?)
I am also wondering if the final material is not too stiff.
I haven't input for now your data in some calculation... To be done
Some weeks ago, I just glued together 2 pieces of 1mm thick balsa (grain of one board being perpendicular to the grain of the second one which leads to an unbalanced assembly). The stiffness in my estimation was closed of what is (in my opinion) needed for its weight. Just a little bit more "spring" effect would have been, I guess, perfect. It was done with some glue in spray i don't intent to use for next tests. Since that, I am thinking to what would be the technique for that. a little bit more stiff with a minimum of additional weight.
Some questions... according to your knowledge/experience :
- according to what is mentioned by the guitar maker in the video you posted Eucy, how are grain for balsa or poplar? open?
- would it be possible to glue 2 layers of balsa together with epoxy (I have no experience of epoxy)?
- if it is not stiff enough w+hat about having some mesh (which material?) just between the 2 balsa board?
By the way if somebody has idea to find low thickness, low density ply, it will be fine! I have found for now only birch ply sources (poplar, basswood?)
Christian
PS : forget the last sentence... writing helps in thinking... I just saw that basswood ply is available in 900mmx300mm in different thickness, starting from 1.5mm for about 10€. So somewhere close to the aspect ratio you propose Eric. What it is not said in the supplier's web site is the number of layers and the weight.
If you want to have a look. It is from Spain. English version : Artesania Latina. I haven't checked more.
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Christian - I built many balsa aircraft models in my youth and still have a supply.
However- I'm not tempted to use it for this purpose
When tested by Tech Ingredients, he specifically used an end grain balsa board which has high(ish) compression strength through the thickness of the board unlike standard balsa sheets.
I may be incorrect but I think balsa is just too soft across the grain to carry the high frequencies - Of course I won't know without trying it but I don't think it offers me any advantages over the very lightweight poplar play (or equal) so I'm unlikely to try it out.
Epoxy would be a good choice for gluing layers. Wood glues like Gorilla etc will work but they are generally water based glues and will most likely distort the balsa. Years ago we used to use acetate based glues (eg Tarzan's Grip), but it only came in small tubes.
Grain - Balsa grain is very open - almost sponge like - wet it and it just soaks up moisture... way, way more than poplar which in turn is similar to birch.
Mesh- As with any sandwich construction, the stiff layers should be on the outside - Having stiffness on the neutral axis is very inefficient and still leaves you with soft surfaces.
Eucy
Eucy and Christian.
Personally, I would be more interested in the panel size, and how to get the correct rigidity and flexibility for that panel size.
As with my small card panels.
I used neat pva to glue the two 0.5mm cards together and then coated with 50x50 mix pva water.
This gave the card a very good performance.
The large 5mm XPS has a coating (layer) of epoxy but I can still easily compress this panel between my fingers.
The xps now has a good response up to 20k.
Having the glue (layer) in the middle of the card gives the strength a and flexibility it needs to stop the card breaking up under pressure.
I was hoping to use this method with 0.5mm veneer but got put off by all the types of veneer and postage.
So compression isn't necessarily a problem.
But rigidity can be a problem, in my experience.
Steve.
Personally, I would be more interested in the panel size, and how to get the correct rigidity and flexibility for that panel size.
As with my small card panels.
I used neat pva to glue the two 0.5mm cards together and then coated with 50x50 mix pva water.
This gave the card a very good performance.
The large 5mm XPS has a coating (layer) of epoxy but I can still easily compress this panel between my fingers.
The xps now has a good response up to 20k.
Having the glue (layer) in the middle of the card gives the strength a and flexibility it needs to stop the card breaking up under pressure.
I was hoping to use this method with 0.5mm veneer but got put off by all the types of veneer and postage.
So compression isn't necessarily a problem.
But rigidity can be a problem, in my experience.
Steve.
Working out really nicely with the frame with printed corners. Sounds even tighter and with much better bass and mid presence. Haven't screwed or glued anything, but holds together anyway and no rattling at max volume I can produce with the amp I have now.
Will work on the look a bit, probably paint the wood orange or something:
Will work on the look a bit, probably paint the wood orange or something:
Hello Eucy
It is because of what you list here all that is stil at idea level; at equal distance from good and bad ideas...
The word "soft" is right while speaking about balsa. Some weeks ago I made a test with a 1mm board, the high frequency extension was not so good. It was a raw balsa.
The fact that epoxy can glue 2 layers without high distortion is a good point and the technique in the video before to fill the grain is also a good point.
There is a good experience from Steve with an epoxy coating on XPS.
About the mesh, I agree that it would be efficient being at the surface. The idea here is more to control the thickness of the central glue.
Let's keep that in the tank of ideas.
Christian
Hello Steve,
What do you mean by "I would be more interested in the panel size"? If it how to design the panel according to the material characteristics, you should find some inputs in previous posts. All what is around the bending stiffness and the areal mass. I think it would be great if you come to this kind of data in our exchanges.
Like you, I had a look to veneers but I was also discouraged by the possibility in veneer, most of them have a quite high density, at least often higher than poplar, at high cost and small dimensions so no real benefit.
Christian
Hello Eric,
I had a deeper look on those data. Seems really promising. Mainly in my opinion the thinner one even its efficiency is a bit lower (1dB?). Let us know when you'll get some panel working.
Christian
I have not completed the mounting yet, and just have the exciters attached with the original adhesive, so this is how it looks on the back:
So 4x DAEX30HESF-4 in a Tectonic style configuration.
No graphs for now since my space is a bit chaotic with various ongoing projects :\
But did some more careful listening and playing around with EQ and the framed plate.
It seems like response below 90hz or so is much lower then the unframed plate, which I hope is not an issue since I plan to high pass them around there anyway. The foam strips I'm using are quite soft, but the plate is pressed quite tightly between them, and think I will need looser suspension if I want them to go lower.
Apart from the sound being much tighter and clearer also at low levels, sensitivity is radically better on this plate. Just tested with a mobile app, which I don't trust the absolute values from, but should should give somewhat useful relative values, and I'm measuring 8-9 dB more!
I did not do the same measurement before suspending the plate, and the plate I'm comparing with is using 4x DAEX25FHE-4 instead, so cannot say what can be attributed to the exciters, plate treatment or suspension, but will do another plate with same exciters and treatment, but free hanging, and see how it compares.
But did some more careful listening and playing around with EQ and the framed plate.
It seems like response below 90hz or so is much lower then the unframed plate, which I hope is not an issue since I plan to high pass them around there anyway. The foam strips I'm using are quite soft, but the plate is pressed quite tightly between them, and think I will need looser suspension if I want them to go lower.
Apart from the sound being much tighter and clearer also at low levels, sensitivity is radically better on this plate. Just tested with a mobile app, which I don't trust the absolute values from, but should should give somewhat useful relative values, and I'm measuring 8-9 dB more!
I did not do the same measurement before suspending the plate, and the plate I'm comparing with is using 4x DAEX25FHE-4 instead, so cannot say what can be attributed to the exciters, plate treatment or suspension, but will do another plate with same exciters and treatment, but free hanging, and see how it compares.
Hi Eric - Just noticed this comment . Your approach with the stiffness ratios on high aspect panels is diametrically opposed to mine - I've explained previously (or tried to) that I firmly believe that the vertical/lateral stiffness ratios should be in proportion to the dimensions (within practical limits), particularly if the sides are supported, so I would be very interested to hear how you have arrived at your conclusions.
Thanks
Eucy
Christian,
Concerning the weight ratio, yes, you are correct, even thin fiberglass layers increase the weight of balsa significantly. But that is the nature of such composites. Consider this, if you choose an even lighter core, like nomex or divinycell PVC foam, then the weight ratio is even higher! As always, the question is if the increase in stiffness is sufficient to make up for the increase in weight.
And yes, too stiff is also very much possible, with such composites. I am generally leaning towards very thin cores (less than 3 mm and preferably closer to 1.5 mm for example) and very thin fiberglass or CF skins (about 0.2 mm or less and preferably .1 mm or less), because of that.
Balsa is interesting. It has pretty high efficiency all by itself, but it is extremely fragile. Also, the properties (of a single layer) are much different comparing the the direction with the grain and perpendicular to the grain. Even more different than almost any other wood species. Applying fg layers to balsa mainly solves those two issues. The fiberglass also makes the surfaces more resistant to compression, and that may help with the higher frequencies.
In principal, I like the idea of gluing two layers perpendicular layers together. Except that, as you noted, it leads to an "unbalanced" assembly. Such an assembly will very likely warp when subjected to any changes in humidity.
Eric
Eric.
Ever since creating a panel out of the crate ply ,which is more flexible in one directions than the other, I have been thinking is it good or bad to have different rigidity in different directions ?
Let's take the long panels you are making, to start with.
Because of its length it will have some flexibility (obviously not if it is edge restrained) but across the thin panel it will be very rigid.
On the other hand if we are using a square panel that is more flexible in one direction than the other, will this help break up resonance reflections, which is the main bugbear of square or round units ?
Or is it that the long edge and the short edge should have the same sort of flexibility by making the short edge more flexible ?
Or should you be able to wobble them in both directions ?
The proplex is less rigid across the flutes for example and is 2ft square and has different responses at the edges.
It is interesting to have another variable to think(worry) about and to consider.
Hopefully that all makes sense ?
Steve.
Ever since creating a panel out of the crate ply ,which is more flexible in one directions than the other, I have been thinking is it good or bad to have different rigidity in different directions ?
Let's take the long panels you are making, to start with.
Because of its length it will have some flexibility (obviously not if it is edge restrained) but across the thin panel it will be very rigid.
On the other hand if we are using a square panel that is more flexible in one direction than the other, will this help break up resonance reflections, which is the main bugbear of square or round units ?
Or is it that the long edge and the short edge should have the same sort of flexibility by making the short edge more flexible ?
Or should you be able to wobble them in both directions ?
The proplex is less rigid across the flutes for example and is 2ft square and has different responses at the edges.
It is interesting to have another variable to think(worry) about and to consider.
Hopefully that all makes sense ?
Steve.
I was initially thinking of making a 6x9inch veneer panel similar to my card panels.
But instead of crossing the grains maybe I should have them going in the same direction using pva in the centre for flexibility.
But if stiffening is needed the use of more pva on the outside is possible or a thin scraping of epoxy similar to how it was done to the guitar in the video.
A very thin coating.
Steve.
But instead of crossing the grains maybe I should have them going in the same direction using pva in the centre for flexibility.
But if stiffening is needed the use of more pva on the outside is possible or a thin scraping of epoxy similar to how it was done to the guitar in the video.
A very thin coating.
Steve.
Hello Eucy,Hi Christian:
I think you are correct wrt the poplar ply - It will be hard to surpass with more complicated and costly materials.
Shellac = French Polishing yes.
I'm far from an expert in this but I have achieved quite good results with a very basic approach. I'm also after a satin finish not a mirror gloss one.
One issue with poplar is that it has a very bland finish - it's very pale and the grain pattern can be uninspiring. I initially only had Gold/Orange shellac and I thought that it would end up too yellow by itself so I tried first applying a very light stain to the ply which worked OK but I think could be avoided by using a mix of Garnet (dark) and Gold shellac instead.
So I bought flake shellac in gold, garnet and platina (blonde). The flakes keep indefinitely if stored in a dry cool place unlike premixed shellac.
3:1 Alcohol / Shellac mix by weight is a good middle mix (just a bit thinner that a "2lb cut' but you can try different ratios. I thinned out the first coat somewhat for penetration.
I didn't do any grain filling - I relied on judicious sanding back between coats which worked OK - I wanted to avoid too much junk in the panel and I don't mind a trace of grain showing. One luthier uses West System epoxy to seal the back and sides of open grained woods but not the soundboard ()
Application- I have tried the traditional cloth method but it's difficult and takes much practice. I found that with practice I could brush it on quite well. When brushing you have to be quick and only brush with a forward or backwards motion, not both, work from one end to the other as evenly as possible across the panel and avoid going back over wet areas. Apply enough to the brush to get a wet finish and as soon as you start to use the brush load up - dip again and go - it's important to get a flow going so you end up with an even wet coat. I used a 30mm wide brush and stored it in a jar of alcohol between coats.
I haven't tried spraying, but it seem to be an ideal candidate as it's very thin and is easily cleaned out afterwards. Maybe I would revert to spraying if my panels were larger - long narrow panels would still be easily paintable however, it's when they start getting wider that makes it a bit more difficult, but you could probably just use a wider brush
It dries very quickly - I help it along with a heat gun on a low setting waved over it if I'm in a hurry.. make sure it's not dusty if you do that.
You can sand back after each coat dries. I use worn 240 grit paper or fine wet and dry paper.
I applied 4 coats sanding between each, and to remove the gloss after the final coat (which after 4 coats is still a bit uneven) I rub down with grade 0000 wire wool which blends the finish and gives a satin look.
I found the shellac finish is surprisingly tough - tougher I think than acrylic lacquer, so I believe it's and excellent way to finish timber in general - I applied it also to some pine feature strips and it turned out great. It's only drawback is sensitivity to moisture on tables etc but that doesn't apply in this case. It's stood the test of time on musical instruments so that's good enough for me.
Oil - I used no oil - I haven't had any issues with the finish on vibrating panels so I can't see the need for oil.
Go for it Christian
Good Luck
Eucy
Sorry...additional questions :
- do you have this finishing on both sides of the panel to keep it "balanced"?
- does this finishing induce warping (when I applied diluted varnish on only one side, warping was important... ok not a surprise!)?
Christian