Precision Flat Surface

john_r_graham · Post by **john_r_graham** » Wed Mar 16, 2011 8:26 am

According to my precision straight edge, my EAA1000 tables aren't completely flat on top. I think I need something rigid and guaranteed flat to measure the ribs against during fluting and I'm thinking about getting 2-3 square feet of granite kitchen counter top cut for the purpose. Has anyone gone this route or am I in the realm of overkill?

- John

Post by **Spike** » Wed Mar 16, 2011 8:57 am

Depends on how much you are off. If your talking < 1/16" Id leave it.

Spike

Post by **bullojm1** » Wed Mar 16, 2011 9:05 am

John,

The "flatness" of the ribs isn't really the important thing. Whats important is the flange of the ribs is perpendicular the the face of the ribs (I used a square to test), and once fluted, all of the holes line up straight (I used a metal ruler to test). If anything, granite would make things worst because of how slippery it is, not to mention the expense of something that could be put towards better avionics!

Good Luck,

john_r_graham · Post by **john_r_graham** » Wed Mar 16, 2011 9:26 am

Mike & Spike,

Thanks for the advice. There's always something else to spend the money on, so I do appreciate the perspective. I'm only about 20 hours in to the build and I know I have a lot yet to learn. The table top is probably less than 1/16" off of true.

HS front and rear spar prep is complete and I'm moving on to the ribs. So far, I'm lovin' it.

- John

bruceh · Post by **bruceh** » Wed Mar 16, 2011 10:37 pm

Go down to the local big box store and buy a large travertine tile or something like that. If and when you need a perfectly flat surface, pull it out and lay it down.

As others have pointed out, you don't need to flute to perfection. Get it close and make sure the flanges are perpendicular. It all comes together with rivets and at that point the matched hole construction will line up and hold everything straight.

N155RE · Post by **N155RE** » Thu Mar 17, 2011 6:36 am

I have a large table saw which has a nice machined surface.
This is what I used.

prestwich · Post by **prestwich** » Thu Mar 17, 2011 2:41 pm

I use a granite "surface plate" when I'm looking for flatness. I actually bought a small one from McMaster Carr, but then ended up acquiring a big beast from a local machine shop that was selling some stuff.

Thermos · Post by **Thermos** » Fri Mar 18, 2011 8:52 am

I just used my Mk I eyeballs and my Chapter 1000 tabletop...that was close enough for fluting purposes. After all, it's only an airplane!

The only time I've looked for a really flat surface was while closing out the ailerons. Our (then) brand new granite kitchen countertops worked really great. They should have, for what they cost.

Dave

john_r_graham · Post by **john_r_graham** » Fri Mar 18, 2011 9:13 am

N155RE wrote:I have a large table saw which has a nice machined surface. This is what I used.

Now I feel silly: I have a table saw.

- John