Bending Sides issue

[CNCWorksNZ]

Hi Guys, first time trying to bend Sides using a Mold.
I've bent Sides on a Pipe before, but this is the first try at this method.
These are for a Baritone Ukulele and are 75mm wide X 1.8mm thick, and are of New Zealand Tawa, (a native Hardwood).

I soaked them in very hot Water for about 3 minutes then bent them up using a heat Gun.
They bent OK, but I have experienced some 'Cupping' at the Waist.

Has anyone else had this issue? Moreover, what can I do to fix it?

I'm thinking that; if the cupping is still present after the Sides are in the Outside Mold with the Lining fitted, I could fit Side Braces each side of the Waist to control it, but .... I will await your enlightenment ...

[kiwigeo]

"I soaked them in very hot Water for about 3 minutes then bent them up using a heat Gun."

This may be part of the problem. If you soak them in water and then apply heat to one side with a heat gun I reckon theres a good chance you're going to get cupping. One side is drying out from the heat gun while the other is still soaking wet.

If you're bending around an internal mod then you need to apply heat over the entire side using a heat blanket on the outside or heat from bulbs on the inside (ie fox style bender).

[56nortondomy]

I don't think a heat gun is really the way to go, if you're going to the trouble of building molds you may as well get a blanket like Martin mentioned and use that. I just give my sides a quick spray with water I don't soak unless it's a cutaway.
Wayne

[CNCWorksNZ]

If you're bending around an internal mod then you need to apply heat over the entire side using a heat blanket on the outside or heat from bulbs on the inside (ie fox style bender).

I used the Heat Gun from both sides. As the Fox Bender only heats from one side I would expect the same issue?
I'm wondering if this is why the Steel Plate are used? To stop deformation like this perhaps?

Murray.

[kiwigeo]

I think the problem relates to the soaking you gave the wood before applying the heat. When I bend using a blanket or iron I spritz the side with water...just enough to get a bend. The side is also wrapped in paper so the moisture can't escape quickly as the heat is applied.

The steel slats would help keep the sides flat as would a larger waist caul.

The sides look like theyre flat sawn (correction)..is this the case?

If you're bending around an internal mod then you need to apply heat over the entire side using a heat blanket on the outside or heat from bulbs on the inside (ie fox style bender).

I used the Heat Gun from both sides. As the Fox Bender only heats from one side I would expect the same issue?
I'm wondering if this is why the Steel Plate are used? To stop deformation like this perhaps?

Murray.

[graham mcdonald]

The wood does not look very much like it is quartersawn, more back sawn with the grain is going across the thin piece of wood. As back sawn wood dries (and heating it with a hot air gun is drying it very quickly) it is going to cup in that way. With some timbers it does not matter very much. I suspect with your piece of wood it does And as others have said, a heat gun in not the best way to bend timber. You need at least 150C to bend timber and either a length of metal tubing with a propane torch heating it or a silicon heating blanket and a mould is by far a preferable way of applying the significant amount of heat to effectively bend a strip of wood for the side of any stringed instrument. It is much about a quick and efficient application of the heat as the temperature.

[TallDad71]

Wood is a sponge where moisture is concerned. Soaking it will change the all 3 dimensions, especially the thickness in ways that cannot be controlled.

Like all luthiers i have tried many different ways of bending sides, the best has always been a heating iron and water sprayer when needed. This is a shame as it is messy, smelly and time consuming.

Certain woods don’t give as well in which case I favour a heat blanket at around 80°C working slowly around a mould.

I’m not too sure I would ever want to soak wood before I started regardless of it pliability.

[rangerdave1]

I recently bent Ebiara sides, soaked in water and used an iron. I got a cupping between the grain lines and a few cracks on the edges.. The second set was birdseye maple which I bent dry and they bent perfect without any burning or issues.

I won't be soaking next time.

[kiwigeo]

My typo..meant to say flat sawn...

The wood does not look very much like it is quartersawn,

[Blackstar1099]

It must be an epidemic. I hope you don't mind me posting in your thread Murray, but I had the same issue with some flame maple on a bending iron. I didn't soak, just spritzed it but I didn't use a steel slat on top as it was bending easily. Now I know to use the slat.

So is there a way to flatten them?

Piero

[CNCWorksNZ]

It must be an epidemic. I hope you don't mind me posting in your thread Murray, but I had the same issue with some flame maple on a bending iron. I didn't soak, just spritzed it but I didn't use a steel slat on top as it was bending easily. Now I know to use the slat.

So is there a way to flatten them?

Piero

No problems Piero, keeping the same Topic in the same Thread is always good .... I'll be taking mine out from the Bender this Weekend and putting them in the Outside Mold. I'll then try the Steam Iron on them & report back ...
.

[Blackstar1099]

It must be an epidemic. I hope you don't mind me posting in your thread Murray, but I had the same issue with some flame maple on a bending iron. I didn't soak, just spritzed it but I didn't use a steel slat on top as it was bending easily. Now I know to use the slat.

So is there a way to flatten them?

Piero

No problems Piero, keeping the same Topic in the same Thread is always good .... I'll be taking mine out from the Bender this Weekend and putting them in the Outside Mold. I'll then try the Steam Iron on them & report back ...
.

I've decided to make a solid MDF inside mould and attach a slat with springs, like a cheap fox bender. I'll put the side on mould and steam with an iron and slowly move the slat down and hope I don't hear a crack.

[Dave M]

This has probably happened to all of us at some time. Unless you are particularly good with the bending iron the most consistent method is with some kind of variation on the Fox bender, using those metal slats to fully support the outside of the bend.

As has been said elsewhere you can do some sanding if you have a decent thickness of side. If necessary adding a lamination to the inside to maintain strength. If the guitar is for yourself of course you can just live with it. It shouldn't matter too much structurally - if you are worried then reinforce with some internal struts.

It does get better with practice!

Dave m

[Dave M]

There is a useful current thread on bending on the OLF. -Bending Different species-

[CNCWorksNZ]

There is a useful current thread on bending on the OLF. -Bending Different species-

OLF?

.

[Gazm]

Official Luthiers Forum, The answer too many topics Murray!!

Gaz

[kiwigeo]

Other Luthiers Forum

There is a useful current thread on bending on the OLF. -Bending Different species-

OLF?

.

[johnparchem]

I bend both on a fox style and a bending iron. I never soak the wood, rather I lightly spritz it with the goal of initially quickening the heat transfer into the wood. On a pipe I like to bend very hot with only a light spritz, I always thought that wet wood would try to limit the temperature in the wood to about 100 C while the water is changing to steam. My uneducated guess is the cupping happens with uneven moisture content in the wood while heating, then the cupping gets set when the wood drys out.

I have used veneer softeners on very figured wood in a fox style bender. In that case I am relying more on a chemical process to plasticize the wood rather than pure heat. I found that that the heat evaporates the veneer softener and the wood is set after bending.