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Top plate joint gel time.


Nick Allen
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Hey,

 

So I'm joining my first top right now. I have the joint all planed nicely and there is no gaps or anything. So this morning I walk into my basement, erm, I mean "workshop", and fire up the ol' glue pot. I do some trial and error testing and arrive at a 60 sec gel time on my current mixture. So, I take my plates, put em in the vise, quickly apply the glue (a generous amount), and hastily position them in the bar clamps and crank them down. This was all within maybe a 15 sec period.

 

Now here is the part that is perplexing me. The aluminum foil gel time was around 60 sec. But as soon as i go to clamp, ITS ALREADY GELLED!

 

What is going on here? Am I using too much glue? Is it too thick? Are the gel times on the foil always going to differ from on wood? I need some advise, this is the third time that this has happened now, and I am afraid of diluting the glue mixture any more for fear of joint failure.

 

I'm using Lee Valley 260 strength glue. I'm stuck and about ready to make a spruce bonfire in my yard soon...

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what is the ambient temp in the 'workshop'? mine is cool and I do my gluing up stairs in a warm place ,on a cool day I will warm the wood a bit as well, I also like to joint and join in one sitting to lessen any chance of the wood moving in the interim . clamps can actually squeeze to much glue from the joint if to much pressure is applied. 

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Was the wood dry dampened. If your glue was too dense it would lose its sliding ability pretty quickly I think.  I'm not an expert on gluing this joint but I learned there should be some slide when you end. I also learned vise clamping vertically one plate and just placing other plate into the air, sliding and leaving the plate works better than clamping. I do drive nails  on each end near the midline and put elastic bands across the nails to pull them together a little.  I just did my last join that way (second of ca  20 clamped) and I have to look carefully to find it. I'm amazed how this works. Something to consider if you want another way to glue this joint

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Gel time on aluminum foil won't always be the same as on a thick piece of wood. Heat conduction properties are different. Since the aluminum foil doesn't have much mass, it will basically be transferring heat to the air on the opposite side of the foil. A thick piece of aluminum would act differently. However, once you get the gel time on the foil which gives you the gel time you want on the wood for a particular job, that will remain pretty consistent and repeatable.

 

Gel time will vary by the thickness of the glue film too. A thin film will lose heat faster, and also lose a little of the water dilution to evaporation, behaving as if you had started with a thicker glue.

 

So the method isn't perfect or foolproof, but it's vastly better and more consistent than trying to get a sense of the viscosity and working properties by watching the shape of the drips off a glue brush, or rubbing it between your thumb and finger, in my opinion.

 

If you prefer, you could test the gel time on a thick block of wood instead.

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So I tried incubating the battens in my oven at around 120 degrees. All it ended up accomplishing was warping the wood. So I had to re joint them. I suppose I could try and spot heat the edges with a heat gun just before I join them.

Also, my shop hovers around a cool 65 digress at all times. That might have something to do with my problem.

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So I tried incubating the battens in my oven at around 120 degrees. All it ended up accomplishing was warping the wood. So I had to re joint them. I suppose I could try and spot heat the edges with a heat gun just before I join them.

Also, my shop hovers around a cool 65 digress at all times. That might have something to do with my problem.

been there ...done that ...not good ...try again. now a days, when I warm the wood it is just mildly , over the steam pot and stove burner , not hot in any sense , just warmed to the touch a bit. ..sorry if I misled you , 

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15 seconds is too long. Gluing center joints should be a 5 second process. I'm not there either, but that is a realistic goal, give or take a second. Practice and use a big brush :)

Yeah. I'm trying to streamline the process as much as possible. I suppose a large brush or even simply pouring the glue on straight from a cup would work too.

 

Another thing. Should the halves feel "gooey" for lack of a better term while rubbing? Or should I be able to feel the raw wood rub up against itself while I glue up?

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Eureka! I've found a good solution!

 

First: Warm with heat gun

 

Second: Apply glue

 

Third: Clamp in pipe clamps

 

Fourth: Warm joint lightly with heat gun again, and the seam closes airtight due to glue liquefying within the joint

 

I made sure as to not overheat the glue to the point at which it would break down. I observed the glue and took the heat source away as soon as the bead started to change state. I then ran the heat over the seam multiple times in order to assure full heat penetration all the way to the core.

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. . clamps can actually squeeze to much glue from the joint if to much pressure is applied. 

 

Ah yes, the notorious "glue-starved joint" ... glue starvation from excessive clamping pressure can only happen when epoxy is the adhesive of choice.

 

When using other glues, be they protein based, PVA, or polyurethane, it is impossible to cause glue starvation by excessive clamping pressure. If any joint fails due to a paucity of glue when using anything except epoxy, all it means is that insufficient glue was applied in the first place.

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You can also heat the glue higher than the standard temperature. Heating it 10 C higher for 3 or 4 minutes longer isn't going to compromise the glue strength much. Discard what glue is left although it's going to be perfectly fine for gluing in things like purfling.

Big brush or dispensing it from a squeezy bottle is an advantage. I prefer gentle heating, Infra red head lamp at a distance.

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Eureka! I've found a good solution!

 

First: Warm with heat gun

 

Second: Apply glue

 

Third: Clamp in pipe clamps

 

Fourth: Warm joint lightly with heat gun again, and the seam closes airtight due to glue liquefying within the joint

 

I made sure as to not overheat the glue to the point at which it would break down. I observed the glue and took the heat source away as soon as the bead started to change state. I then ran the heat over the seam multiple times in order to assure full heat penetration all the way to the core.

Glad you found a way.  There are lots of ways to skin a cat.  My shop is in the basement as well.  60 F this morning.  I used a heat gun previously and it worked.  This time I decided to wrap the plates in a heating pad set to where it's comfortable for my back (the highest setting is very hot to the skin).  After wrapping the the billets in the heating blanket I started the glue had breakfast, blah, blah, blah an hour went by and the glue was up to temperature.  I've done the heat gun trick before and it worked.  My thought with the heating pad is that the wood would store more heat and I wouldn't have to worry about the gluing surface cooling too fast. After doing a quick check that the wood hadn't moved, I did a rub joint, then lightly clamped the plates because I'm too chicken not to.  

 

Cheers,

Jim

 

post-58064-0-85139200-1461509249_thumb.jpgpost-58064-0-10058300-1461521957_thumb.jpg

 

 

Edit: I wish I knew why my photos come in sideways.  They're straight on my computer.  Maybe it's how I hold my I-phone for pictures.

 

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Ah yes, the notorious "glue-starved joint" ... glue starvation from excessive clamping pressure can only happen when epoxy is the adhesive of choice.

 

When using other glues, be they protein based, PVA, or polyurethane, it is impossible to cause glue starvation by excessive clamping pressure. If any joint fails due to a paucity of glue when using anything except epoxy, all it means is that insufficient glue was applied in the first place.

you might be right about that ... I feel like my failed joints all happened when I clamped the bejesus out of the ends , but then other things could also have happened . 

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Hey,

 

So I'm joining my first top right now. I have the joint all planed nicely and there is no gaps or anything. So this morning I walk into my basement, erm, I mean "workshop", and fire up the ol' glue pot. I do some trial and error testing and arrive at a 60 sec gel time on my current mixture. So, I take my plates, put em in the vise, quickly apply the glue (a generous amount), and hastily position them in the bar clamps and crank them down. This was all within maybe a 15 sec period.

 

Now here is the part that is perplexing me. The aluminum foil gel time was around 60 sec. But as soon as i go to clamp, ITS ALREADY GELLED!

 

What is going on here? Am I using too much glue? Is it too thick? Are the gel times on the foil always going to differ from on wood? I need some advise, this is the third time that this has happened now, and I am afraid of diluting the glue mixture any more for fear of joint failure.

 

I'm using Lee Valley 260 strength glue. I'm stuck and about ready to make a spruce bonfire in my yard soon...

 

I have only used a rub joint on violin center joins, no clamps. This reduces your work time.

 

Also, I usually always  creating a micro environment no matter what the shop conditions,  working under two heat lamps,  giving some time for the joining surfaces to pre-heat as well.

 

If your joint does not come out as expected, I would not hesitate to run it through the bandsaw and start over. This is one joint you do not want to fail.

post-38245-0-21003400-1461514460_thumb.jpg

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Glad you found a way.  There are lots of ways to skin a cat.  My shop is in the basement as well.  60 F this morning.  I used a heat gun previously and it worked.  This time I decided to wrap the plates in a heating pad set to where it's comfortable for my back (the highest setting is very hot to the skin).  After wrapping the the billets in the heating blanket I started the glue had breakfast, blah, blah, blah an hour went by and the glue was up to temperature.  I've done the heat gun trick before and it worked.  My thought with the heating pad is that the wood would store more heat and I wouldn't have to worry about the gluing surface cooling too fast. After doing a quick check that the wood hadn't moved, I did a rub joint, then lightly clamped the plates because I'm too chicken not to.  

 

Cheers,

Jim

 

attachicon.gifPlate join prep 20160420.JPGattachicon.gifTop plate join 20160424.JPG

 

 

Edit: I wish I knew why my photos come in sideways.  They're straight on my computer.  Maybe it's how I hold my I-phone for pictures.

 

Hey Jim, I think the forum always wants pictures 'landscape' oriented so if the pics are 'portrait' it will flip them 90 degrees. Annoying!

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Hey Jim, I think the forum always wants pictures 'landscape' oriented so if the pics are 'portrait' it will flip them 90 degrees. Annoying!

Yes, that was the problem.  I retook the second picture holding my phone in landscape orientation and it worked perfect.  Thanks!  My time machine is broke, so I wasn't able to retake the first picture.

 

-Jim

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