Author Topic: about that steam bending.... (Read 14400 times)

half eye · « **Reply #45 on:** June 01, 2016, 10:02:12 am »

Aaron,
I think the biggest difference in using dry heat and steam is what it does to the wood itself. Dry heat will get into the wood and a some point it "plasticizes the resins and proteins etc and there after it hardens the resins (heat tempering a belly) I think of it as turning the inside of the wood into epoxy impregnated cells.....steam on the other hand heats the wood clean through and makes the wood fibers elastic but it does so at the expense of the resins and proteins...a little will make the wood elastic but a lot lets the water in the steam carry away the resins and proteins leaving behind a "hollow shell" so to speak.
I know this view is over simplistic but hopefully conveys the idea behind the thought process.
rich

bubby · « **Reply #46 on:** June 01, 2016, 12:02:25 pm »

With all due respect if your wood is properly seasoned you shouldn't get any checking if steaming for 30 min to an hour and in my experience it doesn't harm the structural integrity of the wood. With a stave thats the best way to get a static bent with no damage

DC · « **Reply #47 on:** June 01, 2016, 12:46:28 pm »

I may be wrong but is seems like every time someone mentions cracking when steaming they are working Osage. I've oversteamed and understeamed and never had longitudinal checking/cracking but I've never worked Osage. I have had cracking across the grain, but that's been my fault.

bradsmith2010 · « **Reply #48 on:** June 01, 2016, 01:53:25 pm »

I have had well seasoned osage check from steaming 30 minutes plus,,
if i coat the wood,, seems to prevent checking
I have not tried only steaming a few minutes to bend,,
Lauben suggest boiling several hours for a 90 degree bend,, I think as suggested trying some scrap pieces might be in order,,thanks for the info guys

bubby · « **Reply #49 on:** June 01, 2016, 01:58:12 pm »

Never had osage to that, 2 hrs seems excessive to me but i have steamed up to 45min to an hr get one ring on the belly and it needs to be thinned down to bend easy. A 5 min steam does nothing in my experiance

DC · « **Reply #50 on:** June 01, 2016, 02:06:14 pm »

I did a little experiment this morning. I cut a 1 1/2" dia piece of Ocean Spray about a foot long. I rifle drilled it in about 5" so I could put my thermometer inside the wood while I steamed it. I wrapped a bag around it and started steaming. At the start the internal temperature was 70 degrees F. At 5 min. it was 84. At 10 it was 132. At 15 it was 170. At 20 it was 186. At 25 it was 194. At 30 it was 200. At 35 it was 203. At 40 it was 204. The temperature in the bag was a constant 212. Ocean Spray is a very dense wood(I've had a few samples that sink SG about 1) so I imagine it conducts heat faster than a lighter wood, I dunno. I looks like after 30 minutes it's about as hot as it's going to get. I'm watching how fast it cools as we speak. After 15 min it's still 150 degrees. I cut the wood in half to measure the thickness and there is 3/4" of wood all around the thermometer tip. Most bow work would be on thinner wood so the time would be reduced. I may try thinner and lighter wood later.

osage outlaw · « **Reply #51 on:** June 01, 2016, 02:26:42 pm »

Good info DC. Thanks for posting your findings.

Aaron H · « **Reply #52 on:** June 01, 2016, 03:59:10 pm »

Quote from: osage outlaw on June 01, 2016, 02:26:42 pm

Good info DC. Thanks for posting your findings.

x2

Arrowbuster · « **Reply #53 on:** June 01, 2016, 08:32:10 pm »

The wood I had check was in fact osage and I had it in the box for well over an hour, I feel like my wood was dry enough, best I remember about an 8 on my cheap moisture meter. Just a green horn mistake. From what I am reading I need to shorten steam time considerable. No more than 30 minutes? I think the stave is going to be ok but time will tell. Getting ready to start the tiller.

half eye · « **Reply #54 on:** June 01, 2016, 08:47:49 pm »

Arrowbuster...
The idea for me is to hurt the wood as little as possible. You can always re-steam if you don't like the short time method with no harm done. Also remember that I bend by hand and can literally feel the wood bend and yield so if it is too stiff I can stop and reheat without breaking anything. Mechanical bending doesn't tell you about the wood till it either bends or breaks.
rich

Danzn Bar · « **Reply #55 on:** June 01, 2016, 09:18:04 pm »

Quote from: Aaron H (Falcon) on June 01, 2016, 03:59:10 pm

Quote from: osage outlaw on June 01, 2016, 02:26:42 pm
Good info DC. Thanks for posting your findings.
x2

X3 excellent info...thanks

bubby · « **Reply #56 on:** June 01, 2016, 09:49:22 pm »

If you are bending it in hand or in a jig it is still mechanical bending

Pappy · « **Reply #57 on:** June 02, 2016, 04:11:51 am »

In my steam tube I usually steam about 45 minutes for a floor tillered stave, no issues. I always have everything set up so I can move fast once it comes out of the tube, I also keep a heat gun ready in case it take longer that I want.

Pappy

half eye · « **Reply #58 on:** June 02, 2016, 09:47:47 am »

Did my own little photo-shoot. After seeing DC's post it got my curiosity up so I grabbed a "roughed out bow stave of black locust. It is roughly knocked down in size to 1" thick and barely over 1-3/4" wide, bored the same type of hole and inserted a meat thermometer. The stave had some cambium/ new growth on it (see photos) but no bark and was not cylindrical in section
I did not want the thermometer to be influenced by ambient steam so I got the water to a boil, placed the stave and tinfoil for 4 minuets, then inserted the thermometer for a minuet more for a total of 5 minuets. The gauge read 80 degrees Centigrade (about 185 F) and bent like butter over the wood block .
There are also some close up pics of the bent wood to show there were no lifted slivers, delamination, or crushing.
Here is the pictures.
rich