Roubo lamination disaster

[Daniel Hartmann]

I recently set out to build a split top roubo out of white oak. A friend of mine help me process the oak 2x6s and glue up the tops. After gluing up I left the tops in clamps overnight. The next day (nearly 24 hours) I removed the clamps and found some delamination. This is almost definy due to the 20 degree temps. I think the shop reach 35-40. I tried to pry off some of the boards where the gaps are largest but they seem pretty well stuck. At this point I have a top with up to 1/8" gaps between the boards in spots but there is still enough good long grain glue surface to prohibit a clean detachment. What are my options?? Should I fill the cracks with epoxy? Or should I try to release the glue joint and start over?

[Steve Voigt]

I would try to get the boards apart and re-joint them. Can you slip a handsaw through the cracks? That would be my first plan of attack.
On my first workbench, around 17 years ago, I glued up some edging on a cold night, probably 45° outside and no heat in the garage. I ended up cutting the edges off and doing it over. Cold weather and glue don't mix.

P.S. Take a deep breath. It will be ok, it's just a temporary setback. Get the boards apart, clean them up, and try again when it's warmer.

[Pete Duffy]

Make a groove where the gap is, then inlay a new piece of oak to match (or something else to contrast.) From what I understand, the slab has structural integrity, just unsightly gaps. If it weren't sacrilege in this forum, I would recommend a rou** and straight bit and a straight edge guide.

[Daniel Hartmann]

Correct. It has structural integrity. It's just unsightly.

[Steve Voigt]

Make a groove where the gap is, then inlay a new piece of oak to match (or something else to contrast.) From what I understand, the slab has structural integrity, just unsightly gaps. If it weren't sacrilege in this forum, I would recommend a rou** and straight bit and a straight edge guide.


Correct. It has structural integrity. It's just unsightly.

Uh, how do you know the slab has structural integrity? It's one thing to not be able to pry the boards apart by hand; it's another thing entirely for them to stand up to repeated pounding on chisels, holdfasts, and the like. If it was glued up at near freezing temperatures, I would guess it does not have structural integrity.

[Daniel Hartmann]

They are sound. Each 12" wide by 7 ft long by 5" thick slab weighs about 150lbs. I've lifted one end of each up to head height and dropped them. Hoping the offending board would just pop off. No dice. And they sound the slab makes when dropped gives a nice reassuring tone. As if it were solid.

[Charlie MacGregor]

You might consider finding someone with a Woodmizer or similar to deconstruct for a do-over. Downside is that you lose a little width.

[Noah Wagener]

maybe bolts?

[Brian Holcombe]

I'll pile on, I think it's time for a do-over. If they remain that way their will be some very strange stresses present in the laminations, it'll be a headache later on down the road.

[Brian Ashton]

If it's 5" thick and the cracks run full thickness you could run it over a table saw then flip and run again; standard 10" table saw cuts 3". Then joint and re-glue. Or if the gaps are only near the edge then you could still run it over the table saw and cut a groove that is as deep as the crack and then glue in a filler piece of the left over oak.

To me is sounds like the wood has moved over night in an attempt to relieve some internal stress which I wouldn't be too happy about. You might want to stress test it by taking it inside the house out of the cold and see what it does. Let it stay there for a few days or more then take it back out to the cold shed and see what it does.

Also you were saying the temp was 20 degrees, fahrenheit or Celsius. If it was fahrenheit I wouldn't be to confident in those glued surfaces unless it was cold cure epoxy you were using and especially it it was PVA glue.

[Derek Cohen]

Here's a simpler solution.

If the boards are stuck fast together, then leave them that way. Instead, rout out a groove about 1/2" deep x 1/4" wide at the join, and then glue in a filler piece (take a slice off one side with a circular saw if you want a match from the filler piece). It should end up an invisible fix.

Regards from Perth

Derek

[Jim Koepke]

if the gaps are only near the edge then you could still run it over the table saw and cut a groove that is as deep as the crack and then glue in a filler piece of the left over oak.


Here's a simpler solution.

If the boards are stuck fast together, then leave them that way. Instead, rout out a groove about 1/2" deep x 1/4" wide at the join, and then glue in a filler piece (take a slice off one side with a circular saw if you want a match from the filler piece). It should end up an invisible fix.

Regards from Perth

Derek

Count me as the third to suggest this route.

The space between boards could also be made with a plow plane. If you can get contrasting strips you truly could make a very nice lemon-aide from the lemons handed to you.

Gluing up in the cold doesn't work well. During the cold part of the year my PVA glue is kept in the house.

Any glueing also takes place in the house or wait until warmer weather.

jtk

[Jeff Bartley]

Daniel,
I wouldn't trust a joint glued under cold temps; especially on something like a bench that will hope last beyond your lifetime. Count me as another vote to redo it! I'd try and use the thinnest blade (whether handsaw or bandsaw or thin kerf table saw) and re-joint and glue. I bet those slabs are monsters to move around the shop!

[Chris Fournier]

If you have 0.125" gaps in places I believe that you had problems well before you tried to glue up in the cold. I'd suggest that your stock preparation was not done properly.

You can cover up this glue up as others have suggested. It will take as long as fixing it properly and you still have a very poor glue up that will most likely fail down the road. This is your bench, you'll stare at it for years and this defective glue up will haunt you.

Pull it all apart (find a pal with a bandsaw) and start all over paying attention to stock prep - do a dry run of the glue up before you commit to glueing (min 65 degrees to be safe - materials and air temp).

We all make mistakes so don't feel badly. Make it right with a proper glue up and you are on your way to being a better craftsman with a solid bench that you and others will admire for years to come.

[Daniel Hartmann]

Thanks for all the wonderful replies. A recent development: one of the delams had opened up enough for me to put a crowbar in and sure enough it peeled right off. Looks like a do over is in the works. Anyone in the Nashville area wanna let a fellow woodworker use their jointer?? Not wanting to do all this by hand!

[Brian Holcombe]

Good to hear, good luck with the do-over.

Curious, did the initial glue up require a lot of pressure to remove any gaps?

[Daniel Hartmann]

Not really, one board had some snipe that we overlooked until glue up.

[glenn bradley]

PVA glue has a working range somewhere around "human" range. If you're happy, its happy. The less happy you are, the less happy it is (35*f minimum recommended for Titebond for example).

Lots of good suggestions but, still your decision. If the glue-up seems sound and you want to just move forward, route out a known width/depth opening that straddles the crack and glue in a filler strip. If the whole thing is in question, rip it (tablesaw, bandsaw, whatever) at the seams, prepare the surfaces and re-glue at appropriate temperatures.

Sorry for you trouble. Good luck with the fix.

[Pat Barry]

Not really, one board had some snipe that we overlooked until glue up.
You really need lots of clamps, top and bottom to pull this monster together. I would estimate you should have no more than 6 to 8 inches between clamps on each side of the lamination so for a 7 foot long piece I am saying at least 21 clamps per side, 42 total. Like Norm says, you can never have enough clamps, especially with stiff wood like white oak. It takes tremendous and uniform pressure. Also, doing this in cold temperatures you really need a heater to pre-warm the boards and then tent the whole lamination with a heater to cook it and 24 hours before clamp removal.

[Paul Incognito]

I'll have to disagree with you there, Pat.
I glued up my bench top using 6 clamps, 3 on top and 3 on the bottom.
If the stock prep is done right, that's all you need. If you get consistent glue squeeze out, tighten them down and you're good to go. If there's a gap in the squeeze out, add a clamp there. That's my strategy and it hasn't let me down yet.
I can't imagine even owning 42 clamps big enough to glue this up. Not only the expense, but where the heck would I store them?
PI

[Brian Holcombe]

I agree with Paul, that seems like quite a few clamps for a project this size. The dry-run should make you aware of these things, if there is a gap you'll see it and will still be able to attend to it.

[george wilson]

I agree with Paul: Boards should not need to be FORCED together. If they are so ill fitted,or curved that they must be forced together,they will eventually pop loose.

Get some new glue before you attempt glueing again. NEVER let your glue stay out in that kind of cold. It will ruin it. I had that happen as a teenager working in an unheated garage. My glue turned into chalk.

[David Weaver]

Do what you need to do to have a heated area to glue. You don't want a cold weld type of bond, it'll just fail early or be weak. Bottles usually have a minimum temperature listed on them.

[Daniel Hartmann]

Nnothing was forced together. We had about 20 clamps on it total and had really good squeeze out. After nearly 24 hours everything looked good. No gaps save the one in the end due to snipe. The gaps appeared over time when the clamps were removed. Most likely due to cupping which broke the Uncured glue bond.

[Paul Incognito]

Daniel, sounds like you had everything right except the temperature!
I leave the heat in my shop at 50 unless I'm gluing, then I turn it up to 60.
Like George says, glue won't set in the cold, it ends up looking like chalk when it dries and the joints fall apart. Follow his advise and if your glue has been sitting in the cold for some time, get a new bottle.
Good luck with the do-over!
PI

[Tony Zaffuto]

Don't just go into a heated area and glue! Let the boards acclimate for a few days (if not longer). Also, do not try to glue over old glue! All remnants of the glue need planed/sanded off.

[Daniel Hartmann]

Good advice. Thanks guys.

[Pat Barry]

You really need lots of clamps, top and bottom to pull this monster together. I would estimate you should have no more than 6 to 8 inches between clamps on each side of the lamination so for a 7 foot long piece I am saying at least 21 clamps per side, 42 total. Like Norm says, you can never have enough clamps, especially with stiff wood like white oak. It takes tremendous and uniform pressure. Also, doing this in cold temperatures you really need a heater to pre-warm the boards and then tent the whole lamination with a heater to cook it and 24 hours before clamp removal.

OK, OK I am prepared to admit that I may have over estimated the number of clamps required for this lamination. I did some research therefore in order to better understand the clamping requirements.

First, I went to the Titebond website and found their recommendations for clamping pressure. Here is what they say:

282107

So they are saying for Oak to use 200 to 300 PSI. That's not so much is it?

I thought I should see how much pressure I can expect to get from my clamps. Here is what FWW had to say:

282109

I use pipe clamps (1000 PSI) and Jorgensen bar clamps (300 PSI?).

FWW also provided some basic formula which, being an engineer, I don't need but here it is anyway:



282108

OK, so I'll use the formula, thank you FWW.

Wait - first I'm assuming this Roubo top is 6 inches thick, figuring its not going to be the 2" thickness. So 6 inches times 7 feet = 504 square inches of glue surface (per joint, but I won't get into that yet).

504 sq in times 250 PSI glue recommendation for Oak results in a force requirement of 126,000 pounds (holy smokes!!!)

How many clamps do I need? I'll be using my pipe clamps obviously, 126000/1000 = 126 clamps. Well, good luck fitting 126 clamps on to that top. I'd recommend putting half of those on the bottom of course and 1/2 on top.

So, what did I say initially? 46 clamps. OK - I was wrong, I can admit it.

Wait, something isn't right, what else does FWW say:
282110

I guess I don't completely buy what they are saying here myself, because I think if you are stacking several glue joints you have to figure that it will take more effort than a single glue joint, how much more is debatable.

Long story, I still think Norm was correct, but the truth is in the squeeze-out I suppose. If you are getting an even squeeze-out on all the joints then its probably success.

I hope I did the math right.

[Brian Holcombe]

That's wild, does the size of the clamp dace have any bearing on this?

[Steve Baumgartner]

I recently set out to build a split top roubo out of white oak. A friend of mine help me process the oak 2x6s and glue up the tops. After gluing up I left the tops in clamps overnight. The next day (nearly 24 hours) I removed the clamps and found some delamination. This is almost definy due to the 20 degree temps. I think the shop reach 35-40. I tried to pry off some of the boards where the gaps are largest but they seem pretty well stuck. At this point I have a top with up to 1/8" gaps between the boards in spots but there is still enough good long grain glue surface to prohibit a clean detachment. What are my options?? Should I fill the cracks with epoxy? Or should I try to release the glue joint and start over?

Since later you say you are in Nashville area, I assume you meant 20 degrees F (also since 35-40 would be quite hot if C!). In that case if it was PVA glue you need to tear it apart and do over in any case. Below about 45-55 F (depending on specific brand and type), PVA "chalks" instead of curing properly. Even the joints that now look tight won't last if that happened.

[Pat Barry]

Well, no one has any comments on the clamping advice from FWW and Titebond?

[Paul Incognito]

Pat,
Take the recommendations with a grain of salt.
Experience will teach you how many clamps you need and how tight they must be.
I've glued up hundreds of panels using all different types of clamps. The only failure I've had is similar to the OP's when gluing in the cold.
I read Fww's article when it was published and didn't think too much of it then, either. If you do a search, I think the topic has been discussed before.
Paul

[Tony Zaffuto]

One other comment is when doing a lot of gluing, such as laminations, use a glue with more open time, so the glue doesn't start to set before all pieces are in place. Titebond III is supposed to have more set time than II.

[Steve Baumgartner]

Pat,
Take the recommendations with a grain of salt.
Experience will teach you how many clamps you need and how tight they must be.
I've glued up hundreds of panels using all different types of clamps. The only failure I've had is similar to the OP's when gluing in the cold.
I read Fww's article when it was published and didn't think too much of it then, either. If you do a search, I think the topic has been discussed before.
Paul

And discussed to death! The article was highly controversial when it came out, with I think the majority of experienced woodworkers saying "Nonsense! I've never used so many clamps and I've never had a problem!". My conclusion at the time was that the professor's guidance was aimed at factory production in which a) the wood would be joined up straight off the jointer without careful adjustment for perfect fit (so the clamps have to take out both ripple and slight curves) and b) the goal was no visible glue lines at all, ever.

[Brett Bobo]

Well, no one has any comments on the clamping advice from FWW and Titebond?

Similar to Paul's suggestion, I view the FWW as merely a guideline or general reference as I personally think it misses some key info. Two important components are the surface area of the particular clamp to be used and the width of the caul and/or material thickness for the material joined. With those two things in mind, the effective surface area of each clamp can be increased at 45 degrees from the perimeter of the the clamp face. So, I'd work the other way and find the effective pressure of each clamp first and then compare to the required pressure of the glue joint to find the number of clamps required.

[Pat Barry]

Similar to Paul's suggestion, I view the FWW as merely a guideline or general reference as I personally think it misses some key info. Two important components are the surface area of the particular clamp to be used and the width of the caul and/or material thickness for the material joined. With those two things in mind, the effective surface area of each clamp can be increased at 45 degrees from the perimeter of the the clamp face. So, I'd work the other way and find the effective pressure of each clamp first and then compare to the required pressure of the glue joint to find the number of clamps required.

The clamping pressure guidelines were from Titebond, not FWW, so the issue reallly has to do wiith what Titbond is recommending for glue-ups. FWW might have built upon the Titebond recommendations, I don't know.

As it regards the clamps themselves however, a clamp applies a force and I don't think FWW estimation of the force applied by the clamp is unreasonable. Pounds are pounds so it doesn't matter the surface area of the clamp (as long as the clamp isn't dimpling the wood itself due to high pressure). Making the clamp pads bigger does not help apply more force at all - that is purely a function of the mechanical advantage of the clamp mechanism (ie: screw pitch), and how much torque you can apply to it.

The FWW formula is nothing special - its pure mechanics 101 - any engineer could tell you the same thing.

[Pat Barry]

And discussed to death! The article was highly controversial when it came out, with I think the majority of experienced woodworkers saying "Nonsense! I've never used so many clamps and I've never had a problem!". My conclusion at the time was that the professor's guidance was aimed at factory production in which a) the wood would be joined up straight off the jointer without careful adjustment for perfect fit (so the clamps have to take out both ripple and slight curves) and b) the goal was no visible glue lines at all, ever.
I would expect factory conditions to be optimum - it sounds as though you are saying that some careful fitting could reduce the clamping pressure? I didn't see anything in the Titebond literature stating that the clamping pressure guidance had anything to do with making allowances for improperly prepared surfaces and materials. Maybe I'm misunderstanding your point Steve.

[Daniel Rode]

I thought I should see how much pressure I can expect to get from my clamps. Here is what FWW had to say:


The graphic listing clamp pressure seems off to me. A parallel clamp is listed as less pressure than a quick clamp and significantly less than I-beam and pipe clamps?

My experience tells me that Bessy 'K' parallel jaw clamps are capable of exerting more force before bending or breaking than any of the others and the quick clamps are the weakest of all styles. FWIW F-Clamps are all over the place depending on the style size and brand.

The newer Bessy Revo parallel clamps are rated at 1500 lbs and my older style K clamps are rated at (IIRC) 1200 lbs. Maybe they divided the pressure by the area of the faces?

[Brett Bobo]

The FWW formula is nothing special - its pure mechanics 101 - any engineer could tell you the same thing.

I am an engineer as well--structural engineer :D

[Pat Barry]

The graphic listing clamp pressure seems off to me. A parallel clamp is listed as less pressure than a quick clamp and significantly less than I-beam and pipe clamps?

My experience tells me that Bessy 'K' parallel jaw clamps are capable of exerting more force before bending or breaking than any of the others and the quick clamps are the weakest of all styles. FWIW F-Clamps are all over the place depending on the style size and brand.

The newer Bessy Revo parallel clamps are rated at 1500 lbs and my older style K clamps are rated at (IIRC) 1200 lbs. Maybe they divided the pressure by the area of the faces?

So you are saying they were publishing PSI numbers instead of force numbers?? That could be. I'll try and find the article again tonight when I get home an see if this is the case because that could be a huge difference maker.

[Mel Fulks]

What is the point of giving force needed numbers for clamps? Was that article in the issue that had the double page color clamp ad with the two FREE computer disks on clamp use? That's where I saw the tip about using spring clamps on a sandwich to keep stuff from sliding out.

[Pat Barry]

Was that article in the issue that had the double page color clamp ad with the two FREE computer disks on clamp use? That's where I saw the tip about using spring clamps on a sandwich to keep stuff from sliding out.
LOL Mel - thats pretty funny stuff right there.


http://www.finewoodworking.com/item/27122/how-to-glue-up-joints-the-right-number-of-clamps


What is the point of giving force needed numbers for clamps? .

The point is, you should know how much force various types of clamps can be expected to exert assuming you actually are trying to figure out how many clamps you need for a particular application in order to satisfy the glue manufacturers recommendations, that's all.

[harry strasil]

FWIW Dept: Gaps in Glue up, Were all the clamps the same kind, so that pressure was equal. Possibly there could have been built up stress in one of the boards that caused the gap. CAUTION, when sawing with table or band or skill or hand and chain saw, make sure you have wedges prepared to drive into the kerf so stress doesn't cause pinching of the blade.

[Steve Baumgartner]

I would expect factory conditions to be optimum - it sounds as though you are saying that some careful fitting could reduce the clamping pressure? I didn't see anything in the Titebond literature stating that the clamping pressure guidance had anything to do with making allowances for improperly prepared surfaces and materials. Maybe I'm misunderstanding your point Steve.

I didn't mean to steal this thread, sorry. There was so much misinformation and naive argument when this first came up that I regret mentioning it...we don't need to get that going again!

Steve