twisting off grade 8 bolts

[Soundguy]

1/2"-20 UNF, gr8 90ft pounds

Torque Chart

no wonder...

5/8-18 UNF are 180 etc

 

[Brant]

thanks for the replies
just got in and havent had time to double check the 165 ftlbs in the manual, im fairly confident on it though. The bolts are 1/2" x 1" fine thread i got them at the local hardware store(True value) I did how ever spray the bolts with WD40 prior to removal. and i havent calibrated the torque wrench either

With the lubricant, you're about 3 times the torque spec. No surprises they twisted off.

 

[Soundguy]

OVER 3x the torque spec with lube..

 

[crazyal]

I would use new grade 8 bolts with crown lock nuts and just use the standard chart for grade 8 bolts for a torque spec and not bother with the manual. I find that the all metal crown lock nuts work really well in applications where they'll see vibration during use.

 

[SSdoxie]

thanks for the replies
just got in and havent had time to double check the 165 ftlbs in the manual, im fairly confident on it though. The bolts are 1/2" x 1" fine thread i got them at the local hardware store(True value) I did how ever spray the bolts with WD40 prior to removal. and i havent calibrated the torque wrench either

165 in/lbs(13.75 ft/lbs) on 1/2" bolt would not be nearly enough for that appliction so 165 ft/lbs is probably correct, but use new bolts & nuts each time. That is stretching bolt to it's limits so no give left when trying to reuse them.
Even if you were able to get them torqued at reassembly, I hate to think of damage or personal injury that could happen if one of those chipper blades came loose at full RPM.

 

[Soundguy]

it's PAST their limits....

 

[Furu]

If as you state they are 1/2"-20 fine thread the standard spec values are 120 ftlbs dry and 90 ftlbs oiled according to the referenced web site

http://www.engineershandbook.com/Tables/torque.htm

http://www.raskcycle.com/techtip/webdoc14.html

Thus if you oiled them and torqued to 165 on 1/2"-20 bolts it is no surprise they broke. If you had a couple survive as you said they are beyond their elastic limit and should be replaced.

If the manual specs it at 165 I would verify the bolt size as you may be too small for the unit using 1/2" bolts. It is hard to tell without knowing your manual and specs. Just verify spec bolts and torque.

 

[chief613]

thanks again, i had already ordered new bolts, only 4 on the shelf. Clean things up and try again. Guess i got a little less dumber today

 

[Gordon Gould]

ordered new bolts, only 4 on the shelf. )

Must be everyone is twisting them off


( Just trying to be funny. Not making fun of your situation at all !


gg

 

[jinman]

thanks again, i had already ordered new bolts, only 4 on the shelf. Clean things up and try again. Guess i got a little less dumber today

Don't be too hard on yourself. Everyone here has made mistakes and will make more in the future. Have you been able to get all the twisted off stubs out? If you get them all out easily, maybe you should stop in and buy a lottery ticket on the way to the hardware store.