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.

IMG_0123.jpg

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:

IMG_0124.jpg

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 2¢ Two Cents.jpg.

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:

YMMV!!!.jpg

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!