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What Filler???

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Topic: What Filler???
Posted By: PolymorphicMark
Subject: What Filler???
Date Posted: 07 March 2017 at 5:41pm
Hi there, I've been using P38 filler for along time on my cabs to fill the counter sunk holes used for the assembly screws. I've noticed on some of my older cabs that I still have in my possession, the filler plug has lifted out of the hole. Upon removing the plug the screw behind has rusted causing it to expand and push the filler out. I know filler is porous so I assume water has penetrated the Aldcroft speaker paint, soak through the filler and rusted the screw.

I think from now on I'm going to use stainless steel screws, but I never questioned the filler i use.

So I'm asking you lot, What type of filler are people using?

Mark


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Free to do what i WANT



Replies:
Posted By: mini-mad
Date Posted: 07 March 2017 at 5:50pm
fine sawdust and pva glue mix. cheap, strong and does the job!

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If it sounds like a gorilla is trying to escape, turn it down.


Posted By: snowflake
Date Posted: 07 March 2017 at 6:10pm
yes, use pva/sawdust or wood filler. use the money you save to buy some decent screws. using car body filler is solving a problem that doesn't exist. it doesn't sand down flush with the wood easily either so you end up making more work for yourself.

if there's a rusty screw in there try and back it out, or at least drill the head out.


Posted By: Marko
Date Posted: 07 March 2017 at 6:31pm
I have the same problem.
Do you know if Warnex will stick to PVA glue?


Posted By: snowflake
Date Posted: 07 March 2017 at 6:40pm
it will definitely stick to wood filler so use that. they call it wood filler for a reason!


Posted By: PolymorphicMark
Date Posted: 07 March 2017 at 6:43pm
Any particular brand of wood filler?



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Free to do what i WANT


Posted By: Marko
Date Posted: 07 March 2017 at 6:48pm
Originally posted by snowflake snowflake wrote:

it will definitely stick to wood filler so use that. they call it wood filler for a reason!

I know it will stick to filler but filler that I used expanded.
I dont know is it becouse of the filler or the screw underneath. The screw does not look rusty.
I'm searching for alternative for wood filler. I read here before about PVA glue with dust but donmt know will Warnex stick to it or I need some primer coat?


Posted By: JonB67
Date Posted: 07 March 2017 at 10:21pm
What size screws are you all using? I was considering using the tonguetite screws as the lost head makes for a much easier safer hole shape for filler to bond into which would eliminate this issue.... thoughts?


Posted By: SouthwestCNC
Date Posted: 07 March 2017 at 10:36pm
Counter bore and plug hoe hoe?


Posted By: DJ-Versatile
Date Posted: 07 March 2017 at 11:11pm
Just to throw my two pence in, I've used Big Boy lightweight filler to great effect on a number of cabs 

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If you are the smartest person in the room, you're in the wrong room....


Posted By: I-shen Soundboy
Date Posted: 08 March 2017 at 12:47am
Devils advocate: Don't use screws, they're a structural liability the moment the glue sets.

Rebate, dowels, biscuits, glue and f*** off big clamps should do it.


Posted By: Shortrope
Date Posted: 08 March 2017 at 7:38am
Originally posted by I-shen Soundboy I-shen Soundboy wrote:

Devils advocate: Don't use screws, they're a structural liability the moment the glue sets.

Rebate, dowels, biscuits, glue and f*** off big clamps should do it.


How is a screw a structural liability?

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My Tinnitus is coming along nicely!!


Posted By: snowflake
Date Posted: 08 March 2017 at 11:51am
in some ways a screw is a liability, in other ways it isn't - depends on the material and the joint used.

in theory a screw will concentrate the stress in the joint at the point where the screw is - this then becomes a point of failure. this only holds for materials that are like theoretical materials eg plastic

it is a bit more complicated with materials such as ply as they have layers and grain. because the layers in ply are glued together over a large area, the glue that they use is often not that strong and there are small imperfections in the layers. the failure mode is often that one of the pieces delaminates. this happens particularly with 90 degree butt joints or rebates joints. In this case screws can help by holding the laminates together.

I did some tests a few years ago with different joints. the strongest joint was one where both pieces were cut at 45 degrees and the cut ends glued together with a biscuit in the joint. no screws but every layer in the wood was glued to the other piece of wood in the joint and could not delaminate.

all that said, screws are a quick and convenient way to hold things together while the glue sets. self-drilling, self-countersinking, non-corroding, smooth shank screws are what you want. no more than one every six inches is enough.


Posted By: ceharden
Date Posted: 08 March 2017 at 8:28pm
In order to get a good glue joint the two pieces need to be held tightly together. Screws are good for that.


Posted By: 70,s hero
Date Posted: 08 March 2017 at 10:17pm
when I made my cabs I looked at different fillers and used the car filler as it sets faster and is finer to sand , that said PVA with sawdust is ok, I think that if a plug lifts then it is unlikely its down to the rust on a screw, more likely movement in the joint and the screw lifting and pushing it out over time unless the filler was put in on a dusty dry joint. Plastic padding sticks like you know what and i have never seen it come out, it doesn't shrink and to my knowledge is non porous.

Looking at the screw scenario and stresses, if I were to screw two pieces of wood together and then use a nail bar and hammer to force them apart, the usual result is that there is a portion of wood left with the screw in it fixed to the other part. The argument that less screws are stronger  is IMO contrary to excepted engineering principles (for wood)

This tells me that the more screws that are used the better, whilst the forces are transferred to the screwed fixing upon failure of the joint, the joint remains intact around the screw fixing. If you have ever broken apart a cabinet, you will see this. When I constructed my cabs I used screws every 50 mm ( a bit OTT I know) but the application demanded structural integrity. In effect the further that the lateral forces are transferred in to each pane the batter.

After talking with a structural engineer friend, I decided to half rebate each section which increased the contact surface area considerably and removed the lateral stresses upon all of the major joints.

The upshot is that in reality, you could fix and glue a batton internally which is a really good way of stabilizing a 90 degree joint. Bona make an excellent filler, usually used for refinishing wood floors, going to try that next time for convenience. 


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Top banana


Posted By: I-shen Soundboy
Date Posted: 08 March 2017 at 10:54pm
Agree - if you use screws, use a lot of them.
The clamping force of an individual woodscrew is several orders of magnitude less than a clamp, so consequently is only effective over a relatively small area. I'd contend a couple of sash clamps could out-clamp a box of woodscrews.

Using screws and corner batons internally is another great idea that avoids having to fill screw holes.

Or, if you absolutely must have external screws, don't countersink them, give them a cup washer, like on the removable back of old guitar cabs - although nowadays you can get solid stainless machined cup washers, colour anodised if you like, rather than the old pressed brass ones. I've got a couple of boxes covered in these raised silver screw heads: Very Metal.


Posted By: SouthwestCNC
Date Posted: 09 March 2017 at 3:16pm
No matter the filler, filler doesn't swell with the ply when paint is applied. Without applying filler to the entire cab filler will always be visible. Plug the counterbored screw holes with wooden plugs is the only way to make invisble with paint.


Posted By: cravings
Date Posted: 09 March 2017 at 3:45pm
i feel like i notice filler shrinking over time rather than swelling.


Posted By: Shortrope
Date Posted: 09 March 2017 at 3:50pm
A lot of the time it's actually the timber swelling.

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My Tinnitus is coming along nicely!!


Posted By: SouthwestCNC
Date Posted: 09 March 2017 at 4:48pm
That's right the filler wont shrink or swell, the wood expands and contracts continuously with temperature and humidity.

Plugged with Birch

https://postimg.org/image/ijn9p8yxh/" rel="nofollow">

wont trap moisture like filler will either.


Posted By: JonB67
Date Posted: 09 March 2017 at 4:55pm
So is it better to just glue and clamp?


Posted By: SouthwestCNC
Date Posted: 09 March 2017 at 5:01pm
Not without biscuits, dowels/dominos, or rebates imo. A glue only butt jointed box will not withstand multiple drop tests like a screwed box will.


Posted By: I-shen Soundboy
Date Posted: 09 March 2017 at 5:37pm
Screw and glue is the simplest and cheapest way to go.
I'd only advise more esoteric/traditional methods if you're getting into your cabinetmaking rather than knocking out half a dozen suicide boxes.

Anyhow, if you've spent a few days laquering and polishing a cabinet (as opposed to ten minutes tuff-cabbing), you're far less likely to subject it to multiple drop tests


Posted By: SouthwestCNC
Date Posted: 09 March 2017 at 7:24pm
Originally posted by I-shen Soundboy I-shen Soundboy wrote:

Screw and glue is the simplest and cheapest way to go.
I'd only advise more esoteric/traditional methods if you're getting into your cabinetmaking rather than knocking out half a dozen suicide boxes.

Anyhow, if you've spent a few days laquering and polishing a cabinet (as opposed to ten minutes tuff-cabbing), you're far less likely to subject it to multiple drop tests


Yep its horses for courses. There are branded touring cabs that are just pinned and glued, There are also youtube vidoes of them being pushed off the top a stack resulting a flat packed cab in a matter of seconds.


Posted By: PolymorphicMark
Date Posted: 10 March 2017 at 7:22pm
Originally posted by SouthwestCNC SouthwestCNC wrote:

No matter the filler, filler doesn't swell with the ply when paint is applied. Without applying filler to the entire cab filler will always be visible. Plug the counterbored screw holes with wooden plugs is the only way to make invisble with paint.


Thanks for that tip :)



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Free to do what i WANT


Posted By: bee
Date Posted: 10 March 2017 at 11:41pm
so much miss information hear guys....
 
screws are used to hold panels in place till the glue drys, they add no strength to cab.
 
glue and clamps are a must, and clamps should remain holding panels in place till glue is firmly dry.
 
adding more screws will not make a box stronger, the weekest point to a box is the cheap ass pva glue people use. best glue for birch ply is commonly known as yellow glue.
 
look for tight bond 2 or tight bond 3, only difference is drying time of glue.
 
best filler, defo not wood filler for speaker boxes, use a good car body filler like upol, available from most car shops (Halfords)
 
wood filler is too soft for speaker boxes and can fall out due to vibrations and moving boxes about. (in and out vans stacking ect)
 
upol also is easy to sand and most paints stick to it.
 
wood only swells if your using water based paint and cheap wood, to stop your cabs swelling using water based paint, put a very thin coat on, let it dry fully, that way it creates a barrier and paint coats added after wont swell the wood. too much paint in one go can also swell the wood.
 
if correctly done with wood filler your filled area wont show when painted, if the paint is too thin then your not coating the cabs with a thick enough coat, again use more coats...
 
best method to join panels on a speaker box is the good old simple rebate, no need for dowels or rabbit's or dominoes or any of the other methods. simple rebate gives the maximum glue to surface area.. and also acts as a guide to aligning your panels.
 
but that said what do I know.....


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https://www.elements-audio.com


Posted By: SouthwestCNC
Date Posted: 11 March 2017 at 12:14pm
I only use quality Birch ply bee, and it doesn't require any paint to swell. Humid conditions are all it needs but all wood is unstable is will expand and contract continuously. When have you had an 18mm sheet actually measure 18mm.

You would need to ensure the humidity is stable in your workshop and the paint applied has no swelling effect on the wood as celulose based paints will still swell or shrink wood (polyurethane maybe an exception), and the cab is completely sealed after the coating, But sanding filler in wood also is not an ideal situation as they do not sand at even rates.

I personally now try to avoid filler at all costs.







Posted By: nickyburnell
Date Posted: 12 March 2017 at 11:25am
P38 shrinks in time, not the wood, does it on metal too. Didn't used to, does today. Something changed?


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It's everything, not everythink!


Posted By: snowflake
Date Posted: 12 March 2017 at 3:05pm
well there seem to be a lot of different views here. still contend that screws will only add strength if the joint is poorly glued or not a suitable joint for plywood e.g. one that sticks one piece of wood to the surface of one laminate on the other piece of wood and relies on the strength of the glue between laminates.

no one has mentioned dry joints. if you clamp/screw together a joint too tightly you will push most of the glue out and not leave enough to soak into the surfaces and glue the pieces properly. whether using PVA or PU I always apply the glue to both surfaces and leave it to soak in for several minutes. then screw together just enough that the joint closes up and glue bulges out the sides along the whole length. as the glue continues to soak in and cure it will pull the pieces a few micrometres closer together if necessary. If done properly the glue is stronger than the wood.

butt and rebate joints are not great for plywood because the right angles follow the structural weakness of the ply layers. they are convenient though because they are easy to machine and, as bee said, easy to align and keep everything square.

southwestcnc is right, best way to do screwholes is with wooden plugs. after this (half decent) wood filler - the people who make this aren't morons. it's formulated to stick to wood, to sand at the same rate as wood, to take paint the same as wood, and to expand with heat/moisture the same as wood. if P38 was that great for filling wood you will find it different tins with 'professional wood filler' printed on it. the only reason I could see for maybe using it would be if your screws aren't countersunk very far so the filler is mostly stuck to metal rather than wood. deep countersinks with all the dust blow out have never given me any problem with filler coming out.


Posted By: bee
Date Posted: 12 March 2017 at 3:11pm
ive seen water based paints, offer no help when it comes to temperature change, and cabs swell shrink, but never bad enough for filler to fall out, even on cabs 30 years old. If your seeing movement that bad, I would question the storage methods of my wood supplier, also all sheets of birch should be left to climatized for 2 weeks to your workshop temp. once painted up, there should be very little change, as that's what the paint is supposed to help do as well as protect. an 18mm sheet can vary in size by around 0.5 of a mm, any more than that and again, the wood goes back to wood yard.

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https://www.elements-audio.com


Posted By: bee
Date Posted: 12 March 2017 at 3:15pm
ive not used p36, I just use the upol easy fill version. its the choice of brands like void, turbo, ass, martin to name afew, so defo good enough for me... never had it fall out yet..

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https://www.elements-audio.com


Posted By: snowflake
Date Posted: 12 March 2017 at 3:53pm
probably overkill but waterproof PVA on the inside of the cabs makes them totally moisture proof.


Posted By: nickyburnell
Date Posted: 12 March 2017 at 4:11pm
Originally posted by snowflake snowflake wrote:

probably overkill but waterproof PVA on the inside of the cabs makes them totally moisture proof.


Always with MDF


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It's everything, not everythink!


Posted By: bee
Date Posted: 12 March 2017 at 5:58pm
100% with mdf, I also pva any cut edges once assembled pre painting. This helps stop the furring you get on edges.

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https://www.elements-audio.com


Posted By: 70,s hero
Date Posted: 13 March 2017 at 10:00am
Screws clamp the joints together and distribute any forces further in to the opposing planes of material effecticevly increasing the area of distibution of force should any lateral or compressive forces be applied.

To increase the contact area for the same purpose and alignment, rebating is better than butt joints,the grain really has no effect as the grain in ply is set upon each layer at 90 degrees in opposition. It is questionable if there is any appreciable soaking in of glue as the ply (grade bb Birch) is compressed greatly with glue at manufacturer making it very dense and the viscosity of PVA and bubble glue is a deterring factor.

I do not agree that a screw does not add to the strength of a corner joint, for sure, the glue does the majority of work in stabilization but screws will help as they help distribute forces.

The idea that glue is the only requirement for the strongest joint is true in say glue beams or ply which are manufactured with hydraulic presses, I am open to be convinced that a corner joint in say 18mm ply does not benefit from additional screws, that's my take on it, hoping to be convinced otherwise.


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Top banana


Posted By: SouthwestCNC
Date Posted: 13 March 2017 at 10:15am
Theres certainly a balance, adding excessive amounts of screws will compromise the structure as panels can then split through its thickness however I agree a minimal amount of well placed screws does increase joint strength over just being glued.


Posted By: nickyburnell
Date Posted: 13 March 2017 at 10:20am
Originally posted by bee bee wrote:

100% with mdf, I also pva any cut edges once assembled pre painting. This helps stop the furring you get on edges.


Cellulose putty good for this too, stops the (different edges) look under paint.

Mind you, when you use MDF for cheapness, then add PVA, 8 corners......comes up a bit


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It's everything, not everythink!


Posted By: 70,s hero
Date Posted: 13 March 2017 at 11:42am
Originally posted by SouthwestCNC SouthwestCNC wrote:

Theres certainly a balance, adding excessive amounts of screws will compromise the structure as panels can then split through its thickness however I agree a minimal amount of well placed screws does increase joint strength over just being glued.

+1

Its something that I cant get my head around, the thought that screws dont help a joint (if done properly)

I screw at 50mm c/c with a pilot but in opposing panels and so that leaves 100mm c/c between them.

I looked at BEE'S corner joints, it never occurred to me that having a rebate with an additional 45 mitre was doable, nice touch, I wonder what the router bit is called?




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Top banana


Posted By: snowflake
Date Posted: 13 March 2017 at 12:03pm
Originally posted by 70,s hero 70,s hero wrote:

Screws clamp the joints together and distribute any forces further in to the opposing planes of material effecticevly increasing the area of distibution of force should any lateral or compressive forces be applied.

To increase the contact area for the same purpose and alignment, rebating is better than butt joints,the grain really has no effect as the grain in ply is set upon each layer at 90 degrees in opposition. It is questionable if there is any appreciable soaking in of glue as the ply (grade bb Birch) is compressed greatly with glue at manufacturer making it very dense and the viscosity of PVA and bubble glue is a deterring factor.

I do not agree that a screw does not add to the strength of a corner joint, for sure, the glue does the majority of work in stabilization but screws will help as they help distribute forces.

The idea that glue is the only requirement for the strongest joint is true in say glue beams or ply which are manufactured with hydraulic presses, I am open to be convinced that a corner joint in say 18mm ply does not benefit from additional screws, that's my take on it, hoping to be convinced otherwise.

imagine you have a perfect glued joint using a perfect material. the joint will bend to some extent without breaking. as you bend it the stress is uniformly distributed being equal at every point along the joint. now imagine you put a screw in at one point. the joint here now becomes stiffer and less able to bend. so when force is applied all the stress is focussed on the point where the screw is. the screw fixing is not able to take all the stress that was formerly distributed evenly along the joint and the wood begins to split starting where the screw is. it is possible to make metal joint reinforcements that strengthen the joint but they would look like brackets, not screws.

this situation with ply is slightly different as the layers of ply are not that well stuck together. the screws strengthen the joint not by holding the two pieces together, but by stopping the piece that is glued side on from delaminating internally.

try breaking some joints apart. if you have done it properly you will find that it is always the wood that has split apart, not that the glue has failed between the two pieces.

if you find your glue is failing you have either not cut the wood straight and there are big gaps in the joint, or you have a very close fitting joint and it has gone dry due to over-clamping.


Posted By: snowflake
Date Posted: 13 March 2017 at 12:06pm
a good plywood joint that can be made with a rail saw and how I would make joints if I could find the right router bits. rebated joints are often good enough and quicker to make though.




Posted By: 70,s hero
Date Posted: 13 March 2017 at 12:52pm
Originally posted by snowflake snowflake wrote:

Originally posted by 70,s hero 70,s hero wrote:

Screws clamp the joints together and distribute any forces further in to the opposing planes of material effecticevly increasing the area of distibution of force should any lateral or compressive forces be applied.

To increase the contact area for the same purpose and alignment, rebating is better than butt joints,the grain really has no effect as the grain in ply is set upon each layer at 90 degrees in opposition. It is questionable if there is any appreciable soaking in of glue as the ply (grade bb Birch) is compressed greatly with glue at manufacturer making it very dense and the viscosity of PVA and bubble glue is a deterring factor.

I do not agree that a screw does not add to the strength of a corner joint, for sure, the glue does the majority of work in stabilization but screws will help as they help distribute forces.

The idea that glue is the only requirement for the strongest joint is true in say glue beams or ply which are manufactured with hydraulic presses, I am open to be convinced that a corner joint in say 18mm ply does not benefit from additional screws, that's my take on it, hoping to be convinced otherwise.

imagine you have a perfect glued joint using a perfect material. the joint will bend to some extent without breaking. as you bend it the stress is uniformly distributed being equal at every point along the joint. now imagine you put a screw in at one point. the joint here now becomes stiffer and less able to bend. so when force is applied all the stress is focussed on the point where the screw is. the screw fixing is not able to take all the stress that was formerly distributed evenly along the joint and the wood begins to split starting where the screw is. it is possible to make metal joint reinforcements that strengthen the joint but they would look like brackets, not screws.

this situation with ply is slightly different as the layers of ply are not that well stuck together. the screws strengthen the joint not by holding the two pieces together, but by stopping the piece that is glued side on from delaminating internally.

try breaking some joints apart. if you have done it properly you will find that it is always the wood that has split apart, not that the glue has failed between the two pieces.

if you find your glue is failing you have either not cut the wood straight and there are big gaps in the joint, or you have a very close fitting joint and it has gone dry due to over-clamping.

Thanks for the explanation,I have seen glued joints take the wood with them, PVA, Cascamite, Poly, I think that its true for general wood glued along a grain which is well clamped but boxes would be open to distortion of thier shape if dropped... say a tendency to collapse although internal bracing and the front and back panels would help stop this, I dont see the forces being applied to a right angle joint as bending as such, more an opening or closing of the angle.We also have to consider that gluing end grain is a great deal weaker than along the grain. Perhaps the only way to be sure would be to mock up two joints, one with just glue and one with screws as well.



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Top banana


Posted By: SouthwestCNC
Date Posted: 13 March 2017 at 1:05pm
There is a joint stress test floating about somewhere on the net, You are right about a screw then becoming the weakest link if the joint has a certain degree of flexibility.

In the test of newtons of force being applied to the joint glue alone scored something like 80, Screw and glue 120, Mortise and tennon 300 and screw and washer no glue also 300.

which backups what you say about distributing pressure.


Posted By: 70,s hero
Date Posted: 13 March 2017 at 1:42pm
Originally posted by SouthwestCNC SouthwestCNC wrote:

There is a joint stress test floating about somewhere on the net, You are right about a screw then becoming the weakest link if the joint has a certain degree of flexibility.

In the test of newtons of force being applied to the joint glue alone scored something like 80, Screw and glue 120, Mortise and tennon 300 and screw and washer no glue also 300.

which backups what you say about distributing pressure.

Thanks
, that makes sense. For the joint on a cabinet Gluing and screwing is stronger than just glue, for simple lateral (long joints say two pieces of 100x50) gluing alone with clamping is strongest.

I wonder if the OP has any idea of what filler is bestLOL




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Top banana


Posted By: SouthwestCNC
Date Posted: 13 March 2017 at 4:14pm
Metrolux 2 part is pretty good imo, Behaves a bit more like wood than automotive fillers. sadly the closest to birch colour is light oak which is not a great match.


Posted By: 70,s hero
Date Posted: 13 March 2017 at 4:57pm
Originally posted by SouthwestCNC SouthwestCNC wrote:

Metrolux 2 part is pretty good imo, Behaves a bit more like wood than automotive fillers. sadly the closest to birch colour is light oak which is not a great match.

Sounds good, I wonder if it stains well, I need to fill some of my oak wood at home this year.


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Top banana


Posted By: SouthwestCNC
Date Posted: 13 March 2017 at 8:36pm
Yes it stains quite well for a 2 part. Sorry its called metolux, comes in decent sized tins for a good price too :)


Posted By: 70,s hero
Date Posted: 13 March 2017 at 9:18pm
Originally posted by SouthwestCNC SouthwestCNC wrote:

Yes it stains quite well for a 2 part. Sorry its called metolux, comes in decent sized tins for a good price too :)

CheersSmile


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Top banana


Posted By: bee
Date Posted: 13 March 2017 at 9:31pm
Originally posted by 70,s hero 70,s hero wrote:

Originally posted by SouthwestCNC SouthwestCNC wrote:

Theres certainly a balance, adding excessive amounts of screws will compromise the structure as panels can then split through its thickness however I agree a minimal amount of well placed screws does increase joint strength over just being glued.

+1

Its something that I cant get my head around, the thought that screws dont help a joint (if done properly)

I screw at 50mm c/c with a pilot but in opposing panels and so that leaves 100mm c/c between them.

I looked at BEE'S corner joints, it never occurred to me that having a rebate with an additional 45 mitre was doable, nice touch, I wonder what the router bit is called?


 
there all hand done, I'm very lucky to have some big boys wood working tools, my mafell 85c can cut upto 60 degrees on a track saw, my main track saws are the kss300 and kss400 again both mafell. I got rid of my big table saw when I get the cnc, but still use my Mafell Erica table saw all the time. Hand router wise I have a few of the trend routers 2 x t11, and a smaller t5.


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https://www.elements-audio.com


Posted By: bee
Date Posted: 13 March 2017 at 9:33pm
Originally posted by snowflake snowflake wrote:

imagine you have a perfect glued joint using a perfect material. the joint will bend to some extent without breaking. as you bend it the stress is uniformly distributed being equal at every point along the joint. now imagine you put a screw in at one point. the joint here now becomes stiffer and less able to bend. so when force is applied all the stress is focussed on the point where the screw is. the screw fixing is not able to take all the stress that was formerly distributed evenly along the joint and the wood begins to split starting where the screw is. it is possible to make metal joint reinforcements that strengthen the joint but they would look like brackets, not screws.

this situation with ply is slightly different as the layers of ply are not that well stuck together. the screws strengthen the joint not by holding the two pieces together, but by stopping the piece that is glued side on from delaminating internally.

try breaking some joints apart. if you have done it properly you will find that it is always the wood that has split apart, not that the glue has failed between the two pieces.

if you find your glue is failing you have either not cut the wood straight and there are big gaps in the joint, or you have a very close fitting joint and it has gone dry due to over-clamping.
 
a good plywood joint that can be made with a rail saw and how I would make joints if I could find the right router bits. rebated joints are often good enough and quicker to make though.


 
very good explanation Clap


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https://www.elements-audio.com


Posted By: SouthwestCNC
Date Posted: 13 March 2017 at 9:48pm
Originally posted by snowflake snowflake wrote:

a good plywood joint that can be made with a rail saw and how I would make joints if I could find the right router bits. rebated joints are often good enough and quicker to make though.




https://www.infinitytools.co.uk/router-bits/lock-mitre-bit/


Posted By: markie
Date Posted: 16 March 2017 at 1:10pm
Is this the answer? Using this would put screw heads inside the cab so no filler needed.

https://www.youtube.com/watch?v=ZHuCMzAIpDs" rel="nofollow - https://www.youtube.com/watch?v=ZHuCMzAIpDs


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If it's got wheels or tits it's gonna cost a fortune


Posted By: 70,s hero
Date Posted: 16 March 2017 at 4:20pm
Thas a handy bit of kit

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Top banana


Posted By: snowflake
Date Posted: 19 March 2017 at 4:22pm
ah they do make these - bit different to my idea but only need one router bit:

http://www.leevalley.com/us/wood/page.aspx?p=69422&cat=,69419&ap=1" rel="nofollow - http://www.leevalley.com/us/wood/page.aspx?p=69422&cat=,69419&ap=1


Posted By: Shortrope
Date Posted: 19 March 2017 at 5:04pm
http://www.kregtool.com/store/c26/pocket-hole-machinery/p322/foreman-pocket-hole-machine/" rel="nofollow - https://www.kregtool.com/store/c26/pocket-hole-machinery/p322/foreman-pocket-hole-machine/

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My Tinnitus is coming along nicely!!


Posted By: bee
Date Posted: 19 March 2017 at 11:53pm
kregs are very nice, another option to the trend look at the ujk pocket hole jig.
 
http://www.axminster.co.uk/ujk-technology-pocket-hole-jig-503726" rel="nofollow - http://www.axminster.co.uk/ujk-technology-pocket-hole-jig-503726


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https://www.elements-audio.com



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