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I am making my first guitar (dreadnought), using Cumpiano's book as my teacher. I am trying to stick pretty close to his method for this first one, but have deviated on side bending by making a fox style bender rather than bending over the hot pipe. It just struck me as being more within my amateur reach. My first attempt using Tasmanian blackwood went quite well but there was a certain amount of springback. If I pull it against my template, the shape is spot on and this only needs mild pressure on my part. So my question is - can you rely on using a form for this with some internal clamps or is it important that it retain its final shape, regardless of whether you use a form or not.
Cumpiano's method does not make use of a form. William's book also says that, when you use a fox style bender, you still need to touch it up with a hot pipe - again because his method does not rely on a form.
For those of you more experienced in using fox benders with silicon blankets or globes, would you expect the actual final shape to be retained after removal. i.e. is it just a function of getting all the variables right for the particular timber you are using eg pre-wetting process, heating time, heating temperature, cooling time etc.
I am quite happy to introduce a form, but I am not sure if later stages of Cumpiano's method will be awkward as a result - will need to read ahead to assess that.

Thanks. Frank.

I would DEFINITELY use an outside mold... especially for your first. Cumpiano is certainly an excellent builder, but my personal opinion is that for your first going sans-form is the harder road.

Regarding spring back. You can put the sides back in the bender clamp them down and heat them for a couple more cycles then let them cool fully before removing them. That will help "set" the bend. Also, as soon as you take them out clamp them into the form. That will also help.

However, (and I know some people are going to disagree with this) if you get some spring back and that helps you keep the sides up against the mold I don't see the harm in it. On Bob Benedetto's tapes his sides are held to the form pretty well due to quite a bit of spring back.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Frank, do a search in the archives there are heaps of advice on side bending, we all have slightly different methods.

Some build a little relief into their bending forms to allow for the springback, while most run the heating cooling cycle a number of times before removing the sides from the bender.

I leave the sides to cool down in the bender after running a couple of cycles, then, next morning, I like to run it back up to temperature and while still hot take it out of the bender (remember to wear your gloves!) and put it into the outside mould and crank up the cauls while still hot and slightly pliable. It's important to use a solid sided mould.

But look at the archives there are many ways to skin a cat. (apologies to the cat lovers)

ColinColin S38709.3758680556

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

http://www.bluescreekguitars.com/ar0005.htm
This link will take you to some basic instructions on the machine.
   I bend about 6-8 sets a week . Heating blankets are the way to go. Also if you have access to Kraft paper Brown paper bag or heavy tracing paper , wet this and place it between the wood and the slats.
   Heating blankets go on the outside. When you are plotting your bending pattern you should ad a touch of compensation for the springback. I tighten the radius about 1/4" off the design and shrink the bout radii about 1/2'". This will all come out in the was when you spread it in the mold.
   When you set the set up in your mold you want to set the neck block first , then with the block attached you want to trim the lower bout about 1/16" heavy to the mold then using a sanding block take tiny bits of till when you close the mold the waist is just starting to come off the mold.
This is make the set fit the mold perfectly and will elimintae the need of a lower bout spreader.
Good Luck .
John Hall
   PS   working temp should be 325 degrees for no more than 5 minutes and let cool , either in the mold on the bender.

I dont worry about springback, I bend my sides in a Fox style Blues Creek bender using one blanket, two heat cycles, then block them in the outside form. I ALWAYS have spring back. That said, after the blocks and kerfing are installed, i can remove the sides from the mold and they will hold true indefiantly.LanceK38709.3989699074

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Lance@LuthiersForum.com

Lance, I have to disagree with you on that. Wood always wants to return to
its' original shape. Every time you take the rim out of the mold the wood is
attempting to move (straighten) and, in fact, does move to some degree.
That is why on some instruments the sides are no longer exactly 90 degrees
to the top and why it is difficult to re-insert the sides in the mold after they
have been removed. It became such a problem for me that I redesigned my
outside molds so that, once the guitar rims are clamped in the mold they
NEVER come out of the mold again util the back and top are glued on. That
solved all of the issues of movement of the sides while they were being
worked on.

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Sylvan
http://www.wellsguitars.com

I agree with the guys that a little spring back is not a problem. Especially if you use a mold to hold it together during assembly. If you decide to go the assembly way as in Cumpiano's book however, don't hesitate to touch up your bends so it stays to your profile. This is not hard to do and you can drape your heat blanket over a pipe to touch up the bends. You don't need to use a torch for heat if you have a blanket.

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Wade
Nashua, NH
http://www.wadefx.com

   I agree with sylvan in that once I set the side in the mold , it don't come out till the top and back are on.
    I learned a few things and get very good results with a machine. I found that if you take them out at 130 and place them in the mold and block them in to cool they pretty much stay there.
john hall

I built my first guitar using Cumpiano's book and just used a hot pipe. It wasn't easy, but it wasn't to bad either.

On my second guitar I am making my own side bender with heating blanket, but I'm still not going to use a mold. I will just touch up the bends on my hot pipe to make sure they fit my template properly.

Thanks,

I built an outside mold before I built my first guitar. I used the plans and directions in Sloane's book, Classic Guitar Construction, to build it. I decided in favor of Cumpiano's methods of guitar building over Sloane's, however, and ended up using an open workboard as Cumpiano shows in his book. Twelve guitars later, just about the only thing my outside mold has been used for is storing a set of sides after they've been bent.

Just prior to gluing in place the sides, I will usually place them back in my bending mold and reheat them to reduce any relaxation that has occurred. This is also usually enough to get them to conform closely to the template outline, so the amount of clamping I have to do to secure them during gluing is minimized.

It's actually a pretty easy way to build once you've done it a few times. More flexible than a mold. I still want to try building in a mold, though, mostly just because I've got the durn thing sitting there, and I haven't even used it yet.

Best,

Michael

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Live to Play, Play to Live

I leave my sides in the mold until the box is closed up, no moving it around. The mold makes sanding a dome into back and top (dished workboards) trivially simple, as it provides weight, stability, and something to hold on to. Works great, and I'm sticking to it. I don't build in sufficient numbers that only having one mold per instrument shape hinders me, and besides, a couple of hours with a router and a template bit and you've got yourself a few new ones.

One thing I have noticed is with reverse kerfing, the rim is very stable out of the mold, I have had rims sitting on a shelf waiting for the top and back for months and they will virtually fall back in the mold with no problem.

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Lance@LuthiersForum.com

Hi Mattia,
I can see advantages to both systems. For me, the Cumpiano work board approach is useful for strange shaped one-off guitars or when I tried a cutaway that conformed to the heal of the neck for the first time. There is likely a way to do this with a mold too, I suppose.

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Wade
Nashua, NH
http://www.wadefx.com

    While the old sytem of the building board is fine , I like the advatage of the building form and mold. I wouldn't think of building it anyother way. The symetry is more perfect on the mold and the neck block is in the same position each time.
   

For steel strings definitely the mould is the way to go. Much less room for cock up, than the Cumpiano work board, but he was writing for people to build using the minimum tooling.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

My take on the difference between using a workboard and molds is that the workboard can accept any shape. Where as w/ a mold, you need a different mold for each new shape.
I also agree with Lance in that using reverse kefing ( The kerfs glued to the sides)...that the sides are much more stable. If I have a side that wants to tip off square during glue up, I use a cam clamp and clamp the side to a post while I spool clamp the sides down.
Just my $0.02.
Merry Christmas everyone, and have a safe healthy New Year,
Glen S.

   I build myself some molds, both inside and out, just to revert to using the work board. When I first bent my sides on the pipe, they actually over-bent quite a bit as they dried. (flamed cherry wood, what was I thinking ?!) not to mention that I got severe cuping as well. But that's another story...
   This is my first guitar, and I'm trying from scratch, but I wouldn't do it any other way. The board offers you a lot of freedom.
   When it came time to glue the sides to the top I just reheated ye ol' pipe, and after much zigging and zagging, I managed to have my sides conform perfectly to the template, cutaway and all.
   The form is probably a lot easier, but with a bit of patience, you can get very good results with the board. Regards,
Alain Desforges

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john hall

[QUOTE=Colin S] It's important to use a solid sided mould.

I'm curious why a solid sided mold is recommended. I'm getting ready to build a mold for an OM and had planned on making it out of 2 pieces of 3/4" birch plywood with spacers to give it the required depth. Why would a solid sided mold be better?

A kerf is a space left by a saw cut. You can't glue one to anything (even with hot hide glue).

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Steve- you can built it that way, I have several that are made from two pieces of MDF with MDF spacers holding the about 3" or so apart. I also have the solid type, I can find no advantage from one over the other.Lance-on-laptop38711.6564351852

[QUOTE=SStallings] [QUOTE=Colin S] It's important to use a solid sided mould.

I'm curious why a solid sided mold is recommended. I'm getting ready to build a mold for an OM and had planned on making it out of 2 pieces of 3/4" birch plywood with spacers to give it the required depth. Why would a solid sided mold be better? [/QUOTE]

If, as in the way I do it, you put the side into the mould hot out of the bender and crank up the cauls, with a hollow sided mould there is a small danger that the side could cup into the hollow space before setting. I just don't take the risk. If you put the side into the mould cold, then no problem.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Here's a set braced with a maple veneer/carbon-fiber wishbone. I use this on my Kasha guitars and once removed from the mold, it's extremely stable. I can slip it in and out of the mold very easily. Just one more way to skin the the proverbial cat.

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Jimmy Caldwell
http://www.caldwellguitars.com