Laminating sides, and a no water no heat bending method

[deadedith]

Rick, John - do you have any proof whatsoever of what you are saying re: a more rigid perimeter lining not adding anything to the torsional stiffness of the side? Or is it based on your experience or what?
Sure I'm a noob; but I can still read, and if you have some facts I could look at I would appreciate it.

[deadedith]

I misspelled 'rigid' in my first post. And as a former editor, I am abashed.

As to the rest, we'll see

[kencierp]

Just for conversation purpose --- seems that stiffness of a drum shell (our guitar rim) is a pretty important consideration relative to energy transfer and what is heard -- no columns/posts in the drum.

From a drum manufacturers site -- referencing drum shells

The number of plies effects how readily energy is transferred from the
heads to the shell. This single factor has a profound effect on the tonal
characteristics and projection of the drum.

Thin shells (4 ply, 5mm) enable relatively easy energy transfer from the
heads to the shells thus causing the shells to vibrate. This vibration
imparts a very rich "wood" tone to the overall sound that can be most
appreciated in near-field applications and especially in recording.

Medium thick shells (6 ply, 7.5mm) have greater stiffness and resist
energy transference from the heads. With less shell vibration, a trade-off
is achieved: the sound is slightly "cooler" than thinner shells but
projection is greater. Drums made to this thickness are ideal for
general-purpose applications and / or situations requiring more
"horsepower."

Thick shells (8 ply, 10mm and 10 ply, 12.5mm) are extremely "efficient"
and allow most of the player's energy to be focused to the audience. These
drums are ideal for coliseum-type venues and other applications requiring
high sound pressure levels. Snare drums made in this thickness rival metal
snare drums in intensity and projection.

[tippie53]

reverse kerf will not NOT change the woods strength properties beyond the point of making the shape more rigid . You can't compare a laminate to this as the laminate is from top to bottom and is part of the total structure . The woods strength across the grain is unchanged no matter what kerfing material you use , That is an engineering fact . Once you are off the kerfing you have no added material and no change in the materials shape therefore you can't the change physical property of the material.
If you are free building the reverse kerfing will help to hold the shape of the side but will not change the materials strength properties .

[deadedith]

I was not thinking so much of the material as the structure. Would the structure be more rigid overall by using a more rigid kerfing? I know Rick Turner has experimented with carbon fiber linings for that very reason.
I might be getting caught up in terminology, as well. Rigidity - stiffness - torsion etc.

No one I have read has said that stiffer linings actually stiffen the side material - that would be done by using thicker material or lamination. It has been said by many that a more rigid lining produces more rigidity in the sides structurally.

[kencierp]

Not getting that logic John -- if there are two rims and one physically, lets say is less flexible before you attach the top and or back that rim stays less flexible and will still have different properties then the other -- the stiffness and all the other the characteristics of the structure just doesn't disappear! The energy transfer properties of the two rims will be different too.

[tippie53]

The analogy of a drum isn't the same as a guitar side . The stiffness will not effect energy transfer from the top to the back . If this were true the strength of the structure would change . I understand and agree that the reverse kerfing will create a truss effect to the sides , but this will not change the tonal transfer of energy.
The fact is that kerfing , solid , reverse or standard will not change the strength of the structure and this can be proved by a simple experiment of yield strength of the structure.
If the structure would collapse with kerfing A at stress point B the different kerfings will not change the load bearing ability of the sides.
do you have any engineering proof ?

[kencierp]

John you are setting up a straw man argument and assuming your view is correct -- The characteristics of the compents in a structure do not change when you assemble them. I believe the analogy of the drum is perfect -- it is what it is -- the rims are as stiff as when they are made and don't change when you place a skin on them. Here's the only fact -- when assembled the RR kerfing the rim is less flexible then the triangle kerfing rim therefore I am assuming the less flexible rim (as with the drum) is less damping reflects/transfers more energy --- that characteristic is there whether the rim is assemble to the top and/or back or not --- it does not simply disappear.

[tippie53]

This is a great discussion so lets take it a bit further. I agree that with reverse kerfing you do get a truss system but once the top and the back are attached you now have a more complex system. Glue is what binds this system together . Lets look at this , glue often has more strength that the materials that it attaches .
While you assume the drum analogy is correct there is a difference in that the drum is a series of lamination's to make a thickness . The strength and stiffness is changed through the side structure. With the kerfing you just have a stiffness of the side shape and not the whole side like a drum would have. There is a difference here in that we are looking at a stiffness on considerable amount as compared to a solid of the same thickness as this is more if a plywood design.
Now once you take a guitar side attach the top and the back we are looking at a glue bearing joint. There is more glue surface on regular kerfing and the stuffiness with the top and back applied will exceed the stiffness equivalent of the kerfing and the structure would be about the same reverse or not .
I agree that if you think it is better to use the system but I don't think there is true engineering proof to say it is better than standard kerfing. The joinery of the regular kerfing will have more glue surface area than the reverse kerfing .

I hope you understand that I am enjoying this discussion and don't mean any disrespect . The one drawback to forums is that written words can sometimes come across opposite of spoken words. We may be agreeing on some points but terminology may be gettin in the way

[kencierp]

No disrespect intended and nothing at all has seemed disrespectful.

I have no idea if RR is better or worse acoustically -- I like because it does make the rim easier to handle early in the construction process and I like the look.

I am the devil's advocate in this because I've read some comments which are stated as absolutes and frankly I don't believe some of scientific interpretation and or the logic.

I've got other things to do now -- but consider this -- Kerfing is actual about 25% of the rim surface area. All other objects can be made more robust by adding to the structure --- sometimes it is value add sometimes not -- We still have not made a case that RR is a plus or a minus. I am not even sure that it does not reduce torsion effect? We, along the way jumped to that conclusion -- because, well there is no comparison tests available to us at this time -- seems Bob Taylor did some? Not sure why I'd want to disregard that?