Official Luthiers Forum!

.

Ok Duders...

This is a Turtle back...sorta like a bowl back but way way different.

Bowl backs have each stave identical...well most of them... and the staves have one curve in them.

Well a Turtle back has no 2 staves the same...other than left and right...and looks like a Turtle
shell . Staves are all different lengths, and different arcs bent in to them and a twist into the stave on both ends.

They are compounded curves...first the arc and then the twists.

This instrument is gonna be an 14 stringer, a Sympatar, 7 above the finger board starting with a low C string and 7 sypmathetic strings under the fret board and tuned to A at 435 hz. So chew on that for a while. Gee me might even fret the sucker...just for to make it easier to play

I do trial and error, scribe, cut and fit and fidget around. Wouldn't have a clue how to do a drawing that someone could follow. I ain't got the grey matter to figure out the maths but I suppose it is possible.

Here be drawing.






Here be pic of standard bent stave on right, then a twisted stave and the one I am holding shows the twist and the fact that the glue edges are not at a 90 degree angle to the face and so the two edges and two sides form a parallelogram.





Here I have taped on two sticks and taken the shot from end to end to show the extent of twisting on some of the staves.




a bent stave






the first stave has no twists...it starts on stave 2 and 3 and then it really starts on the 4 and 5 - right and left side which you can see in the upper left of the photo.




the 4-5 and 6-7 stave are pretty much the same....but with staves 8-9 the arc takes a recurve cure at one end ...gentle at the wide point and not at the base of the instrument.


Here is blank unbent stave #8 with its penciled in ark





Band sawed and being bent on a BBQ starter shoved into a 2 inch exhaust pipe. Works great!





Next shot is the start of the test fitting and shaving by shoot edge on plane and bending and twisting and shooting the edge until it fits .






Rough fit





see where the ends have to now get the twist bent in









As it is impossible for me to calculate the maths for a compound curved edge linings...the lined kurfing was installed a half inch proud of the rib and is carved and filed as me go along for each individual stave.





Takes about 1-2 hours to hand scribe, bend, twist and fit a stave to the previous stave and on to the rib before it can be glued into place.




The next photo shows the recurve starting between stave 7 and 8.







The next three pics should make it easier to see.













Here you can really start to see the turtles shell. This was taken looking down the neck from the back of the nut.




So there you have how to bend up a turtle back. It ain't a piece of cake. However if approached with the right attitude and patients is not that hard. Medium to advanced bending skills and edge jointin ~ shooting the arc on that bent stave ....simply because the staves start to show more and more end grain and end grain is easy to shoot a joint in one direction and a real challenge in the other.


Blessings
the
Padma

_________________
.

Audiences and dispensations on Thursdays ~ by appointment only.


.

That Yurtle wood suess you fine
Ok puns over. Great pix, very neat looking! Can't wait to watch the progress.
What kind of temps do you get out of the grill starter? I am using a propane torch right now. I'd rather not use open flame if I can avoid it

The,
You must have the patience of a saint. If you weren't so far away I'd let you ride my motorcycle if you'd let me try and fit one of those staves.

John, my bending pipe is the same as The Padma's, They can go to about 500f.

Steve

I love it!!
Would love to hear how it sounds when finished.
The thing I love about this forum is you learn stuff you weren't even looking for - that charcoal starter, for example. Iv'e also been using an open flame (found the propane didn't burn hot enough - took forever to heat my pipe, so went to the hotter gas torch. But I also am not real happy about an open flame surrounded by all my wood, sawdust, etc. I'll give it a try.

Cool!
You'll be ready for a nice mahagany runabout soon! Great effort!

_________________
Dave
Milton, ON

Thank dudes,

There are 2 types of BBQ charcoal starters...one has a ceramic coating and is useless in that the elements have to be bent to fit into a 2 inch pipe. This bending will break the ceramic. The non ceramic or metal type are the type to use and are best put into a vice , heated up and then the vice closed which bends the heater elements towards one another making it easy to fit into a 2 inch pipe.
I hot my heater for Reverend Jim's Junk Store ( supports his soup kitchen) for $5 bucks and the pipe for free.

Some dudes go all out an put in a rheostat to control the temp and mount it all in a fancy box. I don't use a rheostat simply because I got use high temps in bending with a propane torch heating up and old cooking pot. Yes I get burn as can be seen in the pics. However all my sides and staves are much thicker than the usual guitar rib or side, as I use this thickness to then sculpt the sides into a curve or do a low relief carving into so therefor burn is not an issue for me. This thickness dose not make for an easy bend however patience does.

I have done 8 staves so far...2 have been rejects. Thats about 20%...and is not bad in my thinking simply because it is such a fit and fidget operation. The rejects are viewed more like a trial run learning process. One was ruined simply because I lost concentration on what I was doing.

Steve, as a young child I was fascinated by bikes, finally got a BSA 500 and realized I was terrified to ride it. Then it hit me that when ever I saw a bike as a child my parents would instill the fear of riding ... the dangers and evils and all that negative stuff. It was deeply ingrained into me. Just couldn't shake it no how...couldn't even relax on the back of one....so sold the bike. Just one of them "oh wells" in life. But I would be glad to let you bend a stave or two regardless.


Oh and I forgot to mention ... I am bending spalted birch....I bought a 20ft stick a 7 years back and had it milled up for different purposes...unfortunatly, it got wet a few times while air drying and of course birch spalts easily. It also has worm holes which if too close to the edge of a bend will cause cracking in the stave.

Blessings
the
Padma

_________________
.

Audiences and dispensations on Thursdays ~ by appointment only.


.

.
So here is the Turtle back off its work board.
The overhand has been rough trimmed.
Next I will continue to sculpt the back of the instrument with scrappers.












Removing the weight by trimming the curfing back. I over curfed in order to have some meat for trimming and scribe fitting each stave to the rim.












Conclusions. Well first thing noticeable is the weight is much light than the first bowl back of a few weeks ago. I am very pleased with the seams...came out much better than I had hoped for......near perfect... only one small spot showing light that maybe a sliver of wood or filler will take care of. Some of the curves are a bit drastic but they still work and can be worked down more gracefully with a scraper. The bulging back and the recurve actually tilt the instrument so that the fret board is quite visible without tilting the instrument or learning forward...you know "guitar neck" The shape is interesting. Don't know if I fancy it. On the next one I will start the twisting on the second and third staves, use narrower staves and lessen the recurve, this will allow for a slightly larger volume enclosed and a more graceful curve to the back.

Ok, on to figuring out some sort of top for it.

blessings
the
Padma

_________________
.

Audiences and dispensations on Thursdays ~ by appointment only.


.

My gosh that looks complicated!!!

_________________
http://www.casperguitar.com

Well me ain't posted to this since April of 2009...thats over two years...oh well.

Me pulled out a lutz top of some flavour or other from Mario da Costa at sprucetonewood.com, was so long ago me no remember, glued her up and thicknessed it.

This morning me finally resolved the rosette for it. It is based on one of my old mandala paintings.

see mandala painting





see resolved rosette.








Me just printed it out, shellacked the sound board and gonna glue her down in a few more min.
Is gonna be a fun carve...stick around for the ride.


blessings
Padma

_________________
.

Audiences and dispensations on Thursdays ~ by appointment only.


.

In it's natural habitat! Free the turtle-backs!

_________________
John Mayes
http://www.mayesluthier.com

Such a neat instrument - I love the way you are doing it.
Neat inlay art, too. Reminds me of some mid-80's King Crimson album artwork.

_________________
"Act your age, not your shoe size" - Prince

Thanks Chris,

glad it makes you happy.

ummm sorry to disappoint you though, but thats not an inlay design... me gonna carve it into the top. The technique is called an incised sound hole.

Sorta like this one from a lute.





blessings
Padma

_________________
.

Audiences and dispensations on Thursdays ~ by appointment only.


.

Very cool! I've been thinking about doing a soundhole like that. Or maybe a parchment rose.

That's some mighty impressive bending and joining work you've done. Love the shot of it in the grass

I think you are having way too much fun with that!

Cool build!

Trev

_________________
http://www.PeakeGuitars.com