Glue-up for large cherry countertop

[Jim Poe]

Hi,
I'm building a built-in entertainment center, 200" wide. The countertop is 4/4 cherry that I milled to .70" thickness. The boards vary from 3" to 5 " in width. I have enough wood for each width to span the width of the entertainment center. I am planning to join the boards end to end with glue and pocket screws to create a single board for each width to span the 200". I then plan to glue and clamp one long board at a time until I have the 30" depth I need. I built a 36" by 194" temporary assembly tabletop for this project. The finished countertop will be supported by a 1" mdf base.

This is the first time I have done something this large. Does my plan sound reasonable? Any obvious gotchas to this plan?


Thanks for any input. I uploaded a Sketchup image of the layout.

310357

Jim

[Kent A Bathurst]

End-to-end glue won't give you much - end grain doesn't have much glue holding capability. Screws will take care of that.

Couple options you may want to consider:

Take a bit std PVA glue, and thin is down to "soup" with water. Brush it on the end grain. Let it absorb. Do it again. You are applying a "sizing" if you will, which will let the end-grain capillaries absorb it and fill up, to an extent - that will help the adhesion.

Or - the big-time answer - route T&G details in the ends, and glue those - now you have added a solid amount of long-grain glue surface.

[Sam Murdoch]

Well you are into it now but I think I would have created T&G boards like with flooring and applied the lay up on a plywood sub top.

When you refer to a 1" MDF base are you saying that you will use the mdf as a sub top or do you mean base in the conventional table and base arrangement? Your answer there might lead to more questions :). In any case this will be a monster build.

I think your plan of creating long boards and then gluing the top up one long length at a time will be a glue up nightmare. The pocket screws will do little to pull the boards together end for end and will likely cause misalignment and the invariable split ends. They will certainly not give you a structurally long board that you can handle as a full length natural board.

My preference at this point would be:

1) Finish the work table with poly or cover it with plastic sheets or platic laminate so that the boards won't stick to it.

2) Apply a very straight and rugged clamp board along at least 1 long length of the work table.

3) Have some glue cauls and plenty of clamps and wedges at the ready.

4) Layout your 1st 200" strake (row of boards) along the clamp board with glue between your butt joints but no fastenings.

5) Start the 2nd strake - glue along the edge and place your boards into place along the 1st strake making certain to get 8" to 18" of overlap at the butts of the previous strake.

6) Build up sequentially as many strakes as you can in the work time of your glue - maybe as much as 1/4 of the table top full length.

7) Clamp these assembled strakes to the clamp board. Use cauls to keep everything flat to each other, hard to the sub surface and tight at the butt joints.

8) Clean the glue off this assembly and walk away for a day.

9) The next day begin building up another gang of planks in the same manner.

10) Etcetera, etcetera.

One mans approach anyway. Haven't done such a large table top so I might be missing something but I applaud your ambition and wish you great success. Curious to read what others might contribute.

[Kevin Jenness]

I hope you have plenty of manpower to move this monster into place once you get it together. And that you don't have to scribe it to fit the walls. In any case, Sam's suggestions are good given that you are committed to this approach. I would probably put biscuits in the butt joints and just wax the assembly table thoroughly. Plastic sheeting has a habit of getting into the joints. I would use epoxy or plastic resin glue, or just do one rank at a time with Titebond Extend. Joining the pieces end to end with pocket screws prior to edge gluing is not likely to work well, both because you will have a long flimsy assembly and because the long edges will not likely be true. We have done glueups like this joining end to end with dominos and pinch dogs, but the parts were short enough to true up after end joining. The butt joints have to be cut precisely to do this successfully. We would normally do a big counter like this in sections joined in situ with dominos and zipbolts. If the sectional look was not acceptable we would lay it in place or as close as possible like a floor as Sam said. Good luck.

[Keith Mathewson]

First consideration is will you be able to get something that long into the room to install it. Other than that the glue-up is very simple, yellow glue will do fine. Don't worry about the endgrain strength issue the next row of material is span the joint. Use pinch dogs to draw the joint tight. I would take it to someone with a widebelt but check if they have enough room to run it.

[Mike Schuch]

I might consider dowels instead of pocket screws. Dowels should increase the glue surface area and provide extra strength to the end butt joint.

You could also consider finger joints. You would want to do the finger joints horizontally so they would not show in the surface of the finished piece. .70" should be enough to give you a few interlocking fingers and greatly increase the glue surface area. The finger joints will also give you vertical alignment of the butt joint. I would make the top finger as thick as your router bit will allow so you can sand the top without sanding through a finger.

Just a couple of thoughts. It sounds like it will be quite a project!

[Brad Schmid]

One of the few methods I've had success and gotten excellent strength with is a half lap joint, glued, and then screwed from the underside. Have the bottom side up, glue the joint, lay a 4ft level along the side, and then drive screws. I've even done this on an outdoor cedar pergola with a 16 foot span using construction adhesive and stainless screws. 10 yrs old now and not a hint of a failing, sagging, or separating joint anywhere. Looks just like the day it was built. Obviously, you'll lose a bit of length in the half laps though... Good luck.

[Jim Matthews]

+1 on the half lap, or scarfed joints to increase long grain surface area exposed to glue.

Half laps will preserve length, but will require precise depth control.

https://www.youtube.com/watch?v=bhKLoXWlSm4

[Pat Barry]

Once the adjacent rows are laminated there is little value in dowels or half laps for the sandwiched parts in your construction. I did the same thing as you to laminate mt workbench top (minus pocket screws) and it is very strong. I think in your case though, the pocket screws make sense to pull things together during glue up and then little additional thereafter. In fact, the half lap joint is a PITA for this type of project

[Robert Engel]

I think screws are asking for trouble with splitting over the long haul since they are so close to the end of a board.

I would join the endgrain using a spline and epoxy glue.
Even though this is a crossgrain situation, but I think the boards are narrow enough not to be a problem.

I would also be inclined to employ a similar kind of self-aligning method such as a spline or biscuits lengthwise, too because alignment on something that long is going to be a bear. I would use a slow setting white glue or epoxy to facilitate any manipulation needed.

As one poster said, I would view this like T&G flooring.

What you're building is more like a stage or dance platform than a countertop!!

Good luck send some pics when you're finished.

[Jim Andrew]

Your butt joints sound like a great use for biscuits. Just be sure to alternate the butt joints.

[Jim Poe]

Hi,

Great ideas from all of you. Thanks for the time and advice.

The mdf base consists of two stacked 1/2" mdf layers glued and nailed to the cabinets below. The assembled cherry top will be screwed to the base from below using slotted holes to allow for expansion/contraction of the wood.

I'm not as concerned about the strength of the end joints as I am about the tightness and alignment. Can I get a tight joint without using fasteners? I've made several test joints using 1 1/4" Hi Lo pocket screws and got good results. Once I've screwed the boards together into one strake I would slide it into position for glueing. There would never be any real stress on the end joints.

I will look at pinch dogs as an option.

The clamp board and "non-stick" surface are great ideas that I did not think about. Thanks

Lots to think about.

Jim

[Frank Drew]

I think your plan of creating long boards and then gluing the top up one long length at a time will be a glue up nightmare.

I totally agree, but maybe I'm just not thinking big enough.

Another problem that occurs to me is how do you plan to joint or otherwise straighten the edges of each of your end-grain to end-grain glue ups prior to final glue up for width, that is, if you want nice, tight edge joints?

If I had to do this job, I think I would have made two 100" panels to the required width, using only full length boards, then joined them end-to-end on the job with a few of those conference table fasteners (or whatever they're called).

[Frank Drew]

Another thing to consider will be the difficulty in safely moving around those ultra-long, skinny end-grain glued and screwed boards; that would be a lot of weight stressing those joints.

[Kevin Jenness]

It is true that once the strakes are edge glued there. will be no stress on the butt joints The problem will be in getting those joints together in such a way that the resulting 16'+ edge is straight enough for a glue joint, the faces are sufficiently flush to require minimal sanding and the joints hold together until you get the edge joints glued. You are talking about 4 to 5 joints along each length of a long thin piece. If you can cut perfectly square ends on perfectly straight segments and glue the butts with no misalignment of the edges, then you can just flip the assembled strake over on your glueup bench with no stress and edgeglue it to its mates- but it is no easy task. You will probably need to true up the edges, and that is where the fun comes in. Do you have a jointer that will handle 16' stock and a friend to help you, or a powerfeed on your tablesaw? Are you confident in your pocket screwed butt joints in this scenario? Not trying to dissuade you, but there are some potential pitfalls there.

[Sam Murdoch]

Using the method I describe above in post # 3 - I would actually lay this up one board at a time and one row at a time. Each butt joint would be cut to perfection to fit against its mate. Each row of boards would be milled straight and equally dimensioned. The one in every row that required the most amount of jointing would set the width dimensions for all the rest in that row. Methodical and true. No forcing joints just accurate milling and a sequential easy glue up. No need for any fastenings or joinery at the butts. If the OP is so inclined and has the tools - biscuits or dominos would certainly help to align the face but would not add much to the integrity of the glue up, though would add lots of work and time (of questionable value) to the project.

All the above based on my assumption - with no supporting evidence - that this OP is not working with equipment that will allow for gang ripping of his stock to insure precise milling.

[Jim Poe]

Thanks Sam,

I will probably follow your procedures.

I am working with a 6" jointer, 12 1/2" planar, and a contractors saw. I milled all the lumber and just need to do the glue-up.

Jim