How Flat is a Flat Table?

dusty · Post by **dusty** » Wed Sep 08, 2010 8:34 am

It is easy to determine if your Mark 5/V table(s) is(are) flat but only if you know what the specification is for "FLAT".

These tables are cast (not milled) and that implies to me that absolute flatness was not one of the manufacturing requirements.

I have used mine for twenty plus years and though it is not "absolutely flat" I have never had a problem that I believe could logically be attributed to the tables flatness or lack there of.

As a side question: Is your work bench flat? Mine is! At least it is "flat enough".

8iowa · Post by **8iowa** » Wed Sep 08, 2010 10:17 am

Dusty:

I have a very handy accessory, the Veritas 50" aluminum straightedge, which is guaranteed to be straight within .003" over it's entire length. With this straightedge I can tell, withing reasonable ranges of accuracy, just how flat my surfaces are.

The most critical measurement I make with this straightedge is when I set roller stands fore and aft of the jointer when I need to joint long boards. (like 104") Using feeler gauges I can get the roller stands "flat" within about a thousandth and a half.

dusty · Post by **dusty** » Wed Sep 08, 2010 10:38 am

8iowa wrote:Dusty:

I have a very handy accessory, the Veritas 50" aluminum straightedge, which is guaranteed to be straight within .003" over it's entire length. With this straightedge I can tell, withing reasonable ranges of accuracy, just how flat my surfaces are.

The most critical measurement I make with this straightedge is when I set roller stands fore and aft of the jointer when I need to joint long boards. (like 104") Using feeler gauges I can get the roller stands "flat" within about a thousandth and a half.

The roller stands are obviously then in the same plane as the main table BUT how flat is the table.

Using that perfect straight edge - corner to corner, front to back and all over the table surface in all possible configurations - are there any low or high spots in the table. I would bet there are not that they will be insignificant (< .005"). My number not Shopsmith's

How flat the table is depends on how and when you make those measurements. I now find that my previously declared specification of .005" is not very practical. Using that criteria, not a single one of my tables (I have four) will pass the flatness test.

keakap · Post by **keakap** » Wed Sep 08, 2010 1:46 pm

dusty wrote:...Using that perfect straight edge - corner to corner, front to back and all over the table surface in all possible configurations - are there any low or high spots in the table. I would bet there are not that they will be insignificant (< .005"). My number not Shopsmith's

That's pretty much what I did with my Main. In every position (using a Veritas 36" SSteel StraightEdge) if I couldn't see light under it, with a sure but not exquisite viewing, I considered that reading as Flat.
I did check a couple of random points and could not get my .0015 thickness gauge under it.
I go on alert when I see .008 or more. If it's algebraically neutral to other errors I dismiss it.

On one of my Aux tables when I looked under the S-E for light, well, I use a flashlight that has 9 LEDs, and if I can look under the S-E and count the number of LEDs I figure somethin aint right. ]

JPG · Post by **JPG** » Wed Sep 08, 2010 1:53 pm

keakap wrote:That's pretty much what I did with my Main. In every position (using a Veritas 36" SSteel StraightEdge) if I couldn't see light under it, with a sure but not exquisite viewing, I considered that reading as Flat.
I did check a couple of random points and could not get my .0015 thickness gauge under it.
I go on alert when I see .008 or more. If it's algebraically neutral to other errors I dismiss it.

On one of my Aux tables when I looked under the S-E for light, well, I use a flashlight that has 9 LEDs, and if I can look under the S-E and count the number of LEDs I figure somethin aint right. ]

Again! the edge is the skinny sides. Is it really balancing on the skinny edge? I would like to see that spinning!

I realize(IIRC) the SE is 36" long. What are its dimensions in the other two rectilinear planes?

keakap · Post by **keakap** » Wed Sep 08, 2010 4:57 pm

JPG40504 wrote:Again! the edge is the skinny sides. Is it really balancing on the skinny edge? I would like to see that spinning!

I realize(IIRC) the SE is 36" long. What are its dimensions in the other two rectilinear planes?

Yes, indeedy, the SE is balanced on the short side. If * I * remember correctly the dimensions are 36" by 2" by 3/8".
This sucker is S-T-R-A-I-G-H-T ! Edge, side, end...

What I haven't tried is balancing it on its end. Now THAT would be a hoot! I'll hafta adjust my table to .9 degrees to match the garage floor... I'll get a "movie" for ya!

BigSky · Post by **BigSky** » Wed Sep 08, 2010 5:02 pm

keakap wrote:Yes, indeedy, the SE is balanced on the short side. If * I * remember correctly the dimensions are 36" by 2" by 3/8".
This sucker is S-T-R-A-I-G-H-T ! Edge, side, end...

What I haven't tried is balancing it on its end. Now THAT would be a hoot! I'll hafta adjust my table to .9 degrees to match the garage floor... I'll get a "movie" for ya!

Put it on uTube.

keakap · Post by **keakap** » Wed Sep 08, 2010 7:45 pm

BigSky wrote:Put it on uTube.

Alas, I don't know how to do that. (A fact that sorrows me not a lot.)

And I have bad news anyway. I was not able to spin the sucker on its end.
But it did stand up on its end, and I got a couply MP3s spinning the SE on its edge and on its side, on the Main table .
Working on that.

I dunno if the SS Forum will allow MP3s. I may have to reactivate my FTP site.

boostfan · Post by **boostfan** » Wed Sep 08, 2010 8:36 pm

Dusty,

What tables are you referring to? Most all of the tables I can think of are cast and then milled. From experience, even milled it is not uncommon to be a few thousandths or more out out of flat.

dusty · Post by **dusty** » Wed Sep 08, 2010 8:54 pm

boostfan wrote:Dusty,

What tables are you referring to? Most all of the tables I can think of are cast and then milled. From experience, even milled it is not uncommon to be a few thousandths or more out out of flat.

You are absolutely correct. The tables are all cast and the work surfaces are milled to their final configuration. However, they typically are not as flat as a milled steel table would be. I can 'see light' under a straight edge in several places (on about nine different tables (main/floating/extension)). On a steel table, it is not uncommon to 'see light' nowhere on the table surface.

Pay attention, though, on the several different woodworking forums, and you'll find many observations about the table tops not being flat.

I do not mean to cast dispersions on these tables. Mine, though not perfect, are totally acceptable to me. I was just asking for the purpose of education and understanding how flat do the tables need to be to meet all of our demands.