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| Author: | Michiyuki Kubo [ Thu Jun 12, 2014 5:02 pm ] |
| Post subject: | Burnt side while bending |
I bent one maple side. Slat paper wood paper blanket slat Sprayed with water not soaked Started bending the lower bout at 250 upper bout maybe 265 and the middle it was about 325. They are about 2.6-2.8 mm thick. After that I turn it down to 200 for a few minutes and let it cool from that. First side turned out perfect a few water spots that's it. Second side burnt hard at lower bout in same procedure. Next chance I get I will try and get a pic of it. It burnt only in the center. Did the wood curl or something before the bend so it burnt? Confused as the first side went so smooth. I'm guessing this is now scrap wood unless I burn the whole dang thing and make it dark. |
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| Author: | Michiyuki Kubo [ Thu Jun 12, 2014 5:34 pm ] |
| Post subject: | Re: Burnt side while bending |
 Here is the shame. I didn't really See any smoke come off when bending either. I did see some come off the upper bout area but that is not the area that burnt. Thought there was a chance I could sand it down but the other side (inside) of the wood also has some light burn on the same spots so it went through. |
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| Author: | Haans [ Thu Jun 12, 2014 5:45 pm ] |
| Post subject: | Re: Burnt side while bending |
Should be able to sand that out. How thick is the rib? I've scorched plenty of flamed maple on mandolins. Are you going for a blond instrument? |
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| Author: | Michiyuki Kubo [ Thu Jun 12, 2014 5:46 pm ] |
| Post subject: | Re: Burnt side while bending |
I don't know if it makes any difference but the burn kind if followed the grain in the small curve there. It is the reason why I thought about the wood curling up as I was bending... Kind of devastated on the step backwards. Will bend my next set tomorrow and see. Should I be bending maple colder than that? |
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| Author: | Michiyuki Kubo [ Thu Jun 12, 2014 5:57 pm ] |
| Post subject: | Re: Burnt side while bending |
Haans wrote: Should be able to sand that out. How thick is the rib? I've scorched plenty of flamed maple on mandolins. Are you going for a blond instrument? They are full size right now at 142mm. Will be bringing them down a lot but no way to avoid the areas  this is from the inside. Do you think it is still manageable to sand out? I thought that since it scorched through it would keep the fiber color of "burnt chocolate  "
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| Author: | Tim L [ Thu Jun 12, 2014 6:13 pm ] |
| Post subject: | Re: Burnt side while bending |
May want to try some oxalic acid. It should remove that scorching. Brush some on the inside dark spots first and hit with a stiff brush. Wipe off. If that gives you what you want go for it on the outside. Easier than trying to sand off a dark spot and thinning the sides in the process. |
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| Author: | Michiyuki Kubo [ Thu Jun 12, 2014 6:35 pm ] |
| Post subject: | Re: Burnt side while bending |
Tim L wrote: May want to try some oxalic acid. It should remove that scorching. Brush some on the inside dark spots first and hit with a stiff brush. Wipe off. If that gives you what you want go for it on the outside. Easier than trying to sand off a dark spot and thinning the sides in the process. Will have to research on where to buy that here. Not familiar with it. |
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| Author: | Hesh [ Thu Jun 12, 2014 6:49 pm ] |
| Post subject: | Re: Burnt side while bending |
Michiyuki I'm not sure that oxalic acid will remove a scorched section. I use it often to clean up a dirty crack before gluing and cleating (don't try this at home....  ) and since it's a wood bleach it will bleach stuff that is bleachable (is this a word...) but it won't remove things that will not bleach out. Worth a try though and it's available at better hardware stores, lumber yards, and places that cater to wood workers. It's a powder that you mix with water and of course take the recommended safety precautions likely listed on the package as well.You may be sanding though as Hans suggested and it also sounds like his "blond" question may be a precursor the the suggestion of a burst if all else fails. My bending stack from bottom to top is slat, paper, wood, paper, slat, blanket, slat. I'm mentioning this because my blanket is never in direct contact with the wood. This may be helpful in the future so much as if there are any hot spots in your blanket they tend to even out a bit when the heat has to be conducted through a slat. |
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| Author: | Michiyuki Kubo [ Thu Jun 12, 2014 7:00 pm ] |
| Post subject: | Re: Burnt side while bending |
Ah I see, i have been googling the acid a bit. I didnt have any expectation of the color. My only thought for the finish was to fp with a blond shellac, not the light blond, the dirty blond(innuendo) I was not going to try and be real technical with the finish but if it saves my butt i wont have a choice will i. Thanks for the stack mention, i will try and pick up some more metal at the store next time im up that ways for an extra slat. Are my temps correct though? I researched this was pretty much in the range. Also Hesh did you ever compile a list of bending temps for wood? I read that in another post from the way way back. |
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| Author: | Hesh [ Thu Jun 12, 2014 7:10 pm ] |
| Post subject: | Re: Burnt side while bending |
I thought that innuendo was an Italian suppository.... (no offense intended to Italians - ever!). Your temps sound right to me and the first side that was not burned indicates this too. Perhaps the duration on the second side was longer. No I never complied a listing of recommended bending temps for common woods and was shot down.... I still think that it's a good idea and my bet is that it would be very useful to many, many OLFers and readily available too. It's true that temps can vary some within the same species but that could be addressed in the "bending guide" I think. If nothing else it would be a clear guide to newer builders clearly indicating some pretty helpful information such as EIRW and Walnut are very easy to bend and highly flamed Mahogany maybe should not be attempted until one has some experience with some of the other choices. Might be something that you may want to champion my friend? |
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| Author: | Michiyuki Kubo [ Thu Jun 12, 2014 7:28 pm ] |
| Post subject: | Re: Burnt side while bending |
Thanks for confirmation. I would have really liked to see that info on bending temps. I will compile my own temps as i go along with them or hear from other guys and jot them down. Totally agree on it being helpful. My last try on cohesion was not a success so i am pretty sure if i were to dare it would turn out the same conclusion. Maybe in some years when i have my own records i can post them and some other fellers could add their own input. |
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| Author: | Michiyuki Kubo [ Fri Jun 13, 2014 3:57 pm ] |
| Post subject: | Re: Burnt side while bending |
I went ahead and tried to sand some out. I started at 120 and it didnt do much. I went down to 80 and it took off just a tiny bit of it off the outside of the burn marks. Then i went back to 120. That color seems like it is embedded in the wood fiber or something. I went at it for a while watching the thickness of it too make sure i wasnt getting too thin. It seemed to go nowhere unless i was taking off more wood than i would like to. I did not try to wood bleach yet, but i have seen some videos on it and it will change the color of the wood as well, meaning it will get that maple to turn yellow. I am not sure i want to risk it turning another color.What are my options here? Appreciate all the info. |
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| Author: | johnparchem [ Fri Jun 13, 2014 4:34 pm ] |
| Post subject: | Re: Burnt side while bending |
Just a thought on the blanket, I recently burned a side in an unlikely spot. It turned out that some how I damaged the blanket and there was a section that was much hotter than the rest of the blanket. I do most of my bending below 300 degrees and always have a thermometer so I was surprised when I burnt the side in the lower bout. It would be interesting to know if others have run into this. |
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| Author: | Michiyuki Kubo [ Fri Jun 13, 2014 4:39 pm ] |
| Post subject: | Re: Burnt side while bending |
I will try another side out and see if i get the same results but i think the blanket is fine. It was recently purchased. http://www.youtube.com/watch?v=5Jfi0sOawT0 I guess i am off to buy some gunpowder from the local hardware store? lol. |
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| Author: | Haans [ Fri Jun 13, 2014 6:08 pm ] |
| Post subject: | Re: Burnt side while bending |
Are you saying the thickness of the rib is 1.42mm? Should have bent like butter at that thickness. Are you using SuperSoft II? |
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| Author: | Nick Royle [ Fri Jun 13, 2014 6:17 pm ] |
| Post subject: | Re: Burnt side while bending |
I think the blanket should be on top of the top slat. Top of the stack. That's how I was taught to do it a few weeks ago. Use foil in your stack, too.
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| Author: | Michiyuki Kubo [ Fri Jun 13, 2014 6:32 pm ] |
| Post subject: | Re: Burnt side while bending |
The thickness of the rib is 2.6-2.8 the width is at 142mm, that will be taken down to about 90-100. It bent easily regardless, it just seemed at those two spots heat from the God Zeus came forth. No super soft, only some spritz of water with a spray bottle before bending. Nick are you talking about aluminum foil? I was just going to stick another slat in there to get the heat distributed a little better next time. Does foil prevent staining or something? |
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| Author: | Haans [ Fri Jun 13, 2014 7:05 pm ] |
| Post subject: | Re: Burnt side while bending |
Michiyuki, I sure would try to get some SS2, it makes things go a LOT easier. 2.6mm is WAY to thick also for guitars. That's around .1". My ribs are usually around .85-.90", and thinner for stubborn wood like figured mahogany. |
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| Author: | Nick Royle [ Fri Jun 13, 2014 7:56 pm ] |
| Post subject: | Re: Burnt side while bending |
I did mean aluminium foil but, more importantly, the bending master who taught me has the following stack.... From form to cauls: (form) - slat - foil - brown paper - wood - brown paper - foil - slat - blanket - (cauls) i.e. There should be a slat between the wood and the blanket. Without that slat, scorching would be much more likely. I've bent my sides at 2mm - 2.2mm so far. And I've just got some SS2 to use for the trickier woods. |
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| Author: | Michiyuki Kubo [ Sat Jun 14, 2014 5:17 am ] |
| Post subject: | Re: Burnt side while bending |
Thanks, for the replies. I did not have any problems bending at the thickness i was at it was mainly the burn marks i was worried about. I figured i will be doing a lot of sanding down so i had left them a bit thick, i will plane them down a bit more next time closer to the 2 mark. My question is what should i do about this side that is already burned?
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| Author: | Hesh [ Sat Jun 14, 2014 6:20 am ] |
| Post subject: | Re: Burnt side while bending |
You will find that lots of us use different techniques, stacks, thicknesses, etc. and many of them will work well. For me my stack used a third slat as mentioned and I even have a third caul too on my Fox style bender making that two cauls on the lower bout. Bending thicknesses NO thicker than .090" (you metric guys can do the math since I am still asleep here....) and usually more like .080 and sometimes .075". My stack consists of form, stainless slat, paper, wood, paper, stainless slat, blanket, spring steel slat. The spring steel slat is over the blanket to prevent the spring back of the spring steel slats from attempting to crack a side when taking the side out of the bender and that third slat helps redirect the heat of the top loaded blanket more into the stack. Craft paper or foil? Either will afford the wood some protection and help prevent your slats from getting stained with messy woods like Coco. But craft paper has the added advantage of absorbing some water to help make steam in the bending process - a good thing. Also if you are bending Koa or Blackwood foil or direct contact with the metal slats will turn the wood green..... not a good thing.... This is why I stopped using foil to avoid the green surprise on these woods. Also some of the stuff that I have read on this forum prior has folks keeping the wood in the bender under heat for long enough to make lasagna. Since we are not making lasagna and don't have that added benefit... I was never keen to do this. My bends from start to finish may only take about 8 minutes or so. Keeping the wood exposed to heat longer than the minimum necessary to do the deed can "case harden" the wood for lack of a better term and make it more likely to crack, less likely to bend, and more likely to scorch too. I have Super Soft II, used it only once but liked it and it does help with seemingly no down side. Spray the side the night before (24 hours or so) and then bend the next day - easy and cheap insurance against having to source an expensive replacement side. Bulb benders we rarely hear of any more although some folks still use them. If you do be sure to use REAL light bulbs not those fat-arse Al Gore CFL bulbs.... Sorry, been telling that joke for nearly ten years here now and just had to subject someone to it again....Blankets really did change the game and make bending easier, safer, quicker, and in my view more of a quantifiable and definable process for us all. And they are cheap insurance as well against having to replace a cracked side. Regarding side thicknesses we see pre-war (world war II...) Martins with side thickness of .055ish.... so don't think that .070 is too thin either. Side thickness is also a function of the species, how you build (side supports, tapes, or both), body shape (cut-away, tight waist) etc.. |
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| Author: | Haans [ Sat Jun 14, 2014 6:56 am ] |
| Post subject: | Re: Burnt side while bending |
As Hesh said, SS2 is cheap insurance. I even use it on oak and that bends easily AND, yes, it only takes a few minutes to bend a rib. You don't want to "cook" it. The trick is to leave in the bender for 24 hours. I bend it, let it cool down to room temp, take the blanket and top slat and paper towel wrapper I use off, and reclamp. Letting it sit for 24 dries it out better and there is less spring back. Then after, I clamp it in the mold and when the other one is done, I fit the ends and the ribs stay in the mold till after the top and back are glued on. By making the ribs thinner and using SS2, you can get away with lower temps, and might not burn. Also, Nick has it right with the stack, and an extra stainless slat would be a good idea as it traps the heat and also saves the blanket. |
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| Author: | Michiyuki Kubo [ Sat Jun 14, 2014 9:54 am ] |
| Post subject: | Re: Burnt side while bending |
The advice you guys has given is sound, and i really do appreciate it. My question still stands though, what would you do with a burnt rib? I have tried sanding it out to no avail again today, is it now a scrap? PS , just thicknessed another set down to 2mm so will be on that next. |
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| Author: | Haans [ Sat Jun 14, 2014 11:16 am ] |
| Post subject: | Re: Burnt side while bending |
Sunburst! |
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| Author: | Nick Royle [ Sat Jun 14, 2014 11:31 am ] |
| Post subject: | Re: Burnt side while bending |
Yeah... If you can bend the other side just as thick, use it for a sunburst! Heavy sides can be beneficial. (please don't anyone think i'm giving advice alongside Haans and Hesh as if my opinion is worth anything compared to theirs!  )About the third slat though... I'm sure it gives extra support but am I right in thinking that it's mainly to give somewhere for the heat to go on the outside of the blanket? I only have the two but I did see mention of a blanket with a silicone "rubber" layer on the outside of the blanket to give somewhere for the heat to go and give a little bit of "padding" when tightening down the stack... Anyone think that seems worthwhile? I've got my blanket now but thought I'd ask. Cheers!
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