Should I make a mold?

Construction and repair of Classical Guitar and related instruments

Should I make a mold?

Postby JeffR » Tue Nov 10, 2009 3:21 pm

I'm awaiting delivery of my first guitar project from LMI, (a fully serviced kit with pre-bent sides and so on). It is the 1937 Hauser plan. Do you think I will need to make a mold for holding the sides and neck? I've read the books by Sloane, Cumpiano and Bogdanovich and they each have a different method.

I am inclined to attach the sides to the neck like Sloane does before attaching the top. In Cumpiano's method they attach the neck to the soundboard first. Which method is more popular?

With pre-bent sides is a mold useful/necessary?

Thanks
Jeff
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Re: Should I make a mold?

Postby Les Backshall » Tue Nov 10, 2009 5:05 pm

Of the books you have, I would go for the Cumpiano. In my opinion, Sloane doesn’t include sufficient information and Bogdanovitch is overly complicated. Better still, try and get hold of Courtnall’s ‘making Master Guitars’ – expensive, but well worth it.

You don’t actually need a mold, whichever method you opt for, and might be better of making a solera with adjustable blocks (Courtnall), which can be used as a mold. If you make a solid mold, you’re stuck with that body shape.

You might need a bending iron of some sort, though. The LMI pre-bent sides will undoubtedly have some spring back, and will probably need tightening up a bit.

This next bit may be out of date now but, if you haven’t been told already, I would encourage you to check with LMI the exact shape the sides have been bent to. They say Ramirez/Hauser, but the two shapes are different and the machines they use are, or were, shaped for the Ramirez.

Good luck, please keep us posted on your progress.

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Re: Should I make a mold?

Postby Robert Webster » Tue Nov 10, 2009 5:42 pm

Les has the right advice regarding adjustable workboards. As for glueing the top or the sides to the neck first, the latter derives from the old Spanish method for working on an open board. It has the advantage of allowing you to get the neck/top center seam alignment perfect and that 's an enormous plus. In that method, the tail block is quite often glued onto the top prior to setting the sides also. Then the sides are set into the neck, glued onto the tailblock, and then the sides are connected to the top via little triangular blocks of spruce, called tentellones, using hide glue and rubbed joints.

With well bent sides, this is a very easy way to put the guitar together. Thus, Les's suggestion to get a bending iron to touch up the prebent side shapes, as well as the workboard with adjustable side supports. The method also allows for working with different guitar shapes. Have fun and keep us posted.

Cheers,
Bob
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Re: Should I make a mold?

Postby Chuck Morrison » Tue Nov 10, 2009 6:46 pm

I "grew up" with Sloane and putting the neck onto the sides first just feels right, especially when working with his style mold. However, when working free form, building a body shape I don't have (or want to take the time to build) a mold for, I glue the neck onto the top first. Then I bend and fit the sides to the top, using the top as the pattern to bend to. This works out nicely using the tentellones method Robert mentioned. The only gotcha with this method is that you need to make sure the sides don't have any twist in them. When bending the sides it's also nice to clamp them into a mold and let them adjust to that shape before gluing to anything. So it's really up to you and how confident you feel. A mold is in some ways a crutch, but it does help you get good results easily.
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Re: Should I make a mold?

Postby simonm » Tue Nov 10, 2009 8:23 pm

Pre-bent sides will almost certainly have been bent in a fox bender or something other bending machine. Coming from somewhere as reputable as lmi, I would expect them to be perfectly bent and very stable. I would expect them to work just fine without a mold. In theory I would like to have a mold, but its a lot of work and so far I haven't bothered. The Spanish method gets you the center line, so it doesn't matter if sides you bend yourself are not 100% symmetrical.

If you make yourself a solera, one thing you can try is making it from a fine plywood - or at least the top layer from this. The advantage is that the layers will tell you visually how deep you have made the contours. By fine I mean something where the plys are 1mm or less and preferably with a contrast color between the layers. I got some like this from computer industry packing pallets.
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Re: Should I make a mold?

Postby Waddy Thomson » Tue Nov 10, 2009 9:13 pm

The pre bent sides will definitely have been bent in a bender, but may not be as stable as you might expect. I have seen a couple of situations where people have cracked their sides by not keeping them in some form of mold. It can be cardboard, but something to keep them in shape until you use them may be important. The difference in humidity, between your location, and the location where they are bent will cause them to mis-shape, if you don't control them. When you are ready to use them, you can use the blocks in your solera, if you use a solera, to control the shape.
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Re: Should I make a mold?

Postby Robert Webster » Tue Nov 10, 2009 9:22 pm

Yeah, to amplify on the side bending topic, every set of wood reacts a bit differently to the same Fox bender routine and will also display different degrees of relaxation after the bending process. The consequence is that, regardless of how careful or experienced you are, you can still count on having to tweek the shape of the sides after the machine bending process and just before you commit them to linings, glueing to the top, etc. Mother Nature's way of keeping us on our toes.

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Re: Should I make a mold?

Postby Les Backshall » Tue Nov 10, 2009 9:36 pm

simonm wrote:Pre-bent sides will almost certainly have been bent in a fox bender or something other bending machine. Coming from somewhere as reputable as lmi, I would expect them to be perfectly bent and very stable...


Although a few years ago, I was speaking from experience. The ones I received were kinked, even though they were done in a Fox bender. After sending them some photos they sent me another set (being in the UK, it wasn't worth sending them back, so if anyone wants some kinked Black Walnut???). They also told me they would fit a Hauser shaped mold, even though they were bent to Ramirez (they didn't). Perhaps they were just going through a difficult patch :?

But, as Waddy says, I wouldn't have expected them to be totally stable in terms of the exact shape anyway, and there was a disclaimer sticker on them to that effect.

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Re: Should I make a mold?

Postby Pepe Vergara » Tue Nov 10, 2009 11:10 pm

If you are new to woodworking (not sure), it would be good for you to build a mold and any other jig you can as practice for the guitar itself. Try to make the mold an jig as perfect as you can.
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Re: Should I make a mold?

Postby Robert England » Tue Nov 10, 2009 11:12 pm

For what it's worth, here is my experience. The 1912 Ramirez plan plantilla and the 1937 Hauser are so close in shape that sides bent to either plan should work with either guitar model. The 1966 Ramirez plan is for a larger guitar and sides bent to that shape would be a problem conforming to the 1937 Hauser shape.

For my first couple of guitars, I used pre-bent sides from LMI. There was some spring-back/relaxation of the shape, but it was uniform (evenly distributed) and not a problem. I built on a Courtnall type solera (highly recommended) with adjustable rib supports, and making the sides fit the plan without any heated re-bending or touch up was not a problem. The LMI sides were not warped, cupped, or crinkled. For my own subsequent bending, I bought the Everett side bending machine from LMI. This has a generic shape very close to the 1912 Ramirez and 1937 Hauser shapes. This is less expensive and more compact than the Fox bender. The only drawback is that you can't bend sides for a cutaway shape with it. I've since make my own bender for the 1976 Miguel Rodriguez Jr. plan, which is a larger guitar, using the springs and parts from the Everett bender. I can switch the parts back and forth and bend either shape.

I think the Courtnall solera design is a perfectly good alternative to a bunch of fixed molds for building various classical guitars.

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Re: Should I make a mold?

Postby Robert Webster » Tue Nov 10, 2009 11:46 pm

One last thought from me on moulds vs flexible outline workboards.

Once you are done exploring different shapes and have settled on one specific shape, there are TREMENDOUS benefits to working with a mould, particularly if you make the body and the neck separately. Body assembly is much easier, more efficient, and consistent than working on a workboard. There are alignment aids and construction conveniences
and a host of possibilities that just aren't possible with a workboard.

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Re: Should I make a mold?

Postby JeffR » Wed Nov 11, 2009 12:23 pm

Thanks for all your replies. It is great to hear about real experiences. It looks like there is a copy of the Courtnall book at the Toronto Reference Library that I will go and have a look at, and see how he designed the adjustable blocks for a solera. It's an expensive book... The Bogdanovich book was only $20 and has a lot of pictures so I got it along with Cumpiano's.

I received the Sloane book in 1976 as a gift and it has been my iconic vision of how to make a guitar in my mind for over 30 years. I figured I better get on with actually building one. I hadn't ever thought of attaching the neck to the top before seeing Cumpiano's book even though it turns out that is the tradition from Spain. So I am going to have to reconsider.
I will have to see how the sides look when they arrive, whether they have moved significantly.

But to that point, is there typically any tendency for the sides to spring back after they have been attached? It seems that if the sides are attached without the use of a mold then the structure would be without tension whereas if the sides were springy in a mold then there would be stress on the glue joints holding the top and back. Do the sides relax and become stable if left in a mold or do they "know" where they want to be after bending and the mold just forces them to be accurate to the plans? Is there sometimes tension between the sides and top/back, and is that a bad thing?

Thanks
Jeff
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Re: Should I make a mold?

Postby senunkan » Wed Nov 11, 2009 2:58 pm

Hi Jeff,

The bent sides which I received from LMI had quite a fair bit of spring back.
So I use an Aluminium pipe coupled with an heat blower, to correct the spring back to the plantilla shape.
I was using a Hauser 37 plantilla which is smaller than the Ramirez plantilla.
The sides were bent to the Ramirez shape as pointed by Les.
So at the same time I took the chance to correct the plantilla shape too.

Spring back
Image

After correction by the heat pipe
Image

My heat pipe setup
Image

Although the sides were bent by LMI, I did learn the feel of how to bent the sides by hand when I corrected the curvature.
I did learn an important lesson of how to bend the side by hand.
With this experience I would be more confident to bend my sides for my next build (at least for IRW)

I am not sure how the guitar would fare in a tension spring back mode.
But I didn't want to take the chance.
Moreover, with the bending correction, I did pick up an important experience of bending the sides by hand.
So that is why I went ahead and correct the spring back to the plantilla shape.

Best of luck for your build!
You would love the experience of building guitars as I did.

Sen
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Re: Should I make a mold?

Postby JeffR » Wed Nov 11, 2009 3:32 pm

Sen
Thanks a lot for posting your photos and telling about your experience.

Is that an electric heat gun (paint stripper) you used for your bending rig?

Thanks
Jeff
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Re: Should I make a mold?

Postby senunkan » Wed Nov 11, 2009 3:42 pm

JeffR wrote:Is that an electric heat gun (paint stripper) you used for your bending rig?

Yes, that's a B&D heat gun.
I am not sure what's the wattage though, as I don't have it with me now.
You can use any heating element (preferably with heat / current control)
I think Waddy has another improved version of a home made heating pipe with a bbq heating element and temperature gauge.
Be sure to check out his photo album.
Alternatively you can use a light bulb withing the pipe (if the pipe has a big enough diameter)
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