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Spalted Maple top...several questions


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Wow, what a weekend. I'm usually more attentive to queries than this.

A vacuum pump should apply a more consistent pressure, yes. The first think I would be thinking about is that atmospheric pressure is only 14PSI. Rather than bending the top, I think it would simply move at the point of least resistance and crack. That is my first thoughts anyway. @verhoevenc (Chris) likely has better information to add into this topic than myself. I can only work from a theoretical standpoint since I avoid doing drop tops. The spalting is a complication perhaps, however probably not so much for this bending exercise. Only if it is compromised by being weak and strong in very closely proximate areas, where a bend would be difficult to produce evenly.

I'm also very conservative with advice when it comes to things that could go wrong, and unpredictably so. I've seen people here bend forearms dry and cold, whilst others do so with heat and water. I'm not one to take chances with stuff that can't be replaced or repaired for obvious reasons.

 

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It looks like the curve is smoother than some of the sharper ones out there. This is a good thing. Like Scott says, doing it gradually with heat, working your way from the start outwards is the name of the game. All without glue at this stage.

The concern about heat here is that you do not want it ANYWHERE near the existing gluelines. Putting a layer of foil over the body seems to spring to mind, however I am unsure whether this will have any qualitative effects.

This makes me sound really apprehensive about getting anything done....I'm the overthinker here....other people would jump right in and get it done. Probably successfully too. I just don't do chances. Not my thing. I play to win.

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 I really appreciate all of your advice from everyone contributing! 

 Here's where I am… I did fair amount of research and it seemed a reoccurring theme that everybody was saying glue first to stabilize the wood a little bit more before you start machining  It.

 

 So I did use CA glue thin and apply that to the whole top . I wasn't totally crazy about the dull brown finish it left I hope I can do something with that when I machine it. 

Once that had dried overnight I started Preparing the book matched edges for joining. After a fair amount of skimming with a plane on the shooting board  followed by some light sanding I was able to get a perfect joint. So now I have just glued up the top and I will leave that overnight and then I'm going to start machining it  (Thicknessing it)  I initially thought it's probably going to take the thickness down to an eighth of an inch.  Should I try to go any thinner than that?  It might help the bending process ? I think I'm also going to work on the contour of the existing body to smooth that out a little bit.

 

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1/8" is a lot better than the usual 1/4" people normally associate with drop tops. Question is, how much was taken off the original guitar? Adding a thicker top might become a bit of a problem with the existing geometry and setup of the trem. I came back to the thread about to ask that, and as to whether you might be able to thin the top down a bit. I made the incorrect assumption that you were working with something of the order of 1/4" or so. 1/8" is far easier to bend by an order of magnitude. The same caveats of easing it in and using heat if possible apply.

Just take care about the glue and heat. CA is nasty stuff and heating it up only makes it worse.

How are the edges going to be finished? If they're left natural, then you definitely need to hit perfect gluelines. That's all down to the clamping at glueup. Don't scrimp on 'em! If you're thinking of binding it, then you could possibly "resharpen" the contour after attaching the top. Easing will make it easier (sounds obvious, doesn't it?) however if that isn't the look you prefer, then you have a bit of fudge room with binding off the edges.

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I have considered that. I'm going to thickness the drop top ready to glue up. Once it is exactly right I'm going to mill the same thickness off the body top.

 

the body is solid mahogany so I'm thinking a dark red brown. It is a neck through body and I hate the maple neck stripe down the back.

 

i was also doing something like this pic...using quilted maple framing the spalted maple?

 

i am definitely doing a binding. It is going to be cream colored.

image.jpeg

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I love that. My thoughts are this...

i will use quilted maple veneer. Cut a template for the center part. Cut the veneer to the template and glue down the veneer.  When that dries rout the inner part out of the spalted maple. Leave it a couple mm taller. Run a 1/8" route around the center part for a binding. Glue up the center part...then the inner binding. When that dries run a chamfer bit on the binding. Then add a binding to the outside.

 

look on the bright side...no bending on the drop top...just the veneer.

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Major pain in the ass proposition. Like I said, you'd probably find it easier to built it from scratch than to retrofit that kind of top. Depends on your abilities of course, however like I've said all along....I play to win, so I tend to have an internal conservative safety margin built in, and anything I recommend tends to translate that safety margin across also.

First problem that springs to mind is getting clean transitions over such a small angle. That requires my favourite annoying repetitious thing about clamping pressure. This is entirely where it is crucial. Laminating thin tops and then cutting a highly acute angle across them can get feathery from fibre tearout, gappy or glue-liney very very easily. Same kind of thing when people veneer a top and then add a roundover to it. Never turns out as well as it does in your head.

Your first proposition (spalted top, binding) has the legs to work really well if you tick all of the boxes. The second is a different league as a retrofit. More viable if it were done as an intrinsic part of a full build.

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Didn't read the whole thread so I hope I'm answering correctly but: Yes you can bend a spalted maple top... however I'm a little weary of the idea since it seems like you already flooded it with CA. I'm not sure how that will affect bending. That said, regardless of whether you have a vacuum bag or not you will have to bend the top to almost perfectly match the arm contour before hand. The bag will only hold it down for gluing. The bag pressure will not bend it for you; period. I do my bends in, preferably, 1/8" tops that I I clamp to the body, then I get a heat blanket and place it over a wetted section to be bent. When it starts to give with hand pressure I will bring in some squeeze clamps. I also make sure to support the top-most flat section with a block all along that spot the bend starts; you don't want it putting in some bend above where it should.

Best,

Chris

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Okay an update...I thicnessed the top to an 1/8". Everything went well  but it took a lot longer than I expected… But then again I want and very gingerly to make sure I didn't tear up the wood .

 I did the pen test and it bent so easy it wasn't even funny . So  I did all my markups and everything and then I glued the top on .  I clamped it all up put a lot of clamps on the armrest area and clamped a board to hold everything flat and then 300 pounds of sand bags on top of the board .  After 15 minutes I took the bags off and all the clamps and just made sure everything was still on track and everything was really good so I clamped her back up I put the weight back on her now I'm just gonna wait a couple days . 

 Put glue up was a very messy event . When I took everything off I took away towel and got all the excess glue off.

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I had a weird problem when thicnessing. I built the router sled jig. I set the router to cut 1/32 the first pass. It started fine but when I finished I went back over it and the router which should have been just barely touching dug in another 1/16"

 

i checked everything and and it kept happening.  I finished up with a plane and belt sander. Not cool!

now how am I going to finish this beast?

man this requires major focus and planning! And of course an unreal amount of sanding.

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