Enlarging Bores in Thick Hardened Washers - Page 3
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  1. #41
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    Quote Originally Posted by strokersix View Post
    You have this backward. Underhead friction is a good thing to reduce chance of loosening. Large underhead surfaces are also a good thing to better distribute the forces and reduce embedment. Sure, it takes more tightening torque but if you care about the joint, you will adjust your torque up a bit accordingly if needed. Do a sample joint with exact materials and measure the torque/stretch relationship if you really care.

    OK, there's friction at the interface of bolt head and washer, and yes, it can help to prevent loosening - depending on the entire friction system. But the other major component of the friction system is the friction between the threads (male and female), due to both greater surface area, hoop stress/wedging due to geometry, and physical deflection of the pyramidal elements leading to increased Hertzian stresses.

    These two zones of friction are where most of the force applied during tightening a conventional bolted joint are lost, and must be accounted for when using (for instance) a regular torque wrench to tighten a cylinder head bolt (twisting head, bearing at under-head to washer or cylinder head, threads in block).

    While the friction under the head is significant (up to 50% of the total friction), it is directly addressable by input of the wrench, while the thread friction is lagging due to the angular twist (torsion) of the bolt shank. Since it's the shank and thread segment stretching that actually imparts the clamping load (the whole reason for a bolt), it's (to my mind) not ideal to count on the under head friction to maintain bolt loading - I'd rather have low friction there, and be able to count on the imparted load acting on the threads only.

    So if you "wind up" the bolt shank, then have the under head loads diminish (relaxation of (say) an aluminum head), or have the head itself twist back due to vibration input while the threaded elements maintain their engagement then clamping loads are lost.

    In my ideal threaded fastener world, all joints would be clamped by studs with hexes broached into the tops, then a torque and angle controlled wrench system would be used to stabilize the thread stud while a defined angular twist would be applied to the nut. That should allow a "no torsion" stretching of the stud shank, and a more "pure" clamping load.

    Absent studs, perhaps a hollow shank bolt with a spline broached into the thread (from inside) with a drive that would apply force to the spline while following the actual rotation of the thread with twisting of the bolt head would give a similar result. Perhaps not realistic in most cases, but hey...

    Or with fewer words - I'd rather use a conventional headed bolt with a hard, smooth washer, and try to ensure as little friction at the head as possible, while accounting for proper torsion/tension applied to the thread itself.

  2. Likes gusmadison, Strostkovy liked this post
  3. #42
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    The vast majority of bolts are now thread rolled so the shank under the head is quite a bit undersize compared to the thread diameter. On some of the larger diameter threads you ain't not no way going to have minimum clearance. The washer is going to flop about like a prick in a top hat.

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    Seems like every point I could have thought was already debated. However, when I need a washer better than those standard zinc plated units I go with the Jergens Heavy Duty:
    Material: High Carbon Steel
    Finish: Black Oxide
    Heat Treat: Rc 40-45 (Through Hardened)
    Flat and parallel within .005 (.01mm)
    Available in FixturePro Design Software

    Available in thicker than standard configurations which do hold up better. I also use these on my mill vises and fixtures as well.

    I do have the occasion to make low volume stainless washers too which have a tight tolerance id for example 2-1/2" od and 1.126 ID in 11 ga stainless. Here, I make soft jaws and hold 2 at a time in a kurt vise using a carbide mill in a pre-punched underside hole. In this larger size-- 2 up in mill was faster than lathe.

  5. #44
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    What the OP is trying to do is what pretty much anyone (with brains) who has ever bolted anything together wants to do - use a washer that actually fits and doesn't look like ass.

    1/64" IS too tight and is begging for trouble. But the average washer is way too sloppy...nothing worse than bolting something up them looking down and seeing an eccentric relationship between the bolt and washer.

    Most flat washers are also way too large in OD. Looks bad, fits bad,

    Most washers - especially non-hardened washers - are also too thin as compared to their diameter. The outer portions of a too thin, too big washer are doing nothing good for you.

    Combine a too-thin washers, too big a hole, and too big in diameter and you get a lousy job.

    The washer needs to be chamfered so it doesn't interfere with the underside of the bolt head? Who woulda thought that?

  6. #45
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    Quote Originally Posted by camscan View Post
    The vast majority of bolts are now thread rolled so the shank under the head is quite a bit undersize compared to the thread diameter. On some of the larger diameter threads you ain't not no way going to have minimum clearance. The washer is going to flop about like a prick in a top hat.
    I keep hearing that yet every bolt I order or buy from anywhere is always cut. Are rolled threads only available in super high volumes or something?

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    Quote Originally Posted by Strostkovy View Post
    I keep hearing that yet every bolt I order or buy from anywhere is always cut. Are rolled threads only available in super high volumes or something?
    Could you be identifying a rolled thread as cut? Because it's true that the vast majority of male threaded fasteners are rolled rather than cut, due to faster operation, less material used and waste, and typically, a stronger, more fatigue resistant product produced.

    If you're using actual cut fasteners I'd like to know what the application is and where you're sourcing them from. From Aerospace to hardware store, thems is rolled, my man...

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    Quote Originally Posted by Milland View Post
    Could you be identifying a rolled thread as cut? Because it's true that the vast majority of male threaded fasteners are rolled rather than cut, due to faster operation, less material used and waste, and typically, a stronger, more fatigue resistant product produced.

    If you're using actual cut fasteners I'd like to know what the application is and where you're sourcing them from. From Aerospace to hardware store, thems is rolled, my man...
    I'm looking at the unthreaded portion of the fastener. It matches the OD of the threads on all of the bolts I've seen from Fastenal and Tractor Supply, along with various online sources.

    That's not to say they couldn't make the blanks with a larger OD on the unthreaded part prior to threading.

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    Quote Originally Posted by Strostkovy View Post
    I'm looking at the unthreaded portion of the fastener. It matches the OD of the threads on all of the bolts I've seen from Fastenal and Tractor Supply, along with various online sources.

    That's not to say they couldn't make the blanks with a larger OD on the unthreaded part prior to threading.
    Lots of bolts start with a "stepped" diameter, where the section to be threaded is purposely made undersize relative to the nominal size, while the remainder of the shank is close to nominal diameter. Then the threads are rolled in the length that's smaller.

    Ask (if you can find an actual competent sales person) at Fastenal if their bolts have rolled or cut threads. Or observe if you can see the remnants of the end of the cut thread chips, there should be four or so "break zones" at the base of the thread-to-shank that would indicate the end points of cutting. But I'd expect they're not there, and you'll see a smooth transition from thread to shank.

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    Default hardened washers

    Quote Originally Posted by sae8425 View Post
    I want to upgrade my heavy equipment bolting methodology by incorporating ‘Extra Thick’ Through Hardened washers.

    I will predominately use these washers in bore sizes from 5/16” to 1-1/2” (8mm to 38mm).

    These washers are from .125” to .250” (3mm to 6mm) thick.

    As manufactured, these washers provide bolt clearances of 1/32” to 1/8”.

    However, I prefer all critical washers to have no more than 1/64” bolt clearance.

    So, I would need to enlarge the existing bores to provide tighter bolt clearances (i.e. a 1” washer with a standard 1-1/16” bore would be enlarged to a 1-9/64” bore to provide a 1/64” bolt clearance with a 1-1/8” bolt).

    What methods/machines/tooling would other forum members employ if faced with the same modification requirement?

    Would it be possible to ‘stack’ say 5 or 10 of these washers so multiple bores could be enlarged at the same time?

    Presumed appropriate machinery at my disposal currently includes a drill press, mill, radial arm drill, and a lathe.

    P.S. No washer supplier that I have contacted will provide non-standard bores unless I order at least 10,000 washers per size.

    Regards,

    SAE
    My first thought, do the washers really need to be harden? Second though is a commercial hardened washer is not so hard that it can be machined to size in the lathe.

    Roger

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    Quote Originally Posted by Milland View Post
    Lots of bolts start with a "stepped" diameter, where the section to be threaded is purposely made undersize relative to the nominal size, while the remainder of the shank is close to nominal diameter. Then the threads are rolled in the length that's smaller.

    Ask (if you can find an actual competent sales person) at Fastenal if their bolts have rolled or cut threads. Or observe if you can see the remnants of the end of the cut thread chips, there should be four or so "break zones" at the base of the thread-to-shank that would indicate the end points of cutting. But I'd expect they're not there, and you'll see a smooth transition from thread to shank.
    Looking at the way the threads end at the bolt does suggest that the blank was formed with stepped radii. I was under the wrong impression that all rolled bolts have a reduced diameter between the head and threads.

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    Once again, many thanks to all the forum members who have replied to my post. The machining methods suggested have been most appreciated.

    And again I must apologize for not providing enough initial information detail–

    The ‘Extra Thick’ hardened washers I use are also MUCH larger in diameter than a standard flat washer: they’re not quite of ‘Fender Washer’ proportions, but they have a MUCH larger OD than a standard flat washer does. They are also two to three times as thick.

    In no particular order, my responses to posts are:

    No, my use of hardened washers is not necessary in all cases, but they are SO much more uniform in dimensions than the crap that passes for normal flat washers available locally (and at short notice), that this fact alone justifies their exclusive use in my opinion.

    LONG ago I worked in industries where measuring thread stretch was commonly done (and not just on engine crank & rod bolts), and I still have the jigs/tools I needed to do this, but this level of precision is not necessary for what I build/work on today.

    1/64” (i.e. .015625”) is not too tight of washer bore to bolt shank clearance according to a plethora of aviation design agencies and manufacturers (especially going back to pre-WWII). In fact, 1/64” is classified as ‘close tolerance’ by many authorities/entities.

    EVERY fastener (including BOTH sides of the washers, the complete bolt head and shank, and the underside/outside of the nuts) that I install is lubricated with marine grade ‘waterproof’ grease, or copper based anti-seize. I also use Loctite on most threads.

    I’ve NEVER experienced ANY issues pertaining to the ‘close tolerance’ washer to bolt shank clearance that I prefer (nor have any of my clients), but I accept that a less anally retentive approach to componentry than I have could lead to problems with fasteners.

    Yes, I could replace broken hardware with OEM items, but if the owners are breaking components/fasteners by exceeding the OEM operating parameters, replacing broken OEM items with new OEM items is not a viable approach to resolving the root problems.

    I have a rather niche market for my services: I re-design failed assemblies (which generally have been repaired numerous times previously, but still keep failing) to SUCCESSFULLY cope with loading stresses that were never contemplated by the OEM.

    My success rate is 100% because I only undertake projects where I have TOTAL control of the process from design to assembly. I tell every client that my solutions won’t break; and if they do I will fix any damage for free. So far I’ve never had to honor this offer.

    An example of my work: a current project involves replacing 1/2” bolts with 5/8” bolts (.620” actual), which will be secured with ‘Heavy Hex’ nuts, and also increasing the joint flange thickness from 1” to 2”. A USS dimensioned 5/8” hardened washer bore diameter is .690” (actual). This diametrical disparity results in a .035” radial clearance: this gap is altogether unacceptable to me! So I will be using a USS 9/16” hardened washer with a .625” actual bore (and a 1.360” OD with a .190” thickness), which I will enlarge to 41/64” (i.e. .641”), which gives me a bit over 1/64” clearance. Lots of work? Yes. Costly? Very much so. Overkill? Not one bit!

    SAE dimensioned washer bores would not provide the 1/64” ‘close tolerance’ bolt shank to washer bore that I insist upon using.

    Back in the mid-1960’s PennDOT was studying bolt shank to hole clearances, which for 1” structural bolts was then mandated at 1/16”, in an endeavor to get the clearances relaxed for ECONOMIC reasons. In their testing they used washers that had holes from

    1-1/16” to 1-5/16”. PennDOT determined that with the larger clearances half of the bolts tightened failed to achieve their minimum tension, showed a 17% decrease in the slip coefficient, and resulted in a loss in tension of about 8% of the initial preload. PennDOT also found that the scatter in bolt tension without washers was nearly twice as large as the scatter in bolt tension with washers.

    Perhaps my approach to washer selection is unconventional, but I do believe that it contributes greatly to my re-design successes.

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    bolt clearance has no effect on washer clearance, especially in shear. after a trip to bolt store today our engineer rehashed a lot said already about cone pressure on washer, the oversized washer hole is to remove stress from the bolt hole. The squish washers are closer tolerance to bolt size, they place load closer to midway of washer ring.
    Hardware | ASTM A325

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    If this is a critical structure, it is also important inspect the contact face of the bolt head to insure that it square to the axis of the bolt.

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    So with all this talk about friction being a large part of the equation, what happens when I use anti-seize compound on my bolts?

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    Quote Originally Posted by EnderDRM View Post
    So with all this talk about friction being a large part of the equation, what happens when I use anti-seize compound on my bolts?
    If you use the dry torque value it will eventually break from being installed over proof if you lubricate it. You can’t lubricate threads that are not intended to be lubricated and use the same torque value.

    A goal of a lot of the anaerobic coatings (Geomet and the like) is to keep the k factor the same if it’s dry or lubricated. They don’t get it perfect but it’s pretty close.

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    Quote Originally Posted by EnderDRM View Post
    So with all this talk about friction being a large part of the equation, what happens when I use anti-seize compound on my bolts?
    It's a question of what the application is, and whether the manufacturer called out using anti-seize when specing how the bolts were to be tightened.

    In an ideal world, bolts are frictionless and all torque input is purely to achieve the proper stretch, then there's no relaxation in the system and clamp load is maintained for operational life.

    Since that can't exist, a manufacturer has to test their hardware under some set of conditions, then try to get the customer or repairer to match them during reassembly. So if you're supposed to use a fresh bolt in a clean tapped hole, do so to the stated torque. If you're supposed to add anti-seize, do so and use that torque.

    If you start changing things, ideally you've done your own testing to come up with the right stretch value for your application.


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