Compound Plank Bending

[Neil10]

Just completed my first plank edge bending initiative to match the deck lift towards the bow of the model using Chuck’s travel iron method. Went well. Now I need to bend the same plank in the opposite plane to follow the curve in to the bow. Started thinking about what to use as a former for this bend and realized that the curve created by the bulkheads was a candidate. In other words bend the plank in situ on the model with the travel iron.

 

Is this a good idea? Will there be a tendency to lose the vertical bend in the same plank as I go down this route? Suggestions please. 

[Bob Cleek]

Dry heat is all you need. There is no need, nor point to using, steam or moisture of any kind when bending wood unless you have to, and that's probably almost never when modeling. The steam or other moisture only serves the purpose of transmitting the heat to the wood. Given the size of the pieces in full size boat building, steaming in a steam box is a good way to heat the wood through and through in order to soften the lignin in the wood which is what it is all about. Even so, dry heat is also used where possible, to avoid the hassles involved in dealing with steam and moisture. (The gondola builders of Venice use open fires to heat their planks for bending.) But why get wet if you don't have to and when you can put the heat exactly where you want it and easily apply more as you need it when bending the piece?

 

A clothes iron as Chuck uses works very well for heating strip wood to bend it on the flat ("edge setting" in boat building parlance.) and you don't have to mess with steam or boiling water which risks burns and wets the wood which then requires drying time and, if moisture remains, often makes gluing difficult. Actually, if you use PVA adhesive to glue your planks in place, applying heat with an iron on the outside of the plank at each glued frame or bulkhead will dry the PVA, effecting a much faster setting time. To obtain curves in another direction (not exactly a "compound curve," which something different than what you are talking about here) a clothes iron can be used, but a heated, curved former is probably more effective. Use the forum search engine. There are posts on ingenious ways to do this. Some use tin cans heated on the inside with a propane torch as a former. Some use a pipe heated with a torch on the inside. Some apply heat from an electric curling iron and press the wood into a form cut from a block of wood. Myself, I am partial to the now-no-longer-made-but-sometimes-available-on-eBay Aeropicola plank bending iron, which is something like an electric soldering iron with a French Curve shaped head on it that allows bending various radii with it. There are other types of electric plank benders sold today that do the same, although not as well, if reports are accurate. 

 

As Chuck has so accurately said, you need to bend your planks, or any bent piece, for that matter, to shape before you try to fasten them up. You can use the frames or bulkheads as forms for bending, but don't expect the planks to stay in place unless they are bent to shape before gluing in place.

 

I would greatly encourage anybody who wants to bend wood to read "the Bible:" Bending Solid Wood to Form (1957) U.S. Dept. of Agriculture - Forest Service. (39 pages.)  https://www.fpl.fs.fed.us/documnts/usda/ah125.pdf  Bending wood is a lot easier when you understand the science and mechanics of what you are doing. 

 

https://www.ebay.com/itm/AEROPICCOLA-Torino-WELLER-SP40-Electric-Plank-Bender-Tested-Works-Italy/383829086822?hash=item595dff1266:g:DhoAAOSwnRpfvwFq   There's an Aeropiccola plank bending head mounted on a Weller soldering iron for a "buy it now" price of $40.00 on US eBay. I suppose the fact that the head is mounted on an aftermarket soldering iron makes a difference for some reason I can't fathom, since the Italian originals were mounted on Italian soldering irons that were nearly identical to the Weller, which may even be of higher quality, for all I know, but these suckers have been listing on eBay for $75 to $100 (solely because nobody is making them anymore) and anybody who has any plank bending to do would be nuts not to grab this one like right now if not sooner.

Edited November 26, 2020 by Bob Cleek

[Neil10]

Wow. Fascinating technical discussion. Thanks.
 

On reflection I realize that the plank probably needs to be bent beyond desired set before applying heat because it will always spring back a bit afterwards. If this is correct, bending around bulkheads probably not ideal because initial overbending obviously not possible. Now have my eyes on the Admiral’s wooden rolling pin as a bending former!

Edited November 26, 2020 by Neil10

[tlevine]

Might I suggest various diameter sauce pans instead of the rolling pin.  It is much easier to secure the plank to the rim of the sauce pan with clamps or bull-dog clips than to a solid surface, such as the rolling pin.  This works well for me.  1. Secure the end of the plank to the rim of the sauce pan.  2. Put a few inches of water into the pan and put the pan on low heat (this will warm the plank without much risk of getting burnt).  3. Gently bend the plank around the pan with one hand while using a hair dryer in the other hand to supply more heat and airflow.  4. Overbend the plank to compensate for springback.  5 Once you are happy with the curve, clamp the other end of the plank to the pan, turn off the heat and come back when it is completely cool.

 

Whenever you are trying to bend a strip of wood, test bend it first to see which direction it is "happier" bending.  Otherwise, you will end up with a lot of splintered wood.

[kurtvd19]

On 11/25/2020 at 11:39 PM, Bob Cleek said:

 

I would greatly encourage anybody who wants to bend wood to read "the Bible:" Bending Solid Wood to Form (1957) U.S. Dept. of Agriculture - Forest Service. (39 pages.)  https://www.fpl.fs.fed.us/documnts/usda/ah125.pdf  Bending wood is a lot easier when you understand the science and mechanics of what you are doing. 

Bob is right - the Bible when it comes to bending wood.  This govt agency more than earns their keep.  We had a speaker from the Madison, WI lab speak at the 2007 NRG Conference.  After he explained what happens to wood when Ammonia is used to help to bend wood I am very sure nobody in attendance that day has ever used Ammonia again and hopefully has cautioned others not to use it.

 

An interesting ship related item - I visited the Wood Services Product lab in Madison when I participated in a building code class at the U of W - and watched some deflection testing of wood beams.  They had a full size hull section of several frame pieces and planking off to the side built by the shipwrights involved with the USS Constitution's 200th Anniversary rebuild.  It was built so the lab could design and test a method of gauging the wood condition of the hull while the before it was moved to the drydock.  Similar to the electronic way a metal hull's thickness is gauged.  Doing so allowed the shipwrights to have a very good idea of what had to be replaced before the ship was drydocked so plans could be made for the restoration.  The lab director said they were going to have to do something with it soon to free us space and that the shipyard didn't want it back.  I volunteered to take it off their hands but the govt is real fussy in how stuff is disposed of - it's probably still sitting there.   If you ever get a chance to see a wood column load tested until it shatters I guarantee you will be impressed.

[glbarlow]

On 11/26/2020 at 4:45 AM, Neil10 said:

bending around bulkheads probably not ideal because initial overbending

Being a Pegasus builder I know the challenge of gun port patterns.  I used the plans to cut a profile of the hull out of a 1x3 inch board then cut various notches as clamp points on the remaining straight side of the board.  No fear of damaging bulkheads and it took as long as it took to get the right shape, which then laid perfectly onto the frame.  I did this for Vanguard which worked great with its buff bow.

 

I am a believer in Chuck’s dry heat, no water method for bending planks, I use a travel iron.  It is dramatic the difference this method makes for me.  I easily can do compound bends, like the in and down curve of the bow and the twist needed at the stern. It worked like a charm for me on Cheerful and has a quick learning curve, it takes little time before your visualizing marking where to start the bend.

 

No better way in my humble opinion, not that every one agrees with me.  Do what works best for your style.

[Bob Cleek]

3 hours ago, tlevine said:

Might I suggest various diameter sauce pans instead of the rolling pin.  It is much easier to secure the plank to the rim of the sauce pan with clamps or bull-dog clips than to a solid surface, such as the rolling pin.  This works well for me.  1. Secure the end of the plank to the rim of the sauce pan.  2. Put a few inches of water into the pan and put the pan on low heat (this will warm the plank without much risk of getting burnt).  3. Gently bend the plank around the pan with one hand while using a hair dryer in the other hand to supply more heat and airflow.  4. Overbend the plank to compensate for springback.  5 Once you are happy with the curve, clamp the other end of the plank to the pan, turn off the heat and come back when it is completely cool.

 

Whenever you are trying to bend a strip of wood, test bend it first to see which direction it is "happier" bending.  Otherwise, you will end up with a lot of splintered wood.

 

I suggest you try this method using a hair dryer on high heat but without the water in the pan or the pan on the stove. Once the hair drier heats the wood sufficiently, I'll be it bends just as well as with the boiling water on the stove and with a lot less mess and risk of burning yourself. A hair curing iron or clothes iron applied directly to the wood are other good heat sources.

[tlevine]

Bob, I never said boiling.  I said low heat.  It heats the saucepan and the water adds weight to prevent tipping.  Back when I was a teenager I used a curling iron all the time...on my hair.  Got burnt more times than I care to remember.  But we all have our unique techniques.