How much flatness is OK on a jointer?

[dingbat]

I think your "always-handled-like-a-sacred-relic 24" Veritas steel straightedge" is no longer accurate to 0.001" tolerance over its length, unless you've also kept it in a supported box and you were careful about temperatures when you used it.

I wouldn't worry about 5 thou flatness in a machine table and I certainly wouldn't expect to receive that, unless I'd paid the money for someone to season their castings for a year before machining them.

If you care, set up a DTI on a long cantilever from one table to the other and then try loading some timber on one end. Machining accuracy means nothing when the deflection under load is far more than this.

I certainly wouldn't expect any better than 1/4" alignment or parallelism between separate parts, until I'd actually set the machine up. "Set up" isn't just ripping the box off it, there really is work to do here. It begins with a stable foundation for the machine, then setting the base to be flat and level, and only then starting to look at the components and tables. This sort of machine is _heavy_, the tables must not only be machined flat when supported, then have to maintain this when sticking out under their own weight. Adjustments like slideways become crucial here - owing to the lever effect of the geometry, a tiny amount of movement against a gib strip gets magnified out at the end of a table.

Plenty flat enough. Enjoy it. Don't sweat the small stuff.

[LKB]

Thanks for the reply. You raise an interesting side issue:

I've always stored it by hanging it on a peg through the hole (i.e., it hangs straight down) in a tool cabinet in my climate-controlled shop. It's stored in such a fashion that nothing can bump into it, etc., and every time it comes out, it gets a quick wipe of Boshield before it goes back on the peg. From what I've been told, that should be OK.

Still, I know it doesn't take much to screw up a precision straightedge, and although when I received it it was packed pretty carefully, there's no way to know whether it was dropped, etc., in shipping.

Ergo, the question: is there an easy / inexpensive way (or place to go) to check whether such a reference is still accurate?

LKB

[Teamcasa]

Hanging the straightedge is fine. Dropping it may have a negative effect. I have several straightedge's two from Lee Valley. I have a local machine shop that tested the flatness when I purchased the 50" aluminum one from LV. It was within 0.001" over it length. The machine shop has a 72" granite flat table that they say is within 0.0005" over its length.

The point is, even 0.005" +2 is dead flat when working with wood.

Dave

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[dingbat]

Have three of them and check them against each other, same as for surface plates (only easier to do). Don't use only two, or you might have matching curves!