two questions about laminated workbench legs

[Phil Stone]

I'm in the middle of building a Rouboesque workbench (not to be confused with "Rubenesque", despite the size of the legs in question). I'm making the 5" X 5" legs out of laminated douglas fir, and all is going pretty well, but I have two detail-oriented questions.

1) Should I fill this gap? Despite what I thought was a good glue bond and adequate clamping, it showed up when I released the clamps, making a little cracking sound as the pressure came off.

293184

If there's a good structural reason to fill it (stop further delamination, etc.), I will of course do so. I have to admit it bothers me a little cosmetically, too, but I remind myself that this is a workbench and not an armoire. What's the best way to fill it? Epoxy?

2) This is a more general question about tweaking mortises. One of the stretcher mortises is just a tad too tight top-to-bottom:

293185

I need to shave the end-grain mortise wall marked "shave" in the picture, I'm guessing by no more than about 1/64". Is there a better way to do this than a sharp paring chisel? If it makes any difference, this will be an unglued joint, using Benchcrafters knockdown barrel nuts and bolts. Any tips or tricks for paring this end-grain with a chisel without ruining the joint?

Also, I know it's probably easier to adjust the tenon, but I'm trying to learn techniques as I go here, so if it's feasible to fix the mortise instead, I'd like to know how.

Thanks for your advice (and patience with my inexperience).

[Jim Koepke]

Remember, this is just my 293190.

For the laminated piece my solution would be to install a carriage bolt through the assembly. Maybe drop a bit of epoxy in just for good measure. Though if you used PVA in the beginning the epoxy might not bond well. Other glues will also be unlikely to bond if there is PVA residue in the crack.

For the size issue a very sharp paring chisel would be the way to adjust the mortise, but the best technique in most cases is to adjust the tenon.

Always remember:

293189

jtk

[Phil Stone]

Yes, it was glued with Titebond, and I'm sure there's glue in the area of the delamination (I think that describes it more specifically than "crack"), so it sounds like epoxy might not bond. Rats.

Thanks for pointing that out, Jim.

[Judson Green]

I wonder if ya couldn't squirt some glue down in that crack and re clamp it. I've used a folded paper or something thin to try and get the glue down there.

And I'd use the paring/bench chisel to shave the mortise a little larger.

[Todd Burch]

Rip the cracked part off, re-joint, and rebuild. That'll teach you. LOL.

I'm the kind of guy that a split leg like that would bug the socks off of me. Some people could care less. It all depends on you.

For that board to kick out/twist like that, and pop the glue joint, there is something seriously in tension there, and I'm surprised you didn't mention that you noticed it before the glue up. Or did you?

Todd

[Phil Stone]

That's an excellent point, Todd. I saw some tension during the glue-up (i.e., that board twisted a bit after machining), but I thought glue and clamps would overcome it. It really didn't seem that bad at the time. I guess I need to recalibrate what I consider "bad" in a lamination.

[Pat Barry]

It looks like glue starvation to me. Where is the squeezeout? Or have yu already cleaned up and planed the surface we are looking at? If its glue starvation I would seriously think about remaking these assemblies.

[Phil Stone]

Hi Pat, yes, it's already cleaned up and planed. There was a little squeeze-out during glue-up, and none of the other legs have this problem at all. I can't rule out some local starvation here, but I tried pretty hard to spread the glue evenly and rubbed the boards together before final positioning and clamping.

[glenn bradley]

Like Todd, I would have to fix that. For me, a squirt of glue worked down into the crack with thread (like dental flossing your teeth) and re-clamping. Like Jim, I would consider a mechanical fastener too. As to the mortise; shave the tenon ;-)

[Jim Matthews]

I'm considering the possibility that the joint will serve, as it is
and reworking may weaken what you have.

I would suggest that you laminate a stout piece
of 3/4" plywood over the leg, covering the splayed laminations.

That would keep lateral forces checked.

If you have a fine pull saw, you can saw down the middle of the split
and retrofit with a thin wedge, but I think the "cover panel"
would be sufficient.

I was trained to fit tenons to mortises, rather than make mortises larger.

Remember that the strength in the joint is from long grain/face grain glue bonding surfaces.
The end grain/face grain bonding surface of the joint offer little in the way of strength.

In short, trim the tenon rather than risk damage to the leg.


FYI - I'm a fan of making voids like these with laminations, and it's instructive to see what happens in real projects.
Gary Knox Bennet does this all the time, using spacers the size of the intended tenon wrapped in plastic for removal after glue up.

[Brian Hale]

I'd handsaw/bandsaw up to the mortise and fill the gap with a thin piece of scrap. Glue and clamp.
Fit the tenon to the mortise......

Brian :)

[Jessica Pierce-LaRose]

I'd be tempted to kerf that crack out with a table or circular saw, and fill it with a piece of 1/8" wood. But I have no idea if that's a good idea or not.

I agree with Jim about fitting the tenon to the mortise. If nothing else, it's easier. If your shoulders are good, you can get away with a bit more play with that bench crafted hardware, since that's going to be doing the majority of the holding in that joint.

[Chuck Nickerson]

On the delamination, Titebond glues (and most others) come to full strength after 24 hours.
For future reference, anytime you're clamping and the joint seems stressed leave it in the clamps longer.

My DF laminated Roubo had a delamination in the top, which I saw-kerfed and filled.

[Pat Barry]

Hi Pat, yes, it's already cleaned up and planed. There was a little squeeze-out during glue-up, and none of the other legs have this problem at all. I can't rule out some local starvation here, but I tried pretty hard to spread the glue evenly and rubbed the boards together before final positioning and clamping.Thats good news then. With that in mind I think I would be tempted to stick a chisel in the split and give it a bit of a stress test by applying a bit of a whack. If the split doesn't change significantly then I would probably just leave it or try to fix the cosmetics and be done with it. If it falls apart then you know what needs to be done. by the way, is this the top of the leg or the bottom?

[Phil Stone]

Thats good news then. With that in mind I think I would be tempted to stick a chisel in the split and give it a bit of a stress test by applying a bit of a whack. If the split doesn't change significantly then I would probably just leave it or try to fix the cosmetics and be done with it. If it falls apart then you know what needs to be done. by the way, is this the top of the leg or the bottom?

It's the bottom of the leg. My intuition is that this split is not too significant structurally, as the majority of the lamination is well bonded (it's only separated at this one corner), but if I can bring myself to stress-test it as you suggest (yikes!), I'll give that a try.

My overall take from all this excellent advice is:

1) I will try to work some glue into that crack, with paper/thread/floss/old paint brush, and clamp it with a couple of pipe clamps. I think I may not have put enough clamping force right on this spot -- just one Jorgensen, and perhaps not cranked very hard. I may bury a screw or two in the joint between the two boards, too, counterbored and plugged at the entry point. If it releases again, I will rip out a kerf and glue in a strip.

2) I will shave the tenon! :-)

I really appreciate the thought that went into your replies. Thanks everybody!

[Brian Holcombe]

Stressed joints are much more likely to slip over time, or in this case to separate further. Considering the purpose of this glue up I would, at a bare minimum, cut a groove down past the part where it is separating and put a strip of wood in.

Some of the best advantages of hand tools are that you can fine tune a fit up with a hand plane that would be otherwise difficult with machine tools. Even if I am cheating by using a lunchbox planer to get the stock to rough size I will work the remainder of it with hand tools to ensure the surface is flat. You can, of course, do this with a jointer (machine) but it's easier to work the fine end of the spectrum with hand tools.

To to trim the end grain I often do not pare, Instead I will clamp a block, which is perfectly 90 degrees to the area in question and chop it with a mallet while holding the chisel tight to the guide block. A dull chisel will make a mess of this, so it's important to use a sharp one.

Mark with a knife prior to doing this, so that you can use that to start your cut.

[Phil Stone]

Stressed joints are much more likely to slip over time, or in this case to separate further. Considering the purpose of this glue up I would, at a bare minimum, cut a groove down past the part where it is separating and put a strip of wood in.

Hmm, this is the fear that prompted the post. OK, I will consider this. It will be a good lesson in mistake-fixing, at least.


Some of the best advantages of hand tools are that you can fine tune a fit up with a hand plane that would be otherwise difficult with machine tools. Even if I am cheating by using a lunchbox planer to get the stock to rough size I will work the remainder of it with hand tools to ensure the surface is flat. You can, of course, do this with a jointer (machine) but it's easier to work the fine end of the spectrum with hand tools.

I very much want to do my final fitting/surfacing with hand tools, for the very reason you describe (as well as for the joy it will bring me to have this skill). As they say, though, "it takes a bench to build a bench", and I just don't have the work-holding capability right now to joint with a hand plane. I do have access to a shop with a nice jointer and planer, though, so this build has depended very much on machines.

Thanks for your input, Brian.

[Brian Holcombe]

Anytime!

If that is the case, then make sure you are checking for flatness with a ground flat straight edge and winding sticks. It's annoying to do all the time, but will save you a headache or two when doing glue ups.

When you're bench is finished and flattened, you can use the surface as a quick check and that saves a lot of time on smaller pieces. I prefer to check the big stuff with a straight edge and feeler gauges if it is critical. Straight edge and eyeball if it is not.

[Phil Stone]

Anytime!

If that is the case, then make sure you are checking for flatness with a ground flat straight edge and winding sticks. It's annoying to do all the time, but will save you a headache or two when doing glue ups.

When you're bench is finished and flattened, you can use the surface as a quick check and that saves a lot of time on smaller pieces. I prefer to check the big stuff with a straight edge and feeler gauges if it is critical. Straight edge and eyeball if it is not.

I was relying on the jointer infeed table to check for straightness. Either I missed the twist on one of the parts of this joint, or it moved after machining -- this is a risk that comes from having to go out to an external shop to machine, then come back (maybe a day later) to do the glue-up. I should have re-checked for straightness right before gluing.

[Jim Koepke]

I was relying on the jointer infeed table to check for straightness. Either I missed the twist on one of the parts of this joint, or it moved after machining -- this is a risk that comes from having to go out to an external shop to machine, then come back (maybe a day later) to do the glue-up. I should have re-checked for straightness right before gluing.

This is something that occurs in my shop all the time. Most of my projects are made from species of fir/pine. The stuff moves.

Often when cutting dovetail if the joint is not going to be cut and fitted right away, the second half of the joint will not be laid out and cut until there is time to finish the joint.

jtk

[Phil Stone]

This is something that occurs in my shop all the time. Most of my projects are made from species of fir/pine. The stuff moves.

Often when cutting dovetail if the joint is going to be cut and fitted right away, the second half of the joint will not be laid out and cut until there is time to finish the joint.

jtk

Knowing that I wouldn't have time to glue the legs for a day, I dry-clamped all the leg components together when I got them home, hoping this would prevent movement. I also dried the wood pretty thoroughly before machining.

Oh well, best laid plans ganging aft agley, again...

[Shawn Pixley]

1 - Kerf the gap and glue in an appropriate size insert. I think that that needs repair. While the strength for gravity load is largely unaffected, the lateral strength is not there.

2 - Trim the tenons. You can fix the mortise if you want, but it is more difficult.

[Prashun Patel]

Looking at the pic, I think you have to rip and reglue it. If it fails, the mortise will suffer. Beware that this leg will be thinner than the others, so either do the same on all analogs or make sure you recalc your stretcher/rail dimensions.

[Tom Vanzant]

I'd kerf just the separated area and glue in an insert. From the location of the mortise, I'd say the "loose" board is the outer board, so a screw would be very visible. As far as all the mortises having to be identical/interchangeable, no. Treat each joint as unique and individual.

[Phil Stone]

I'd kerf just the separated area and glue in an insert. From the location of the mortise, I'd say the "loose" board is the outer board, so a screw would be very visible.

I'm now leaning towards the kerf/patch solution, due to all the excellent arguments in favor of that approach. My hope is that it will relieve the stress and allow a long, happy and laminated life for this leg.


As far as all the mortises having to be identical/interchangeable, no. Treat each joint as unique and individual.

Thanks. You have uncovered the obsessive-compulsive reasoning behind my wanting to adjust the mortise instead of the tenon. I have now seen the light. :)

[John Sanford]

The crack doesn't go all the way down. It looks like the left timber's face wasn't flat, which means it doesn't matter how much you try to glue and clamp it together, it's going to separate. Best solution now would likely be to simply cut a kerf using a table saw/circular saw and glue in a plug, or fill it with epoxy.

[Phil Stone]

The crack doesn't go all the way down. It looks like the left timber's face wasn't flat, which means it doesn't matter how much you try to glue and clamp it together, it's going to separate. Best solution now would likely be to simply cut a kerf using a table saw/circular saw and glue in a plug, or fill it with epoxy.

Would epoxy be structurally adequate in this situation? The kerf cut would cut out the wood with Titebond on it, allowing the epoxy to bond, but is epoxy good at this kind of gap filling?

[Jessica Pierce-LaRose]

On smaller sized issues of the same variety, I've used a trick that Tage Frid mentions in his book, kerfing the cut out with a hand saw, and inserting a slice of veneer. If the veneer doesn't fit, you squeeze it a bit in a machinists vise. I wonder if this would work at this scale?

[dan sherman]

Maybe I'm just to anal, but I would saw/plane the entire board off, and then laminate a new one to the remaining three.

[Prashun Patel]

Epoxy is actually great for gap filling. If you go that route, then I would use epoxy to bond the tenon to the mortise in that hole too. If there is epoxy on the wall of the mortise, it will affect the Titebond's adhesion.

It may seem daunting to rip the leg free and re-glue it, but that feels like the simplest and most secure method. It does not require any measuring of the kerf for veneer; it does not require any special glue. In fact, if you rip it clean, the two sides will be self jointing off the blade.

If cosmetics are not a huge issue for you, you could even drive a couple screws into the leg through the seam before you rip it clean. Then remove the screws, rip, apply glue, and use the screws to align the two pieces so they don't squirrel around on you when you clamp. Then you can either plug or leave the holes.

[Phil Stone]

It may seem daunting to rip the leg free and re-glue it, but that feels like the simplest and most secure method. It does not require any measuring of the kerf for veneer; it does not require any special glue. In fact, if you rip it clean, the two sides will be self jointing off the blade.

The reason I am staying away from ripping the whole outside off is that the twist is in the inner board, the one that has the mortise notch. In order to get rid of that twist and end up with a completely straight joint, I'll have to rip through the mortise, and then it becomes a bit complicated to re-constitute that mortise. I'll have to make a new outer board that is wider and put a corresponding portion of the mortise in it. None of this is impossible, but it just seems a great deal more work and error-prone (not to mention I'll have to find some dry Doug Fir for that new piece) than kerfing and patching the split.

I very much appreciate your thoughtful reply, Prashun.

[Jim Koepke]

My thinking could be totally wrong on this...

This is the leg of a bench. The question is will this flaw have a deleterious influence on the use or purpose of the bench in the long run?

In my shop it would have a bolt or two to secure it from further splitting and become a permanent reminder of a small step not taken before the glue up. Most people who enter your shop will never know.

If this was a piece you were making for a client then other corrective means might be required.

jtk

[Prashun Patel]

I am not sure I follow the logic. If you rip down the center of the split (assuming your saw kerf is wider than the split), the saw blade will effectively joint that minor twist out. The two halves will come together perfectly. The downside is your mortise will now be a tad smaller by a smidge (~ 1/16"). All this means is you have to trim the mating tenon a little.

I'm going back and forth on this. Now that I think about it, a perfectly mating tenon will serve as the 'key' to hold the joint as is from further splitting. You could even peg the tenon (with a screw or dowel) through the side wall of the mortise.

[Phil Stone]

Jim, I really appreciate that perspective. It's what I meant in my original post when I said it's a bench, not an armoire. While I want it to look good, I favor a structural repair (that hopefully isn't too ugly) over perfection at this point.

[Phil Stone]

I am not sure I follow the logic. If you rip down the center of the split (assuming your saw kerf is wider than the split), the saw blade will effectively joint that minor twist out. The two halves will come together perfectly. The downside is your mortise will now be a tad smaller by a smidge (~ 1/16"). All this means is you have to trim the mating tenon a little.

I'm going back and forth on this. Now that I think about it, a perfectly mating tenon will serve as the 'key' to hold the joint as is from further splitting. You could even peg the tenon (with a screw or dowel) through the side wall of the mortise.

As to your first point, this is the outer edge of the leg, which needs to be flush with the outer edge of the top (although this is the rear leg, I still want to maintain this Roubo-inspired principle). I can't therefore just rip width out of the finished leg.

Secondly, this is going to be a knock-down M&T, using barrel nuts and bolts from Benchcrafted.

[Harold Burrell]

One more perspective...

You are using construction grade lumber. Pretty inexpensive. You might want to make a new one entirely.

Why not? You know if you leave it as is that it will "eat your lunch". ;)

[Phil Stone]

Heh, I've thought a lot about that, Harold. I know I can be obsessive sometimes, but I've also learned to accept my own lack of perfection. I don't think it will eat at me too badly as long as I don't do a hack repair.

I'll add that it is *well-dried* construction lumber; I don't want to wait another three months for my replacement piece (yeah, I should have dried ample extra -- another lesson learned!)