New Workbench Slab Top

[Tapper]

I'm considering building a new woodworking workbench. I like the Roubo style and am still looking at options for vises. The top is the most difficult part of a bench build, at least in my experience when I built my present bench many years ago. Typically the boards, after milling are glued on edge rather than flat. Im my case I'm planning on a bench ~24" in width.

Today I discovered that a friend who previously owned a cabinet shop, has a couple of red oak slabs that might work. The only problem is they are only 1 1/2" thick, thinner than I had planned. My question is this - can two slab pieces be glued together, one on top of other with the grain running in same direction of course, to form a 3" thick top without having any wood movement problems?

Doug

[FS7]

Same species, you should have no problems at all. I have done this many times with no problems.

With different species, you could theoretically have cupping problems if one expands significantly more than the other, but I've never had that happen either.

[jteneyck]

Sure, as long as you can get enough clamping force on them to affect a good glue bond.  Epoxy would make that less important.  

John

[Tapper]

Sure, as long as you can get enough clamping force on them to affect a good glue bond.  Epoxy would make that less important.  

John

Thanks guys - John, could you elaborate please on the advantages of epoxy over say, Titebond?

Doug

[FS7]

Thanks guys - John, could you elaborate please on the advantages of epoxy over say, Titebond?

Doug

Well, there are different ways to do this. I have made "framed" tables, where the center piece is plywood or an epoxied slice. Depending on thickness, instead of routing (or cutting on the tablesaw) a rabbet, I have glued two pieces together in an "extruded L" shape. It makes it easier to ensure straight and square surfaces. Gluing these together is easy, because you can clamp the entire thing (supposing the pieces are, say, 3" or 4" wide) easily and ensure good glue contact.

A "slab top" makes me think of two panels that are something like 24" x 72". If you intended to sandwich these together, it would be difficult to ensure good clamping force in the middle, though proper cauls would work. Now if you were gluing this up from 4" wide stock, you could stagger these things and do it piece by piece with smaller clamps, but that would be very time-consuming and tiresome. If the pieces are flat enough, epoxy would bond to both surfaces as it's higher viscosity and not penetrating. Glue, on the other hand, does not tolerate gaps, and if you're at a minimum 12" in from the nearest edge, for example, then you'd need a bunch of extremely deep C-clamps, cauls, or something else to ensure a good bond in the middle. Though mechanical fastening would probably work too.

ETA: I think the widest I've done this with "regular" clamps - I use dozens of the Irwin trigger clamps around the edges - is probably around 10"-12". I of course have no idea how well the surfaces bond in the middle without sawing it through, but I will tell you that if the pieces were not dead flat I would align them in such a way that the deformation maximized contact in the middle.

[jteneyck]

Thanks guys - John, could you elaborate please on the advantages of epoxy over say, Titebond?

Doug

As FS7 said, yellow glue will not bond well without intimate contact between mating surfaces.  It also requires a lot of pressure (over 175 psi), according to Titebond, but clearly the bond is plenty good enough at much lower pressures because a vacuum bag is less than 14.7 psi.  The takeaway for me is you need really good contact of the parts.  Epoxy works best when it forms a real film between mating surfaces meaning it tolerates less than perfect contact between parts.  It also means low clamping pressure is preferable.  

Back to your bench top, whatever wood you use, I would rip it to the thickness needed for the top and edge glue it.  It will be easier to work with, expand and contract less, and be more durable than a slab.  

John

[Tapper]

John,

I should've been more definitive. The slabs I spoke of are already built, i.e. red oak planks were glued together on edge just like the tops on a traditional woodworking workbench and are 1 1/2" thick. They are actually 3' wide; will need to be ripped down to 2' for my purposes. I plan to stack them making the top 3" thick.

Doug

[jteneyck]

John,

I should've been more definitive.  The slabs I spoke of are already built, i.e. red oak planks were glued together on edge just like the tops on a traditional woodworking workbench and are 1 1/2" thick. They are actually 3' wide; will need to be ripped down to 2' for my purposes. I plan to stack them making the top 3" thick.

Doug

Why don't you rip them to 3" wide and then edge glue them?  Would be a lot easier than trying to glue 2 ft wide slabs.  

John

[FS7]

Why don't you rip them to 3" wide and then edge glue them?  Would be a lot easier than trying to glue 2 ft wide slabs.  

John

Definitely easier, but then the downside is going to be flattening a slab that size. Even with a drum sander you'll need an extra pair of hands at least as that will be impossible for one person to handle.

[EdL]

Build a router sled to flatten, works great....

Ed