want straightness of my straight edge checked

[bswartz]

Hi,
I have a three foot steel straight edge. I think it may be cupped. I want the straightness checked and, if necessary, fixed. I intend to start calling machine shops here in Albuquerque. Does anyone have a local machine shop to recommend?
Bill

[dstrip]

Have you checked it against another straightedge or the infeed/outfeed tables of your jointer? That would be a good first step.

[droff]

It is hard to tell how precisely straight a straightedge is. Checking against a verified standard is the best way, and few of us have access to one of those. I would be interested in learning more about the YouTube video’s method of checking a straightedge against itself. The only approach that I have read about requires three references. By comparing the three, it is supposed to be possible to tell if any or all of them are straight.

When we can meet in person again, a group of interested people could bring in their references, and compare them. That would be a good hands-on small workshop.

[bswartz]

I have 4 pieces of extruded aluminum. Compared to them, the straight edge, or the aluminum, appears cupped. I have no jointer. I saw a YouTube video showing how to test the straight edge against itself. That will be my next test.

[dstrip]

If you compare two of the extrusions against each other are they straight? If so, then it would seem it is your straightedge.

[bswartz]

Here is a YouTube link from Practical Metrology for testing a straight edge against itself..

I implemented the method in the video using clamps, marking knife, and blue tape on a flat surface. The test showed a cup in my steel straight edge. The test also showed my extruded aluminum is straighter.
Thanks to all for the feedback.
Bill

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