Bending New Guinea Rosewood

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Woodsy23
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Bending New Guinea Rosewood

Post by Woodsy23 » Thu May 19, 2016 7:52 am

I attempted some trial bending of New Guinea Rosewood last night in preparation for building an F style mandolin. Using a bending iron, I found it quite difficult to bend. The gentler curves could be achieved eventually but I could not get the tight bends that would be required at the head, scroll and points without cracking. The piece I tried to bend was 2mm thick. I figured that reducing the thickness to 1.6mm or 1.8mm would help (as for the horns on cutaway acoustic guitars).

Does anyone have any advice or tips for bending NGR? Does the level of difficulty vary much within the species? I have read about using fabric softener (SuperSoft??) but don't know which softness available in Australia would be suitable. Any suggestions?
Richard

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peter.coombe
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Re: Bending New Guinea Rosewood

Post by peter.coombe » Thu May 19, 2016 9:28 am

Not sure what the problem is. I made one mandolin from NG Rosewood and it was easy to bend, although it was an A not an F style. Maybe it is the individual piece of wood, try a different piece from a different tree??

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blackalex1952
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Re: Bending New Guinea Rosewood

Post by blackalex1952 » Thu May 19, 2016 1:23 pm

this might help...
viewtopic.php?f=1&t=6993&p=77672#p77672
I admit I am not as experienced a builder as some of the guys on this forum, but here is something I have experienced. I made myself a bending iron, using Chinese elements, a temperature controller, a temp sensor-all from ebay cheap. I burned the first few sides, until I used a surface thermometer and realised that the temperature controller and sensor were not properly calibrated and could not be calibrated! Wrong sensor, I guess, but one sourced locally would cost heaps. So, I compensate on the digital temp readout by setting it 40deg C lower and it works fine. I have found that some timbers are more susceptible to case hardening, even if the scorching is not obvious.The point I am making is that perhaps a lower temperature, steady as she goes approach and regular spritzing would be help. Also, if you don't already use one, a bending support strap. I have also heard of people using a wet scotch brite pad between the iron and the wood-or maybe it is betn the wood and the strap? I think it was posted on this forum...Is 2mm a bit thin on an F style mando at the scroll? I have never built one.-Cheers, Ross
"Everything I say on the topic is based solely upon inexperience and assumption!"

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Allen
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Re: Bending New Guinea Rosewood

Post by Allen » Fri May 20, 2016 5:47 am

Any NGR that I've used has bent like butter. It the timber I give students to have a go at bending in classes because it's so easy to use. Many of them bend the stuff into corkscrew type sculptures just because they can.

You would certainly want to thin it down to at least 1.6mm for tight bends. That would go for any timber really. There is a huge difference in how easy timber will bend between lets say 2.0mm and 1.6mm

Use a bending slat on the outside of the bend to help reinforce the piece as pressure is being applied. It helps to even out bends, and also keeps heat and steam int the piece itself.
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Woodsy23
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Re: Bending New Guinea Rosewood

Post by Woodsy23 » Fri May 20, 2016 7:52 am

Thanks everyone for your advice.

I can check all suggested improvements. I have another piece of NGR from a different purchase which is a very different colour. I can check the temperature of the bending iron. I too have a home made one using a Chinese heater element and a controller but I do also (usually) attach a second thermocouple temperature sensor as a check. My bending temperature could also be too cold. I will thin down to 1.8mm then 1.6mm and see what difference that makes.
Richard

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Steve.Toscano
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Re: Bending New Guinea Rosewood

Post by Steve.Toscano » Wed May 25, 2016 2:21 pm

I've bent pieces of NGR at 2.2mm and found it bent like butter even at that thickness (i was trialing thicker sides at the time). No cutaway.

Just soaked in hot water for 10 mins then bent on my high tech iron - a pipe with a butane torch jammed up the middle at my normal precise bending temperature of: "when it's hot enough that a spritz of water immediately evaporates" degrees. :lol:

Woodsy23
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Re: Bending New Guinea Rosewood

Post by Woodsy23 » Thu May 26, 2016 12:56 pm

I have only had time to check the temperature of my bending iron and to try a 1.8mm piece (from the same source) using a metal bending strap. That bent more easily, as expected, but still a bit of a struggle.

I checked the temperature of the bending iron with another thermocouple thermometer and I also borrowed a "laser gun" thermometer from a friend. Both showed that I was getting the 160 degree C temp, at least on the part of the iron I was using most. However, the laser thermometer showed that the temperature varied considerably around the egg shaped iron. 160 on one side, 90 on the other and about 110 on the point of the egg. I guess that sort of variation would be typical of the more primitive bending irons and one might only expect uniform temperature on commercially made ones like the Ibex.

I will soon try bending pieces from another NGR stock and also try soaking for 10 mins.

Thanks again all.
Richard

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Steve.Toscano
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Re: Bending New Guinea Rosewood

Post by Steve.Toscano » Thu May 26, 2016 1:20 pm

Woodsy23 wrote: Both showed that I was getting the 160 degree C temp,
Probably not hot enough, as above i have no idea what temp my 'iron' runs at, but i reckon it's a lot more then that. I'm estimating around 200C + .

Woodsy23
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Re: Bending New Guinea Rosewood

Post by Woodsy23 » Sat May 28, 2016 10:18 am

I think the piece I was trying to bend is particularly difficult for some reason although the iron was probably not hot enough also.

I bent a 2mm thick piece from a different NGR stock after a light spray with water and it was really easy to bend to a tight radius. Iron temperature was closer to 200C. This piece has a much richer colour - rose to orange.
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I then tried a 1.6mm thick piece from the original stock after soaking it for 30 minures. It was still difficult to bend and did crack a little although I probably could have avoided that if I went a little slower. I used a metal strap. This piece is much browner and relatively pale.
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