Violin Forum/Message Board

Mark Sullivan · Posted: Thu Jan 28, 2010 7:16 pm Post subject: Rib Bending

I am bending c-bout violin ribs about 1.1 mm thick on a common aluminum bender.
Water will just jump off.
Thin stainless backing strap.
I have one bent so far not using water.
I have the second rib upper bout tight bend close and the middle close.
The lower bout is not yielding to the heat like the first tight bend.
The first tight bend will yield to heat within 15-30 seconds, the middle in the same time. The lower bout does not want to yield after 60-90+ seconds.
I have not scorched the rib yet, I have scorched some earlier attempts.
Should I turn up the heat, add a little water or some combination of the two?

Thanks,
Mark

Michael Darnton · Posted: Thu Jan 28, 2010 8:31 pm Post subject:

Turn the heat up first. A little scorching isn't a problem, since it can be scraped off. I keep my bending iron at the point where the wood will burn after a couple of minutes.

Then, go slowly. Preheat the wood thoroughly on the flatter part of the iron to the point where it will bend, before you move it around to a more curved spot to bend it.

actonern · Super Member Joined: 15 Aug 2007 Posts: 444

Michael:

Have you ever tried microwaving the ribs? I experimented with heavily flamed maple and dipped the ribs in water, followed by a 40 second microwave. They came out very steamed and easily yielding to the bending iron.

E

Michael Darnton · Posted: Thu Jan 28, 2010 10:59 pm Post subject:

I haven't tried that. It's an interesting idea, and I'll try it at the next opportunity. Thanks. I hardly ever hear an idea that's totally new!

Mark Sullivan · Posted: Fri Jan 29, 2010 1:31 am Post subject:

I turned the heat up and practiced on the scrap.
The higher heat made things happen faster and I realized I had cut the c-bout blanks too short. I was working too close too the ends trying too save material for the inevitable errors. I was caught in a loop..javascript:emoticon(' Laughing

')
Thanks for the help.

Mark

BK · Member Joined: 10 Apr 2011 Posts: 60

actonern,

I experimented with the microwave method, and I found it to work surprisingly well. I think the microwaves really have the ability to penetrate through the rib wood evenly and it does seem to enable you to bend the ribs easier on the bending iron.

However, I have become a bit frustrated with bending the C bout ribs. When I bend the C bouts they always seem to break on me. I tried thicknessing the ribs down to 1.5mm and then 1mm, microwaving them, not microwaving them, cutting out the negative space of the C bout arch to bend the ribs on so that the ribs had some backing, soaking the ribs for 15 minutes, just bending with the ribs slightly damp, and no matter what experimental approach I take, the ribs always seem to crack on me. Also, they never quite have the ability to perfectly touch the corner blocks. They only have the ability to touch the very tips of corner blocks. I was thinking that perhaps the arches on the corner blocks are too sharp, but I'm not sure. I think I'm just going to have to go with what I've got for now unfortunately, and hope for the best.

Does anyone out there happen to have a magic "tip" for C bout rib bending? I think I'm following the procedures correctly as far as I can tell, but perhaps there's something I might be missing here.

Thanks y'all!
BK

BK · Member Joined: 10 Apr 2011 Posts: 60

Actually, I was just playing around with it a bit more. I think the conclusion that I reached is that you're not ever going to bend the ribs to exactly the correct shape of the corner blocks. You can get close, but it won't ever match exactly. So what I ended up doing is filing down the blocks a little bit in order to get them to match the curve of the ribs. That seemed to work out alright. Of course, this alters the corners of my original design plan a little bit, maybe by 1/2 a mm or maybe even a full mm. Not ideal, but at least I will have a more structurally secure instrument in the end.

byacey · Posted: Sat Aug 06, 2011 2:46 pm Post subject:

Thin your ribs more just in the area where the sharp bends are. I dip the rib in water for a second before I start bending.
_________________
Bill

Chet Bishop · Posted: Sat Aug 06, 2011 3:30 pm Post subject:

"...filing down the blocks a little bit in order to get them to match the curve of the ribs. "

Wouldn't it be better to make clamping cauls, get the ribs as close as you can, then let the clamps and cauls (and hot, wet glue) bring the rib into compliance with the block? There is no need to change the blocks.
_________________
Chet Bishop
https://bluefiddles.com
https://fivestringfiddles.com

BK · Member Joined: 10 Apr 2011 Posts: 60

Thanks for the further feedback!

I experimented with this a bit more and I found that if I bend the ribs to the rough general shape, then put the ribs into the mold, and then put the bending iron up against the ribs that are in the mold, the heat will allow the ribs to conform to the exact shape of the mold.

Also, I think I still had not thinned the ribs down enough. I think after you do this for awhile, you get a feel for exactly how thin they need to be. And by "feel", I mean that you can put them between your thumb and index finger and can instinctively tell if it's the correct thinness or not. I also found that when it's at the right thickness, you can hold it up to the light and actually sort of see through the ribs, which is pretty cool. When you are holding the ribs up to the light, you can also see spots that need to be thinned out a bit more, because these spot will be more opaque.

Chet, I wasn't exactly sure what you meant when you were referring to a caul. Did you mean to trace the inside of the C bout onto a piece of wood, then cut it out, so that you can hold the ribs in place while the glue is drying?

Thanks again everyone!
BK

actonern · Super Member Joined: 15 Aug 2007 Posts: 444

Do you have rib stock from multiple trees?

I find there's an enormous difference in the ease of bending equally flamed wood from different trees. You may have some extremely difficult wood...

E

Chet Bishop · Posted: Tue Aug 09, 2011 10:56 am Post subject:

A clamping caul is a block cut to the shape of the piece you are clamping, so that the rib, in this case, is forced into perfect contact with the corner block. I use a separate caul for each corner block.

The caul has to be pretty much a parallel curve to that of the corner block, offset by 1mm.

Sam Compton made these, and then padded them with bathtub caulking, in a little mold, made for that purpose. The result was a padded clamping caul with exactly the right curve, but with some give to it, so it was unlikely to cause dents or other damage.
_________________
Chet Bishop
https://bluefiddles.com
https://fivestringfiddles.com

John Cadd · Posted: Wed Aug 17, 2011 6:45 pm Post subject:

I never hear about using small wedges to press the wood to the corner blocks. I use them all the time to get it all snug and firm. You need a gap to allow for them so the centre ribs blocks have more space on the ends When it`s all released the tiny pressure marks are removed by damping some cotton cloth in 3 layers and rolling the shaft of a soldering iron over the area for a few seconds. I only press the ribs on the aluminium heater with curved wooden blocks a bit wider than the ribs. I never use any metal straps as they seem more bother than anything. I get all the ribs in shape without any burning at all .Sometimes it`s best to bend a stubborn piece so far and clamp it in that shape .Then try it again next day for the final shape.

BK · Member Joined: 10 Apr 2011 Posts: 60

Yes, I stopped using the bending strap, mostly, as well. I found it to be more of a bother. The only time I do use it, is when I'm trying to get the rough shape of C bouts. But I could still probably get by without it.

John Cadd · Posted: Thu Aug 18, 2011 2:31 pm Post subject:

Some articles in the Violin Society of America write about metal straps and concluded that a brass strap will make blue stains on the wood. Now I am writing about it I realise that the metal will draw away heat which the wood needs for itself. The wood needs to be heated first ( in it`s flat state ) before you start trying to bend it. I think some do not approve of using water but I can`t see any disadvantage . The Roger Hargrave articles talk about Guarnerius and his hair-raising methods. He tried to avoid wood cut in a certain way as it tended to split too easily. Read all the Hargrave articles to get a dramatic picture of how Del Gesu made his violins. One man in a big hurry.