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-   -   Bending Italian Poplar (https://www.woodworkingtalk.com/f27/bending-italian-poplar-64725/)

johnywhy 08-01-2014 03:34 AM

Bending Italian Poplar
 
hi

i need to bend some 1/8" Italian Poplar just a little a bit further than it wants to. It always snaps right before I get the needed bend.

Basically, I performed an experiment: I soaked it overnight in lukewarm water. Also, I heat treated some of it. This thread describes the two batches, with questions.

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After soaking, i was able to bend the poplar to the needed radius (and beyond).

Anything that could be improved with my soaking method? Is it bad for the wood in any way?

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Continuing the experiment, I put some of it in a microwave for a minute. The micro'd wood offered less resistance and less spring-back than the soaked-only wood. That's a good thing, right?

Anything bad about the microwave method?

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I braced both the micro'd and non-micro'd samples on jigs.

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Continuing the experiment, i put the micro'd wood in a toaster oven for 5 minutes. That seemed to extract most of the moisture. I could remove the wood from it's brace shortly after, and it held it's shape.

Will toasting make the wood too brittle, or have any other drawbacks?

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After 6 hours, i removed the non-micro'd, non-heated wood from it's brace. It is still moist, and has some springback. I re-braced it, and plan to keep it braced until naturally dried, probably another day or two.

Will the naturally-dried wood be stronger or weaker than the heated wood? Anyone have experience with soaking, microwaving, or toasting wood?

It seems that the full regimen of soaking, microwaving, and toasting quickly produces bent wood with no drawbacks, but i wanted to get a second opinion from someone who's done any of these things.

thx!

TimPa 08-01-2014 07:09 AM

welcome to the forum.

i use the traditional method of steaming the wood until it bends the amount i need. have you tried that? it seems that you may be doing it in a round about way (soaking/heating). you have taken the process further than i have. i suspect that the soaking will take much longer to dry.

johnywhy 08-01-2014 07:57 AM

hi TimPa

i'm familiar with steaming, and i'm seeking a simpler, quicker, kid-friendly alternative. (i mentor disadvantaged youths in fabricating stuff).

since i may have hit on a working recipe, i think it makes sense to continue down this route unless i discover some flaw.

this guy thinks his pieces will take a week to dry, but his stock is 1.5" x .5" --thicker than what i'm bending. http://youtu.be/nwTFw8Ol2o4

and i'm using wood designed for bending without any heat or water --i'm just helping it go an extra bit.

and he's not doing the toaster-oven stage :)

thx

epicfail48 08-01-2014 11:28 PM

I dont think youll have any issues with the methods you described. People have been steam bending wood for centuries, which is what youre doing. Mostly. As for the toaster oven, its just a smaller way to kiln-dry wood. Id for cracking on thicker pieces, but should be fine

johnywhy 08-02-2014 01:17 PM

hey epicfail48, right before i saw your msg i discovered kiln drying! yes, i thought what i was doing might be a kind of low-budget, low-volume kiln. cool!

Now i'm trying to determine the best temp and time. 15 minutes at 120F left the wood still a bit springy. at 400F the wood became very brittle in it's bent pose. But i think 400F is much hotter than a real drying kiln.
Quote:

High-temperature dry kilns operate at temperatures of 200 to 240F. This type of kiln was developed to dry softwoods.
http://www2.ca.uky.edu/agc/pubs/for/for55/for55.htm
this doc has a list of drying temps for most woods. Italian poplar in thicknesses 8 to 16 times thicker than my 1/8" stock is given at <200F. tho i'm not understanding why they show higher temps for thinner, dryer poplar. Not sure how to interpret that. Feel free to help :)

microwave bending is described here, and demonstrated in this video. Not sure it qualifies as steaming.

bending by cold-soaking-only is described here and here. tho, i'm starting with hot-from-the-tap water.

here's what Italian poplar can do before any treatment. It’s designed to bend dry, straight from the warehouse. i need to bend it only slightly tighter than what it can do new:
http://www.hofcraft.com/images/itali...g-poplar_1.jpg

epicfail48 08-02-2014 09:20 PM

I actually do something similar from time to time. My theory is that higher temperatures are more likely to burn the wood, an undesirable outcome to say the least. The temperature only NEEDS to be hot enough to evaporate water. Personally, i go for 250f for temperature. As for time, that depends on the thickness. I dont know of a good hard and fast rule, but ill go from 30 minutes and see where it goes from there

johnywhy 08-03-2014 12:00 PM

My results suggest 250F for 30 mins may be too long and too hot for wood this thin. I'm getting great results at 200F or less for 15 minutes. This was baked while on the jig.

It retains a bit of spring, which i think is good-- if i baked longer or hotter it becomes brittle. i'm still learning about this, but i believe brittle wood is not as strong. Also, the flex it retains means i can fine-tune the bend when i glue it-- if it didn't flex a little, then i would not be able to fit it.

http://s19.postimg.org/jznwx7fcj/IMG...802_125944.jpg

http://s19.postimg.org/v0j2287lf/IMG...802_130003.jpg
(Both photos are the same piece, same curve. Curvature on the 2nd photo is symmetrical- it only appears distorted due to perspective of the photo.)

johnywhy 08-03-2014 05:37 PM

(that's not a crack in the 2nd photo, just a cosmetic defect)


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