Rib Bending

chris clay · #1 11-11-2007, 02:33 AM

i am about to start bending the ribs for a 3/4 upright bass that i am building.
the ribs are 2mm thick sycamore.
my design for the bass incorporates violin type corners.
should the ribs be bent such as the fit to the blocks is
(a) slightly overbent so that they need springing to fit
(b) slightly underbent so that they need pulling in to fit, or
(c) like in Goldilocks and the three bears...just right.

any thoughts and advice are welcomed

Ken McKay · #2 11-11-2007, 08:51 AM

Quote:

Originally Posted by chris clay

i am about to start bending the ribs for a 3/4 upright bass that i am building.
the ribs are 2mm thick sycamore.
my design for the bass incorporates violin type corners.
should the ribs be bent such as the fit to the blocks is
(a) slightly overbent so that they need springing to fit
(b) slightly underbent so that they need pulling in to fit, or
(c) like in Goldilocks and the three bears...just right.

any thoughts and advice are welcomed

(c)

Certainly not overbent. Don't need to get the bouts exactly bent though, underbent is okay on an outside curve.

Did you first bend the C bouts and glue them in?

Good luck with it!

chris clay · #3 11-11-2007, 10:43 AM

thanks for that Ken

no..i haven't bent any of the ribs yet although i was intending to get the C bouts bent and glued first.

i've been practising on some of the narrow offcuts that resulted from cutting the rib stock to width

my other main concern is avoiding singeing the wood..but i guess its a matter of taking it slowly...like most things to do with building this bass of mine

Don Harris · #4 11-13-2007, 08:42 AM

When I first started practicing bending ribs, it seemed like I'd not have enough heat...., nothing..., nothing..., nothing..., SCORCH!!! (or crack!). It seems like there's a sweet spot temperature wise that you can find with practice. Also, getting the wood wet enough without getting it too wet is tricky. Not wet enough and it doesn't want to bend. Too wet and you can get a lot of cross grain ripple and distortion. Some of the first ribs on the bass I'm building are a bit wavy (cross grain). They got better as I went.

I'd recommend getting the ribs bent so that you are happy and then do some touch up before you glue. I didn't want to clamp any tension into the instrument- to force it into shape.

This is my first instrument, so consider that before you take my advice.

chris clay · #5 11-13-2007, 12:55 PM

This is not only my first bass, Don, but my first instrument ever...hence the go-slow approach. there seem to be so many conflicting opinions about how to best bend the ribs but one thing is for sure and that is that probably the only way to find what works best is by doing it... its just the thought of that expensive wood that makes me cautious.
i agree that it makes sense to not build any un-neccessary tension into the instrument and that therefore it is important to get as exact a fit as i can achieve without relying on the clamps to make it good. when you talk about touch-up before gluing are you meaning rebending where needed ?

Don Harris · #6 11-13-2007, 02:44 PM

Yes, I was talking about re-bending to get it even closer. For me, after spending a bunch of time over the bending iron, I was happy to be close and done. It was nice then to come back to it fresh and fine tune after the fact.

This is my first instrument too, but I've spent an awful lot of time thinking and reading about it over the years. Good luck on your bass!

**Matthew Tucker** · #7 11-13-2007, 02:44 PM

Its hard to get an exact dry fit, but you can get close. The clamping stage is important in bringing the ribs tightly onto the block, so the clamping cauls etc and angles need to be well designed. I used a heat blanket to warm and soften the ribs a bit during glueing, this helped me get a good close fit. Some makers thin the ribs a bit more in the blocks area to make the tight curve easier to bend. That makes sense. 2mm is pretty thin enough I'd say. By all accounts, a gamba shape would be easier to make. What model are you making, Chris?

Darren Molnar · #8 11-13-2007, 04:11 PM

All great advice so far.Also, do you have some kind of backing strip made, to make a bending sandwich? that is, heating iron on the bottom, wood to be bent over that, backing strip (aluminum flashing works) over the wood as a suport for bending. And How's you're camera working?

chris clay · #9 11-14-2007, 02:50 AM

Thanks for the interest everyone.
At the ripe old (young) age of 66-about a year ago-i got hooked on double basses and can't seem to get enough of being around them...hence the urge to build one
I did buy some plans off an amateur builder here in the UK but soon discovered some fairly unhelpful errors in the layouts.
Being a sculptor at heart i also wanted to make the shape my own and so drew up my own plans based on photos of basses whose shapes appealed to me...i guess you could call it Italian in style.
Mathew, i like the idea of the heat blanket...is this something you made yourself or is it another of those expensive specialist tools that make one-off building so pricey ?
Darren, i've been able to acquire some stainless steel pieces to use as backing as you suggest...they do seem to make it more difficult to sense that moment when the wood wants to bend
i have been keeping a photo record of the building and can see if i can work out how to post them to site...but i'm not sure where they would best be posted- which forum etc

**Matthew Tucker** · #10 11-14-2007, 03:32 AM

You need to search this forum for "heat blanket" and you'll find about twenty threads where this is discussed in more detail than even you might need to know!

start here: bending iron advice

Don Harris · #11 11-14-2007, 06:42 AM

This is where I bought one: http://www.omega.com/Heaters/pdf/SRMU_HEATER.pdf (about 4 pages down). I got the 10"x18", 5 watt per inch blanket (SRMU051018) for about $60 USD. I also got a 30" long one for the lower bout, but ended up only using the heat blanket on the c-bouts. I wanted to have the experience of doing some of the ribs on a bending iron. Next time I'm not sure which I would do. Maybe a combination again.

chris clay · #12 11-20-2007, 09:26 AM

This is a very late reply to Matthew's question about what sort of bass i'm building...reasons of grappling with the technology of posting images i'm afraid. However this is yet another attempt which may yet be successful.
This design draft was never intended to be a working drawing but became just that by default.I was able to draw up the mould plates using this as a guide.The dimensions in bold type are millimetres
I accept that life moves on and this thread has probably run its course but i would be happy to hear any comments on what is very much an original and untried layout

Don Harris · #13 11-20-2007, 09:36 AM

Only my two cents of course, but the upper and lower bouts look a little narrow to me. The whole thing looks a little squished from side to side.

**Matthew Tucker** · #14 11-20-2007, 12:45 PM

Narrow was my reaction too, although there are plenty of old narrow basses in Elgar's book.

I'm always interested in FF placement, angle, spacing and "FF tab" angles and corner angles, analysing how they sit geometrically, why they look balanced on some instrument and not on others. Basses are interesting, aren't they?

I'm looking at your diagonal lines and where you put the top of the FF.

Darren Molnar · #15 11-20-2007, 01:44 PM

Design is fun and fascinating to me, Thanks for sharing Chris. I'm looking at you're curves. Are you freehanding them, or is the design based on some kind of compass construction. I have a feeling that the appearence of narrowness comes from where these curves are sitting, and less so, the actual measurements

chris clay · #16 11-20-2007, 03:28 PM

every two cents worth is worth having Ken...I think some of the squishy effect is the result of distortions to the image in the down/uploading processes.
this is the plan of the mould plates so there will be close to a further 1/2" to each of the bout widths for the finished overall size of the bass.
I've just checked the actual finished sizes of the mould as it was eventually made and the top bout is now 18 3/4", the lower bout 25 1/2" and the body length from endpin block face to neck mortise face is 42 1/2".
the violin corners do lead towards a slimmer looking body shape as well.
thanks for your interest

chris clay · #17 11-20-2007, 03:50 PM

Don, my apologies for attributing your two cents to Ken.

Matthew, the f-holes were not positioned with any great precision on what was never meant to be other than a first sketched outline.There seems to be a scarcity of advice available on the theory of f-hole placement and I have to acknowledge my indebtedness to Chuck Traeger's guidance for the probable way that I will tackle the placement calculations, always with the proviso that it will have to look ok to me from an aesthetic viewpoint.

Darren, the curves were created by establishing the extreme points of width and length as per the design sketch and then freehanding the curves to fit these points. It was important to me that there was a large measure of being guided by what I can only call my own aesthetic judgements

**Damon Rondeau** · #18 11-20-2007, 04:27 PM

OK, when it comes to bass shapes, I actually have a little bit to contribute...

Some years ago I got heavy into this subject. It meshed well with some interests I have in history and in the sociology of knowledge, so I went kinda deep down the hole...

Here are these two images of basses. One of 'em (the second one attached here) belonged at one point to our own Don Higdon, the other is a Bob Ross bass. Over top of the images I've overlaid a grid work and some circles. The thing I was trying to get across (to myself -- I've never really let this out of the lab very much, so to speak) is that these two basses seem to have shapes that consist of modular circles. That is, these circles all have a radius that is an even multiple of some number. So, for example, the circles are 4 modules, 2 modules, 5 modules, etc. Some of 'em aren't even, but they're close: 1/2 module. I've never pursued this too much, but my thinking is that "the number" comes from some other proportion -- mostly likely some kind of golden proportion type ratio involving aspects of the scale length.

Other people from the violin world have gotten heavy into this stuff. Too heavy, some of them.

What's the practical import? Well, back in the renaissance days it wasn't too common to find tradespeople -- even architects and engineers -- who had today's kind of competency at math and mechanical drawing. Measurement systems, too, were multitudinous and extremely local. You couldn't give an apprentice a bunch of formulae and have him lay out a complicated piece of work. But you could develop a layout method that used modular geometry and you could easily assemble good-looking (and holy) designs and layouts for almost any size instrument.

Modular design and construction methods were invented by the Romans -- it's how they built so many awesome structures using less-than-sophisticated labour. I think the Rennaissance craftsmen must have revived or reanimated a bunch of these concepts.

Anyway, my working hypothesis is that instruments that adhere to the modular concept are the "most pleasing" to look at. I certainly saw some ugly ones that weren't close. But I looked at a lot of instruments and there's likely something there.

Some people who are into this type of thing want to say that classically-designed instruments sound better, but I'm not touching that one with a ten foot pole.

I think all that stuff about f-hole placement in really old instruments probably works on those old modular principles, too.

Darren Molnar · #19 11-20-2007, 04:42 PM

Here, you'll like this ,Damon;

http://www.fiddleheadstrings.com/mic...t_1_8_sept.pdf

Darren Molnar · #20 11-20-2007, 04:59 PM

Francois Denis is the man who a lot of us think unlocked the key to classical design.

His book is out, called "Traite de Lutherie"

And once again, showing that what is new is old. Pythagarus old.Before standardized measurement, designers thought not in numbers, but in comparative ratios. As in width of upper bout to width of lower bout, 5 to 4. Lots of ratios are used in the design of classical instruments, not just the golden ratio.

Common ratios like 3 to4, 1 to1, 2 to 3, 7 to 12, etc. If you read music, you recognize these. Very elegant.

Here's one of my violas.