Bending iron

[Felefar]

5 hours ago, Jerry Pasewicz said:

There must be another explanation, otherwise our houses would get taller when it is raining.

They do. Wood shrinkage and expansion with changes in humidity have to be taken into account when building any large wood construction. Space needs to be left in for differential expansion.

[PASEWICZ]

4 hours ago, Felefar said:

They do. Wood shrinkage and expansion with changes in humidity have to be taken into account when building any large wood construction. Space needs to be left in for differential expansion.

Of course.  It is longitudinal expansion we are talking about which is so insignificant it is not even listed in the charts of expansion/contraction characteristics.  Tangential and radial are the dimensions in question, and even Hoadly writes “longitudinal shrinkage is considered negligible” when giving an example of a green 8ft 2x4 taken to 8% MC would shrink only about 1/16”.   I do not know anyone that would build a house from green wood, so the 1/16” inch is from worse case scenario....I am sure we could do the math and calculate the difference in wood moisture content between when it is not raining compared to the end of a 4 hour rainstorm.....but I think you get the point.

[Okawbow]

12 hours ago, Andreas Preuss said:

Using a bending iron seems to me like waste of time. Soaking ribs I water let them dry on a special mould and then give them the final shape on the inside or outside mould is more time efficient. Ribs simply need to be thin enough.

Interesting. 

I make recurve archery bows, and use maple laminations that are over 1.5mm thick. I use a form to hold the parts and press them together until the glue dries. No problems with cracking.

 I would think a form could be made for ribs, that could be heated along with the rib wood in a small oven. The wood could then be clamped in the form and heated to about 90 degrees C for a few hours. Let cool in the form for 12 hours, and the ribs should hold the shape. No water needed. 

 

[PASEWICZ]

1 minute ago, Okawbow said:

Interesting. 

I make recurve archery bows, and use maple laminations that are over 1.5mm thick. I use a form to hold the parts and press them together until the glue dries. No problems with cracking.

 I would think a form could be made for ribs, that could be heated along with the rib wood in a small oven. The wood could then be clamped in the form and heated to about 90 degrees C for a few hours. Let cool in the form for 12 hours, and the ribs should hold the shape. No water needed. 

 

If you look at a good Lithiers catalog, that is very common with guitar makers.

[Felefar]

Furniture makers (at least in Scandinavia) use steam forming, steaming the wood under pressure and then bending it to shape. I imagine that is a bit of the same as using an iron, except that the steaming is done in a separate step?

[Carl Johnson]

1 hour ago, Okawbow said:

 I would think a form could be made for ribs, that could be heated along with the rib wood in a small oven. The wood could then be clamped in the form and heated to about 90 degrees C for a few hours. Let cool in the form for 12 hours, and the ribs should hold the shape. No water needed. 

heated molds have been done for guitars  - Arthur Overholtzer made a guitar side shaped and sized mold out of aluminum with an integral electric heating element - but it's easier and cheaper now to use a silicon heating blanket. you can purchase them quite cheap from china on eBay. use a positive mold made from MDF/plywood/chipboard , then various springs/clamps to bend the heated rib over the mold

with steam bending in my experience you have problems maintaining surface flatness the more the width exceeds the height of the workpiece.

[Okawbow]

2 hours ago, Carl Johnson said:

heated molds have been done for guitars  - Arthur Overholtzer made a guitar side shaped and sized mold out of aluminum with an integral electric heating element - but it's easier and cheaper now to use a silicon heating blanket. you can purchase them quite cheap from china on eBay. use a positive mold made from MDF/plywood/chipboard , then various springs/clamps to bend the heated rib over the mold

with steam bending in my experience you have problems maintaining surface flatness the more the width exceeds the height of the workpiece.

I was thinking more about a two piece mold that would compress the rib all at once. My recurve form uses a fire hose with the ends plugged and filled with air pressure after the two halves are bolted together. The pressure forces the wood strips flat against the lower half of the form, that has the exact shape needed. 

 

The hose might not be needed if a rubber pressure strip is used and a mechanical clamp system is used to bring the two halves smoothly together.

[Muswell]

11 hours ago, Jerry Pasewicz said:

   I do not know anyone that would build a house from green wood,

I did .  I once had a project to design a large meditation hall for a buddhist monastery and suggested to the architect that we use green oak.  That's what we did and the monks love the way it has aged and moved over the last 20 years.  Traditional oak building was to cut down the tree and immediately make the components in-situ in the forest.  The quicker you shape the wood and cut the joints, the easier it is and then you transport the least weight. The building was then assembled ASAP.

[David Burgess]

On 9/1/2019 at 2:28 AM, Andreas Preuss said:

Using a bending iron seems to me like waste of time. Soaking ribs I water let them dry on a special mould and then give them the final shape on the inside or outside mould is more time efficient. Ribs simply need to be thin enough.

I bet I can do it in fewer labor-minutes with my bending iron.

[saintjohnbarleycorn]

3 hours ago, Muswell said:

I did .  I once had a project to design a large meditation hall for a buddhist monastery and suggested to the architect that we use green oak.  That's what we did and the monks love the way it has aged and moved over the last 20 years.  Traditional oak building was to cut down the tree and immediately make the components in-situ in the forest.  The quicker you shape the wood and cut the joints, the easier it is and then you transport the least weight. The building was then assembled ASAP.

yes green wood houses are not rare the do move though 

[Andreas Preuss]

@David Burgess Would be a funny race! Maybe we should stop the time independly (without cheating!) 

[GoPractice]

On 9/1/2019 at 3:35 AM, Andreas Preuss said:

 ( ... )  Looking at the rib thicknesses of Strad however their measurements strongly suggest that the ribs have been bent by soaking and dried on a mould to give them their shape. Usually they are around 0.9 - 1.0 mm in the long arcs of the ribs and thinner at the narrow arcs of the corner blocks.  

I use this method for my Strad copies. I soak the ribs in cold water over night and the press them on a form. The form has a slightly narrower curve than the curve I want to achieve because when taking the ribs out they open up a little. If I can I let them dry for a week. When glueing them on the mould I wet them again when necessary. 

I am preparing to start some experiments based on soaking. 

But have doubts on any personal successes. This method is appealing in many ways. Firstly, though, to get more uniformly supple ribs, I have intuitively added more water to the ribs and essentially have been steaming the ribs into shape. Not knowing the long term consequences of this, i checked under a microscope looking for flaws to the maple compared to using an iron with more direct heat. I certainly noticed where i was still tearing out material when the blade would skip. Some types of figure in the wood still pose difficulty to my level of technique, which leads to thicknesses questions. 

My thicker material, closer to 1.2 - 1.7mm ( average < 1.5mm, thinned to 1.2mm ) were previously attempted at being shaped. Perhaps it would be wiser to first experiment with bending thinner ribs. My physical perception was that too much heat made the ribs more brittle, and in some places more than others - obviously - even though i also believe they become more supple over time. Would the water formed ribs also relax over time?    

Are the forms ( moulds ) used to bend the ribs, solid? Is there a good way to dry the ribs in the form, ( sunlight, fan? ) or is an effort made to slow the drying process. Or it just dries? 

The thought of using 1mm ribs has me re-thinking the construction. Are any sections of the rib areas reinforced? Is this too thin for thin spirit varnish?

[Andreas Preuss]

3 hours ago, GoPractice said:

I am preparing to start some experiments based on soaking. 

But have doubts on any personal successes. This method is appealing in many ways. Firstly, though, to get more uniformly supple ribs, I have intuitively added more water to the ribs and essentially have been steaming the ribs into shape. Not knowing the long term consequences of this, i checked under a microscope looking for flaws to the maple compared to using an iron with more direct heat. I certainly noticed where i was still tearing out material when the blade would skip. Some types of figure in the wood still pose difficulty to my level of technique, which leads to thicknesses questions. 

My thicker material, closer to 1.2 - 1.7mm ( average < 1.5mm, thinned to 1.2mm ) were previously attempted at being shaped. Perhaps it would be wiser to first experiment with bending thinner ribs. My physical perception was that too much heat made the ribs more brittle, and in some places more than others - obviously - even though i also believe they become more supple over time. Would the water formed ribs also relax over time?    

Are the forms ( moulds ) used to bend the ribs, solid? Is there a good way to dry the ribs in the form, ( sunlight, fan? ) or is an effort made to slow the drying process. Or it just dries? 

The thought of using 1mm ribs has me re-thinking the construction. Are any sections of the rib areas reinforced? Is this too thin for thin spirit varnish?

Actually I didn't expect that my comment here would create so many responses. I'll make a new thread on this soon. 'Cold fusion ribs'.

[Janito]

18 minutes ago, Andreas Preuss said:

'Cold fusion ribs'.

You do know, don't you, what happened to the 'Cold Fusion' delusion?

[Guest]

Cold bending ribs....my thoughts drift to ct 

[FiddleDoug]

On 9/1/2019 at 2:28 AM, Andreas Preuss said:

Using a bending iron seems to me like waste of time. Soaking ribs I water let them dry on a special mould and then give them the final shape on the inside or outside mould is more time efficient. Ribs simply need to be thin enough.

You're kidding , right? You mentioned in a later post that you let them dry for a week? That's what I would call wasted time! It takes less than a minute for each rib section on a bender.

[Okawbow]

I’m making a double bass in my spare time. What a chore it was to bend those ribs!

I used a steel pipe with a gas torch aimed inside and adjusted for the right heat. Took lots of heat and water just to get them bending. Had to bend them. close and clamp to the form while still wet, then dry out the wood with a heat gun. Left them clamped a day or two before gluing. Used ash wood, which probably bends easier than maple. 

[not telling]

26 minutes ago, FiddleDoug said:

You're kidding , right? You mentioned in a later post that you let them dry for a week? That's what I would call wasted time! It takes less than a minute for each rib section on a bender.

Hmm, but some people want to remove tension from the structure. If I had to guess, I'd  guess that's what he wants to do. Why is everyone suddenly so rude to each other here?  Apparently I must return to help civility and sweetness prevail on these forums once again. Yes, that was a joke.

[Jim Bress]

45 minutes ago, Okawbow said:

I’m making a double bass in my spare time. What a chore it was to bend those ribs!

I used a steel pipe with a gas torch aimed inside and adjusted for the right heat. Took lots of heat and water just to get them bending. Had to bend them. close and clamp to the form while still wet, then dry out the wood with a heat gun. Left them clamped a day or two before gluing. Used ash wood, which probably bends easier than maple. 

The ash wood looks really nice.  Will this have a single or double mast? 

[Okawbow]

I like the two masted schooners. Here is the one I built 7 years ago.

 

[Jim Bress]

Awesome! 

[FiddleDoug]

1 hour ago, not telling said:

Hmm, but some people want to remove tension from the structure. If I had to guess, I'd  guess that's what he wants to do. Why is everyone suddenly so rude to each other here?  Apparently I must return to help civility and sweetness prevail on these forums once again. Yes, that was a joke.

I don't think that air drying wood removes any more tension than heat bending, where the heat actually softens the lignin structure of the wood, and allows the bend to lock in after it cools.

https://www.fpl.fs.fed.us/documnts/usda/ah125.pdf

[HoGo]

1 hour ago, not telling said:

Hmm, but some people want to remove tension from the structure. If I had to guess, I'd  guess that's what he wants to do. Why is everyone suddenly so rude to each other here?  Apparently I must return to help civility and sweetness prevail on these forums once again. Yes, that was a joke.

There is quite simple physics/ chemistry behind bending wood. Perhaps a bit simplified, water and heat act as plasticizers (both work alone, but most effective when combined) - they loosen the bonds beween the wood fibers and after drying and cooling the bonds will reconstitute. So if you use cld bending with just some water the bonds don't get as plastic as possible and bending stresses will remain in the wood (they will stabilize after time) If you use heat the wood becomes more plastic and after cooling less stress is left in the wood (you don't need to add too much water to thin ribs as wood contains some water already and the extra water acts more as heat conductor than plasticizing agent and can cause wood become weaker along the cross frain on curly maple - water and thus heat penetrates faster along the open endgrain).

Especially important thing is what stresses you induce in the wood during bending. Thick beams must be supported by metal straps on outside of bend anchored at both ends of wood so only compression is applied - otherwise the wood will break. for thin pieces like ribs this is far less important but good bending strap holding the piece tight against iron will make the curly maple behave better.

BTW: here is some sophisticated bending jig by Tom Ellis:

https://www.ruttlist.com/features/lets-build-a-mandolin-tom-ellis-464-2

[Andreas Preuss]

2 hours ago, FiddleDoug said:

You're kidding , right? You mentioned in a later post that you let them dry for a week? That's what I would call wasted time! It takes less than a minute for each rib section on a bender.

As I said above, 1 week is not taking my working time. But you can actually put the ribs on the mould before you finish work and use them the next day. If you are really impatient you could use an oven, but I have never done that. 

The thing which is quite different with the cold bending is that you learn somehow to adjust the thickness to the bending properties when thinning down the ribs. With hot bending this is completely irrelevant as long as ribs are not way to thick. 

[Anthony Panke]

Greetings all. Having read the suggestions on this thread (thanks!), I bought a bending iron from dictum. This is button operated, no dials, and temperature-regulates to 2-3’C accuracy. I made a solid base out of some maple, and it works really nicely- the curves are good for bending, being quite flowing. 

I will put up a video of me using it soon