twisting off grade 8 bolts

[chief613]

i am changing the knives on my Wallenstein 6" chipper. So i remove the bolts flip the blade , tighten the bolts with a ratchet then a torque wrench to 165 lbs as the manual calls for. on the first knife i stripped the threads off one bolt. The second knife i twisted 2 bolts off at the knife. that's where i stopped. I have only used the torque wrench once before to do the exact same procedure with out any problems, i do realize new things can be broke in the box. I bought new bolts, the first knife 2 of the 4 torqued the other 2 feel like the are now stripped, that's where i quit for the nite.
Thanks for any help

 

[KWentling]

Counterfeit bolts? Those were a big problem years ago. Do they have the 6 marks on the head? What size are the bolts?

Kim

 

[jinman]

You are not confusing in/lb with ft/lb are you? What size hardware are the bolts? 165 ft/lb sounds like truck wheel lug bolts to me, and I'm pretty sure your blades don't have that size of bolt. I would use the torque wrench to measure the amount of torque required to loosen the bolts. It will be higher than your torque value, but also will give you a baseline for the bolt's torque failure limit. If you can take them out without twisting them off, you should be able to use the same value minus a few lb for a safety margin.

 

[Gale Hawkins]

jinman I think may be correct. That is about the value for our 19.5" motorhome wheels.

 

[1fastbob]

Sometimes lubricating and torquing a fastener when it is supposed to be torqued dry can give the result you are describing. Note, I am not suggesting this is the case here as this is just food for thought.

 

[Furu]

Not familiar with his model and robustness of it but .....
My manual specifically states to replace the bolts when you swap blades. OP confused me in that in one sentence he implies he put the old one back in and in another he says new bolts had 50% failure. Grade 8 9/16 torque up to 169 ftlbs and 5/8 torque up to 230 ftlbs so his 165 does not surprise me if his unit is very robust and as 6" capability I would guess it is robust enough. I think the dry vs lubricated torque value may be a possible and where he got the bolts. I like home despot but not for bolts that I care about and definitely not grade 8. The idea that it is 165 inlbs is not a likely scenario unless they are small bolts which I doubt as that would be for a 1/4 " bolt which is not likely on that size chipper.

 

[MHarryE]

Have you calibrated your torque wrench? At our plant we have a weekly calibration schedule for all of our torque tools but I think 10% is the limit. It is not unusual to find one that has shifted 35% in a week. We have a calibrator but I check my personal wrenches against a beam type because the beam type does not really have moving parts, just a main rod, measuring rod, and dial. I had it checked on our dead weight calibrator at work. This could be your problem.

 

[jinman]

Grade 8 9/16 torque up to 169 ftlbs and 5/8 torque up to 230 ftlbs so his 165 does not surprise me if his unit is very robust and as 6" capability I would guess it is robust enough. I think the dry vs lubricated torque value may be a possible and where he got the bolts.

You are correct, and our missing info is the exact size of bolts. Sometimes people mistake the hex head size for bolt size. 9/16" and 5/8" bolts are very large. Those are the bolts used to hold on my tractor's loader sub-frame. They should take that kind of dry torque with no problems whatsoever. For our advice to be meaningful, the OP needs to let us know the diameter of his bolts.

I find the hardware sold by the pound at Tractor Supply to be great quality and value. They normally stock grade 5 and 8 bolts up to 1" diameter in their bins. If you go to a hardware store where they sell the bolts individually, you'll pay 2 to 3 times the price. I just bought a 1" dia x 8" grade 5 bolt at our TSC for the axle bolt on my rotary cutter's tailwheel. The bolt and nut weighed 2.2 lb and was about $10 with tax. The hardware store had those for around $17 each.

 

[Gordon Gould]

This is an interesting exercise in guess work.
Here is some more info to mull over. My 5" chipper has 4 knives. Fastened wit 5/16" bolts torqued to 20 ft-lbs or 240 in-lbs.

 

[chief613]

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