How flat is flat enough?

[nhk750]

I was checking my cheap straight edges and I couldnt really tell if they were straight or not, so it is hard to know how flat my building surface is. I ordered a 24" straight edge that is within 0.002" so now I can really know how flat is flat.

But, so far my planes have been coming out ok, so how flat does a build board really need to be?

 

[TEAJR66]

As flat as it takes to make you happy with the square of your build.

Most of the times, the plane is as square as the cuts you fold along. Regardless of build surface or DTFB warp, straight cuts make a difference. So, that straight edge might help make a difference.

I am working on a plastic table that is pretty bowed, with cheapest straight edge I could get sent from Amazon, and things still seem to come out pretty decent.

 

[PsyBorg]

Straight is irrelevant it seems in the aero dynamics of flight as proven decades ago by a bunch of college nerds.

 

[JimCR120]

There's a highly scientific term we use often. TLAR (that looks about right).

 

[nhk750]

Straight is irrelevant it seems in the aero dynamics of flight as proven decades ago by a bunch of college nerds.

Ummm, ok...;}

This question in my mind actually came about while building the balsa wings for my Hog Bipe. I was trying to check things with my cheap straight edges and couldn't really see if they were accurate or not. I'm just trying to make sure I build quality. For DTFB, it probably doesn't matter as much.

 

[TexMechsRobot]

I think with an error of .002", you're getting a little crazy....

 

[nhk750]

I'm striving for precision, I just need to know how flat my table is as the top wing on the hog is one piece and before I build it I just got to know if I need to address my table. I may pull the hollow core door off of myUline maple table and put my steel board directly on the Uline table as I'm sure that is perfectly flat. I use the door because I like the extra space it gives me and it looks flat, but my crappy straight edges show it to be not flat. I will know in a few days when the good straight edge shows up.

 

[nhk750]

Flat enough!

I got my new straight edge today and had some fun with it checking everything. My other straight edges are close but they all seem to have a bow to them, but I can only see a little light in the middle of them so not to bad. I did check my table and found something interesting. The edge of the hollow core door that is not supported by the table has a slight warp to it as the steel building board weight causes it to sag. So, simple fix, just moved the building board in toward the supported area of the table and fixed that. I checked my wing so far and it is absolutely flat with no space or warp, so it looks like flat is flat enough.

Wing is very true!


Edge of door hanging over table will sag if excess weight is on it, so no building in this area anymore.