Official Luthiers Forum!

How do you guys get take car of this tricky spot meeting the inside of the mold? Just a better spreader than what I have? (Not the clams pictured.)



Sent from my iPhone using Tapatalk Pro

1) I use a shaped caul in my spreader that distributes the spreading force more evenly than the single point of the clamp
2) My waists are usually over bent a bit so the waist spreader tends to make the side straighten out a bit and fair into the rest of the mold.
3) This is my hobby only and my guitars are handmade, so I don't sweat it if it is not a perfect analog for the shape of my mold; I promise no one else will ever notice.

_________________
Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I've used turnbuckles like Haans is showing. I cut slots in the blocks the rounded ends fit into that don't allow the ends to turn so the turnbuckle can be tightened or loosened but is not otherwise secured to the blocks. I make sure the blocks are small enough to be removed through the soundhole after the box is closed up.

That spot would get hit with the bending pipe. IMHO, cauls should not have to force sides into submission. After a final round on the pipe, I use a center spreader at the waist (similar to the photo above) and one at the lower bout (less substantial than the one in the photo above).


Sent from my iPhone using Tapatalk Pro

_________________
Aaron Craig

I'm not aware of an arrangement of spreaders that would push that part of the side against the mold and still allow you to get the spreaders out through the sound hole. I would take care of that gap by fine tuning the shape of that area on the hot pipe for a better fit.

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

I think part of this is that this is my first time working with wenge. It bent really easily but wow did it spring back!


Sent from my iPhone using Tapatalk Pro

Waist caul, like in Haans's photo.

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

Ditto.

Pretty similar.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

Should have added some words, I guess, but thought it was self explainitory. The top and bottom spreaders are used only during neck and tailblock glue-up, the waist has screws that are removed when the top and back are glued on. Then it all dis-assembles and comes out though the soundhole.
You can see the blanket type bender, and the ribs fit almost perfectly by themselves.

"I'm not aware of an arrangement of spreaders that would push that part of the side against the mold and still allow you to get the spreaders out through the sound hole. I would take care of that gap by fine tuning the shape of that area on the hot pipe for a better fit."

I make mine a cross between what Haans and Terence are showing - I drill and chisel out a short slot for the ends of the turn buckle. It is just a variation on a theme and all of those methods can allow the spreader to come apart and be removed through the soundhole. Like Haans, I generally only leave the waist caul in place when the box is closed up. The cauls help when sanding the rim set on the radius dish, but even then aren't totally necessary.

What I was trying to say is that spreaders that are small enough to be removed through the sound hole don't make direct contact with the section of the side where SnowManSnow has a gap between the side and the mold because of the geometry of the opposing sides in that section of the sides. Based on the gap in the photo, I'm dubious that a waist spreader and a lower bout spreader would be enough to remove that gap. Maybe really cranking on the waist spreaders would remove most of it, but IMO, it would be better to improve the fit in the first place.

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

I am REALLY NOT trying to be a smart a**, but -- why does it matter?

Yes I have spreaders here there and everywhere but since I am really not great at bending the fit isn't always that good. I'm with Bryan, I'm an amateur, it's a hand built guitar. So there are some imperfections in the outline.
What really counts is the geometry of the neck/body. It is the playability that I concentrate on. Obviously as well as the sound.

Dave M

No functional reason, but speaking for myself, two reasons: aesthetics and the principle of the matter.

I'm blessed/cursed with an eye for symmetry/asymmetry, right angles, and parallel lines. I can see small discrepancies in those things and they really bug me. If SnowManSnow's guitar has the same gap on the opposite side and the transitions of the curves of the sides are smooth without kinks because of the gaps, I could live with that from an aesthetic point of view. If there's not the same gap on the opposite side, I would have to fix it.

My body molds aren't an approximation of the final shape I want for my guitars. They are the exact shape I want. I put a lot of effort into designing the final body shapes and that's exactly how I want them end up so I put the effort into making the sides fit the molds as close as possible. So a gap like that would be a problem, but that's just me.

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

My mold is to shape and to get the perfect fit it is all about the trimming. I don't need or use a lot of spreaders. 1 waist spreader and when I trim my sides I start with about a 1/8 rise off the mold as I close it. Then the spreader will set the side against the mold nicely. I then screw the neck and tail block to the mold from the outside. I found that for a spreader to work , it has to remain in the guitar till the body is closed.
https://www.youtube.com/watch?v=FcM3GErOI_A&t=70s

here is a video showing the side set up in the mold
https://www.youtube.com/watch?v=QYHPCeVRUA4

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Spreaders can help hold the body to the mold when using a motorized radius dish. I don't always use them but there are times when I should have.

Oops, that reminds me that I did use the upper and lower bout spreaders for the sanding of ribs and kerfing in addition to the center spreader. Very important when you are using a 10' radius. Never much liked a pipe for guitar ribs. Just too wide to bend, better results with the blanket system.

We use a two or three spreader system in a three ply (usually hardwood, poplar core, birch face stock - much lighter than MDF and so much nicer to work), 2-1/8" depth outside mold, with relieved curves in the waist to tension the side through the waist. An under-bent waist will close up nicely with this treatment, while an over-bent waist will show a gap, so an accurately bent side that fits without much tension is still the goal. Having to touch up side shape is usually not a problem using our side bending process, but we have had a number of kit builders in to get some help on sides which relax in shipment or storage...not hard to do, and the results are worth the investment of time and attention.

The spreaders shown are gotten out of the scraps from the mold-making process, and end up 3-1/2" - 4" in length, 2-1/2" or less in width, and about 2-1/8" thick. With the relieved corners show, they are removable through the sound hole without issue, so can be used to maintain square registration of the sides with mold during the closing of the box, or at least down to the Size 5 instruments which are usually the smallest openings for removal we deal with.



Longer, full-length spreaders would likely do a better job of maintaining exact shape, but would be a bit of a challenge in terms of removal after the box is closed, so spreader size looks like a compromise between perfect shape and utility in the building process. In terms of shape, most variations we see with this minimalist approach are between spreaders, under 1/64", and symmetrical, so acceptable, given the larger variations observed in the vintage Martin and Gibson instruments which we see for repair and setup work.

_________________
For the times they are a changin'

- Bob Dylan

I'm with Hans on this one. As long as it is close and looks symmetric, I'm OK with it. I feel that wood has a way of taking the shape that it wants. So I don't try and fight it too much.

_________________
Tony Thatcher
Bozeman, Montana

Same for me.

_________________
http://www.Harvestmoonguitars.com

My wife has that same cur...blessing and I feel the same way about everything else you said. Aesthetics were a prime consideration.
Dave, if you think that asymmetry makes it "hand made", yes, you are right, but your road is long, grasshopper...sure, tone and playability are important, but handmade is more than just making a dugout canoe...

To be clear, I wasn't advocating a disregard for symmetry or compromising one's standards. I was trying to give a list steps for him to get an acceptable fit in the mold.

First being good shaped cauls that would probably take care of most of his issue and would serve him well going forward rather than just using clamps. Second being that you can tweak the bend at the waist (or where needed) on a pipe to get everything to fit in with the cauls (I say this well in my post). Finally, especially for the early builds, don't drive yourself crazy trying to get the fit perfect. There are plenty of other things in the early goings to stress out about. After a few guitars, you get a better handle on bending more consistently and getting the shape set the way you want it. If you don't get it perfect right away, (almost ) no one will know.

I think everyone should chase perfection to the level they feel suits them. Few of us will ever obtain perfection. The first few attempts will be gloriously imperfect in many respects and that is okay.

_________________
Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

In the past I've always built in a mold. Though I've not always gotten perfect mating of sides to the shape of the mold, I've used spreaders to minimize the discrepancy. After gluing on the top and back, the sides had no choice but to yield to superior force.

My current build is being done without a mold (thanks to suggestions from Bruce Sexauer). The shape is less "perfect" than I've previously achieved, but the sides will meet the top and back without the strains that I embedded using a mold and spreaders. Will that affect the tone? Or longevity? Or anything else? Who knows -- and even after it's built, I'm not sure I'll be able to tell. But it seems, intuitively, that sides without strain might have some advantage. FWIW. (And, hey, it's hand made.)