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What Filler???

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snowflake View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post 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.
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70,s hero View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 70,s hero Quote  Post ReplyReply Direct Link To This Post 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. 


Edited by 70,s hero - 08 March 2017 at 10:28pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote I-shen Soundboy Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SouthwestCNC Quote  Post ReplyReply Direct Link To This Post 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.
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cravings View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cravings Quote  Post ReplyReply Direct Link To This Post Posted: 09 March 2017 at 3:45pm
i feel like i notice filler shrinking over time rather than swelling.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shortrope Quote  Post ReplyReply Direct Link To This Post Posted: 09 March 2017 at 3:50pm
A lot of the time it's actually the timber swelling.
My Tinnitus is coming along nicely!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SouthwestCNC Quote  Post ReplyReply Direct Link To This Post 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



wont trap moisture like filler will either.

Edited by SouthwestCNC - 09 March 2017 at 4:52pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JonB67 Quote  Post ReplyReply Direct Link To This Post Posted: 09 March 2017 at 4:55pm
So is it better to just glue and clamp?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SouthwestCNC Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote I-shen Soundboy Quote  Post ReplyReply Direct Link To This Post 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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SouthwestCNC Quote  Post ReplyReply Direct Link To This Post 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.

Edited by SouthwestCNC - 09 March 2017 at 7:27pm
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