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#1
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Why do lap joints work?
I used to make lots of them. Now, less because I have more tools but I
still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? Someone might say it is because each piece is narrow and doesn't move much. That is true but I've often made fairly wide laps. For example, all our toilet seats are wood, each made with four pieces about 3" wide lapped at the corners. Discussion is invited. -- dadiOH ____________________________ Winters getting colder? Tired of the rat race? Taxes out of hand? Maybe just ready for a change? Check it out... http://www.floridaloghouse.net |
#2
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Why do lap joints work?
dadiOH wrote:
I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? Someone might say it is because each piece is narrow and doesn't move much. That is true but I've often made fairly wide laps. For example, all our toilet seats are wood, each made with four pieces about 3" wide lapped at the corners. Discussion is invited. I'll throw out the thought that it's because the wood does not move at the joint. The glue successfully holds that joint together as a unit. This might be easier to see with edge glued boards. The boards may move some with varying conditions, across their width, just not at the joint where it is glued. -- -Mike- |
#3
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Why do lap joints work?
On 11/20/2013 5:22 AM, Mike Marlow wrote:
dadiOH wrote: I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? Someone might say it is because each piece is narrow and doesn't move much. That is true but I've often made fairly wide laps. For example, all our toilet seats are wood, each made with four pieces about 3" wide lapped at the corners. Discussion is invited. I'll throw out the thought that it's because the wood does not move at the joint. The glue successfully holds that joint together as a unit. This might be easier to see with edge glued boards. The boards may move some with varying conditions, across their width, just not at the joint where it is glued. Plywood is just a huge sheet of lap joints. It seems to hold together OK. |
#4
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Why do lap joints work?
Subject
It's the glue and the geometery. Glue provides the highest strength when glue is thin and loaded in shear. A half lap joint takes advantage of both those features. SFWIW, a butt joint places the glue joint in tensile loading which is why it is weaker than shear loaded joints such as the half lap. Lew |
#5
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Why do lap joints work?
"Just Wondering" wrote in message
On 11/20/2013 5:22 AM, Mike Marlow wrote: dadiOH wrote: I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? Someone might say it is because each piece is narrow and doesn't move much. That is true but I've often made fairly wide laps. For example, all our toilet seats are wood, each made with four pieces about 3" wide lapped at the corners. Discussion is invited. I'll throw out the thought that it's because the wood does not move at the joint. The glue successfully holds that joint together as a unit. This might be easier to see with edge glued boards. The boards may move some with varying conditions, across their width, just not at the joint where it is glued. Plywood is just a huge sheet of lap joints. It seems to hold together OK. Main difference is that the layers are thin. -- dadiOH ____________________________ Winters getting colder? Tired of the rat race? Taxes out of hand? Maybe just ready for a change? Check it out... http://www.floridaloghouse.net |
#6
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Why do lap joints work?
dadiOH wrote:
"Just Wondering" wrote in message On 11/20/2013 5:22 AM, Mike Marlow wrote: dadiOH wrote: I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? Someone might say it is because each piece is narrow and doesn't move much. That is true but I've often made fairly wide laps. For example, all our toilet seats are wood, each made with four pieces about 3" wide lapped at the corners. Discussion is invited. I'll throw out the thought that it's because the wood does not move at the joint. The glue successfully holds that joint together as a unit. This might be easier to see with edge glued boards. The boards may move some with varying conditions, across their width, just not at the joint where it is glued. Plywood is just a huge sheet of lap joints. It seems to hold together OK. Main difference is that the layers are thin. I don't thing that "main difference" makes any difference. -- -Mike- |
#7
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Why do lap joints work?
Just Wondering wrote:
On 11/20/2013 5:22 AM, Mike Marlow wrote: dadiOH wrote: I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? Someone might say it is because each piece is narrow and doesn't move much. That is true but I've often made fairly wide laps. For example, all our toilet seats are wood, each made with four pieces about 3" wide lapped at the corners. Discussion is invited. I'll throw out the thought that it's because the wood does not move at the joint. The glue successfully holds that joint together as a unit. This might be easier to see with edge glued boards. The boards may move some with varying conditions, across their width, just not at the joint where it is glued. Plywood is just a huge sheet of lap joints. It seems to hold together OK. Correct. -- -Mike- |
#8
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Why do lap joints work?
I won't try to get into the "why" of it too much, but let me just throw
this thought out the A piece of plywood is basically one big set of multiple lap joints... -- There are no stupid questions, but there are lots of stupid answers. Larry W. - Baltimore Maryland - lwasserm(a)sdf. lonestar. org |
#9
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Why do lap joints work?
On 11/20/2013 6:05 AM, dadiOH wrote:
I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? Someone might say it is because each piece is narrow and doesn't move much. That is true but I've often made fairly wide laps. For example, all our toilet seats are wood, each made with four pieces about 3" wide lapped at the corners. Discussion is invited. I make lap joints on every one of my back face frames, typically 6~8 on every one of 20 in the last 2 years. The joints are any where from 3/4" to 3.5" wide. I use the regular water based wood glues which always have some degree elasticity to them so the wood is able to move. Basically the same goes for mortise and tenon and floating tenon joints where the grain is not matched in direction. Wood moves but typically not enough to out stretch the glue's ability to stretch until you get in to wide panels like cabinet sides, solid wood door panels, and table tops. |
#10
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Why do lap joints work?
On 11/20/2013 6:05 AM, dadiOH wrote:
I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? Someone might say it is because each piece is narrow and doesn't move much. That is true but I've often made fairly wide laps. For example, all our toilet seats are wood, each made with four pieces about 3" wide lapped at the corners. Discussion is invited. What are you calling a "lap joint"? What many call lap joints these days are traditionally called "halving joints", most common being what is traditionally known as a "half lap" joint. Halving joints are mostly moderate strength and generally require some type of pinning to stand the test of time. The modern vernacular, "rabbet joint", is actually a "lap joint", and its moderate strength is reinforced by adding a pin of some type (Leon's Domino drawers, etc), or a locking cut: https://www.youtube.com/watch?v=1w7iQFW4hq8 -- eWoodShop: www.eWoodShop.com Wood Shop: www.e-WoodShop.net google.com/+KarlCaillouet http://www.custommade.com/by/ewoodshop/ KarlCaillouet@ (the obvious) |
#11
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Why do lap joints work?
"Swingman" wrote in message
On 11/20/2013 6:05 AM, dadiOH wrote: I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? Someone might say it is because each piece is narrow and doesn't move much. That is true but I've often made fairly wide laps. For example, all our toilet seats are wood, each made with four pieces about 3" wide lapped at the corners. Discussion is invited. What are you calling a "lap joint"? What many call lap joints these days are traditionally called "halving joints", most common being what is traditionally known as a "half lap" joint. Yeah, those. Halving joints are mostly moderate strength and generally require some type of pinning to stand the test of time. That would certainly help but some of my toilet seats are more than 25 years old and doing fine so far -- dadiOH ____________________________ Winters getting colder? Tired of the rat race? Taxes out of hand? Maybe just ready for a change? Check it out... http://www.floridaloghouse.net |
#12
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Why do lap joints work?
On 11/20/2013 8:06 AM, dadiOH wrote:
"Swingman" wrote in message Halving joints are mostly moderate strength and generally require some type of pinning to stand the test of time. That would certainly help but some of my toilet seats are more than 25 years old and doing fine so far Hell, that's just a half a second in the history of wood joints. My wooden ones use both finger and half lap joints. Cross grain "lamination" is not always bad, sez the plywood manufacturer. The "bottom" line, just finish it real well. -- eWoodShop: www.eWoodShop.com Wood Shop: www.e-WoodShop.net google.com/+KarlCaillouet http://www.custommade.com/by/ewoodshop/ KarlCaillouet@ (the obvious) |
#13
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Why do lap joints work?
On 11/20/2013 8:22 AM, Swingman wrote:
On 11/20/2013 8:06 AM, dadiOH wrote: "Swingman" wrote in message Halving joints are mostly moderate strength and generally require some type of pinning to stand the test of time. That would certainly help but some of my toilet seats are more than 25 years old and doing fine so far Hell, that's just a half a second in the history of wood joints. My wooden ones use both finger and half lap joints. Cross grain "lamination" is not always bad, sez the plywood manufacturer. The "bottom" line, just finish it real well. Finish it real well! Heck just let the natural oils and fluids seal the wood! I guess you would call that the "Out House" finish. |
#14
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Why do lap joints work?
"right angles to each other yet they remain nice and solid. How come?"
********************** They work because glue sticks. Oh really? Trivial but true, lots of surface, lots of pull and twist resistance. And even if the surfaces are not flat or the joint was poorly clamped, it still holds because some of that surface has been "welded". Moreover, to be sure, most laps are at right angles changing shape in conflict and they still hold because of mechanics and the magic of glue. Make them too big & without a fastener, and they will creep and loosen. I agree it is a surprise they last so long. A fastener, in my view, on occasion is called for. Make a gate that kids swing on and the connection may fail; add some steel and they won't bust it. Lap the surfaces with a dovetail bit and gain some more interlock and easier assembly. http://patwarner.com/images/dovetailed-lap.jpg |
#15
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Why do lap joints work?
wrote in message
"right angles to each other yet they remain nice and solid. How come?" ********************** They work because glue sticks. Oh really? Trivial but true, lots of surface, lots of pull and twist resistance. The glues we have now are a marvel! And even if the surfaces are not flat or the joint was poorly clamped, it still holds because some of that surface has been "welded". Moreover, to be sure, most laps are at right angles changing shape in conflict and they still hold because of mechanics and the magic of glue. Make them too big & without a fastener, and they will creep and loosen. I agree it is a surprise they last so long. A fastener, in my view, on occasion is called for. Make a gate that kids swing on and the connection may fail; add some steel and they won't bust it. Damned steel is going to rust though Lap the surfaces with a dovetail bit and gain some more interlock and easier assembly. http://patwarner.com/images/dovetailed-lap.jpg Yes, I do those from time to time. -- dadiOH ____________________________ Winters getting colder? Tired of the rat race? Taxes out of hand? Maybe just ready for a change? Check it out... http://www.floridaloghouse.net |
#16
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Why do lap joints work?
The glues we have now are a marvel! Amen .... As someone who grew up in the 1940s and 1950s, I remember what an ordeal it often was to glue things. It seems the choices were mainly the old Duco for model airplanes and other light gluing, and "Iron Glue", a fetid, fish-based stuff in a small bottle. After WWII, we saw better and better adhesives available. I would also add the same is true of lubricants. What a difference! |
#17
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Why do lap joints work?
"dadiOH" wrote in :
Damned steel is going to rust though Sometimes, that's considered a good thing. If the fastener is thick enough (like a 16D nail), rust occuring on the fastener serves to lock it in place. Of course, they do occasionally rust through, and that's a bad thing. Puckdropper -- Make it to fit, don't make it fit. |
#18
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Why do lap joints work?
"dadiOH" wrote in message ... I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? Someone might say it is because each piece is narrow and doesn't move much. That is true but I've often made fairly wide laps. For example, all our toilet seats are wood, each made with four pieces about 3" wide lapped at the corners. Discussion is invited. -- dadiOH I do lots of woodworking on our house. but never thought about making a toilet seat. WW |
#19
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Why do lap joints work?
On Wed, 20 Nov 2013 07:05:44 -0500, dadiOH wrote:
I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? I think a lot of it is the sealing effect of the finish and the climate control in modern houses. Either dewaxed shellac or oil based polyurethane do a good job of retarding moisture exchange. And with a lot of houses having air conditioners, hunidifiers and or dehumidifers the seasonal humidity changes are almost nullified. And the glue itself seals the unfinished surfaces of the joint. Someone who's made lap joints for unfinished outdoor stuff, or who lives in an area with extreme humidity changes might have a different experience. I live in the west. Humidity is low in the summer and high in the winter, but the house heating in the winter lowers the indoor humidity quite a bit so the swing is lessened considerably. -- This message was for rec.woodworking - if it appears in homeownershub they ripped it off. |
#20
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Why do lap joints work?
Larry Blanchard wrote:
On Wed, 20 Nov 2013 07:05:44 -0500, dadiOH wrote: I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? I think a lot of it is the sealing effect of the finish and the climate control in modern houses. Either dewaxed shellac or oil based polyurethane do a good job of retarding moisture exchange. And with a lot of houses having air conditioners, hunidifiers and or dehumidifers the seasonal humidity changes are almost nullified. And the glue itself seals the unfinished surfaces of the joint. Someone who's made lap joints for unfinished outdoor stuff, or who lives in an area with extreme humidity changes might have a different experience. I live in the west. Humidity is low in the summer and high in the winter, but the house heating in the winter lowers the indoor humidity quite a bit so the swing is lessened considerably. Good point. Wood does not shrink or swell unless its moisture content changes . Ship a piece of furniture cross country and movement becomes a detrimental fact, as many furniture manufacturers have learned. Modern furniture production is quite concerned with, and spends a lot of money keeping factory/shop RH and wood EMC as close to 7.0 percent EMC and 35 percent RH as possible. -- www.ewoodshop.com (Mobile) |
#21
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Why do lap joints work?
Swingman wrote:
Good point. Wood does not shrink or swell unless its moisture content changes . Ship a piece of furniture cross country and movement becomes a detrimental fact, as many furniture manufacturers have learned. Modern furniture production is quite concerned with, and spends a lot of money keeping factory/shop RH and wood EMC as close to 7.0 percent EMC and 35 percent RH as possible. Good point indeed, but not as good as we tend to think. Think about all of the glued together musical instruments that are shipped worldwide, furniture of differing qualities that are glued up and suffer the conditions of differing environments. There is far less movement than is often spoke of here. Not to say there is none, but often times there really is none. Look where stuff is manufactured, and look at where it ends up. We tend to make more of this movement thing in this newsgroujp than can actually be found in most real world situations. IKEA may me junk, but - how do they ship products around the world without 1/4" gaps? How about Martin guitars? Think about something as precise as that Martin... An extreme movement would be considered to be less than 1/8", and that is at the neck - over an almost 2' span. Look how all of those cross grain structures hold together to keep the body intact, the bracing intact, and the bridge intact. Certainly movement of far less than 1/8" would be catastrophic. So - I'm not aruging with the prevailing logic, but I am suggesting that we tend to apply that logic too universally, in the face of obvious eveidence. -- -Mike- |
#22
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Why do lap joints work?
"Mike Marlow" wrote in
: Good point indeed, but not as good as we tend to think. Think about all of the glued together musical instruments that are shipped worldwide, furniture of differing qualities that are glued up and suffer the conditions of differing environments. There is far less movement than is often spoke of here. Not to say there is none, but often times there really is none. Look where stuff is manufactured, and look at where it ends up. We tend to make more of this movement thing in this newsgroujp than can actually be found in most real world situations. IKEA may me junk, but - how do they ship products around the world without 1/4" gaps? How about Martin guitars? Think about something as precise as that Martin... An extreme movement would be considered to be less than 1/8", and that is at the neck - over an almost 2' span. Look how all of those cross grain structures hold together to keep the body intact, the bracing intact, and the bridge intact. Certainly movement of far less than 1/8" would be catastrophic. So - I'm not aruging with the prevailing logic, but I am suggesting that we tend to apply that logic too universally, in the face of obvious eveidence. Wouldn't a finish tend to retard the movement of moisture into and out of the wood? If it's moisture changes causing the movement, and not something else like temperature, then could the finish play a part in allowing pieces to be transported with little difficulty? Puckdropper -- Make it to fit, don't make it fit. |
#23
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Why do lap joints work?
On 11/21/2013 2:45 AM, Puckdropper wrote:
Wouldn't a finish tend to retard the movement of moisture into and out of the wood? If it's moisture changes causing the movement, and not something else like temperature, then could the finish play a part in allowing pieces to be transported with little difficulty? A finish indeed has a slowing effect on EMC, but does not stop wood from moving toward it. -- eWoodShop: www.eWoodShop.com Wood Shop: www.e-WoodShop.net google.com/+KarlCaillouet http://www.custommade.com/by/ewoodshop/ KarlCaillouet@ (the obvious) |
#24
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Why do lap joints work?
Puckdropper wrote:
Wouldn't a finish tend to retard the movement of moisture into and out of the wood? If it's moisture changes causing the movement, and not something else like temperature, then could the finish play a part in allowing pieces to be transported with little difficulty? Yeah but that's where it gets even worse - instruments are only finished on the outside. The inside of a guitar for example, or a fiddle, etc. is raw wood. That's a worst case scenario for wood. To be fair - the wood does move, and guitars fall out of tune due to changes in humidity, and they are all glued together with cross braces inside, and the like, so there is an understandable reason why they don't move as much, but then there's that stuff from IKEA. I still don't understand how it holds up. -- -Mike- |
#25
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Why do lap joints work?
On 11/20/2013 11:48 PM, Mike Marlow wrote:
Look where stuff is manufactured, and look at where it ends up. We tend to make more of this movement thing in this newsgroujp than can actually be found in most real world situations. Think about how much real wood is in today's factory furniture. Most of it is veneer with a substrate of particle board, which is not subject to the same dimensional instability ... about the only real wood is the trim elements. One of the reasons why you rarely see solid wood panels on modern factory furniture any longer. Also, as I stated, manufacturers spend a good deal of money dealing with the dimensional instability of wood in their plants, to include purposely maintaining a narrow limit to RH and EMC ... they learned the hard way. IKEA may me junk, Ikeas uses real wood? Coulda fooled me. How about Martin guitars? Think about something as precise as that Martin. Woods used for guitars and other instruments, are specifically chosen for dimensional stability. AAMOF, there are very few woods used by luthiers. Spruce, maple, mahogany, walnut, ebony, rosewood, and in particular, Honduras mahogany are all woods that are extremely stable when properly dried and chosen. You will rarely see any other type of wood on a musical instrument. Not to mention that successful luthiers and instrument makers spend a whole lot more time and effort choosing their woods for stability, grade, tone, and grain than a furniture manufacturer. So - I'm not aruging with the prevailing logic, but I am suggesting that we tend to apply that logic too universally, in the face of obvious eveidence. Not in my book ... dimensional instability of wood is something you ignore at your own peril. Most of us just don't see it because our furniture has reached EMC and because _wood does not shrink or swell unless its moisture content changes_. -- eWoodShop: www.eWoodShop.com Wood Shop: www.e-WoodShop.net google.com/+KarlCaillouet http://www.custommade.com/by/ewoodshop/ KarlCaillouet@ (the obvious) |
#26
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Why do lap joints work?
On 11/21/2013 8:15 AM, Swingman wrote:
On 11/20/2013 11:48 PM, Mike Marlow wrote: Look where stuff is manufactured, and look at where it ends up. We tend to make more of this movement thing in this newsgroujp than can actually be found in most real world situations. Think about how much real wood is in today's factory furniture. Most of it is veneer with a substrate of particle board, which is not subject to the same dimensional instability ... about the only real wood is the trim elements. One of the reasons why you rarely see solid wood panels on modern factory furniture any longer. Also, as I stated, manufacturers spend a good deal of money dealing with the dimensional instability of wood in their plants, to include purposely maintaining a narrow limit to RH and EMC ... they learned the hard way. IKEA may me junk, Ikeas uses real wood? Coulda fooled me. How about Martin guitars? Think about something as precise as that Martin. Woods used for guitars and other instruments, are specifically chosen for dimensional stability. AAMOF, there are very few woods used by luthiers. Spruce, maple, mahogany, walnut, ebony, rosewood, and in particular, Honduras mahogany are all woods that are extremely stable when properly dried and chosen. You will rarely see any other type of wood on a musical instrument. No doubt due to supply and demand, I see Taylor using a lot of "Sapele" on their guitars these days. I never heard of it before they started using it. http://www.taylorguitars.com/guitars/acoustic/woods Not to mention that successful luthiers and instrument makers spend a whole lot more time and effort choosing their woods for stability, grade, tone, and grain than a furniture manufacturer. So - I'm not aruging with the prevailing logic, but I am suggesting that we tend to apply that logic too universally, in the face of obvious eveidence. Not in my book ... dimensional instability of wood is something you ignore at your own peril. Most of us just don't see it because our furniture has reached EMC and because _wood does not shrink or swell unless its moisture content changes_. |
#27
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Why do lap joints work?
On Thu, 21 Nov 2013 07:15:25 -0600, Swingman wrote:
Spruce, maple, mahogany, walnut, ebony, rosewood, and in particular, Honduras mahogany are all woods that are extremely stable when properly dried and chosen. You will rarely see any other type of wood on a musical instrument. Well, I did use spanish cedar for a soundboard on a hammered dulcimer, but that was a floating soundboard :-). BTW, the spanish cedar is gorgeous. But it has too much sustain. Next time I'll make one a little thicker. -- This message was for rec.woodworking - if it appears in homeownershub they ripped it off. |
#28
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Why do lap joints work?
On Thursday, November 21, 2013 7:15:25 AM UTC-6, Swingman wrote:
List of woods & experience: Spruce, maple, mahogany, walnut, ebony, rosewood, and in particular, Honduras mahogany are all woods that are extremely stable .... . You will rarely see any other type of wood on a musical instrument. Nope ... it is experienced based, .... 25 or so yrs ago, several teenage nephews visited for a few summer weeks, brought their guitars to jam, one or 2 for simple repairs, etc., etc. They asked about making a guitar from scratch. I had an air dried sycamore log, so "we" decided to try carving a whole (single unit) "guitar" from it. Got pretty far with carving the body, neck, ram's head headstock, hand planed 1/8" soundboard, etc., but never assembled/finished it. When the boys left, I stuck it in the old shop and.... It hasn't moved, since. Sonny |
#29
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Why do lap joints work?
On Wed, 20 Nov 2013 07:05:44 -0500, dadiOH wrote:
I used to make lots of them. Now, less because I have more tools but I still do on occasion and I wonder why they work? We all know that wood expands and contracts and lap joints have to pieces of wood doing that at right angles to each other yet they remain nice and solid. How come? Someone might say it is because each piece is narrow and doesn't move much. That is true but I've often made fairly wide laps. For example, all our toilet seats are wood, each made with four pieces about 3" wide lapped at the corners. Discussion is invited. It has to do with the better bonding of long grain faces versus the end grain which basically sucks up the glue and has poor bonding. I think it is like no on prefers butt faces. |
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