Wood Chart (for side bending)

rienk
Posts: 94
Joined: Tue Nov 27, 2012 9:56 pm

Wood Chart (for side bending)

Post by rienk »

It would really be awesome if a bending chart could be put together for the various woods that are used for backs and sides. A "rule of thumb" chart, showing the normal thickness for each species, as well as the temperature and times for bending the various woods. Obviously, a number of woods will be the same, so maybe a chart showing combinations might work (e.g., setting "A" for Rosewood, setting "B" for Padouk, etc).

A simple spreadsheet that can be updated would be fantastic. I would be willing to maintain it, though it would be great if a moderator on the forum would do so.

If any of you can respond with your input on various woods, we can put together a great resource for both beginner and experienced luthiers. Thanks for your help!
tippie53
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Re: Wood Chart (for side bending)

Post by tippie53 »

all species .090 +/- .005
you also have to take into consideration flat ,rift or quarter sawn
Next some woods like less water than others and lastly
The bending technique you use may differ from technique to another.
I bent over 200 sets this year and have done consultant work with a large manufacturer of guitars.
Here is what I can tell you. I use a 5 watts per sq inch blanket.
Most woods will bend using this technique
slat - wet paper - wood - wet paper - heat blanket - slat
where you read the temp is also important . I place my thermometer between the heat blanket and top slat.
I allow the heat to hit 220F then bend lower bout , I will run the ram down about 1/2 way and do the upper bout. Before bending I will be sure the wood is still damp. Then complete the waist bend.
Allow heat to rise to 325 for all woods except Padauk ( 375 F ) allow 10 minutes at 220F then let cool to room temp,

I will say that 80% of bending is wood selection.
Maple prefers less water. Also using wetting agents like Super Soft on high risk woods may help .
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
Ben-Had
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Re: Wood Chart (for side bending)

Post by Ben-Had »

tippie53 wrote: slat - wet paper - wood - wet paper - heat blanket - slat
John, did you mean "slat - wet paper - wood - wet paper - slat - heat blanket" or have you changed the way you sandwich the wood?
Tim Benware
tippie53
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Re: Wood Chart (for side bending)

Post by tippie53 »

yup
changed the set up. I found that the wet paper is a good separator with the blanket. I can bend with less heat off the blanket and heat is directed to the wood a lot faster.
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
rienk
Posts: 94
Joined: Tue Nov 27, 2012 9:56 pm

Re: Wood Chart (for side bending)

Post by rienk »

tippie53 wrote:Allow heat to rise to 325 for all woods except Padauk ( 375 F ) allow 10 minutes at 220F then let cool to room temp,
I will say that 80% of bending is wood selection.
Maple prefers less water. Also using wetting agents like Super Soft on high risk woods may help .
I saw the separate thread about Padauk, which is why I thought this might warrant a separate thread for the various woods and such. Are there other woods beside Padauk which require higher temperatures?

Which woods need to be wet light - medium - heavy?

Which woods is it best practice to use Super Soft on?

Etc.
rienk
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Re: Wood Chart (for side bending)

Post by rienk »

Ben-Had wrote:
tippie53 wrote: slat - wet paper - wood - wet paper - heat blanket - slat
I heard that the guys at LMI have a process where they use three slats...

slat - paper - wood - paper - slat - heat blanket - slat.

Apparently they preheat all the slats with the blanket, then throw the whole layup in the bender preheated (obviously using gloves). The claim is that they can bend everything up in less than a minute that way. they let it cool down a bit, and then the sides can be transferred to a cooling form (if you have/use them).

Anyone familiar with this protocol?
tippie53
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Re: Wood Chart (for side bending)

Post by tippie53 »

there are many techniques . I bend 200 sets or more a year. That is 400 bends. I know my method works but you are free to do it anyway you wish.
There are many ways to do this but you have to look at Thermal mass , Thermal load and heat loss.
Also what blanket or heat source you are using. If wood get hits the temp it doesn't matter how it gets hot as long as it does.
It took me over a year to perfect my bender design. There is some information I just can't give out but I can tell you this Wood has 3 stages to bend , Softening . cell collapse , and setting.
Too much material will make a heavy thermal load and that will also hold heat . It is about controlling the heat at the cellular level. Paul Reed Smith have 5 of my machines and Fender is also using them. So they are a proven design. I am completed bending within 4 minutes.The rest of the cycle is cool down.
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
tippie53
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Re: Wood Chart (for side bending)

Post by tippie53 »

There are many ways to bend but it comes down to process control. How other manufacturers bend is the process they developed. I designed my bender and took about a year and a 1/2 to perfect. So if you want to design a bender you start at what you know that works.
Finding temp ranges is part of the equation but you also have to look at the engineering points of it. What thickness do you want to bend , the thermal load , The blanket wattage and design and so forth. There is not one answer for all the questions.
I have no idea on how LMI does it. Like me they bend to fit a kit design but then I also build. Most woods are similar in that they are considered thermoplastic , it take heat to make them bend , and once cooled the bend sets. There are some exceptions to the rules as it is a natural substance so it isn't like you will be bending plastic. I have changed my bending method as I am often experimenting to see if there are better methods. Often what seems like a good idea may not be so you have to be careful what information you put out.
Any process that you design that is repeatable and works is a good design. I do not believe you can make a permanent bend in 1 minute. CF Martin takes 6 minutes. They used a design similar to mine then engineered it into a nice CNC unit. Now we can see the big difference in machine design but the process is similar. Heat , bend , set .
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
rienk
Posts: 94
Joined: Tue Nov 27, 2012 9:56 pm

Re: Wood Chart (for side bending)

Post by rienk »

I'm sure I'll start with your procedure, but will try other stuff on some grade B sides, to experiment.

I am also adapting my bending molds to have the ends inset - so that the sides are over bent at the ends. The idea is that it will reduce any spring back, and have even less stress built into the rim. Probably overkill, but it is a fun experiment. It sure was a pain laying out the cad so that the distances around the curves were the same. Thus, I won't mind if it doesn't help, as I'm not looking forward to doing it on the rest of my shapes. But again, one more step in trying to improve the process.

I machines the plastic parts for my new side bender today - the fit up worked pretty well (of course, I CNCed a dry run in MDF first, and found a few mistakes). I designed around 15mm baltic birch, and then realized that I have 12mm and 18mm, and my supplier is closed until Wednesday - so I'll have to wait to make the machine base and the bending jigs.

Then it's off to the races bending my first set of sides!
tippie53
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Re: Wood Chart (for side bending)

Post by tippie53 »

The variables you need to play with are heat, duration and water quantity.
As stated previously, some woods like more heat. Some like less water. Using wet paper is a controllable way of using water as an anti-scorch agent. Measure the heat off the blanket, not the wood, since water coming off the wood will be steam and that is usually 212F.
Now work as stated above and play with cool down a support methods and cooling methods. With all the info out there you will soon understand it is about the unit and the process .
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
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