Workbench top construction question

[Jerome Hanby]

My workbench top is two layers of 1 1/2" beech counter top that I'm going to glue in a stack to make a 19" x 71" x 3" thick top. While trying to think of good ways to clamp the two slabs together for the glue up, I thought about laying out the locations for my dog holes and using screws in those spots to "clamp" the layers together while the glue cures. After everything is dry, I could remove the screws, bore the dog holes, and leave no screws or screw holes left to contend with later. Any reason not to go this route?

[ian maybury]

Hi Jerome. Sounds like a possibility to me. I wonder if a reasonably sized screw is strong enough to apply enough pull to properly squeeze what are fairly thick layers together? I guess a bit depends on the screw size (coach screws/lag bolts?), on how flat the pieces are, on avoiding creating any raised area when you drill/run in the screws, on where you plan to place dog holes, and on how many there will be - there could well be areas not very well covered.

Screws won't pull the lamination flat unless it's clamped down to something while you drill and screw - but maybe that's not an issue.

Depends a bit on the type of cutter with which you plan to bore your dog holes, but the screw holes would need to be a clearance fit in the top layer - and as such the holes could make locating something like a brad point bit a bit awkward if they are not accurately placed.

Might (if you could borrow the kit) a vacuum bag be more straightforward?

ian

[Prashun Patel]

It might work for that area, but you'll need a lot more clamping pressure at other parts of the bench. Yr best bet is to make a few cambered cauls that'll provide even, strong pressure along the entire widtth of the slab.

Are the individual slats quartersawn or oriented so there won't be that much expansion in the width? It may be a non-issue on narrow slats (someone else chime in) but I'd be concerned that each slab effectively constrains its mate's ability to expand and contract without cracking.

[Jerome Hanby]

I'll be plunging routing the dog holes, so I don't think the screw holes will throw me off, plus I was planning on driving them from the bottom, so the top would be smooth when I start the plunge.

The cauls are definitely a good idea. I'd like to think I would have known to do that anyway, but I'de done far siller things in the past. I still think the screws would help if nothing else to keep things from sliding around. I'll have to check on the quatersawn question. You would think that would be a no brainer for the counter-top manufacturer since these things are made from fairly narrow strips and minimizing expansion and contraction across the width would definitely be a benefit, but who knows how much they even care <g>?

I might be the first person to split, stack, and glue up one these counter-tops this way, but I've seen other projects where they glue up two counter-tops stacked this way. I saw no initial or follow-up posts where that had splitting problems due to the stack (did see some non-stacked uses where the factory glue joint between strips failed). I don't recall any details where they made an effort to stagger the stack so the seams didn't line up. I'm just rolling the dice hoping that any expansion an contraction will be along the same plane and pretty close in both levels. I'll make sure I finish it the same top and bottom so hopefully a difference in moisture absorption won't cause an issue (probably use the workbench finish that Woodsmith talked about in their workbench article, BLO, MS [or may have been turpentine, I can't recall], and Beeswax). I'm hoping the threaded rod for my shoulder vise and the framing (do you call that the skirt?) on the ends, front, and back will help discourage the seams between the strips from separating. It's not needed or the tail vise, but I may route a channel on the tail vise end for a threaded rod like the shoulder vise end will have to lend some front to back compression support. think that (and maybe one in the middle to boot) would help? Cutting those channels is easy (and the slots for splines for the end caps) is easy prior to gluing up the stacks.

I thought about a vacuum bag arrangement. I've got a small kit that uses a hand pump (from that skate board company). It works great and has me interested in a larger setup, but I really need to spend my meager funds getting my shop back together and it's kind of a catch 22, if I had the vacuum arrangement I could use it to build the workbench and if I had the workbench I'd have a place to setup the vacuum arrangement.

Thanks for all the great comments and suggestions!

[Carl Babel]

Hi Jerome,

Depending on the spacing of your dog holes, one option would be to pre-drill your dog holes through both slabs and use nuts and bolts to clamp the panels together through the dog holes. You will probably need fender washers and MDF "cauls" (clamp pads) to distribute the clamping force. You will also need to have some well waxed dogs in a few of the holes to make sure that the slabs don't slide around. Hmm, PVC pipe might even work if you are lucky enough to find some just the right diameter. With PVC pipe, you could use that in every dog hole and run the bolts right through.

However you end up going, I would love to see some pictures afterwards and a description of how it went.

[Ben Hatcher]

While it sounds like a great idea to put them in the dog hole locations, what happens if you break the screw off? Your dog hole would be screwed, so to speak. If you're going to remove them afterwards, you could really put them anywhere.

[Larry Browning]

So, how about oversize pre-drill just one of the slabs and drive the screw into the other one. Could you not just screw from the underside of the bench? That will not be seen anyway. I would oversize pre-drill the underside all over the place, not worrying about where the screws go. Then glue and screw the bottom to the top. I wouldn't over think this. Don't ever forget, this is a WORK bench! Function before form. How well it works as a work bench is WAY more important than how pretty it is.

[Greg Hines, MD]

Presuming you are going to perforate the top with dog holes anyway, why not just drill/rout out a couple of them in the middle, put bolts and cauls on top and bottom, repeating as necessary? This would allow you to tighten it as flat as you need it to be.

That said, I used screws to laminate my top, but it is out of 4 layers of 3/4" plywood, and it worked for me just fine. I put two layers together, with screws, until the glue had set. Then I added a third layer with screws, after removing them from the first layer. After I was up to 3 layers, I removed all the screws, and clamped the last layer around the edges, and put a couple of anvils in the middle to weight it down, and it has worked out fine for me.

Doc

[Jerome Hanby]

Good ideas! I'm taking pictures as I go. I'm so slow, mostly because I'm trying to work on to many things at once <g>, that I'm going to at least get a section done before I post.


Hi Jerome,

Depending on the spacing of your dog holes, one option would be to pre-drill your dog holes through both slabs and use nuts and bolts to clamp the panels together through the dog holes. You will probably need fender washers and MDF "cauls" (clamp pads) to distribute the clamping force. You will also need to have some well waxed dogs in a few of the holes to make sure that the slabs don't slide around. Hmm, PVC pipe might even work if you are lucky enough to find some just the right diameter. With PVC pipe, you could use that in every dog hole and run the bolts right through.

However you end up going, I would love to see some pictures afterwards and a description of how it went.

[Kent A Bathurst]

You could always come up from the bottom with short lag screws - heads & washers countersunk flush, if that is an issue. And then......you don't even need to bother with glue. Maybe for a few inches around the edges, and no cauls needed there, if that's what you wanted to do.

[Jerome Hanby]

Probably doesn't make any practical sense, but I'd like the top to be metal free. Yet the idea of running all thread across the middle in prerouted center channels doesn't' bother me at all. Like I said, no sense <g>.

[Kent A Bathurst]

It's your bench in your shop. Nobody here is going to bring up "making sense"...............:D

[Jerome Hanby]

It's your bench in your shop. Nobody here is going to bring up "making sense"...............:D

I hear ya. If was really into making sense, I would have bought a top of the line workbench and not spent nearly the money I've expended in dribs and drabs over the last few years on this project...but I wouldn't have had nearly the fun!

[Van Huskey]

Vacuum press... :D

[Kevin Presutti]

If you are thinking of putting screws in where the bench dogs go why not drill a thru hole and just use nuts and bolts. Way better clamping than using a wood screw. Plus you shouldn't damage them in any way and can always reuse them. Use a 2"x2" block of hardwood on the surface so as not to damage the top and you will have it clamped 10x's better than any screw:D

[Jeff Duncan]

There's one other alternative that may be more work, but easier to clamp. Assuming you have a decent set of clamps, you could rip the 2 tops down into strips of the thickness you want to make your bench top. Then you glue up the strips with your bar clamps....a fair bit easier clamping than the 2 flat slabs, (at least w/o a vacuum press).

good luck,
JeffD

[Jerome Hanby]

If you are thinking of putting screws in where the bench dogs go why not drill a thru hole and just use nuts and bolts. Way better clamping than using a wood screw. Plus you shouldn't damage them in any way and can always reuse them. Use a 2"x2" block of hardwood on the surface so as not to damage the top and you will have it clamped 10x's better than any screw:D

I'm thinking this is the better route to go. Think I'll leave a few holes unbored and use screws there just to prevent the layers from sliding during glue up. Build some slightly curved cauls with bolt holes in the right spots to pass the bolts through the dog holes and tighten away. Would think I would get really good pressure with that arrangement.

I'm thinking I'll route my all thread channel(s) and my spline slots first. Use those to get me aligned and lightly clamped with my lamination seams top and bottom not aligned. Measure and mark all my dog holes. Pre-drill and screw througth the 3 or four I'm going to use to keep the top from sliding. Bore out the rest. Mark the waste along the front and back (towards flushing them up post glue-up) Unscrew, unstack, trim waste, paint on the glue (find something with a longer open time, any suggestions?), re-stack, line up, and re-screw, position the cauls, insert the long bolts and washers, and crank everything down. Once everything has had time to cure, unbolt, unscrew, clean up, then do my final trim to even things up front and back.

I think I have a plan! that's usually a good sign that things are about to head south <g>.

[David Giles]

I'd put two 4x4s on top and park a car on it for a day. Or a dual axle RV to spread the load. Or put it under a concrete parking garage beam and jack it against the ceiling from two ends.

[Carl Beckett]

My vote is to drill and use bolts to pull it together - I have done this before and with some pieces on both sides to distribute the load you can get some pretty high clamping pressure.

But this has merit:


I'd put two 4x4s on top and park a car on it for a day. Or a dual axle RV to spread the load. Or put it under a concrete parking garage beam and jack it against the ceiling from two ends.

You dont have to jack it per se - just cut some 2x4's a bit longer than the space between the top of the clamp stack and the overhead beam (1/2" long). Then tilt the 2x4's into place and hammer towards being vertical. This creates a mechanical cam leverage and you can get tremendous force. Add however many of these you want. (just dont lift the overhead structure - I am in a shop/garage setting so this works well)

Ive done this for a glueup stack of relatively narrow pieces, not necessarily for a wide surface such as a table top.

[ian maybury]

Whatever the clamping method it sounds like a good slow adhesive might be the plan. Maybe an epoxy or something. A couple of coats might be good to minimise soakage. Epoxy doesn't always bond all that well to itself, so a priming coat that was let dry might not be such a good move...

ian

[David Giles]

Carl's idea is even better. Make giant Bowclamps from 4x4 or 4x6s. Large bolts on each end to tighten them down. Post pics and claim your SMC position as King of the Clamp. It's not everyday that you get the chance to be famous.