| Author | Message | ||
     Parrick |
I was doing some light reading today about torque wrenches and came across some interesting info here: http://home.jtan.com/~joe/KIAT/kiat_1.htm The first thing that caught my attention was the statement that, regardless of the accuracy of the torque wrench being used, the margin of error for the resulting clamping force of the joint was +/- 25% !!! The second thing that impressed me was the increase in accuracy which resulted when using the "Angle Torquing" technique. This involves using a torque wrench to set the fastener to a starting torque which is much lower than the final target torque. Then the fastener is turned an additional number of degrees to achieve the final target torque. The number of degrees used to reach the final torque must be calculated based on the pitch of the threads of the fastener involved. (This is where the ME challenge comes in) I have done this before when torquing head bolts on an automotive engine but I was just following the shop manual instructions. I had no idea that it was actually a BETTER technique. This got me thinking about the 300 ft/lb torque that is being recommended for the rotor. Several people have posted that they had difficulty finding a torque wrench that goes up that high. I have one but the 300 ft/lb mark is the highest setting it has. The far ends of a torque wrench's range are its most inaccurate settings so using a wrench like that compounds the inaccuracy of an already imperfect technique. So here is the challenge... If someone could provide the thread pitch of the rotor nut perhaps one of the ME's on here could do the math and provide us with a procedure to achieve the 300 ft/lb mark while using more commonly available tools. The bonus would be greater accuracy. The ideal procedure would employ a starting torque in the 50-150 ft/lb range and then finish off with an easy-to-determine finishing stage of something like 1/4 turn additional rotation. Any takers? | ||
| Musclecargod |
I don't think that can be calculated accurately. The coefficients that govern losses to friction, thread condition, etc... would be very difficult to determine. I would guess that the 300ft/lb has a margin of error built in. I also don't think there is enough information to support the authors claim of +/- 25% clamping force of the joint. Especially if he was trying to get the fasteners to the yield point. The "angle torquing" the author is referring to is a torque to yield fastener situation. Which is an entirely different situation. It is much easier to determine fastener elongation for a given angular rotation due to thread geometry, than it is to determine it from input torque. | ||
| Nillaice |
i'd think you wouldn't want to torque something to it's yeild point. plastic deformation is where stuff starts to fail. elastic is good. http://www.google.com/imgres?q=yield+point&hl=en&s a=X&rls=com.microsoft:en-us:IE-SearchBox&biw=1280& bih=819&tbm=isch&prmd=imvns&tbnid=KX_-6hQDYpSgAM:& imgrefurl=http://blog.gxsc.com/graphics_systems_so lidnot/cosmos/page/2/&docid=2J6urC1tYw05UM&imgurl= http://gxsc.typepad.com/.a/6a00d8349cbbac69e201116 83ab984970c-800wi&w=800&h=473&ei=UiSXTqunEYTk0QGqq ZzTBA&zoom=1&iact=hc&vpx=942&vpy=162&dur=20950&hov h=173&hovw=292&tx=180&ty=95&sig=108260844498328814 301&page=1&tbnh=112&tbnw=190&start=0&ndsp=24&ved=1 t:429,r:5,s:0 | ||
| Nillaice |
but, yeah. it's hard to calucualte. it can be done with enough time punching #'s in a claculator. personally; i'd just use a torque wrench | ||
| S21125r |
Doesn't address your challenge per se but the KISS way to get to 300 f-lbs is to make a 1 foot breaker bar and put 300 lbs of weight on the end of it. Or if you weigh 200lbs like me you make the bar a foot and a half and stand on the end of it. Not precision, but better than nothing. | ||
| Motorhead102482 |
 You get a 600 lb/ft impact wrench, put in on number 2 setting, and then you turn the air compressor regulator to maximum recommended pressure. | ||
| Motorhead102482 |
Here's my ME math behind it. 4 setting diveded by 2. is 2/4 which is reduced to 1/2. If your maxed out on 1/2 it gives you 300 which is half of 600.  | ||
| J2blue |
Matthew, you beat me to it! | ||
| Nm5150 |
Ya'll are making this way too complicated.I torque stuff together pipelining that gets tested up to 3500 psi for a living.Make sure the threads are lubricated,measure the best way you can(+/- 25%)go 50%-80%-100%-100% and it will be good.FWIW I weigh 160# and with near maximum effort can easily put 350# of torque on a bolt with a 30" bar and socket. | ||
| Rt_performance |
If i was taking mine apart i could do this easy. Sanpon 1/2" techwrench on torque angle it gives you the torque in #'s as well. I will make you a deal send me a 08 stator and rotor and i will get you a easy method of torqing | ||
| Datsaxman |
Parrick, I am with Musclecargod here...it is easy to get a fastener to yield "% elongation" by turning a specified angle past the point at which the fastener stops turning freely. Say 10%-20% of the specified torque to "set" the fastener, then twist away, allowing the fastener to stretch from there. But this is certainly not a torque value substitute, although it might work very well. Lots of old skool mechanics tighten fasteners by feeling this stretch begin, like Nillaice mentioned. I do this where there is no delicate material involved. It works quite well. Irony: I work in the Theoretical Physics business, and leave the torque wrench in the drawer most of the time. Torque values? Weee don't need no stinking torque values! | ||
| Parrick |
The article is not about cranking fasteners to the point of failure, guys. You kinda gotta read the thing to get the point. I must admit that I probably would not have gotten it at first read if I had not had the experience with the technique before. Like I said, I did this not too long ago torquing the head bolts on another vehicle and it was the procedure that was described in the shop manual. Not the Chilton manual...the FACTORY shop manual. The procedure was: Torque to X ft/lbs then turn an additional 1/4 rotation. At the time it was a head scratcher. Why would the factory specify this procedure instead of just giving a torque specification? Now it makes sense. It is because this method gives better results. But that was not the point of the post. I just thought we might be able to save some members from having to go out in search of that 300 ft/lb wrench. I expect that that '08 rotor conversion is going to become increasingly popular. | ||
| S21125r |
Exact same torque angle procedure is done on the sportster and old school buell heads since the cylinder wall is thin. Too little torque and you have head gasket leaks. Too much torque and the cylinder goes square around the stud holes. On those it wasn't a torque to yield either, however the studs were so long that they had a pretty large elastic zone. Interesting story when I was at the dealer a few months back. Guy brings a traditional harley in and needs the rotor torqued to a specified amount. Service writer tells him to save his money, take it back home and impact it on and it will be fine. Guy insists the specific torque amount as that is what is stated in the manual. Guy walks out of ear shot and service writer says under his breath "were just going to impact it on until it stops turning..." | ||
| Musclecargod |
Industry standard is to oil threads and friction surfaces with 30W oil, and torque. That should be plenty accurate for the rotor. Typically when using torque values to tighten a fastener, 90% of the applied torque is overcoming friction while the remaining 10% is tightening (read stretching) the fastener. Parrick, the factory method you describe was a torque to yield situation. You are correct they do this because it gives better results. But I think the article has given you the wrong impression of why the results are better... Torque to yield is not about cranking fasteners to the point of failure. It is about cranking until the fastener transitions from the elastic deformation region into a region of plastic deformation. Basically elastic means the bolt will return to original shape when loosened, plastic deformation leaves permanent distortions in the bolt that do not return to original shape when loosened. Why is this important? In critical fasteners, ie. head bolts, a simple torque procedure would probably be fine...for a while, if you never start the engine. Head bolts must hold the heads on through wide temperature swings, gasket relaxation, varying load conditions, etc... Torque to yield techniques accomplish this through stretching the fastener into the plastic region slightly. If the head expands the fastener will yield slightly further, but on the other hand if the gaskets relax slightly the fastener will still provide sufficient force to the head. For example if you tightened two pieces of aluminum together at say 500F, and made sure they were tight but the fastener had not yielded, when they cool chances are they would be loose. This may not be the case if a correctly designed torque to yield fastener is used. I would recommend doing a little research on these fasteners if it interests you, lots of good information out there. There are more accurate methods, even beyond torque to yield, but hopefully this shows they are not an apples to apples comparison. I realize this is off topic a bit, hopefully someone finds it interesting. That said if it was my rotor, I would tighten the piss out of it and call it good. | ||
| Parrick |
Musclecargod, That's actually some of the most interesting stuff I have read on here in a while. Thanks for taking the time to post. I do need to dig into this deeper. In the article I was referencing the author never seems to get into the area of plastic deformation. His descriptions seem to assume that the fastener-in-question is operating within the elastic zone. I think when I brought up the head bolt example I threw the whole discussion into another realm. From what you are saying that seems to be an entirely different application. I definitely have a hole in my understanding on this topic somewhere. It has always been my understanding that when a fastener reaches a point where it becomes permanently deformed it is then useless because its strength can no longer be accurately predicted. It would seem that, in the head bolt example, you would want that fastener to remain in the elastic zone so that it can effectively stretch and spring back in concert with the expansion and contraction of the head. But then, what you said makes sense also due to the fact that head bolts are not supposed to be re-used. I just always assumed that the reason for that recommendation had to do with metal fatigue rather than the bolt being permanently deformed as a matter of design. So my misconception lies somewhere in that area of plastic deformation. Apparently there is "good" permanent deformation where the fastener still retains some elasticity and then there is "bad" permanent deformation such as when a bolt will not reach its torque spec because it is continuing to stretch but has not yet snapped. I hope none of this comes off as me questioning your knowledge. I'm not. I greatly appreciate your input. I just gotta figure out what I'm missing. This is good stuff! | ||
| Dannybuell |
Parrick good topic. Datsaxman - My old friend of many years speaks almost the same, "anti-seize and 'you can tell' ". Musclecargod - THX very clear and informative. elastic and plastic deformation, wow. |
