grade 8 bolts with cut threads?

I have no information, but if the threads have been cut with a die head, they'll have the characteristic termination points of each of the chasers where the thread ends. You'll see steps in the threads at 90 degree intervals towards the grip of the bolts. They will be as long as the lead angle on the chasers, usually a couple threads or so. A rolled thread is generally much stronger than a chased thread, so you may be on the right track regards grade 8 bolts. Dunno.

Harold

yes they have the pie chaser marks , I was uncomfortable with them and told fastenal that I would not accept them and as they were a time critical item would not be paying for them

ended up getting some from msc , called on Saturday at 11 am and picked them up at the airport off a delta plane at 6 pm , and get this , it was still cheaper than what fastenal was trying to charge,

I will have to write a letter to msc for such the great service

It would have been interesting to put one of those die-cut bolts into an intstron tester and see if it really did meet the spec.

Jim

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What spec? "Grade 8" is not a spec. There is a spec that has fasteners that are referred to as grade 8. But if you don't know that spec number is, I would bet you did not by the fasteners to it. I don't know what the spec number is, but I would bet that there are actually several. The world of fasteners are much more complicated then most people think.

But to answer your question, it depends, some spec's require it, some don't. Some that require rolled threads will relax it for larger diameter threads because the equipment does not exist to do them. I forget at what size it becomes a problem, but I believe that 1" could be rolled.

Are cut threads as strong as rolled thread? Yes and no. They should have the same strength, but they have terrible fatigue strength. If fatigue is not an issue, then cut threads should be fine.

Vince

P.S. I'm not a bolt expert. And I'm constantly learning something new every time I answer a post ;-)

williamhenry wrote:

You need to read Caroll Smiths book "Nuts Bolts Fasteners and Plumbing." It's a pratical discussion of fasteners and such that explains exactly why a die-or lathe-cut bolt will be weaker than its rolled-thread counterpart. Often by a lot.

This means if you compare a rolled-thread bolt of any size to the same cut thread fastener of the same size and shape, the rolled thread one will fail at a much higher load than the other one. Factors of two are not uncommon.

The reason for this has to do with a) the stress risers that are inevitable at the thread roots of cut threads, which weaken the bolt, and b) the forging and grain alignment that strengthens a rolled-thread bolt at that same critical thread root location.

This is not just a fatigue issue.

Jim

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well I am not a bolt expert either , but I know this much

took the torque multiplier to one of the cut thread bolts it sheared when I hit the 1200 lb ft mark

the rolled thread Brighton best that msc shipped me maxed out on the multiplier

method of testing{ not scientific

snap on 18.5 to 1 multiplier snap on socket driver 3/4 inch

bolting two plates together with 2 inches of 75% tapped threads in bottom plate ,

1.0625 clearance hole in top plate grade 8 machine washer and high collar lock washer

the cut thread bolts I got from fastenal sheared at on of the tooling marks from the die chaser

even though they have the six dashes and triangle I associate with grade 8 fasteners there is no appearance of it being quenched and tempered,

glad I spent the money on the other bolts

as they hold a robot on top of an injection molding machine in a cantilevered load

5 bolts in tension and the other five in shear ,

Just for my education, what is a "torque multiplier".

If I didnt have one would I just use a piece of water pipe over the handle of a breaker-bar that had the right socket on it?

Al

a torque multiplier is a tool that you drive with a torque wrench and through planetary gears inside and a reaction arm on the outside that is braced against the work it multiplies the input torque a specific amount based on the gearing

the ones we use are a 4 to 1 that goes up to 2000 foot pounds with 500 ft lbs input and a 18.5 to one that goes up to 3450 ft lbs with 180 ft lbs of input

really handy to use to tighten large bolts if only a couple to tighten

if we have a lot we get the hydraulic wrenches out got one that will go to 70000 ft lbs,

The "correct" way to do this is to load the bolt in pure tension. An Instron machine does this, and has measures displacement vs load force as the force is ramped up linearly.

Then they plot it and you can see the yield and failure points.

Typically a fastener will fail at the first thread that enters a tapped hole - even with the surface of the plate it is tapped into.

Your test had some uncertainties in it, like the lubrication state of each bolt. If you had them about the same then I would say you more than proved your point. :^)

The fail at the stress risers from the die head marks is quite expected - your guess was right on point.

Jim

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When I was a millwright foreman, we worked with a vendor specialist on some Westinghouse steam turbines that had mating flanges on the casing halves that combined, totalled 12 inches thick. The bolts were spaced as closely together as possible, just enough to allow the use of wrenches. The flanges were hand stoned, boiled linseed oil was applied as gasketing, and the through bolts installed. Each bolt was hollow, and after hand tightening, a

200 watt soldering iron was inserted into each bolt's center hole. After all night heating, the bolts were torqued further, several hex flats, then the irons removed to allow the bolts to shrink. I was in my 20's, and this was pretty impressive stuff. All tools were inventoried in and out of the turbine room, and we had to tie all hand tools to our wrists to prevent losing them in the turbine condenser area below.

RJ

both bolts were torque with oil under the head and washer only , dry threads

yeah I cant wait to see the purchasing guy on Monday , my correct bolts cost less than his , including the delta dash freight charge, will be a real interesting Monday

Thanks, Al

"Torque amplifiers" are X-celite black handles that fit over small diam. handled tools. Typically a plastic case of nut drivers and amplifier or screwdrivers... (says so on the handle).

The Multiplier must be the big one. :-)

Martin

Let us know the outcome. Someone shoudl get a kicking. G

-- 'The first thing we do, let's kill all the lawyers'

- William Shakespeare 'When my client says "kill all the lawyers" he actually means render all legal practitioners, present, past or future, practicing or retired, hereinafter referred to as lawyers, notwithstanding their actual legal status, expressed or implied, non-vital in the usual legally accepted sense of that term' - Wm. Shakespeare's lawyer

-stolen from Nigel Eaton

well Monday came and went wittthout much fanfare the fastenal guy said he did not know what happened , but was real sorry, I concurred that he was sorry and the communication flow got stopped up right there,

purchasing guy was "out sick"

I doubt that the "grade 8' bolts you got were made in America. Now before some of you get your "Knickers in a twist", realise that our envirionment allows foriegn bolts to be used in making parts here. The problem lies in the term "Grade 8" and our own ANSI 1962 standards. In America, makers of fasteners are guided by the 1962 standards which not only spells out sizes etc, but materials as well. many foriegn makers do not adher to these standards, so the world out there is a free for all when it comes to bolts. I admire your test procedure ! While it is not perfect, it did show you the fallacy of the cut thread....A REAL NO_NO in high stress envirionments We built dies for the plastic industry and saw pressures of up to 20K PSI and loads in excess of 3 million pounds on some of our stuff. We used only the best screws for our applications, due to the liability and some of ours bolts went upto 36mm in size...thats a

3,000 ft/LB torque for preload for those of you not familiar with that size. If you are dealing with a dangerous situation, don't use a hex head cap screw ! Use Allen Socket heads ! Socket Head Cap Screws (SHCS) made by Unbrako , Allen, Camcar, must meet the 1962 standards and must use 174,000 Tensile steel, not some crap that fell out of a steel mill in a jungle. Your Grade 8 is really a medium-carbon steel of 150K tensile.( Like 0-1 !) so .601 (root area/sq.in.) x 150,000 (tensile) X 60% (yield strength ratio)= 54,118 pounds at Max load per 1" screw. If the Heat treat is off, you can see the problem here . This may or may not be enough for your situation, but gives you an idea of the capacity of a 8 screw...but the cut thread will surely mean a failure due to stress fracture....never use cut threads for any heavy loads...its like having a fuse with an unknown time span ???

FYI There are 3 "standards" for metric screws, and they are not marked as

8's 10's or 12.9....only American made Metric screws are ALways made to 12.9 standards.. like I said...it's a Jungle..