Torque Wrench


22 replies to this topic
  • qadsan

Posted January 08, 2005 - 09:56 PM

#21

I guess i'm a torque wrench fanatic I torque everything .....I know I'm a sick puppy .

*** PART 1 of 2 ***

I’m glad someone here is as nutty as me about tools, but I’ve met a few people far nuttier than me. I have lots of torque wrenches ranging from Snap-On, Mac, Proto, Sturtevant Richmont, CDI, Sears, etc, including many torque screwdrivers, etc. I also had one of my calibration engineers test various torque wrenches and we graphed all the data for comparison and the results were very interesting, but this was ~15+ or so years ago. When it comes to torque wrenches, my favorites and most commonly used torque wrenches & torque screwdrivers are my Proto dial gauges & screwdrivers. I don't own any super high end digital mega-dollar torque tools that are good to 0.01 % and I'd like too, but the accuracy of Proto’s dial torque wrenches are plenty good for our applications and in fact they’re certified for use by NASA and other high end applications.

A good torque wrench will usually come with a graded torque sheet that shows exactly how accurate it is at various increments throughout its torque range. You’ll find these sheets come with wrenches like Proto, Snap-On, Armstrong, CDI, Sturtevant, Mac, etc, but not with the wrenches from places like Home Depot, Autozone, Harbor Freight, Sears, etc. Just because a torque wrench says its accuracy is within 3% doesn’t mean it will be that accurate through its entire torque spectrum. Most torque wrenches are only accurate to their specification in the meat of their torque range with the outer limits being less accurate, but their accuracy generally suffers much more at the lower end of the scale than anywhere else. This is one reason you need more than a single torque wrench if you plan to torque various sized fasteners. I can guarantee you that if you use a Sears, Harbor Freight, Huskey, etc, half inch clicker type torque wrench that has a range of 0 to 100 lb/ft to torque a smaller fastener to lets say 8 lb/ft that it will not be accurate and you’ll risk stretching the bolt (tightening it past the yield zone) or breaking the bolt as opposed to keeping it in the elastic zone.

FASTENERS
Bolts have a certain amount of elasticity to them and if you’re a science nut, then you’ll know that steel is more elastic than rubber. When a nut is tightened, it compresses against a surface and stretches the bolt. When the nut is loosened, the bolt will rebound like a spring to its original size if it’s kept within its elastic limit. Fastener can be cycled this way thousands of times or more or even millions of times with high quality bolts such as from ARP when properly used. It’s this spring tension that provides the clamping force which keeps things together, but if you exceed the elastic limit of the bolt, then you’re into the yield zone and the bolt will no longer rebound correctly and will stay permanently stretched, thus coming loose rather easily, especially if heat and vibration are present. You can generally tell you’re in the yield zone when the nut eventually becomes easier to turn while tightening it, which is just before something breaks. Generally, you want to tighten fasteners within 50% to 60% of their elastic limit, which is where nuts and bolts tend to stay together, but this number can be a moving target with the use of heat, lubrication, vibration, etc. This may all sound pretty basic to some folks and perhaps it’s too much info for others, but it would take a lot of time to get into the dirty details of fasteners because this topic can get deep very quickly. Truly understanding fasteners is a very complex business when you get right down to the nitty gritty, but fortunately we don’t or shouldn’t need to get to that level as a user. Here’s a quote I saved from ARP “Automotive Racing Products” who specializes in making high quality fasteners for various markets such as aerospace, automotive, racing, government, industrial, etc. “To thoroughly understand it all would require at least 4 specific engineering degrees and 20 years of hands on experience in each.” OK, I’ll be the first to admit I don’t understand it all and probably never will, but learning is a life experience for me and I enjoy it.

There are several different ways to properly tension a fastener. Measuring the amount that a bolt has stretched is the most accurate way, but it’s not very practical for most folks here. Another way is to turn the fastener a predetermined amount of degrees after it has been properly snugged down to a given point, but this is only valid if the fastener has been previously calibrated by measuring the amount of stretch which isn’t very practical for most people. Another way is to use fasteners with direct tension indicators (DTI fastener components) and we may see more of these in the future once costs come down. The most common way to tension fasteners besides using your calibrated wrist is to use a torque wrench based on the specs given in service manuals, but those values are only good with OEM components under specific conditions. If you replace an OEM bolt with another bolt, the torque specs can differ if the new bolt is made from a different material, or has a different surface finish (plating, polished, black oxide, etc), or is lubricated, heated, etc, so keep that in mind if you swap out a bolt here and there. The most common change you’ll see is lubrication being added to bolts with the use of anti-seize or more commonly engine oil getting on the threads. In those cases you’ll need to subtract ~20% of the specified torque value to be safe, but this number can vary considerably based on the type and amount of lubrication used.

Probably the most significant thing you can do on ‘new’ fastener applications to make sure they stay properly tensioned is to first torque it to spec, then loosen it a half turn, then torque it to spec again, then loosen it a half turn again and then torque it once more. The reason for cycling a new fastener a couple times is because its friction will be higher the first time it’s tightened, but it will lessen with each cycle until it finally evens out. There’s a pretty significant change in friction from the first to second cycle, but after that the difference is usually quite small and cycling it three times is good enough for what we’re doing. Keep this in mind if you replace your spokes and torque them with a torque wrench (i.e. www.fastco.com).

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  • qadsan

Posted January 08, 2005 - 09:56 PM

#22

[color=black]*** PART 2 of 2 ***[/color]
[color=black]
TORQUE WRENCHES
There are three common types of torque wrenches including the beam type, the clicker type and the dial types. The beam type torque wrenches are good for general purpose work, but accurate reading of the indicator is difficult at various angles unless you’re looking directly on the pointer. These are often the least accurate types of torque wrenches.

The micrometer or click type of torque wrench found more commonly at home and auto centers will vary in accuracy depending on the manufacturer & model. Some can be as accurate as +/- 3% or more, but you’d be surprised how far off some of them may be at certain points in their torque spectrum. One of the downsides to these types of wrenches is that the release point can sometimes be difficult to manage without over tightening a fastener. Another downside is that this type of torque wrench does not measure actual torque in real time or rolling torque. If you have a clicker torque wrench, make sure you store it at 0 lb/ft (no tension), otherwise storing it while tensioned will alter the accuracy, especially if stored at higher torque settings and you’ll need to have it recalibrated more often if you care about accuracy.

The dial type torque wrench is often the most accurate of these types and is my personal favorite. Some can be as accurate as +/- 1% or better, but this varies by brand / model and 2% accuracy is more common in the higher end dial wrenches. The downside with this type of wrench is being able to accurately read its dial in some positions unless you’re looking square at the dial. This type of wrench gives you accurate real time torque while tightening and it also allows you to read rolling torque (pinion bearings, etc). It also stays in calibration longer unless of course it’s dropped or used as a hammer. OK, I know you may be thinking that using a torque wrench as a hammer is stupid and nobody would ever do that, but I’ve seen it done many times from various places including from my local Firestone dealer, a Ford dealer, etc.
Here’s some links to various torque wrenches and torque screwdrivers from Proto to check out.

http://www.stanleypr...ltCatalog=PROTO
http://www.stanleypr...que Screwdriver
http://www.stanleypr...que Screwdriver

A great place to shop for new and used tools at a discount is eBay, but you can also get stuck with junk if you don’t pay attention. I’ve seen brand new Proto dial torque wrenches go for as little as $40 and seen brand new Proto torque screwdrivers go for even less sometimes. The Sturtevant torque screwdriver link that was posted earlier in this thread is something else I’ve seen sell used on eBay for as little as $1 (yes one single dollar!) and this same product is sold under various brand names. You’ll also find great deals on torque wrenches from CDI, Utica, Snap-On, Mac, Armstrong, etc. New deals are always coming along on eBay, so if there’s something you want but don’t see, then bide your time and it will probably come along sooner or later.

GOOD TOOLS
Good tools really can make a positive difference while servicing various kinds of equipment. Many of the Proto torque wrenches are high quality tools. If money is no object then you can get something very specialized that costs a bundle with incredible specifications of 0.05% accuracy or better. Proto tools are built with tight specs and put through more testing than many other tools and meet the specifications & certification of certain military applications, NASA, GM, and other industries unlike some of the other brand names. When you get right down to it, there are really only a few main players in the tool industry. I may have some of the following mixed up because there have been changes over the years, but I believe many Craftsman hand tools were formerly made by Stanley up until 1994 and many are now made by Danahar, who hires companies from Thailand and China to make some of their tools, although Craftsman uses various companies such as Ryobi for their cordless power tools. Many of the MatCo hand tools also come from Danahar. Mac tools on the other hand comes from National Hand Tools, which is owned by Stanley, and so is Husky, and Proto, but they’re made to different specifications and some are made at different plants under different direction. Kobalt tools used to be made by JH Williams, which is a completely separate division of Snap-On, but that doesn’t mean they were made to the same standards or quality as Snap-On. I believe Kobalt is now made by Danahar. S&K is another brand you may have heard of and those tools come from Facom. Many of these tool companies also source specialized tools from other supliers, so just because it has a brand name on it like Snap-On doesn’t mean it’s made by Snap-On.

In summary, I think JackAttack said it best "Quarter" "Inch" "Ratchet". I have all kinds of very accurate torque tools, but I don’t always use them. My favorite assembly/disassembly tools for general purpose work on bikes are the inexpensive MotionPro T handles in the 1/4 & 3/8 inch shank sizes that are designed to work with your own sockets. I consider these tools indispensable and I highly recommend them to anybody that frequently takes their bikes apart. The 1/4 T by nature makes it less likely that you’ll apply too much torque, unless you really twist it hard or incorrectly use it on the smallest of fasteners.

Here’s some links regarding Direct Tension Indicating fasteners, nuts & washers that may be of interest.
http://www.smartbolts.com/
http://www.appliedbolting.com/
http://www.fastorq.com/dti.htm

Here’s an excellent link to NASA’s Fastener Design Manual that provides a wealth of excellent info on this topic.
http://gltrs.grc.nas...990/RP-1228.pdf

If you want to get into the nitty gritty of fasteners, then check out the following link to ‘Bolt Science’ where you can learn gobs of tech info, take a training course pertaining to fasteners, purchase some very kool calculators and other kool programs pertaining to fasteners if this is a topic that really rocks your boat. You’ll also find tutorials, presentations and real world examples with pictures of failed fasteners along with failure analysis and respective solutions, etc.
http://www.boltscience.com/index.htm

And here are more excellent links that contain all kinds of excellent details on fasteners if you’re really into this kind of stuff.
http://www.mech.uwa....reads/home.html
http://www.tech.plym...es/desbolta.htm
http://euler9.tripod...base/index.html
http://www.croberts.com/bolt.htm
http://www.boltcouncil.org/guide1.htm
http://www.co-design...ol/bolhome.html
http://www.appliedbo...df/yielding.pdf
http://home.jtan.com...KIAT/kiat_1.htm
http://www.mitcalc.com/en/download.htm
http://www.arp-bolts.com/

If the amount info contained in my post including the info inside these links doesn’t quench your thirst for fasteners and proper tensioning, there are some very good engineering books on this topic which I can dig up if you’re interested. If you must hire a top notch consultant regarding metallurgy and structural mechanics in support of fastener system design and analysis, I have several experts (highly experienced PHD level people) I can highly recommend who have their own laboratories filled with state of the art equipment that can help solve any of your fastener or metallurgical problems, but their services are considerably more expensive than your local auto shop who typically gets anywhere from 70$ to $100 per hour to work on your car or bike. [/color]

  • HeadTrauma

Posted January 08, 2005 - 10:22 PM

#23

[color=black]The dial type torque wrench is often the most accurate of these types and is my personal favorite. Some can be as accurate as +/- 1% or better, but this varies by brand / model and 2% accuracy is more common in the higher end dial wrenches. [/color]


This is one of the more interesting points I saw. It seems that just about everyone thinks clickers are the hot setup. Its a little off topic, but I was thinking of using a 1/2" torque wrench on a small engine dyno. :cry:





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