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Jigs and Tools #2: A Bee's Knees Wood Bender Thingy

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Blog entry by GnarlyErik posted 11-29-2016 11:31 PM 1362 reads 8 times favorited 10 comments Add to Favorites Watch
« Part 1: A One-Handed Clamp with a Deep Reach Part 2 of Jigs and Tools series no next part

(See update below, at bottom!)

In a long career, I’ve used all sorts of rigs to bend wood, from steam boxes, steam jennies, wood boiling rigs, rosebud torches played on wet rags and heat guns. Some time ago I built myself a propane fired steam-box for bending things like boat frames and plank ends. But it is so big and gawky it mostly just serves as merely another shelf in my garage workshop.

I’m on a kick building stringed musical instruments right now, which requires bending extreme curves in thin and narrow wood parts. Based on past experience in wood bending, my observations and recent research, I’ve come up with a bee’s knees apparatus for bending thin, narrow and not-too-long wood parts. This thing works so well I wanted to pass it along.

Essentially, this rig is merely a common hot water heating element in a tube. The element is installed in an elbow to get it out of the main tube and protect it from being damaged by whatever is in the tube.

Most hot water heating elements are 220 volts, but you can find them in 110 volt versions too. In this case, the element is 110 volts rated at 1500 watts, which has proved to be more than enough for my needs. Theoretically this will draw a little less than 14 amps current, and in the first trial run of my rig a 15 amp circuit breaker had no problem at all with it. It is probably important to use a short extension cord to keep the resistance low. I wanted to run my rig outside and it worked fine with a 16 gauge by 25 foot cord.

The element is installed in a PVC end cap. I ground off a flat spot before drilling a pilot hole for the element which is threaded for a 1-1/4” pipe thread. A 1-1/4” Forstner bit makes exactly the right sized hole for the element threads. I cut the threads in the PVC cap by tightly clamping an 1-1/4” pipe nipple in vise grip pliers, and moderately heating the nipple with a propane torch. By using the nipple like a tap, and working carefully, the threading went surprisingly easily. I found it helpful to insert a short wooden rod inside the nipple to help with keeping everything properly aligned. Once the threads were made, I installed the element in epoxy just to make sure everything held and would not leak.


Once the element was installed, the wiring was hooked up, and an 1-1/4” PVC end cap was an exact fit for a protective cover, glued on with PVC cement. The PVC end cap with the element installed was fitted to an elbow, and the elbow to a length of PVC pipe. I used 4” PVC, but 3” would have been a better choice for my needs – and cheaper too – 20/20 hindsight you know! I calculate a four-foot length of 4” pipe and elbow together hold a little less than 4 gallons of water. Incidentally, if someone wanted something longer, PVC pipe comes in lengths up to 20 feet long.

I built a wooden stand to hold the apparatus not quite vertical and made a couple of half-hollow brackets as chocks. The PVC pipe is held in place by hose clamps linked together near its bottom. In hindsight, it would have been better to extend the bottom of of the wooden stand a few inches more and install some sort of blocking as insurance to help hold the elbow in place.

When the finished apparatus was filled with water and plugged in it took less than ten minutes to get the water quite warm. I placed my wood inside, and used a spring clamp to hold it down and provide a handy grip to pull it out when ready. As long as it is plugged into power, the water will keep getting hotter with no thermostat or switch to shut the element off. I suppose it would be a good idea to have a thermostatic switch if you were doing a lot of bending, but for my needs it is not necessary. I just unplug things when I need to. Theoretically schedule 40 PVC is rated for 140 degrees Fahrenheit, but I’m sure it can stand far more, especially since there is almost no water pressure involved. In my test I’m sure it got up to at least 140 degrees, although I did not attempt to measure the temps. It was plenty hot! (12/15/2016 edit: The second time I used this rig I dipped a regular household thermometer in the water and it quickly exceeded the limited 120 degree capacity of the scale. I’m pretty sure this would boil the water in time if the PVC could stand the temps.)

In about twenty minutes, I pulled out my piece of cherry, which was a strong 1/8” thick by a little over 2” wide. It was more than limber enough for my bending, which in this case was a radius of about 5”.

I saw a length of sheet metal stove pipe with soldered joints used this way once, which gave me the idea. The problem with that is any ferrous metal will seriously discolor any wood which it comes into contact with when wet and heated. If you look closely, you can see the black mark where my spring clamp held one end of my cherry stock.

I hope someone can make use of this!

9/5/2017 UPDATE:

I’ve used this rig quite a bit now, and just the other day I used it to ‘steam’ (boil) some cherry which I want to use for making new rockers for an antique rocking chair. I’ve been cautious about getting this rig too hot since the PVC is rated for only 140F degrees. But, I’ve wanted to try and began thinking; the PVC rating likely has about a 50% safety margin, plus the water is not under pressure either, so I gave it a whirl.

It worked so well it just blew me away, pun not intended. After 25 minutes or so, the water began to boil, and in another five minutes it was really roiling, and I had to unplug the element to keep my water from boiling completely away. There was no sign of failure in the PVC at all, so I’m guessing there won’t be any problems.

I found I could leave it unplugged for about five minutes or so and allow things to cool down some, then replug it in for another five minutes, etc., etc. The back and forth was a little unhandy for sure, but I got my wood nice and bendy after a little over an hour. I’m either going to put a timer or a thermostat on this rig next time around for convenience, but all in all I’m very happy with this little guy. Just passing this along for what it’s worth.

I’m posting a short video showing how this works:

https://vimeo.com/232545548

-- "Never let your dogma get run over by your karma!"



10 comments so far

View tyvekboy's profile

tyvekboy

1664 posts in 2769 days


#1 posted 11-30-2016 12:13 AM

That’s a very cool … hot … idea. I’ve got to keep that one in mind.

Thanks for sharing.

-- Tyvekboy -- Marietta, GA ………….. one can never be too organized

View Mrkixx's profile

Mrkixx

70 posts in 1735 days


#2 posted 11-30-2016 12:52 AM

Awesome rig, did you put a cap on the end while in use or did you leave it open

View GnarlyErik's profile

GnarlyErik

296 posts in 1890 days


#3 posted 11-30-2016 03:05 AM

No cap. The PVC is about 1/4” thick and holds the heat well. I guess you could throw a cloth on top if you wanted. Honestly, I haven’t used this enough yet to know all the tricks but don’t think a cap is needed.

Cheers,
Erik

-- "Never let your dogma get run over by your karma!"

View shipwright's profile

shipwright

7683 posts in 2554 days


#4 posted 11-30-2016 03:52 AM

Looks like a keeper Erik.
I too have a large propane fired steam generator that I built years ago and now rusts in my garage. This is a clever idea and should work a treat for small pieces.
Well done.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees. http://thecanadianschooloffrenchmarquetry.com/

View hunter71's profile

hunter71

2980 posts in 2942 days


#5 posted 11-30-2016 11:45 AM

Simple and it works, what more could you want.

-- A childs smile is payment enough.

View johnstoneb's profile

johnstoneb

2537 posts in 1929 days


#6 posted 11-30-2016 03:31 PM

Thanks for sharing. I will be using this idea. I have poured hot tap water into PVC for bending and it works on oak but is marginal. This get that extra bit of heat to take it where it need to be for bending.

-- Bruce, Boise, ID

View hnau's profile

hnau

88 posts in 298 days


#7 posted 11-30-2016 05:30 PM

-- Spammer in processed of being removed.

View Jim Rowe's profile

Jim Rowe

988 posts in 2068 days


#8 posted 11-30-2016 09:20 PM

A really neat solution for smaller projects. Must give this a try.
Jim

-- It always looks better when it's finished!

View Edwardnorton's profile

Edwardnorton

190 posts in 1683 days


#9 posted 11-30-2016 11:56 PM

Most all residential water elements in america are 115v which makes this an easy project to do. Pretty nice idea !

-- EdwardNorton

View bhuvi's profile

bhuvi

97 posts in 297 days


#10 posted 12-01-2016 01:49 PM

-- Do NOT click links. Spammer in the process of being removed.

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