First Day in Shop for Six Months - Disaster Struck

[Kim Strode]

After building a bender and new moulds in April I thought I was set to start a Weissenborn. I even had the wood sitting there from Tim and a new heat blanket from MEI.

I finally got back out there in the past few days. After preparing the sides I began the bending today with my first side and the new system - but all was in vain.



I sprayed both sides of the timber and layed the blanket on top followed by a stainless steel sheet. I turned it all on and after 2 - 3 minutes there was a lot of steam.

I turned off the blanket as I thought it was getting too hot and began the bending process. Centre partly down, then large bout, followed by the small bout.

The wood still seemed a little stiff so turned on the blanket again for another 2-3 minutes. I again began tightening everything up and turned off blanket. However, I heard cracking and realised the side had broken and part of the side was burnt.



Above is a pic of my bender.

I am now at a loss to know what to do differently with the other remaining side. I should at least sacrifice this to hopefully get a little closer to getting the bend right.

Any advice gratefully appreciated.

[Richard]

The problem to me sounds like you dried out the wood before starting the bend.

My procedure for bending is to firstly run the sides quickly under a tap, then get everything in place, switch the blanket on and start the bending procedure ( bringing down the waste clamp, working the cauls down the bouts) as soon as it reaches 100ºC which is never more than about 20-30 seconds in. The whole process of getting everything in place is generally done within about two minutes and from there I spend a few minutes monitoring it and switching the blanket off every time it reaches about 150º and on again when it's down near 100º.

Is the wood Alpine Ash? I just bent my first set of it (for a Weiss) the other day and it bent fine. The intense figuring had me a bit aprehensive but it's quite a nice timber to work with.

[Dave White]

Hi Kim,

What a bummer!! What thickness was the side?

I don't think having the blanket in direct contact with the wood is a good thing as the wood will likely scorch/burn before it reaches bending temperature. My set up going from the binding form upwards is slat - side wrapped in brown paper - slat - blanket - slat. I just lightly mist the side and wrap it in brown paper (the stuff that comes with Stew Mac orders is fab). Also did you have a digital thermometer to check the temperature at the wood before you started bending? And do you have a temperature control system for the blanket?

You need to get the temperature up to around 140-150C before you start the bending process and keep it there as you bend. Then you can turn it down for a few minutes and let the moisture escape.

If the sides are too thick then all of the above may not help and the sides may still crack or delaminate.

Hope this helps.

[kiwigeo]

Kim,

I wrap my sides in al foil after spritzing with water. The foil helps keep the moisture in.

I wouldnt get too worried about wrecking that side. So far this week Ive buggered my Stewmac thickness caliper and yesterday I totally stuffed up cutting side slots in a classical. Looks like were both having a bad week.

Cheers Martin

[graham mcdonald]

Try spraying the sides so they are fairly wet (or giving them a good dip in the bath). Wrap them in kitchen paper towels, just one layer, give them a squirt of water and then wrap that in aluminium foil and seal it up pretty well. Then slat - wood - blanket - slat. Heat it up for 2-3 minutes and start cranking down the waist. By this time it should be hissing and steaming a fair bit so get the rest pulled into shape, give it a couple of minutes of cooking (Do not leave the room - this is very important!) and then turn off. Smell as well as the hissing and steaming (or lack of it) is a good way of telling if the side is drying out too quickly. If you get the cooking just right most of the moisture will have been cooked off and by the time it cools down.

It only takes a few minutes for the water to steam off and then you have a rather hot heat blanket very close to a dry bit of wood. I came very close to burning the workshop down a few months ago. I don't have a thermometer or a timer on my blankets so a maximum of 4-5 minutes cooking after it is clamped to shape is my usual rule

cheers

graham

[ap404]

I can sympathise ... as I take a break from pulling out freshly installed frets and making a mess of a lovely sheoak fretboard ...

At least nobody got hurt.

When i see a disaster topic heading like that, i steel myself for the sight of luthier blood.

Deep breath, more luthier lubricant ... as a matter of fact ...


Cheers, AP

[Allen]

Luthier Lubricant. I like that. I think I'll have another thanks.

Kim. My set up is a bit of an idea that I stole from some other benders that I saw out there. I have my slats riveted together at the butt with a spacer the approximate thickness of my sides and heat blanket combo. The wood gets wet and then excess water squeegeed off. Then wrap in brown kraft paper and then a tight wrap of al-foil. This is then slid in between the slats with the heat blanket on top. Metal spring clips hold the slats together at a few points along the length to help concentrate the heat. I just lay this sandwich across the bending form in the approximate place that it will be bent.

I then switch on the heat, and set the timer for 3 minutes. By 2 minutes everything is sizzling and steaming. Also the sandwich is starting to sag at each end. I know then that the wood is getting elastic. I then pull the slats down around the lower bout and attack it in place. You can see a picture of this attachment in my Weisenborn thread.

Then I start to crank down on the waist press so that it pushes the waist about 1/4 of the way home. Then the upper bout is eased into place and clamped partially down. By now the 3 minutes is up, and I turn off the heat.

I continue to alternate between easing the waist tighter and the upper bout into position. Turn the heat on every now and then as you see fit. I don't have a thermometer. Just have a spritz bottle handy to spray the slats to gauge the temp.

I really think that the key is to wrap the wood in the al-foil. Makes a steam packet that really helps getting the wood elastic, and while it's still wet, it won't burn.

My 2 cents worth. And it's a real shame to see that side ruined. Hope that all the advice you get here helps you out.

[Kim]

Bummer Kim,

I go the same rout as Graham, damp wood wrapped in a single layer paper towel, wrap that in foil and seal. This slows down the escape of available moisture which in turn allows time for steam to build up and plasticise the wood. The entire sandwich then has a .010 spring steel slat for support both on the top and bottom.

I've only bent sides a few times using a direct plug from the blanket to the wall and just pull the plug when the steam, sound and feel tells me it's right but soon I will get around to wiring in a digital controller I have sitting there which will make things a little more scientific. But for now, using solid male/female forms ,I lay my sandwich on the female form and then line up my waist mark. I then lay my blanket on top of the sandwich and the hinged male form goes on top of the blanket and the blanket is then turned on.

As the heat builds, the steam rises and I hear the sizzle, it should smell like wet wood in a fire by around this time and I watch as the ends of the side begin to droop a little. When I see this happen I give one end a little bounce with my finger, if it does not spring back so well, say any more than around 75% of where it sat before, I know I am right to commence the bend.

First I bring down the waist to within around 1/2" of the form, then the lower bout all the way, and then the upper bout all the way. I clamp just enough to gently hold the ends against the form and then I bring the waist down the final 1/2" to pull down or iron out any issues. I then secure the ends more firmly and shut down the blanket for a while and then after a few minutes I plug the blanket back in for a few minutes and I do this cycle a couple of times.

I then let it all cool off to room temp and then hit it with the heat again but not for very long this time, just a few minutes until I feel it's back up to around where it was last time I shut it down. I then leave it sit over night or, I pull it out while still very hot and clamp it in the build mold using spreaders to hold it in shape.

Hope this help

Cheers

Kim

[Kim]

Must remember when I start to type something to stay put and get it done :shock Poor Kim has been flooded with solutions but the one reoccurring bit of advise here is the foil..

Cheers

Kim

[Allen]

Back to the Luthiers Lubricant Kim.

[Paul B]

You could always use that broken side for a mando, it looks big enough.

[matthew]

I turned off the blanket as I thought it was getting too hot and began the bending process. Centre partly down, then large bout, followed by the small bout.

The wood still seemed a little stiff

Although all the preceding is true, I don't think that's what broke your side.

If you only bent the centre bout partly down, then bent the upper and lower bouts, then you have little wriggle room left to complete the centre bout. Already the wood would have been cooler and stiffer and winding down the centre once the upper and lower are already fairly tightly curved and clamped in place would, in my humble bass-makers opinion, have put too much strain on the slat. Bang. Wood doesn't stretch.

I would have wound the centre bout ALL THE WAY DOWN first, carefully, THEN done the upper and lowers.

[Bob Connor]

How thick were your sides?

[Dave White]

I'm not sure about the foil thing. There should be enough moisture in the wood itself with a little light spritzing and the wrapping in craft paper and slat "sandwich" should be enough to let the moisture plasticise the wood at the correct temperature - plus you want to cook the moisture out once the side is bent to avoid rippling. The Taylor Factory Friday's videos on bending are worth a watch/listen for this.

The crack seems to have happened at the upper bout bend going into the hollow neck area. I suspect this was because the wood was too dry at this stage of the bend, plus the support on the bending form in this area may not be enough. Kim - is your bending form solid or hollow with cross slats in this area? Any chance of a pic?

Also as I asked and Bob echoed - what thickness was the side? Hard to tell from the pic you posted.

[hilo_kawika]

After years of heart (and wood-) breaking disappointment in dealing with highly figured koa wood for sides, I finally have a system which works consistently for me. Bob Gleason (Pegasus Guitars and Ukuleles) gave me some very useful leads for this process, some of the elements of which have been mentioned above.

In any case, here's the gear list:

1. To control the heat in the silicone blanket, I use a router speed control box set at ~60% of the full setting. The blanket gets hot (it only needs to be a little less than boiling water temperature) but not too hot.

2. A darkroom timer clock obtained from a garage sale for $1 about 20 years ago. OK, I paid too much but WTH...anything for lutherie. This device shuts off the heater after a predetermined time. But you should still watch the process, right?

3. 6" wide aluminum (I know I spelled it wrong) flashing from the hardware store. A roll of this stuff is pretty cheap and can be used for all sorts of stuff besides gutter repair.

4. Paper work "cloth". This stuff is from the automotive supply place and basically is heavy duty paper towels disguised to look like cloth for wiping greasy hands.

5. Aluminum foil.

6. Bending form

7. Side(s) to be bent

8. Silicone heating blanket

9. 2 pinch clamps

The process:

1. Cut a piece of the aluminum flashing ~ 2" longer and the same width as the largest width of the sides. Also cut a piece of the work cloth the same length and width of the sides. Cut a piece of aluminum foil a little longer than the sides and a couple of inches wider than twice the width of the sides.

2. Make a mark on the side of the bender at the center of the waist. Take the piece of aluminum flashing, and place it on the bender such that it is everywhere touching the bending surface of the form and overlapping an inch or so on each end and mark on the flashing where the mid-waist point is on the side of the bender.

3. Now moisten the paper work cloth such that it's wet but water isn't dripping off of it. You can squeeze it out a little more if you wish. Put the work cloth on the underside of the side to be bent and wrap the whole thing with the aluminum foil. Now make a "sandwich" of the silicone blanket (bottom), wrapped side ( next) and finally the flashing. Hold the whole thing together with the two pinch clamps about 10" apart from one another.

4. Place the "sandwich" on the mold, lining up the bender mark with the flashing mark, and slowly lower the waist clamp onto the side. At this point you only want to have the "sandwich" held in place by the clamp. Align the "sandwich" so that it's parallel to the long axis of the bender.

5. Preheat the silicone blanket for about a minute. Steam should start to come out of the ends of the foil soon. Now begin tightening the waist clamp a little and then the other clamps. Return to the waist clamp and so forth until all clamps are firmly down. This takes me about 3 minutes for any sized ukulele so a guitar might take another minute or so.

6. I continue to heat the form for a TOTAL of ten minutes at which point the timer shuts off the heater and makes a very loud noise. I allow the sides to cool either naturally or with a fan on them. Usually they're pretty dry, but clamping them in the form after removing them from the bender is always a good practice.

After I began using this setup, I never broke another set of figured sides. If pictures are wanted, I'll be happy to dig some up.

[sebastiaan56]

I hand bend, no foil no nothing, it was the bloody timber! Now wheres the lubricant gone.....

[Kim Strode]

Thanks everyone for your advice, I will experiment with the remaining side, before bending the new sides Tim has put in the mail.

The sides are Alipne Ash and were 2.5mm thick.

I am bending over a solid mould made with 20mm custom wood with bracing side to side, which has a stainless steel sheet screwed to the sides.

[Craig]

G'day Kim,

I guess that's fairly thick for most woods and probably has a lot to do with your breakage.

I bent my last at 2.5 mm. , but it was a very easy bending type of wood ( Oregon Myrtle ) and got away with it.

You may have to resign yourself to bringing the side thickness down a little to maybe around 2.1 mm. ( .083 " ) or there abouts . Maybe even thinner if it's figured

Bob would have better info on this as he has recently bent some Tas . Oak ( Alpine ash ) ,I haven't !

Pleased to see you up and about again Kim ! ' Ya can't keep a good man down '

Cheers Craig

[Bob Connor]

I use .080" as a standard thickness for sides and the Tasmanian Oak that we used recently was indeed that thick.

[Richard]

I just measured the side offcuts from my alpine ash and they came in at 2.2mm (0.087"). I tend to leave the sides a tad thicker on Weissenborns than I would for other guitars of a similar body size because of the integrated neck. 2.5mm for me is relatively normal.

I think the scorching tells it all... the side had dried out before the bending got underway.

Interesting how everyone seems to have their own "failsafe" bending methods. I guess there's truly more than one way to skin a cat.

[kiwigeo]

Im with Richard....the wood was just a bit too dry.

[Kim Strode]

Thanks for the tutorial Bob.

I tried bending side number two this afternoon, following a combination of advice received throughout the day. There was no cracking sounds this time, or smoke, but I'm leaving the side in overnight to see how much spring back occurs.

After a preliminary peak, the bend nearest the Weissenborn neck doesn't seem to be holding it's shape and is springing back considerably.

We'll see what the morning brings? I'll post a picture of the end result in the morning.

[kiwigeo]

Kim,

Good to see you back in the shop mate.

Once that sides cooled down try giving it another quick blast with the blanket. I follow Hesh's method where you heat the wood and bend, let it cool and then give it another blast with the blanket. It works for me.

Cheers Martin

[Allen]

I did the same with the Backwood. Let it cool and hit it again for another 3 minutes. Very little spring back. I make most of my sides between 2 and 2.5 mm, most closer to the 2.0 mm mark.

[Kim Strode]

After reading all the helpful comments I tried bending the second side yesterday. This bend was far more successful, but there still is tearing in the wood in the bout closer to the neck. Next time I think I should bend the smaller bout first, while the wood is warmer, and then bend the large bout secondly.


I measured the thickness of the sides again this morning. The first bent side was around 2.6mm thick, while the second attempted side was more like 2.75mm - a little too thick.

As these sides are for a Weissenborn I think they should be around the 2.3-2.4mm thickness?

When I attempt my next bend I'm still not sure what changes to make in my procedure, apart from side thickness?

The temperature was close to 150º when turned it off and started bending. I thought the wood was wet enough and wrapped well. The side was wrapped in paper, then foil.