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Nick Allen

Edge swelling after purfling installation?

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So I just installed the purfling into my latest fiddle. But I noticed that the edge, on the underside, bows considerably after much moisture from the glue and hot water. 

How much of this is normal, and should I be worried, and will it go down?

Am I just paranoid? Perhaps. 

Thanks guys!

IMG_20190802_233045.jpg

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54 minutes ago, David Burgess said:

It will probably shrink back very close to its original shape.

Yeah, unless the purfling is inserted too forced in the channel (if not enough space has been left for the swelling of the purfling and the channel caused by the glue). If we are not careful enough this can happen sometimes in some place, where therefore the edge might not return to straighten up.

So if Nick is a paranoid like me he could always do this to be less anxious :lol::

 

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3 hours ago, David Burgess said:

It will probably shrink back very close to its original shape.

Well. It did. 

 

2 hours ago, Davide Sora said:

Yeah, unless the purfling is inserted too forced in the channel (if not enough space has been left for the swelling of the purfling and the channel caused by the glue). If we are not careful enough this can happen sometimes in some place, where therefore the edge might not return to straighten up.

So if Nick is a paranoid like me he could always do this to be less anxious :lol::

 

I actually watched that video as I put this purfling in. Your channel is much cleaner than mine! :rolleyes:

How much room do you typically leave? I figure that it doesn't matter as much at the end grain sections, as I've never observed much swelling there. 

Thanks guys.

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1 hour ago, Nick Allen said:

I actually watched that video as I put this purfling in. Your channel is much cleaner than mine! :rolleyes:

How much room do you typically leave? I figure that it doesn't matter as much at the end grain sections, as I've never observed much swelling there.

I could not quantify, because while it is easy to accurately measure the purfling thickness, it is difficult to precisely measure the width of the channel at this degree of tolerances.

What I do is evaluate the ease of extraction (and insertion) of the purfling from the channel before gluing,  enlarging it with the knife in the points where I feel resistance. I don't want to feel any resistance, it must come in and out easily.

 

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2 hours ago, Nick Allen said:

How much room do you typically leave? I figure that it doesn't matter as much at the end grain sections, as I've never observed much swelling there. 

I think that the endgrain sections will swell more than any other area... but the swelling is crossgrain, and might not be obvious locally, if you're using a straight edge like in the photo.  

The endgrain sections will soak up glue like a sponge, and expand, then shrink back down when the glue dries.  This is why I might be even more paranoid than Davide, and glue size the endgrain sections and allow them to dry/shrink first.  The purfling is longitudinal grain, and will not shrink lengthwise.  If the endgrain areas of the plate have expanded when the purfling is glued in, then the plate edges will tend to crack as they shrink back, and are prevented from shrinking by the purfling.  I admit that you'd hardly ever see any cracking normally... but having residual crossgrain stress might show up as a crack later, or on a very dry day...

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19 minutes ago, Don Noon said:

I think that the endgrain sections will swell more than any other area... but the swelling is crossgrain, and might not be obvious locally, if you're using a straight edge like in the photo.  

The endgrain sections will soak up glue like a sponge, and expand, then shrink back down when the glue dries.  This is why I might be even more paranoid than Davide, and glue size the endgrain sections and allow them to dry/shrink first.  The purfling is longitudinal grain, and will not shrink lengthwise.  If the endgrain areas of the plate have expanded when the purfling is glued in, then the plate edges will tend to crack as they shrink back, and are prevented from shrinking by the purfling.  I admit that you'd hardly ever see any cracking normally... but having residual crossgrain stress might show up as a crack later, or on a very dry day...

Excellent observation, the less obvious things are the most insidious. I also do this glue sizing but only before cutting the channel, on the edge endgrain.

Do you glue-size the already cutted channel?

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9 minutes ago, Davide Sora said:

Do you glue-size the already cut channel?

Yes.  It's amazing to watch the glue soak in.  You can fill the channel with glue, and then it goes away.  I do run a tool thru the purfling groove before the glue dries, to scrape out the excess glue (of which there is usually not much) and burnish the groove to the right size.

The glue might soak in far enough so that your method would have similar results.

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On 8/4/2019 at 12:53 AM, Don Noon said:

Yes.  It's amazing to watch the glue soak in.  You can fill the channel with glue, and then it goes away.  I do run a tool thru the purfling groove before the glue dries, to scrape out the excess glue (of which there is usually not much) and burnish the groove to the right size.

The glue might soak in far enough so that your method would have similar results.

Don't you have problems with glue ghosting in the end grain areas if it soaks in too much?

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If you do purfling on the finished box you wouldn't spend a second to think about it. -_-

Looks almost as if you had hammered a wedge into the channel (which I hope you didn't do) but watery glue can do a lot of local warping. I know a maker who soaks the underside surface before closing a couple of times with watery hot glue. Maybe this procedure helps to stabilize the edge if you do the purfling on the loose plate.

(Didn't try it myself because I belong to the purfling-on-the-box group)

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1 hour ago, Mampara said:

Don't you have problems with glue ghosting in the end grain areas if it soaks in too much?

Maybe a little... but there's the opposite problem of varnish soaking into the endgrain areas and burning/blotching if it isn't sealed.  Since I do some things to seal the endgrain, it's hard to say how much effect the glue sizing has.

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21 hours ago, Don Noon said:

Maybe a little... but there's the opposite problem of varnish soaking into the endgrain areas and burning/blotching if it isn't sealed.  Since I do some things to seal the endgrain, it's hard to say how much effect the glue sizing has.

Makes sense, thanks.

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