How to / DIY > Everything else
Bolt Strength
mike90045:
https://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx
Had another bolt break today. 1/2" di, 20tpi ( fine thread ) It was magnetic SS, USA made not chinese pot metal (the cast iron was not damaged, I caught it early)
I've been wary of grade 5 & 8 because I've understood they are tough, but brittle and would not last long on a listeroid
What does the hive mind think ?
I've heard tell of get graded bolts, heat them up to temper their brittle hardness and let them cool slowly. But would that soften them too much ?
ajaffa1:
High Mike my understanding is that High tensile bolts should be heated until glowing red, they should then be quenched in water to harden them. They should then be heated again until the steel starts to blue, allow to air cool. You should now have a hardened and tempered bolt. The process does vary somewhat depending on the type of steel.
May sound like a silly question but are the bolts snapping or shearing? If they are snapping it could be that they first work loose allowing the engine to hop up and down a fraction increasing the stress on the bolts.
If they are shearing it could be that the base of your engine is rotating a fraction and the bolts are getting guillotined. If it is the later you could fabricate some steel plates one for each corner to stop it rotating. I believe the original specification for mounting these called for a very substantial concrete foundation, the four corners then had to be shimmed to ensure they were level and then set in cement grout before tightening the bolts
Bob
mikenash:
The good news is that 1/2" bolts are cheap (or at least 12mm and 14mm ones are here) so I assume imperial (inch) ones are for you guys
I have 14mm bolts as hold-downs on the Lister
I wouldn't have thought that M12 8.8 bolts would be "brittle"?
And I'd consider trying some stainless bolts - in pump applications we regard them as "tough"
Better-educated folk than me will have a good handle on the properties
mike90045:
Bolts are torqued up tight, then a nyloc nut snugged on as a jam nut. In the past, they all have snapped, not sheared. Looks like I've got a bit of flex in the I beams the frame is made out of. Wow.
Frame is anchored to 8 (or 10) inch slab. Frame members are 4" i-beams, laid over 4" plywood strips on the concrete, so the wood should take up any irregularities. Large welded "U" bolts trap the i-beam over the wood strip and pinch it to the slab, with a total of 8 nuts over a 3/4" SS all thread epoxied into the slab. All that stuff is tight.
mikenash:
My own off-the-cuff diagnosis - FWIW - is maybe you haven't got a bolt problem . . .
Maybe there's a load problem, in that if there is imbalance in the flywheels, the forces they are generating as the imbalance rotates - maybe lateral, maybe vertical, maybe tangential - but all forces wanting to lift/move the base off its mounts . . . maybe those forces are greater than the bolts can withstand
If that is the case, imbalance may have to be addressed?
just my $0.02
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