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I am wondering how hard you set the waist and/or cutaway cauls on your fox? Can you actually crush the wood? What would that look like?

The cutaway I am doing has a fairly tight inside the curve. So it takes a little more pressure to bend then lets say a normal waist due to bending the one edge almost 90* along side the neck while you are also bending the tip. It can be difficult to tell if it has completed seated itself into the form, so I tend to continue tightening the caul until it is firmly pressed in place. I don't think I "crank" it down, but it is tight for sure. I make sure it stops. The Caul is 1.5" thick and matches the center of the inside bend of the cutaway pretty much exactly to shape.

Last night I bent some aspen sides and they turned out really nice, but I notice a very small amount of rinkles in the cutaway and waist. I am not sure if this is due to the craft paper bunching up and leaving impressions or what. At this point, the wood and fibers do not appear broken of facetted (like my previous trouble), but there are some marks in the tight inside bends. They are surface only and will sand out, but I am currious to what this may have been. The marks almost look like worming.

THanks,
Joe

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Joe

Here is a picture of a simular cutaway. The arrow shows where it feels like a lot of presure is needed to bend both the curve around the outside of the guitar as well as pushing the wood into the cutaway. When it is not all the way seated but close, it is a little hard to turn. So it makes it difficult to know you are seated unil you have it pretty tight. BTW: I used a heat gun to warm up the wood in the cutaway area as a precaution due to previous attempts not having enough heat from the bulbs in that area. It seems to have worked real well. I think the marks have to do with either the craft paper bunching or the pressure I put on the finished bend.


One thing that this makes obvious (DUH!) is that I should cut peek hole windows into the side of the arms to see where the bend is at. I don't have the long slots cut in our FB like some of yours. I have channels down the sides that the caul slides between.

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Joe

Joe buddy does your waist caul have a layer of steel over it? It you are getting crinkles that are not from paper or foil bunching up I would guess that more heat in this location would be desirable. If your caul is not lined with steel the heat from the blanket could be wicking into the wood caul and causing the waist to not get hot enough during the bend.

I crank my waist caul down so it is firmly in contact. Just a good firm one-handed turn is about as much pressure as I use. Think turning the lid on a jar of Skippy Super-Chunk Peanut Butter...... Bet you can't guess what I am having for lunch.....

Hesh my friend....

No, the two cauls are solid rock maple. No metal linings. That might make them slide a little better....hmm. Ok so what should I line them with? Can I use any flexible metal for this?

Thanks for the suggestion.

Joe

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Joe

If your sandwich (slats wood and blanket if used) is tight it is not at all hard to know when seated. I tighten just too full touch out and do not over tighten.

The crinkles you refer to are cause by lack of support between the wood and inner slat. and is the dreaded faceting vs. smooth bending. Not enough heat leading to the wood fiber not being plasticized enough at the time of the bend can also play a part in this

I think Joe is using light bulbs for heat here, is that correct? This may be the problem you are having with the wood wrinkling. I've never tried a cutaway with light bulbs so I'm not sure how well this would work. My advice is to use a pipe to bend your cutaway, if you have a light bulb type bender, I think you would have better luck with it.

Cal

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Remember, there are no stupid questions, only stupid answers!

Thanks again everyone. Yes, I use light bulbs but I added the use of a heat gun in the cutaway area to add heat this time. It seems to work fine with no faceting. I think I have the slats nice and tight now and have used Dave Stewart's (I think) idea of a little clip on the sides of the form to hold the slats flat. I use it while bending too and everything stayed flat. The bends are smooth and consistant. The current wrinkles I got were nothing like the faceting I was getting earlier. It looks more like worming...that is why I wondered if the craft paper wrinkles could mark the wood too. I had cranked the cauls pretty tight, so I figured it could have been remenence from the paper.

The set of sides I bent now look real nice and very useable. I decided to go back and add metal to the cauls anyway. I may do some more bending to test them soon, but for now I am good. I do think the wood caul wasn't sliding against the metal slats that well either. Bending the cutaway, the slats are touching a large portion of the caul as it goes in. So I think it could have been "binding" as it pushed the slats inward toward the cutaway. I think the metal on metal may help this as well as reduce heat disapation in the wood caul.

Thanks again,

Joe

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Joe

One thing I find helps is to keep the cutaway caul tangent to the form as you bend the cutaway rather than plunging the caul. I have attached a spring to the top of the cutaway press frame/ top of waist press frame that keeps tension on the frame and keeps the caul in contact with the form as I crank down on the screw. I bend the entire upper bout using the cutaway press. I add downward tension with my hand till I round the horn then the spring maintains the pressure.

I find this greatly reduces incidents of faceting.



My way




Plunge method

Hi Michael, Thanks for all the help...I am very close to getting this all working!

I use a very simular method via a bungie cord connecting the upper tower with my cutaway tower. It is good to see that you concure with this pratice. I am headed in the right direction with all of this. I will be posting some progress pics in a new thread in the next day or so.

I have the top carved and braced. The back is carved. The neck is done and waiting. I just have to add linings to the sides now that they are bent and neck/tail blocks are glued in.

Joe

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Joe

That's an interesting concept, Michael. Somewhat like using a wiper die vs. air bending in metal forming.

Yep I have even thought about spring loading the cutaway caul down towards the pivot point and only using the screw once I have turned the horn.

In any case this helps to prevent the sandwich opening, gaping or crinkling at the apex of the bend load. Thereby avoiding faceting.

At the recent GAL conference, the man himself (Charles Fox) gave a demonstration of his bender. He manually held the cutaway ram up as he rounded the horn with the explanation that this helped prevent fractures. The spring idea seems to be an enhancement to this concept. Good job Michael.

Thanks Barry,
For me the idea all came about from dealing with a tight cutaway on some extreme quilt sapele. I noticed as I bent via my old method of bending the horn with the standard upper bout caul then engaged the cutaway caul I would get separation of the sandwich at the apex of the caul till the caul was tangent and flush with the form. This separation followed the apex of the caul as the caul traveled down into the cutaway valley. i also noticed that the wood seemed to be sounding as if it was lightly fracturing at the point this gap was at any given time. I figured I needed to be able to keep tension on the sandwich in front of the cutaway caul but this would require a free hand. The spring came from finding a way to free my spare hand while working the press screw.
I did not say before but I hold the bottom of the sandwich with a high temp glove just in front of the caul till I have no more room to do so. by then the remaining sandwich is flush against the front corner of the form and needs no extra support to keep from gapping.