Temperature for bending wood --- a discussion

[tippie53]

Most woods do bend well at the 275 375 range. The only woods that I found to scorch at low temps was lace wood. I am not a fan of soaking but it if worked great. If I have a questionable piece of wood I use wet paper to separate the wood between the slats.
One thing that I can't stress enough is that the bender isn't as important as wood selection. The better the wood the higher a degree of success . Mahogany , and Maple like a tad more heat and less water. Maple likes to keep bending for a day or so if you use too much .
Enjoy the hobby and thanks for posting

[kencierp]

Water boils at 220 degrees --- For past couple hundred sets, my process formula is simple, make steam, it's pressurized and forces heat through the material. My Benders are unlike the styles sold today but the concept is similar -- I set it and forget it at 250 degrees which is a little higher than boiling to compensate for the wood drawing off some of the heat, not unlike a cook's concern and calculations -- so, time is a major factor as well. The point is you can lower the "dwell time" (how long it takes a given type wood to become plastic) time by increasing temperature, but that also increases the chance of damaging a side beyond repair -- do that a few times and the cost of your hobby goes up siginficantly!

[tippie53]

Ken brings up a good point : DWELL TIME . With wood , you need to reach a point to which the wood cells will collapse . This allows the wood to bend. Moisture allows you time to manipulate this . Too much heat can hurt the wood not enough won't allow you to bend the wood.
One thing that Ken's and my post shows is that there is more than one way to make this work. Again and I believe that Ken will agree , that wood selection is very important . I like to bend wood starting at 220 degrees and till I am done I like to see the 275 to 350 range for most woods .
There are some woods that will require a higher temp to get to bend . After the bending you need to allow cool time to set the bends . Wood is stupid , it get hot , it bends , it gets too hot , it scorches , if too cold it won't bend , bend too fast it may crack , wait too long it may crack. Too much water it may warp to little water it may lift grain .
Check out this link and you can see the bending process that I use . I also use paper with resinous woods so that the resins don't stick to the slats .
http://www.youtube.com/results?search_q ... nding&aq=f
Ken's advice to allow the heat to penetrate is sound. I use a weight on the end of the slat ,when it falls off it is time to bend .

[Ken Hundley]

Good discussion here! COuple of suggestions....when you get scorching or burnt exhudates, rather than sanding on a spindle sander (I just cringe....don't have the talent to do that consistently on such a thin peice, nor the budget to learn how) try scraping with a typical stanley razor blade turned scraper...make a burr on the edge....easily controlled, gives a good fresh surface to the wood, and doesn't create dust.

Also, not sure if you didi this nor where I read this, but when "cooking" the sides, cooling time is just as important as dwell time. If you allow the side to cool in the mold until all surfaces are cool to the touch, you drastically reduce the chances of spring back. Using this method, I have NEVER had any spring back on my sides. I have had one side set that I bent two years ago, have not stored in a mold, that still hasn't any springback using this method. My $.02.

[kencierp]

Its OK to pull the side off the form when it is still hot as long as you put it in the mold or a restraining fixture of some sort. Its a good idea to over-bend it a bit with a wedge or whatever. The waist curve will be compressed and cannot change unless the side is allowed to spread out length-wise. I will check to see if there is any visible mosture -- if there is I will reheat for another 15 minutes to burn it off -- this aides in preventing cupping. Here's a Taylor FF where Bob gets his hands a little too warm handling a just bent set.

http://www.youtube.com/watch?v=ybYdRtthNOs

[kencierp]

As John has pointed out -- "different strokes for different folks"

If you view the Taylor bending videos you'll note they do not add water. On the other hand, Tacoma uses a steam source to facilitate their operation -- 180 degrees in process design, yet both work just fine! Their cutaway bender is pretty nifty and simple too.

[Tom West]

Have never measured temp but rather let the wood tell me when it was ready to bend. A slight amount of water is much better then too much and .010 in thickness can make the differance between an easy bend and a fracture.
Tom

[David L]

Here's what I got so far, and I may be way off base with this view, call me a cynic if you like, hope I don't offend anyone but here goes. I find it disheartening that a major company refers customers that purchase thier products to a forum regaurding helpful information about the use of one of thier products considering that this company does not support this forum fianancially or otherwise. If I am skewed in this manner of thinking, someone please straighten me out

David L

[deadedith]

I found this somewhere:
Bending Sides
by John Mayes


Ok so I get lots of questions e-mailed to me about bending sides and while I am always happy to answer the questions to save some repition here are my methods to bending sides that I learned/worked out in Maine working under Dana Bourgeois. Dana did all the hard part I just fine-tuned the temps and side thickness to the size I thought worked best. Ok so here it is.

For side thickness it will vary from model to model and for each species of wood as well. But as a general rule here are the thicknesses you should thin the sides to.

Dreadnaught .085-.090
Slope D .085-.090
OM .080-.085
SJ .080-.085
anything with a cutaway (unless it is a sharp cutaway) .075-.080

The best bending method I have used so far is to use TWO silicone heating blankets available from LMI/Watlow and other places too. Two blankets ensure that you get quick even heating across the whole piece of wood. One on top and one on bottom with the wood sandwiched between two pieces of spring steel .010 that is essential when bending to avoid cracks and reduce springback.

There are a couple different things to keep in mind while actually bending the wood. 1st is the point in which you can start the bend. There are a few ways to do this but I approach it this way. The boiling point of water is 212f so at about 225-240 you will start to see steam coming from the blankets. When you see steam you want to bend. Since the water is steaming the steam loosens the fibers in the wood and therefore makes it possible to bend the wood. As a steadfast rule you can start bending at 240f if you see steam or not. If you do not see steam it may be because you did not put extra water on it, and that is ok as long as you put enough on. Enough would be a thin coating over the whole side but not dripping off. You can know what temp you are bending at by buying as digital thermometer from wal-mart. The kind used for cooking. They have the long stem that would normally be put into a turkey or something like that. They read temps up past the highest we would use.

So at 240f you have started your bend. You move somewhat slowly..not so slow that by the time your almost done there is no water left in the fibers as that can run the risk of scorching, but slow enough so that you don't break the wood. On highly figured woods such as quilted mahogany use extra care as they can be very tough to bend. The process I use for bending is to bend the wasit first and then the lower bout and then the upper bout. Not the only way but the way that suits me best.

I regulate my temperatures via a potentiometer or a dimmer switch. I then can bring the temperature up the mark that I want and then keep it there for as long as I want with less plugging in and unplugging of the cords, but either way works.

So the waist press is down, and the sides are also curved. You will want to bring it up to a temperature and hold it there for around 5-7 minutes to really 'set in' the bend. Each wood has a different temperature to go to and some woods are less prone to scorch than other so here is a list of woods commonly used and what temperature to bring them up to:

Indian Rosewood: 300f
Mahogany: 310f
Maple (bigleaf): 290f
maple (European): 280f
Brazilian Rosewood: 305f
Cocobolo: 310f
Koa: 300f
Paduk: 310f
Walnut: 300f
Other Rosewoods: 300f

You will want to keep the wood at that temperature for about 5-7 minutes. Then unplug the wood or turn off your dimmer switch and wait for 30-45 minutes before taking the wood out.

With these methods I have bent hundreds of sides and using them should help you to feel confident in your bending and not afraid that you are going break a side.

Again these are just my findings. Above all be flexible and be prepared to find your own methods. I hope this helps!