First time bending..

LabRat_3k

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A new thread for a new project/build.
History: This will be my fifth Ukulele, with the first four being "Stewmac Concert Kits". See forum threads:
Builds #1 & #2 and Builds #3 & #4.

This next build will be different, in that I won't be using a pre-made kit. Instead opting to try and prepare the wood myself *including BENDING!!
The neck, fretboard, and tuners, have been sourced from Aliexpress, along with a pre-made bridge and nut.

Wood : Cherry bookmatched pieces from EdCo Fine Woods

The Work so far: Building the bender

The Buck: based on the profile of the StewMac kits, I used the laser cutter on 3 mm plywood, to create a master template. This template was then duplicated onto left over 3/4" plywood, and mdf scraps, to create the 4" wide buck. Simple 1/4" eye bolts with washers and wing-nuts to secure the clamps that will be used to hold the wood in place.

The controller: Along with the 350W heat blanket, I purchased (Amazon) a simple PID controller, that can be used to keep the blanket at a consistent temperature. However, as I wanted to be able to run the blanket for a pre-determined time (exact length to be determined), I created an adjustable timer circuit that will drive power to the PID controller. This will enable turning the heating blanket on for no more than... .. 10? minutes .. and then entering the cooling off period.

Here's a photo of the setup, with my "Bender 1.0" controller, the heat blanket, the buck, and the first side mocked up for bending.

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Close-up of the BENDER 1.0 - showing temperature measured at 25C, and counting down 1:56 for this demo.
The green/red buttons will add/subtract 1 minute to the timer, for each press. When the timer hits 0:00 power to the PID is disabled.

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The wood for the sides has been sanded down to approx 1.5mm (I was aiming for 1.7 but over-did it). This has been several weeks (months) in the planning, and I think the next steps are to go ahead and try to bend. Just a little nervous about this first attempt (Cherry), with three other side/sets in the queue.
The plan is to start with the cheaper wood(s),and work my way up to the more challenging (and expensive) ones.
So the first will be the Cherry, followed by Sapelle, English Oak, and finally KOA.

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Any advice for "gotchas" on that first bending attempts, would be welcome.
 
Well you certainly approach these things well prepared. Impressive... Your sides are nice and thin at 0.062" which should bend nicely. Are you going to wet the wood before bending? Using a wood softener? I wrap mine in foil too.

Since I don't use a heat blanket and just bend over a form with heat, I use feel to know when it is time to clamp down. As for heat, I think you want to aim for just below boiling, but again I don't use a controlled heating source so not really sure here.

My advice: Wood will bend when it wants to so don't rush things. It will actually begin to feel a little rubbery. It really usually isn't that big a deal and is quite satisfying to do. Good luck.

PS: When I used to use Koa, I found that it was well behaved and easy to bend.
 
@sequoia Thanks for reading and jumping into the thread.

I am basing most of my plans on the combination of "reading way too much on the internet", and the specific video of "Pat Hawley Bending Sides for a Ukulele". Yes, the plan was to WET the wood then sandwich with wet brown paper, foil, and sheets of spring steel. I have read that amonia can be used as a wood softener, and that amonia based WINDEX is a suitable low cost alternative to "veneer softener". But as with "all things on the internet", I think it wise to take such claims with a healthy dose of scepticism. So I was going to try with just water the first time.

Mr. Hawley's KOA based build used 2mm thick sides, without issue, but when I had my cherry sides at 2mm they felt 'very stiff', so I was gun shy and opted to go a little thinner. (I think it was a thread here in the UU forums, about someone who had several sequential "broken cherry sides during bending" that got me nervous.
 
Cherry and oak both bend willingly and easily, and have the benefit of minimal spring back in my experience. They are good choices to learn with.
I start the bending process at about 250 degrees at the waist and let the temp get up to but not above 300 for 10-15 mins.
The real trick to begin with is resisting the temptation to remove from the form too early to see how you did. Let it cool right down.
 
Looking at your setup:

1. Get some leather rigger/gardening gloves - you'll be pushing the ends down by hand and they will be hot!

2. When tightening down the waist it's a good idea to press it down with gloved fingers first - you'll feel if it's ready. And when you get the waist down to the form don't tighten too much - I made a similar bender but with light bulbs, and on my first try managed to press a dent into the waist.

3. Make sure your heat blanket is in contact with the sides everywhere - maybe wooden clothes pegs? When you press the ends down to the form the last inch or so might not want to bend, so I cut my sides over length to allow for this.

4. The purpose of water is to turn to steam and drive the heat into the wood. So I wouldn't soak the wood - rather, I'd put wet paper (something which holds more water than copy paper, but less than blotting paper - I read of kraft brown paper in the US being used) between the blanket and the wood. For the same reason I wouldn't wrap completely in foil, as the steam needs to get through the wood and escape. Too much water will lead to cupping of the sides.

My experience is the same as Orra, cherry and oak bend quite easily. Koa is usually easy too, unless it's highly figured.

Sapele can be really hard to bend - I suggest less water, maybe more heat for a shorter time, and fingers crossed. Some boards just won't cooperate, others bend OK but feel really stiff until they finally let go. I find that if you heat sapele and mahogany too long it gets stiffer and won't bend at all.
 
@ProfChris & @Orra. Thank you both for your insights.

Hoping that tonight will be the night I pull the trigger. Wiping down the boards with water, and then layering with the damp brown paper (sliced off from a standard "leaf bag/garden refuse"). Based on your feedback, it seems I should change my project order and shift the Sapelle out from being second to third. Why third? To keep the KOA last, as that's the one for which I wanted to have the "most experience" before tackling.

Gloves are present and ready. Sides are pre-cut trimmed with approx 1" extra at each end.

Thoughts on running a second "heat/cool" cycle before removal from the buck? I've read one or two articles that mentioned doing this if there was too much springback. Am I overthinking the situation?

Based on readings and your feedback above my plan is...
  1. - set the temp to 150C / 302F - 10 minute timer
  2. - start clamping down the waist temp hits 135C /275F
  3. - then the neck end, followed by base/bottom end.
  4. - tighten the waist further (but not so much as to dent the wood (I hope))
  5. - once bent .. leave at temp for remainder of 10 min.. then auto-shutoff and allow to cool.
  6. - re-start a 2 minute timer (bring temp back up to 150C/302F)
  7. - allow to cool - remove from the buck.
  8. - repeat for the "other side" or 'study results and theorize what went wrong' ;)
 
You have enough variables and learning to do that you should try some wood that you don't plan to use for anything, just to get a feel for the process. Reading about the process is not the same as doing it. Good luck!-Bob
 
I'm not sure you said you are wrapping your wood in aluminum foil but that is a must for me, both from moisture and preventing staining. Also I leave the waist up about 3/8" and only crank it down that final amount after the ends are clamped loosely down into their final position. I want the wood to be pulling at both ends rather than compressing. This reduces breakage at the waist. Leaving at full heat for ten minutes after bending would be for me. I shut down after bending allow to cool then run back up to 275F then shut down and allow to cool. If you are a little under on your bending and have a little moisture in your sides it is far better than scorching in which case your wood is lost.
 
Funny how what works for some does not work for others. I'm always interested in improving bending.A few years ago I tried aluminum foil wrapping on koa. The stains were so bad that I threw the wood away. I have not tried it on other woods. Same deal with ammonia. Total disaster, stainwise. Those are only results with koa, so I've never tried it again on any other woods. I also never have problems with breakage at the waist. If breakage occurs, it is always at the front bout. Since I start bending fron the tail on my bender, doing the easiest bend which is the lower bout first, the waist and front bout are always well heated before I get to them. Maybe that helps me with less breakage. Now that I've said that I'm likely to break the next set I try!!!!!! The more curl, the more exciting things get. Cheap thrills!
 
If breakage occurs, it is always at the front bout.
That has always been my experience on breakage, and usually due to grain run out or extreme curl which is sometimes related. Every type of wood bends a little differently. I thin to about .08 inches and it always seems to bend fine. I bend on a similar bender and don't go through all the extra wrapping etc, just spray the wood with water as the blanket warms up and by the time the blanket is ready I start bending directly on the heat blanket at 120 degrees celsius without anything on top. You will find the method that works best for you, it is not as hard as you may think it will be.
 
Funny how what works for some does not work for others. I'm always interested in improving bending.A few years ago I tried aluminum foil wrapping on koa. The stains were so bad that I threw the wood away. I have not tried it on other woods. Same deal with ammonia. Total disaster, stainwise. Those are only results with koa,

It is also funny that I do methods and techniques that might be inefficient or just plain wrong, but I keep doing them because, well, that's the way I do things. Changing that is harder than I thought...

I use ammonia with aluminum foil and have never had (much) of a staining problem. If there is some discoloration, it is not deep and sands away quickly... Really the only problem I've had bending is with ebony (never again) and some really curly koa bindings.
 
Have not had a staining problem with foil and Koa. Looks like hell out of the bender but as Sequoia experiences its right on the surface and comes off in normal sanding. If it was a problem I would use paper bag strips as a barrier. Many woods bend very easily. Most Koa, Walnut, Myrtle bend very easily. Some like Leopard Wood and Rosewoods can really be a tough. One of the reasons I use foil especially on the really hard to bend woods is so I can spray the sides with veneer softener keep it in the foil wrap so it doesn't dry out and let it sit for a day before bending.

Nice job and making that temp controller. You obviously have skills.
 
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The cherry was meant to be my “practice wood” so I went ahead and took the plunge this evening (for the first piece). Stuck pretty much to the proposed plan. Picture of the bend in progress, and the amount of rebound in the wood when completed. So not a 100% success, but certainly a workable first attempt. The last image shows the side clamped into the mounting jig.

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And…
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After a day clamped in the jig the spring back was all but gone. So I went ahead and tackled the second side. Smooth as silk but again a fair amount of spring back. Spent overnights in the jig and I’m calling the experiment a success. (Minor water staining on the interior sides)
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(And from the sides)
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The snafu was finding just how inaccurate my placement of the waist was. This last photo will capture the pencil line for the waists, and the gap between them.
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Very pleased with the first attempts. Next steps for this build.. decide on the "bling" to add to the front, and get the laser to cut it out for me. For the next next build.. I plan to make a 'shooting board' as I'm not completely satisfied with the joinery I managed on the cherry front & back. (I'll post pictures of that later)
 
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All looks good.
The only reason to be concerned with the mismatch of waist positioning in practical terms, assuming you have enough length to play with of course, is having a nice mirror image of grain at the tail end joint of the 2 sides.
This is more of an issue in more radically grained/patterned wood, where the mismatch stands out more. This can be negated somewhat with the use of an end graft/butt wedge (call it what you will).
Your cherry seems fairly straight and even grained, and I’d guess it will be relatively forgiving in making it look quite nice with or without some kind of end graft.
Good job.
Btw, how far have you got with your top and backs?
If you’ve not yet done a rosette, or cut a soundhole in the top, and you have enough material in the lower bout area, then you could consider cutting it in half again and re attempting the joint if you are not happy with them.
If you have straight edge and a router then perhaps rout a thin shallow channel up the join in the back and insert a back strip. That will both mask an imperfect joint, as well as adding some strength and stability, along with an internal centre seam.
Of course, there’s also a lot of mileage in just cracking on with a first build, especially if you are fairly sure it will be the first of a few/several/many, and simply applying the knowledge gained to the next one.

When you are pressing down on the waist caul during bending it is quite easy for the side to slide slightly in one direction or the other. I mark my desired waist position in pencil on the sides and then transfer it to the foil in pen as I wrap it. This gives an easy reference to keep the piece located as the waist caul is pressed.
 
@Orra Thank you for your insights.

For the first four Kits (Stewmac) that I built, I added an end graft "bling" (with my daughter's "Maker's Mark"). I was anticipating doing that for this cherry ukulele as well. The graft will be a contrasting wood, and I will use the same for a headstock veneer. Haven't decided just yet on what that would will be. ;)

After trimming the ends, here's how the grain aligns (where it would be seen).. before the triangular wedge/graft. Some of it lines up quite well, so with the graft in place, I think it's going to work out quite well.

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Tops & Bottoms:
Nothing cut (rosette or sound hole) yet, and yes.. slicing the panels apart and re-jointing is certainly a possiblity. Here's some photos of "where I'm at" with that joints.

The Top (or maybe the bottom?): Very happy with this seam, as it's almost invisible.

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The bottom (or maybe the top?): might need to expand the images). The seam isn't horrible, but is visible.

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and from the back side.

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As I was typing this up, I realized that I have been assuming that top/back selection for this build would be purely cosmetic. Is that the case? The wood purchased simply states "Back &Sides (with Front)". Or do I have additional learning to do here, identifying which panel is for the front, vs the back?
 
simply states "Back &Sides (with Front)". Or do I have additional learning to do here, identifying which panel is for the front, vs the back?

Yes, there is a difference between what you call the "front" (I call the "top") and back plates in that the thickness of the top plate is more critical than the thickness of the back because of its acoustic properties. The top is what drives the ukulele.

I'm interested to see how a cherry top sounds. The WD says it has about 1,000 janka hardness which puts it in the softer of the hardwoods.
 
Oh yes. I knew about thickness differences, but each piece (as shipped) is close to 6m. My original plan was 2mm for the back and 1.7 for the front/top. However due to this thread and reading about softer (of the hardwoods) for the top, I’m starting to think I should be a little thicker on each. Perhaps 2.3 for the back and 2.0 for the top/front. Of course these number are coming straight from the ether as I have no practical experience here.
 
Oh yes. I knew about thickness differences, but each piece (as shipped) is close to 6m. My original plan was 2mm for the back and 1.7 for the front/top. However due to this thread and reading about softer (of the hardwoods) for the top, I’m starting to think I should be a little thicker on each. Perhaps 2.3 for the back and 2.0 for the top/front. Of course these number are coming straight from the ether as I have no practical experience here.
I made a ukulele using cherry a while ago and I thought it turned out quite nice. I believe my top ended up around 1.6mm thick and the back around 1.8mm, keep in mind that was for a teardrop soprano and it was single flatsawn piece. At a certain point I stop measuring and thin based on how it flexes. Good luck!
 
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