Shaping the sides of a Selmer/Maccaferri guitar

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Shaping the sides of a Selmer/Maccaferri guitar

Postby Darren King » Thu Apr 25, 2019 1:42 pm

I am building a Petite Bouche copy with a sharp creased (rather than wider bend) pliaged soundboard. Has anybody created side templates which would allow me to get the sides more or less to shape before final sanding? The geometry of these guitars is pretty odd to say to say the least and I am struggling a little to understand exactly what is going on. I have both Michael Collins' book and François Charle's plans but both show different geometries with regards to the shape of the braces. Michaels Collins' pliage form is quite different to mine so I am probably going to work more closely to the François Charle spec and therefore I am not sure if the raised block technique would necessarily work for me. Ideally I want to come up with a process or jig that will allow me repeat the shaping of the sides accurately rather than it being a fairly subjective 'by eye' exercise each time.

Has any one been through this process and come up with a definitive method?

I have attached a few pictures showing the pliage press that I have built and the resulting glued up soundboard. The press has three pneumatic cylinders that push down a heated 1" aluminium tube onto the soundboard which is then pressed into an 8° bevelled machining on the press bed. There is a little spring back but the resulting 5-6° pliage is very stable and the process very consistent. It takes about 45 seconds at 2 bar pressure to the cylinders which equates to about 120kg of pressure on the soundboard and I place a strip of damp cotton fabric along the line of the pliage under the pressure bar so there is an element of steaming going on as well as the heat.

Regards

Darren
Pliage Press.jpg

Press Bed Machining.jpg

Pliage Press With Soundboard.jpg

Glued Soundboard.jpg
Darren King
 
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Re: Shaping the sides of a Selmer/Maccaferri guitar

Postby Chuck Tweedy » Fri Apr 26, 2019 12:17 am

omg - nice press!
you may have to make your first guitar first to get a side template.
or find a very similar guitar in a shop, and trace the sides - ask first :-)
Likes to drink Rosewood Juice
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Re: Shaping the sides of a Selmer/Maccaferri guitar

Postby Bill Raymond » Fri Apr 26, 2019 12:32 am

Shaping the sides is really easier than is explained in Collins' book. Essentially, the soundboard surface of the sides lies in a plane, i.e. there is no shaping, they're just straight--except for the cutaway area. Tracing along the side from butt to neck, the edge of the side is straight until you reach the cutaway. At the cutaway, the edge "rises" as it enters the cutaway, and then falls back to be even with the edge of the non cutaway side. This is done because of the transverse arch of the top over the upper bout. If you lay a straightedge across the inside of the braced top at the "horn" of the cutaway, you can measure the height of the arch from it and cut your side accordingly. Same with the back; the sides are not cut to accommodate a spherical dome, but are straight up to the cutaway. I hope this explains it in enough detail for you. Good luck.
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Re: Shaping the sides of a Selmer/Maccaferri guitar

Postby Bill Raymond » Fri Apr 26, 2019 12:46 am

P.S. There is no contouring for the pliage. Although bent at the center of the top, the bend flattens at the edge to meet the straight sides. Francois Charle showed me a petite bouche when I was in Paris too long ago, and this feature was quite apparent. Apparently, Maccaferri wanted to make a true "cranked" top as well as a molded arched back, Selmer couldn't or wouldn't do it. When Ibanez made some Maccaferri models that he endorsed, they did make a cranked top. As far as I know, the backs were laminated flat, as Selmer did it, and then braced to be arched.
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Re: Shaping the sides of a Selmer/Maccaferri guitar

Postby Darren King » Fri Apr 26, 2019 12:14 pm

Hi Bill,
Thank you very much for your feedback, that's very interesting and useful. If I understand you correctly, the top and back adopt the lateral geometry of the braces and are pulled down to the straight edges of the sides, with the longitudinal curvature of the sound board and back being created by the angle of the neck and tail blocks and the pliage. The only part of the sides that needs to be shaped is the cutaway and the opposite side towards the neck block where they are running parallel to top brace 1 and therefore need to be shaped to the same radius. If this is the case then I think I have a plan!

Could you explain exactly what you mean by a 'cranked' top? Would this be one where the sides are shaped to the same angle as the pliage? If I could find an Ibanez Maccaferri I'd go and have a look but they seem to be almost as rare as the real thing!

I have another question relating to the shape of the top and back braces. I have taken the measurements from François Charle's plans, for both the Petite Bouche and the D Hole models, and the main difference in their geometry seems to be that the curvature of the sound board braces of the Petite Bouche gets tighter towards the neck (R2050 down to R1920) whereas the soundboard of the D Hole does exactly the opposite (R1620 out to R1815). Is this the accepted practice amongst makers of these instruments or just an anomaly? The plans for the Petite Bouche only show the shapes for front braces 1 & 3 and back braces 1 & 2 but the difference on the D Hole plan (which shows all braces) is certainly there.

Thanks again for your help and advice, it's much appreciated.
Regards
Darren
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Re: Shaping the sides of a Selmer/Maccaferri guitar

Postby Bill Raymond » Fri Apr 26, 2019 11:37 pm

Darren, I believe you have understood what I attempted to communicate re: the shaping of the sides. As far as the longitudinal arch, I haven't studied the petite bouche plans of late, nor compared them to the grande bouche. I've only made grande bouche guitars. If you draw a side view that accurately allows for proper neck angle to establish sufficient string clearance, that will then dictate the height of the transverse arches. I do recall that my friend, Peter Davies had had a similar question about the height of the brace arching and had some email correspondence with the draughtsman who drew the plans. I don't recall the details, but it seems that there was some discrepancy that crept into the actual drawings, so I would suggest you work it out yourself from a profile drawing; if you should deviate some from the actual Selmer construction, it shouldn't make any difference in the sound of the guitar.

A "cranked" top is as you surmised, one where the sides are pared away to accommodate the pliage, much as in an Italian bowlback mandolin.

I'll take a look at the 2 plans and compare the longitudinal arch to see just what the situation is, but I suspect it' just a feature of the drawing.
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Re: Shaping the sides of a Selmer/Maccaferri guitar

Postby Bill Raymond » Sat Apr 27, 2019 1:14 am

I pulled out the plans for the Selmer models and compared the longitudinal "arch" of the top in each. It is drawn as I thought: there is no real "arch", but instead, the side view of the top rises in a straight line from neck block to pliage, then falls from pliage to but in a straight line in both models. I suggest you follow this configuration and make the lateral arch of the braces to conform to this geometry, ignoring the drawings of the braces.
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