Quote:
Originally Posted by paul.dornfeld
We are reducing the weight by drilling into our 1"X4" hollow, rectangular Al tubing (1/8" thick-walled). Two questions: - What would the best spacing pattern (i.e. square grid, diamond, circular, etc.?)
- What would the largest structurally "safe" diameter be?
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I agree with the posters that say round holes are best. Also, smaller holes are better for stress (but the same for weight if you remove the same square inches), they'll affect buckling loads less.
I've had good luck making 1 to 1-1/2 inch dia holes with a conduit punch--they look nicer than any drill and they go quickly. You mentioned diamond, so maybe you're intending on NC machining
Also, all of the people worried about strength, I can't think of many areas where you need the amount of strength a 1 x 4 x 1/8" aluminum rectangular section will provide. But I don't know your loading.
Another way to shave weight from such a section would be to thin it using a table-saw with an aluminum blade. This would have the least effect on stress, less than any holes.
Another note: if the tube sees mostly bending, remove holes or thin evenly. across the faces. If the tube sees lots of torsion (twisting), remove more toward the corners and leave the centerline of each face intact. Highest stress in torsion is down the center axis of the face.