Nick Allen

Top center joint gluing suction gap...

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So I'm gluing up a viola top. I'm aware that the general consensus is to leave a little baby gap in the middle that tapers off to the ends. I have left that gap, but is it too much? Or too little?

It may be hard to see int the photo, though...

Also, I can assure you that it extends a little farther than in the photo. 

IMG_20180415_134638.jpg

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I would not say that a sprung joint is "consensus", even in a general sense.

I wouldn't consider that to be an acceptable center joint, but as with almost any statement about any operation in this trade, other well trained individuals may/will disagree.

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Yeah I think you're right about it being a contentious point. My mind may have been left in my other jeans when I though that. 

14 minutes ago, duane88 said:

I would not say that a sprung joint is "consensus", even in a general sense.

I wouldn't consider that to be an acceptable center joint, but as with almost any statement about any operation in this trade, other well trained individuals may/will disagree.

When you say you wouldn't consider that to be acceptable, are you saying that you don't think that it's an acceptable amount of spring? Or that you just aren't cool with sprung joints?

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12 minutes ago, Nick Allen said:

are you saying that you don't think that it's an acceptable amount of spring?

I see a gap.

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I would not accept any gap at all. And I don't "spring" the joint. With a well set up plane and bench you should be able to make "perfect" contact between the 2 halves.

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43 minutes ago, Nick Allen said:

Yeah I think you're right about it being a contentious point. My mind may have been left in my other jeans when I though that. 

When you say you wouldn't consider that to be acceptable, are you saying that you don't think that it's an acceptable amount of spring? Or that you just aren't cool with sprung joints?

I don't spring joints. 

Make it fit all the way, to your eyes, than rub the 2 pieces against each other. If you don't feel significant friction then the joint isn't tight and flat on both sides. If they slide easily against each other with moderate pressure, you aren't there yet. If I have a little gap on an edge where something tore out but it feels right, I'll glue it, but only a small gap that I can confirm is along the edge, because that is going away in the end.

 

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26 minutes ago, duane88 said:

I don't spring joints. 

Make it fit all the way, to your eyes, than rub the 2 pieces against each other. If you don't feel significant friction then the joint isn't tight and flat on both sides. If they slide easily against each other with moderate pressure, you aren't there yet. If I have a little gap on an edge where something tore out but it feels right, I'll glue it, but only a small gap that I can confirm is along the edge, because that is going away in the end.

 

That all makes perfect sense to me. 

Do you glue size the joint at all? 

These particular battens just really drink up the glue. 

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I do spring the joints. I put one half in the vice, and place the other on top. If I move the top piece side to side I want it to rotate on the very end. When I rub the joint, the slightest turn of the clamp is enough to close the centre. It really is very little hollow, but enough to insure that the ends are closed tight. Sometimes a flat joint can open a whisper at the ends because of the wood swelling when the glue is brushed on.

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14 minutes ago, Conor Russell said:

I do spring the joints. I put one half in the vice, and place the other on top. If I move the top piece side to side I want it to rotate on the very end. When I rub the joint, the slightest turn of the clamp is enough to close the centre. It really is very little hollow, but enough to insure that the ends are closed tight. Sometimes a flat joint can open a whisper at the ends because of the wood swelling when the glue is brushed on.

So the suction joint must be clamped then?

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29 minutes ago, Nick Allen said:

That all makes perfect sense to me. 

Do you glue size the joint at all? 

These particular battens just really drink up the glue. 

I don't size the joint, but if they are that porous you might have to. Then you have to go back and touch up the joint, not to mention what glue does to your plane blade.

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52 minutes ago, duane88 said:

I don't size the joint, but if they are that porous you might have to. Then you have to go back and touch up the joint, not to mention what glue does to your plane blade.

I did size it, and then ran it across my 4 1/2, which did a surprisingly good job despite the fact that it's rather short in comparison to my #5. 

So it has no gap now. 

I think I'm gonna do a rub joint and then put a clamp or two on it just to be safe. 

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19 hours ago, Conor Russell said:

I do spring the joints. I put one half in the vice, and place the other on top. If I move the top piece side to side I want it to rotate on the very end. When I rub the joint, the slightest turn of the clamp is enough to close the centre. It really is very little hollow, but enough to insure that the ends are closed tight. Sometimes a flat joint can open a whisper at the ends because of the wood swelling when the glue is brushed on.

Exactly so. 

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Hi All - On my first joint I couldn't understand why my apparently light tight fit disappeared between the vise and the glue pot. Took me a good few hours and many shavings to learn that the mere action of clamping the plate distorts it. I've been meaning to cobble a "holster" to keep the plate unstressed while planing the edge.

cheers edi

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31 minutes ago, edi malinaric said:

Hi All - On my first joint I couldn't understand why my apparently light tight fit disappeared between the vise and the glue pot. Took me a good few hours and many shavings to learn that the mere action of clamping the plate distorts it. I've been meaning to cobble a "holster" to keep the plate unstressed while planing the edge.

cheers edi

Yup. I haven't had the best outcomes from either clamping a plate in a vise while planing, or during gluing. End-to-end clamping while planing (if any sort of clamping is needed during planing) seems to produce much better results, imposing no twisting force on the plate.

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On 4/15/2018 at 2:40 PM, Salve Håkedal said:

I would not accept any gap at all. And I don't "spring" the joint. With a well set up plane and bench you should be able to make "perfect" contact between the 2 halves.

Ditto.

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I clamp the plane to my bench on one side and ride the wood on perfectly flat piece of laminate along the plane. This keeps the planed wood flat during planing. Few passes will yield perfect joint.

I do clamp plates but I do it on jig I made of flat piece of laminate and few thumbscrews just to hold the halves together. And I lightly clamp the plate halves to the base so they will stay aligned and flat. Actually, I lay them flat and rub them together till they grab apply two spring clamps to keep them flat and then lightly tighten three screws at side to hold the halves together.

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1 hour ago, HoGo said:

I clamp the plane to my bench on one side and ride the wood on perfectly flat piece of laminate along the plane. This keeps the planed wood flat during planing. Few passes will yield perfect joint.

I do clamp plates but I do it on jig I made of flat piece of laminate and few thumbscrews just to hold the halves together. And I lightly clamp the plate halves to the base so they will stay aligned and flat. Actually, I lay them flat and rub them together till they grab apply two spring clamps to keep them flat and then lightly tighten three screws at side to hold the halves together.

Can you post a photo of your jig? ...............I use a something similar/

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On 4/15/2018 at 1:15 PM, duane88 said:

I don't size the joint, but if they are that porous you might have to. Then you have to go back and touch up the joint, not to mention what glue does to your plane blade.

I don't size spruce, but if the maple is porous or if it is not perfectly quartered at the joint, it can really suck glue, so I'll size that.

For touch-up, I chalk-fit the surface to a granite surface plate, using a scraper.  I wouldn't even try planing a glued surface.

BTW, I don't do the gap thing, just a dead-flat, unclamped rub joint.  With the sizing of porous wood, I haven't found any problem of expanding when the glue is applied.

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2 hours ago, lpr5184 said:

Can you post a photo of your jig? ...............I use a something similar/

Here it is in action. It is simple prototype I made out two decades ago of scrapwood and bolts I had at hand and as usual I've used it ever since in that rough form. I'm gluing up a bit longer piece so I added the extra clamp at the end. The other hockey stick can be moved closer (with three woodscrews from underside) for narrower pieces. And there is an elongated window underneath across the joint so you can inspect how well the joint is closed on the inside. After clamping I just lean it agains wall till the glue dries.

DSCF3170.JPG

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I use big gap for fresh wood, smaller gap for aged wood.

But the distribution of gap is much more important than the size of the gap.

I use a strong clamp and use wedge in the center for cello or violin.

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