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| Author: | Ronald Lenz [ Mon Jul 23, 2012 2:34 pm ] |
| Post subject: | side bending |
What is the consensus on steam bending sides, bindings etc, especially with difficult woods like curly maple or mahogany |
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| Author: | bluescreek [ Mon Jul 23, 2012 6:26 pm ] |
| Post subject: | Re: side bending |
Some woods really hate it . This is great for rake handles but not guitars. |
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| Author: | Ronald Lenz [ Tue Jul 24, 2012 12:27 pm ] |
| Post subject: | Re: side bending |
thanks for your help. I can't help but wonder, if you're adding moisture and heat with a bending iron or heat blanket, how is this different from adding moisture and heat in a steam box. Has it to do with the amount of moisture, or would the steam actually force moisture right into the cellular walls? |
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| Author: | Billy T [ Tue Jul 24, 2012 2:02 pm ] |
| Post subject: | Re: side bending |
As I understand it, and I'm not an expert here, but it's not really the moisture or steam directly that bends the wood but the heat. You're in essence melting the part of the wood that holds the fibers of the wood together. Yes, steam is a great means of transferring heat but it also brings moisture which can create its own problems. When moisture is not really needed why use it? The main procedure used is a light spray of water, a wrap in kraft paper, into the Fox bender. I've seen some like to soak sides in a trough and do bending by hand but I've only seen it once. In hand bending, it is common to see a wet rag wrapped around the pipe using steam to facilitate bending, that's quite common. Many here use a Fox bender and heating blankets. Some use 200 watt light bulbs as a heat source. I've personally noticed a drop in the number of complaints about broken sides when switching from bulb to blankets. Can you bend using steam, of course. Of what I've seen, again, of steam bending, even grained stock sits in the steamer for quite some time, is usually much thicker than guitar sides and it has to be worked right away or risk breakage from stock cooling quickly. From blanket to bulbs one doesn't have that problem, which seems to help with the fact that most here are bending pretty wildly figured wood, which by that very figure, makes the grain quite unstable. With pipe bending, one is only working a small part of the wood at a time but that part is under constant heat. Less breakage than classic steam bending!! In furniture making, one may be working already formed and shaped wood and bending say in a bent wood rocking chair. It's difficult to get a blanket to fit all the contours of the stock for a safer bend. In that case, steam makes great sense because steam transfers heat evenly to all parts of the work and the bends can be made quickly, in again, much more stable grained stock cut just for purpose. |
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| Author: | B. Howard [ Tue Jul 24, 2012 3:37 pm ] |
| Post subject: | Re: side bending |
Having steam bent a few things over the years, here are my thoughts. Steam bending is for large cross sections. The steam serves a few purposes, first it re-hydrates the wood cells, allowing them to deform without rupturing. Second it conveys the heat through the wood quickly and efficiently. The combination of these two conditions renders the wood "plastic' for a brief time. The bending must be accomplished very quickly as the wood will start to cool and loose it's pliability as soon as it comes out of the steam box.It is generally a one shot deal. Wood that has been steamed and bent will not respond well at a second attempt. Something changes in the cellular structure of the wood during the process that prevents the cells from softening again. Wood in thin cross section behaves much differently, heat alone is usually enough to bend it. I found that Mahogany seems to bend it's best worked over the pipe almost completely dry. The difference in thickness means that less compression of the cells is required to effect the bend, so the water is of less benefit. |
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| Author: | David Malicky [ Wed Jul 25, 2012 1:51 pm ] |
| Post subject: | Re: side bending |
As Brian described, both heat and moisture plasticize wood. Moisture lowers the "glass transition temperature" of wood -- the approximate temp when wood changes from elastic to plastic. Bending with moisture means less heat is needed, so less risk of fiber damage and charring. Now, for thin stock bent over relatively large radii (guitar sides) the ~8% of moisture already in the wood may be sufficient, so long as the bend is accomplished quickly -- before most of that moisture is converted to steam and driven out. And, the more moisture added, the more risk of warping and splitting after the wood has returned to equilibrium, especially for thin stock. So, the goal is to find the right combo of moisture and heat that minimizes all the risks while accomplishing a stable bend... for example, the often recommended light spritz and ~300F for ~5 minutes. Some refs... Page 8: http://www.fpl.fs.fed.us/documnts/usda/ah125.pdf Page 19-1: http://www.fpl.fs.fed.us/documnts/fplgt ... ter_19.pdf |
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| Author: | Ronald Lenz [ Sat Jul 28, 2012 4:28 pm ] |
| Post subject: | Re: side bending |
Thanks again for your input - very interesting and informative |
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