Variations on a Macca.

[Nick]

Well after thinking about double backs e.t.c & that there probably won't be any difference in the sound. I decided to go ahead anyway and try one, unless I did it, it would always sit in the back of my swede fermenting and I'd be left wondering "what if". I haven't got a customer so under the guise of "experiment" is justification in my mind to build another
I know and am trained to work on the principle of only changing one thing at a time to see what difference it made but I can't afford cupboard space or cash building 4 or 5 to get where this one will end up so I'm going to include all my idea's on this sucker.
The specs for this one are:
A double backed guitar with Mahogany for the 'outer' back and sides. A Maple 'inner' back (with the idea of giving the tone a bit more cut). Maccaferri used an inner soundbox on his design in order to isolate the back's movement from the dampening factor of the player and hence increase volume. I have used the same principle but just used a seperate back rather than building an inner box.
Sitka spruce for top and bracing, I thought I would use the "grande Bouche" D soundhole on this one.
My favourite 25" scale with a mahogany/ maple laminated neck. Probably stick with Ebony fingerboard & headplate but haven't quite decided that factor yet. Cantilevered from the body.
Headstock access to the trussrod, originals had alloy rods and my two previous petite bouche's had soundbox access but due to the small soundhole it became a pig of a job adjusting it! I'm also changing the non-adjustable bridge for an archtop style adjustable two piece.
So I thought I'd post a few progress pickies and add to them as I go.
So far I have the sides bent (nothing new in this picture!)


The spare neck & tailblock were just there as packers at this stage.
In order to keep the box a reasonable & comfortable size I made the sides wider by 8mm so it didn't feel too big for the player (hopefully they don't feel any difference) but retain most of the original internal volume of the box. I have decided to have 16mm between the two backs so the inner back is in by 8mm from standard. Some shots showing the profile of the sides.




To get the inner back following the outer I marked a line parallel & 13.5mm in from the back (+2.5mm thickness for the maple gives me the 16mm), this gives me a line for the top face of the linings to follow. The sides are sitting in my dish that has the correct arching/shape on it so providing my sides match the dish, the pencil must follow the same profile.


Because the linings act as spacers as well as corner fillets I made my own so that I could put a 'shelf' on the top for the inner face to sit on and glue to.I also made the kerfing 4mm instead of the standard 6mm so that the lining better followed the tight curve of the upper bout cutaway 'point'.
Thinking also that once both backs are glued on, the air space between them would be sealed & effectively a closed chamber, which would act as a dampener/compressor. I added slots at each of the blocks to allow air to move freely between chambers. Here's a shot showing that and also the linings I came up with. I glued them onto the head & Tail blocks to give the inner back something to glue to in these areas.



& a final picky.

I've just joined the inner back plates so will post some more shots as I go if anybody's remotely interested.

[Localele]

We are always interested Nick.Everybody will learn at least something from a photo diary of the build.
Not to get off topic straight away but being a bit of a tool perve I noticed the sides resting on what looks to be a Dyco Superfine table saw.How good is the saw?

[Nick]

Not to get off topic straight away but being a bit of a tool perve I noticed the sides resting on what looks to be a Dyco Superfine table saw.How good is the saw?

Pervert
I am fortunate to work for the local university. My department are kind enough to let me build in the department's wood shop (in my spare time of course!) as the environment is stable all year round. The saw was bought by the department when it had a carpenter full time who was fairly fastidious in it's upkeep and general condition so as a consequence is still in excellent condition. It cuts really well and accurately. The neck block on a Selmer Maccaferri has a compound taper on the cutaway side (4.5 degrees from top to bottom & 1.29 degrees front to back), I set the blade angle up to the 1.29 using the built in blade angle gauge, the 4.5 using the angle fence and cut my block oversize expecting it to be out and allowing for correction. Well bugger me, everything was spot on . The tipped blade needs a good soak to get gum/glue buildup off the tips (due to the numerous sheets of MDF that gets run through it!) but apart from that it's excellent, tables true and the construction is solid. And considering it didn't cost me anything I can't complain.
The department also has a DYCO 6" buzzer which I believe needed alot of machining work done to it to make it accurate. The fence wasn't at 90 degrees and the two beds weren't parallel with each other, so I would hazard a guess and say that the quality control at DYCO wasn't/isn't always at it's best, maybe too much Tui intake by the inspectors or the Buzzer was a first thing Monday morning job

[John Steele]

Nick;
You are a crafty buggar after my own heart! That was a nice solution with the the lining to create a shelf for the "interior" back plate. I like the slot/baffle idea as well. Is that spruce you are using for the neck block? I have always had a liking to the Maccaferri design and look. In fact the post of mine with the cracked top seam is something I've been contemplating for a bit. Sort of a Maccaferri meets dreadnaught affair. Sadly, I did not take pictures of the build, but now that my building chops are coming back I am thinking I should bend another set of sides....
Keep up the good work!
J

[Nick]

Thanks John & yes it is Spruce I've used for both blocks. It was through watching Bob Benedetto's fine archtop DVD's that got me onto using Spruce. Maybe a little 'stringy' but just as strong as Mahogany (your sides act as a perpendicular grain to strengthen up the 'wings' of the dovetail) and the difference in weight to the completed instrument is lighter too. Several people have picked up my guitars and the first thing they've said is "It's light ain't it!" As Bob put's it "it's one of those little things people can feel is different but can't put their finger on".
As for the linings I want everything in behind, linings, centrestrip & bracing, so as to create as smooth a face as possible inside the box, again falling back onto an Archtop design but without the large arching obviously!
And yeah, any times a good time to be bending up sides

[Localele]

Does all this mean that the 2 backs will be seperated by 1 set of back braces and 2 centre seam reinforcements?

[kiwigeo]

That bldi lino hasnt changed in the Chem Dept since I was doing Chem 101 back in 1983.

[Nick]

Does all this mean that the 2 backs will be seperated by 1 set of back braces and 2 centre seam reinforcements?

No I plan on staggering the back braces, the inner back will have 3 braces and the outer 4 that way the inner back will behave as it usually does & isn't 'tied' to the outer back in anyway. There is a 13.5mm gap between the two plates so my braces will be 11.5mm high giving a 2mm gap between brace & plate to allow for resonance & air movement, I know it won't exactly be pumping gallons of the stuff but I wasn't sure what to allow so 2mm seemed like a good figure.
Because I've decreased the height, the outer back braces will be laminated to give it the stuctural strength the back usually provides and seeing as they don't need to move with the resonating back can be abit stronger/stiffer. As the outer back will carry all the structural load that is usually required of a back plate this allows me to try another idea of not carrying the inner back's braces right out to the linings, they will only be there to hold the inner back in it's curved shape, this in turn will allow me to 'tune' the back plate as I do on the archtops by scraping wood away at the outer edge, letting the whole plate vibrate more freely, I think Taylor employ a similar technique on their soundboards but only use a narrow groove, where as mine will be more like a traditional recurve. It may not need to be very deep at all,I won't know until I start tapping the top and tuning the back. As I say, it's all one big experiment.

That bldi lino hasnt changed in the Chem Dept since I was doing Chem 101 back in 1983.

It was a cheap job lot Chem-safe lino doesn't undergo any radical design changes unfortunately, they've just spent millions doing the gaff up (woodshop included) and the floors still look the same.But we did end up getting rid of the crappy lino tiles in our workshop for this shiny 'one piece' stuff

[Allen]

Thanks for taking the time to document this Nick. I'm going to be watching with great interest.

[Nick]

Thanks for taking the time to document this Nick. I'm going to be watching with great interest.

Thanks Allen & I must admit I'm quite enjoying having to think about what would be an interesting picture or point to post about. The nut's and bolts of the build are much the same as any other Acoustic but hopefully anything I do that is different will be of use or interest to somebody else I don't mind sharing plus I'm always open to suggestions/ differing viewpoints so I could incorporate anybody elses ideas or even correct flaws others can see with my design that I can't (can't see the bleedin' obvious for the weeds sometimes).
Which reminds me, those Mahogany linings look a bit ragged close up, it's out with some sandpaper tomorrow I think! Even though it'll be closed up in the rear chamber, Call me anal but I hate seeing "loose ends".

A Question for you, when you cantilevered the fret board on one of your builds, how far off the soundboard did you make it? I'm thinking 1.5-2mm, I thought this a reasonable amount and wouldn't give the player too much of a 'step up' off the top to feel uncomfortable?

[Hesh1956]

Very interesting and fascinating project Nick buddy and beautiful workmanship too - nice going!

[DarwinStrings]

You're anal Nick. Just the same though you have my attention and I doubt you'll have much trouble keeping it on this one.

Jim

[kiwigeo]

Nick,

Those linings need to end up looking as smooth as that Chem Dept lino. Micromesh should do the trick.

[J.F. Custom]

A double backed guitar with Mahogany for the 'outer' back and sides. A Maple 'inner' back (with the idea of giving the tone a bit more cut). Maccaferri used an inner soundbox on his design in order to isolate the back's movement from the dampening factor of the player and hence increase volume. I have used the same principle but just used a seperate back rather than building an inner box.

Hey Nick,

Nice work so far as is to be expected from your previous work. I too will be watching with interest in how all these mods eventuate for you, especially as I am planning to build one.

I'm curious though in the double back. If I understand correctly, you are wanting to reduce the dampening effects from the player? Is that the main drive behind the double back for you? Are you also concerned with the dampening on the soundboard? Do you have anything planned for this?

I know you mention that Macca used to build with an inner soundbox though according to the old thread, most players removed these. I'm wondering what effect the extra mass in your deisgn will have. You mention you will use three braces on one back with four on the other. This will add considerable mass (guitar wise) which will have quite an effect of its own. What about some sort of 'leg' bevel, similar to the arm bevel seen on some classicals and steel strings - working in a similar principle as the violin chin rest as an alternative means to the same end without the work and mass? But then, where's my sense of adventure??

None of this is criticism btw and I hope you take no offense - just grasping at the whys and hows of your decisions...

I love the experimenting ambition you have and expect a full report on your conclusions at the end!! Having said that, isolating which mod had which effect will be challenging to say the least
It's looking great Nick, good luck with the rest, I look forward to more posts!

Cheers,

Jeremy.

[Stu]

Thanks for posting in depth pics and explanations , Nick.
Loving this stuff.

I'm glued to my seat............no.. literally !!!!!! Bloody C.A.


cheers, Stu

[Nick]

Thanks Jeremy for your comments, firts let me congratulate you! I was on the carba-tec site the other day & an add at the top rolled over for Titebond, I thought "I've seen that guitar before" & a quick visit to your site confirmed it for me. :serg
Your comments aren't criticism they are all valid points & I guess the reason why luthiers can all build the same guitar differently, we all have different reasons for doing things.

I'm curious though in the double back. If I understand correctly, you are wanting to reduce the dampening effects from the player? Is that the main drive behind the double back for you? Are you also concerned with the dampening on the soundboard? Do you have anything planned for this?

If I understand you correctly you're thinking of the player's arm effect on the top causing dampening? i.e corner bevels e.t.c. At this stage I'm not looking too deeply into altering the soundboard's construction other than lightening bracing but how far I would take that without comprimising strength is an unknown at this stage so I'm sticking to the tried and true for this one (although I have removed one of the braces completely from the top on my previous build which had a positive effect).
The dampening effect is not the only drive behind doing a double back hence the reason for putting bracing and linings on the back, I wanted to see if presenting a totally 'clean' back face inside the box has any effect on the voice of the instrument, I suspect minimal. But yes I am hoping for an increase in both response and volume. I know from the archtops I've made that dampening the back has quite an audible difference on the sound out the front of the instrument.
As for the added mass of extra bracing, whilst there will be some increase in weight, the braces won't be as high, the originals & Micheal Collins make them 19mm high where as I'm planning on 11.5mm, the reduced height should lighten each brace so the extra weight will only be in the effective region of maybe adding an extra brace or two.
I have thought about bevels for the player but any leg bevel I would actually make an external support similar to the violin chin rest you mention. My experience of the ones I've made so far from players is they would like the box to sit higher up. Because they are a smallish instrument they actually have to lean quite a way over them to play them and the two guys (one was my first Selmer customer) that play gypsy Jazz (well!) here in Christchurch actually use a classical footrest to raise their guitars up to a comfortable level, hence why I would use an external device.
You are right, doing a build this way will make any positive effects hard to pin down to any one mod but unfortunately I haven't got the luxury of being able to build several guitars with a new mod each time, so at this stage it's all or nothing

And thanks also Stu......Stick with it

[J.F. Custom]

Hey Nick,

Thanks for the reply and insight.

Too right dampening on the back has an effect on the sound produced so it will be interesting to note how much this addresses the issue. You are right that the smaller size of bracing will not be much additional weight though you forgot to mention that the weight of the additional back itself needs to be factored in too! This may end up a bonus - who is to say? Some luthiers build extra weight into headstocks and necks etc to increase sustain among other things so perhaps this will occur here too, though the coupling to the strings is not direct as in the headstock for example. The clean look will be cool in any case It'll keep the punters guessing too. Some sort of external brace was what I had in mind - perhaps one could be made that lifts the instrument up and addresses dampening of the back and front all in one... Mind you - it wouldn't look very appealing most likely and certainly not the nice clean effect yours will have. Look forward to the results so can you stop replying to time consuming posts and get building?

I'm for all or nothing! I suspect there are not too many luthiers who can afford to build complete instruments just to try a minor change each time - purely for research value without commissions. I think we chose the wrong profession to get rich

Also, the bridge. Did you use the adjustable style on your archtops? Bob Benedettos thoughts on this are interesting as I'm sure you've read/watched. The solid violin style makes sense to me acoustically (!?) but you do lose the adjustments. I recently made a solid style bridge and tailpiece (all ebony) as a mod for an Epiphone Archtop that had an adjustable bridge and steel tailpiece. The difference in tone and volume was very obvious and pleasing. Had a photo somewhere but can't find it at the mo, can't imagine why - it was called something completely memorable like DSC_17994.jpg

BTW, *shudder* - you are delving into a dark and disturbing history with your congratulations which I assure you, is not necessary - but thanks anyway

Jeremy.

[Kim]

I reckon Nick should get this month 'Clever Bugger' award, the prize is he gets banned so he stops making everyone one else look so average.

Well done Nick, love u'r work, love u'r tablesaw (you lucky dog), and the lino is not to too foul either. Very clever of you to vent the cavity and stagger the back braces IMO. Not that I am in any way qualified to comment but I think your right on the money with your thoughts and ideas on this one and it's really good to watch you bring it all together.

Your a sharp and skilled builder Nick, so what you post here will always be interesting and most welcome by those of us lucky enough to share your offerings.

Keep it up mate.

Cheers

Kim

[Nick]

Woohooo My first banning
Thanks Kim I'm flattered with your comments & Yes I am fortunate to have an employer that lets me access & use the equipment, tacky lino an' all .

Jeremy the adjustable bridges ala Benedetto are what I use for my archtops, they're surprisingly easy to make and do a good job. I agree with your thoughts on the solid bridge though, obviously not going to get a full transfer of frequencies that you get with the solid bridge but the Selmer Maccaferri's only have a small footprint at the bridge/top contact point anyway but I am giving a 'work around' some thought for this part too.There is a wedge style bridge out there (I forget who "invented" it and currently uses on their guitars) but I think it's patented so I can't use that!
Also as you say Benedetto's thoughts on the bridge/tailpiece area are both very interesting and informative. The section he has at the end of his DVD set on his talk at a guitar school about these issue's were brilliant, not only did he give his thought's on the matter but then went on to prove them with his 'inferior' pine archtop. Even the difference between metal vs Ebony tailpiece was marked and even the size of the bridge's foot print and it's mass had an audible effect.

[J.F. Custom]

I'd have banned you but I don't have the supreme power...

I really look forward to seeing how this turns out Nick. I'm impressed with the level of thought and workmanship you craft with. I hope you take lots of photos on the way, and post them so I can looksy err, and others of course...

With respect to the wedge design - I believe you are referring to the Brekke (by Vern Brekke) bridge of Weber Instruments - patented to Sound to Earth, Ltd. Many makers use variations on the theme (avoiding patents?) such as Peter Coombe on his mandolins. Having said that - Benedetto still uses the adjustable system for the most part, possibly only due to customer demand though.

Geez, poor old 'inferior' pine archtop. Bob B if you happen to be reading this, I'll happily take such an inferior instrument off your hands

Jeremy.

[Nick]

Well here I am at the next stage of the build, the inner back halves have been jointed and I've cut the outline to roughly the outside dimensions of the sides. Once it's been braced I'll sit it on the back of the guitar and add a temporary brace down the length to simulate the final back curve. Then working off the sides (as reference), mark an outline 2mm in (the thickness of my sides) around the perimeter.This should, hopefully give me a back that fits neatly inside the box without gaps between it & the sides.
Some more pickies for your perusal.
The three inner back braces just sitting on the curly maple back before gluing, they have a 12 foot concave radius to them. The tailblock end brace is wider (by 3mm) than the other two to hopefully add a little extra mass across the lower bout to bolster up & focus the bass response of the plate.

I haven't taken them right to the edge so that it will give me some room to add a recurve if needed to the back to make it responsive.
I've also scooped the sides of the braces and triangulated them to lighten them but still retain some longtitudinal strength and hence their curve/shape.

Another blurry shot sort of showing the same thing.


Then finally a shot for the jig perves (you know who you are!) my rough and ready method for shaping the curved/scooped sides on the braces. The MDF behind the brace has the same 12' curve as the bottom of the braces so that the braces "rolls" past the sanding drum at the same height all the time.

Like I say, it's real rough and ready, I may never reproduce this style of brace again so I couldn't see the point of making a permanent jig (does that make me a luthiery outcast?? )

[Nick]

Whoops double posted

[Nick]

Braces are all glued on and I made a 'spine' brace to get the longtitudinal arch,plus it acts as a clamp to hold the inner back whilst I mark then trim back level with the sides so that my compass will follow the profile of them accurately.


Once the inner back was trimmed, I set the compass to 2mm and followed the sides around, this hopefully would give me the right shape of the inside at the shelf where this back will sit.


Once I had this line I carefully belt & drum sanded it back. There are still a few gaps between the inner back & sides due to having to remove the spreaders to fit the inner back in, & it never sat back in the mold exactly the same as I had it before removing them. I'm hand sanding the high spots down & things are getting closer to where I want them to be.
Here are a few shots I couldn't resist taking, nothing's glued in yet and as I say,there's still some more fitting work to go but it gives you an idea of what I've been prattling on about if you couldn't picture what I meant
From the back with the inner back sitting on it's 'shelf'


The "air" slot in the tailblock end from both sides of the inner back.





a slightly blurry picture of how it will look once it's all glued in.


& finally a shot showing the gap between the two back plates using my radiused MDF form to represent the radius of the outer back.

[J.F. Custom]

WOW!

This is great work Nick. Very inspiring - way to go!

What a schmick unit.

Jeremy.

[kiwigeo]

If only people knew what's REALLY going on behind the drab walls of Canterbury Uni's Chemistry Department!!

Impressive and intriguing stuff Nick.