new counter top... and a flat reference surface?

[Bob Riefer]

As part of my upcoming home and shop renovation, I will be gaining a 15+ foot long x about 18" deep counter along a wall that was previously blocked by a set of stairs (the stairs are moving outside the building).

The location of this new counter top is near enough to my jointer that it would make for a handy place to check lumber for flat surfaces.

Currently I use my table saw and jointer surfaces to check this, but am limited by the size of each of those reference areas.

My thought is that my new counter top could represent a nice alternative if some care is taken to ensure it's flat (enough).

I have read about true "graded" reference surfaces... I'm not sure I need to get to that level of precision in order for the new counter top to be very useful (and certainly a better alternative than what I have in place already).

So, here's the question...


What would you use as the counter top (and assuming that the base cabinets have been carefully installed/leveled)?


My first thought is to double or triple up some MDF, maybe topped with hard board, with some wood along the front edge to protect it. My father has a workbench built like this and it's heavy, tough, and seems like a very stable option. Would this be flat enough in your opinion?

If you don't think that would be sufficient, I would consider a true counter top such as laminate or granite, or other ideas.

If it was really necessary, I would be willing to build a torsion box counter top... but if easier option will work, I'd like to get back to woodworking instead of shop outfitting.

[Jamie Buxton]

A tool to help you get flat is a laser level. For less than a hundred bucks, you get a plane of light which is horizontal to the precision of a laser line.

[Bob Riefer]

Good tip... but I am building a counter top regardless of whether there are other ways to determine "flat"... so having a reference surface would be of value while I'm at it. (and I'm not sure a laser is as useful for determining flat face... simply placing a board down and checking for rocking is what I desire)

[Jim Becker]

If you have access to a laser leveling system it's conceivable that you could build a base that's about as flat and level as possible and then top it with a layers of MDF which typically is "pretty good" relative to consistent thickness, but it's not going to be like your cast iron surfaces that you have been using already. Certain aluminum extrusions can be "pretty good", but again...they are not really reference surfaces. Even a torsion box will not be perfect, even if you have a perfectly flat surface in both directions to build it on. And temperature/moisture affects things, too. You could certainly check jointing results "in general" with your surface, but unless you spend really big bucks for something certified as flat or similar...

[David Walser]

Bob -- Doubled up MDF is more than adequate for making a flat countertop. Covering it with laminate or hardboard will make the top more durable, but not flatter.

For determining whether a board's edge is straight and square, or whether the face of the board is flat, I recommend a good quality straight edge of an appropriate length and a good machinist's square. Using your new counter top for determining if the edge of a board is flat will work fairly well -- as long as the board is not too thick. And, it should work, but not too well, for checking the flatness of a board -- particularly if it's wide. Using the countertop won't help with determining squareness. For that, you need the square. And, while the countertop may work for checking for flatness or straightness, it won't do it as well as a good straight edge. With a straight edge, you can quickly check for flatness or straightness in several spots along the edge or width of a board. You won't be able to do that with your countertop.

[Bob Riefer]

I’m not suggesting replacing other methods and will of course use a square etc. But, I currently derive utility from my known-flat table saw surface.... so having a similar (but longer) version would useful too it seems.

If I use my straight edge once to ensure a flat countertop I could use that surface ongoing.

So my question is... could i construct that from MDF or am I better finding a piece of granite or similar?

[Tom Bender]

The challenge may be shimming it flat. The laser should work well. Make an elevation stick with a piece of wood about 3 x 3 x 1/2. stick a piece of a manila folder about 3 x 3 to one edge. Set the laser up about 2" above the surface and make a horizontal pencil line across the paper at your desired height. Move it around shimming as you go. You might find yourself erasing and redrawing the line a couple of times. Patience will be rewarded.

Once you get the lower course flat fasten it.

[Bob Riefer]

Thanks Tom! I think it’s doable with patience. One time pain for long time gain

[Jim Becker]

I agree that the shimming is the challenge, but it starts with the base, not the top. The more level and stable the base is, the easier it will be to insure that the top is flat, level and stays that way as practically as possible.

[Bill Dufour]

I pulled the long bar from a drafting machine from a dumpster. It is an aluminum extrusion about 6' long. I lean the wood against it to see how flat it is. You could mount something like that top the front or back of the top like a fence rail on a tablesaw. Just allow it to float a bit so it does not get bent out of shape as the table top move with seasonal changes. I do not think a simple Al extrusion would be straight enough without some tweaking which will require three pieces to compare against each other just like scraping a straight edge.
Bil lD