> How much strength would be sacrificed?
At some time in life, about half of road-gear will get a 100-Gee shock.
Murphy's Law ensures this will be in the worst possible direction. (In this case, not pure tension or compression, but bending.)
Assume 4 pound PT. Assume (foolishly) each of four bolts takes =equal= strain. 1 pound per bolt. Times 100 Gees, is 100 pounds.
Some basic beam-strength formulas on a 1/8" -square- beam 1" long give:
Required strength: 38,400
A round beam is much less strong, will need much more strength.
Good (not hi-strength) bolt-steel is 50,000+ yield strength. Good engineering allows 3:1 maybe 2:1 safety margin from yield. Steel buildings are/were often designed to 16,000psi stress at maximum load.
Including round-beam, and the fact that threads deduct a LOT of useful metal, plus add stress concentrations, I'd say there's a good chance an amp will come back "busted". If the bolts fail completely, there is a small cannonball ripping out other parts; and as I see it a serious electric-safety issue with sliced power wires.
KEP-nuts both sides of the chassis don't really reduce the stain. A little because shorter unsupported length.... but sheet metal chassis will bend so there isn't the kind of solid stiffness needed for a calculable connection.
Conventional design works. What does it take to rip a PT out when bolted solid, no leverage? In tension or sheer we have (1 lb at 100G) 100 pounds per bolt. 1/8" round bar is 0.01 square inches, times a safe 16,000 psi spec is 200 pounds needed to nominally break (and generally more like 600 pounds to permanent stretch, twice that to break). Even deducting for threads, it is safe. (It is better to use unthreaded shanks through the sheer plane; but in this size and cost category it is cheaper to over-size than to fancy-shape.)
Your plan "may break" at 100 Gee impact. Conventional plan "will not" break at 200 Gee impact, "may break" more like 600 Gee. While we don't see a lot of solid-mounted PTs break loose, I'm not sure I'd go six times weaker unless I _knew_ it would NEVER meet such shocks.
Sluckey gets stuff padded to survive the 50 Gee expected in UPS, if it arrives bent he sends it back, else he bolts it to a rack bolted to concrete. Domestic Hi-Fi may be similar. I'm a little surprised DL's QSCs can use stand-offs in a road-rack amp, altho standoffs have better (less) leverage than bare bolts. Coathanger can take 99% of road-gear shocks (most are 5G-10G, 100G is rare), why Butter's amp was not busted (yet).
A Z-bracket 3" wide 1" tall in 1/16" needs 12,000psi material. Since you can't get steel cheaper than 48Kip yield 16Kips safe design load, this is safe.
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> suggested 24 tpi bimetal blades
A saw should have at least TWO teeth in the cut at all times. If there's only one, the next tooth SLAMs the edge.
So 24tpi is good for 1/12" stuff.
Chassis steel may be thinner.
If you can find 32tpi, that may be more important than magic-metal teeth.
When you must violate the 2-tooth rule, cut gently.
It may help a lot to clamp oak to the back. Damps the tooth-impacts and also guides a dozen teeth so the one tooth in metal does not get too far ahead of the next tooth.
Eastlake Auto sells tools for cutting (and patching) cars. There's a 3-tooth sheer like 1/2" scissors with a power-drill motor. Zip a strip all around rotten tin so you can replace with new metal. Goes fairly straight (or mild curves).
The Bessey is the hand-powered version; my hand hurts looking at it. Probably great for A/C ductwork. Let us know how you like a PT hole in chassis steel.
Classic vertical nibblers are hard work and wander. Power nibblers wander faster; you can cut amazing shapes quickly. How "amazing shape" do you want your PT hole?
Topic: PT mounting alternative - different idea? (Read 4593 times)