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The Impossible Rod Coupling - Does it exist?
5

The Impossible Rod Coupling - Does it exist?

The Impossible Rod Coupling - Does it exist?

(OP)
Hello,

I am in search of 1/4" to 1/4" diameter Steel Rod Coupling with the following requirements:
1. Low profile (minimal expansion beyond 1/4" cross section of rod)
2. Quick connect/disconnect
3. Structurally sound and near equivalent strength to 1/4" steel rod itself
4. The catch all - practical to incorporate in mass produced product

Please send a hyperlink of a rod coupling that meets the criteria and I'll make custom rap about your username and grant an additional wish.

Thank you,

Edison


RE: The Impossible Rod Coupling - Does it exist?

Does it have to allow angular or lateral displacement of the two rods, or do you want it to be 'rigid' in some sense?
Are tools allowed, or just bare hands?
How much load does it need to carry; axial? radial? moment? torque?
Can the rods rotate relative to one another?
Any specific end prep of the rods? Threading? Grooving? Upsetting?
Are there time limits on assembly or disassembly?
How many will you be needing each year, and how much are you willing to pay for each?
Carbon steel, corrosion resistant steel, or anticorrosion coating?
Environment?
Expected service life?



Mike Halloran
Pembroke Pines, FL, USA

RE: The Impossible Rod Coupling - Does it exist?

"Any specific end prep of the rods? Threading? Grooving? Upsetting?"
ditto. I have something in mind.

RE: The Impossible Rod Coupling - Does it exist?

Sleeve with internal splines, shaft ends made with external splines.

I use the term "splines" loosely, as the profile may not need to be anything fancy. A square or hexagon may suffice.

RE: The Impossible Rod Coupling - Does it exist?

and that'd be as strong as the rod away from the joint ... ?

do you need the coupling to disassemble ? (ie could you weld the rods ?)

what sort of temper are you thinking of ? 125ksi (pretty common, 1/4 hard) 90ksi (annealed, normalised), full hard (220 ksi) ??

another day in paradise, or is paradise one day closer ?

RE: The Impossible Rod Coupling - Does it exist?

DistressedNerd,

Are you planning to attach this (somehow) to 1/4" shaft?

--
JHG

RE: The Impossible Rod Coupling - Does it exist?

oops should have read the problem statement better (point 2)
however "minimal expansion" might mean a diameter of 1/2" (or maybe 3/8")

another day in paradise, or is paradise one day closer ?

RE: The Impossible Rod Coupling - Does it exist?

(OP)
All,

With 7 replies no and solutions or even answers I am upping the ante - I'll throw a video of a simple Rube Goldberg Machine that spells your username for a solution

Clarification:
1. Low profile (minimal expansion beyond 1/4" cross section of rod) - Ideally less than or equal to 3/8" in diameter

Additional design constraint:
5. Rigid when coupled in all planes of motion

The majority of questions are related to design constraint #4 - anything goes as long as it satisfies constraints 1 - 5:
4. The catch all - practical to incorporate in mass produced product

MikeHalloran - thank you for your interest
Design constraints, details, and specifications halt creativity - open ended parameters help creativity. I need at least a few ideas, answers and hyperlinks before we dig into the details.

Thanks,

Edison

RE: The Impossible Rod Coupling - Does it exist?

Quote (DistrressedNerd)

Design constraints, details, and specifications halt creativity - open ended parameters help creativity

I call BS on that assertion. Mapping the solution space, especially in terms of constraints, forces focus on the possible solutions that might actually begin to solve the extant problem.

Dreaming about solutions that obviously don't fit may solve some other problem than the one you want to solve, but that's really a waste of time.

... and money. If you had to pay market rate for the advice you've already received for free, you'd be out several tens of thousands of dollars. Being coy about what you actually need does not drive the discussion in a useful direction.

Star for Greg.


Mike Halloran
Pembroke Pines, FL, USA

RE: The Impossible Rod Coupling - Does it exist?

Easy stuff. A female thread in one shaft and a male thread on the other. If it turns bidirectional and unscrewing is a concern, use the appropriate Loctite.

RE: The Impossible Rod Coupling - Does it exist?

Agree with Dicer re: threaded connection, but I would say that neither rod can have female threads as it would significantly reduce their CSA and thus reduce the strength of the joint.

But, a rolled in fine (to reduce radial size requirements) thread to the rods, and a double sided female threaded sleeve made of a harder material would do the job.

A more interesting (Read: cool but ineffective) solution would be a frictional fit between an outer sleeve and the two rods. Imagine a spring steel female tube, with a close sliding fit over the rods, with 3 slots cut in each end to 40% of its length (so basically, a double ended collet), with a fine taper so its diameter is larger in the middle.

A pair of second sleeves (one for each end of the collet) of matching taper could be pushed up it, or even have threads and flats so it can be driven home by a spanner, which would then clamp the collet down. You get as much frictional force as you want because you can increase the length infinitely. As the collet/sleeve is widest in the middle, it has all the cross sectional area it needs to have equal strength to the 1/4" bars (there is more CSA in a 3/8 OD 2/8 ID tube, than there is in a 2/8 rod), and you can make it out of a stronger steel anyway.

RE: The Impossible Rod Coupling - Does it exist?

Fishing Pole - I win!


Cheers,
Jon

RE: The Impossible Rod Coupling - Does it exist?

By your own admission, you're being intentionally vague. Therefore, we're all giving responses that are strongly colored by our own experiences. Anyway, I'm a simple engineer with grit under my fingernails, so see the attached for a simple solution.

RE: The Impossible Rod Coupling - Does it exist?

(OP)
Dicer & Nereth1:
Threaded connection with locktite violates 2. Quick connect/disconnect

Nereth1:
Double sided female threaded sleeve - I am thinking one end of the sleeve is permanently attached the other is not threaded, but has a hexagonal female opening for the hexagonal. See attached picture.
I can't get a visual on the pair of second sleeves / collet idea.

Jon286:
Distraction force separates fishing poles violates 5. Rigid when coupled in all planes of motion

Clarification on Design Parameter:
2. Hand operated Quick connect/disconnect

The attached picture is a proposal I made in CAD - however drilling a 1/16" hole in the rod compromises its strength and for the pin to hold in place hand operation may be difficult (may need a lot of friction on the pin and require a pin punch tool)



One step closer,

Edison

RE: The Impossible Rod Coupling - Does it exist?

You know this guy is selling all our solutions on "Borrow an Engineer", don't you?

I made $7,000 on e-bay last month selling free solutions. You can too!

RE: The Impossible Rod Coupling - Does it exist?

Re: Your interactions with Mike Halloran, You may be right that leaving things very open ended gives you a better brainstorming result, but unfortunately, you're not paying anyone here for their time to brainstorm. This website has some of the most experienced/talented engineers I've ever interacted with, but they don't have the time or inclination to throw ideas out for you for an hour straight in the hopes that one of them randomly suits the project you haven't fully disclosed to them. Ironically, if you were paying the people here for their time, you would probably give them full disclosure ASAP so you wouldn't have to pay for said hours of throwing random ideas out.

With your hex joint and pin, either the pin shears off or you get failure from the bearing stresses when it goes into tension.

With regards to the tapered idea, let me know my cut of whatever you're making and I'll draw it up. How do you know if it's suitable? You don't, and I don't, because I don't know your capital budget for setting up or production quantities, I don't know your per part cost expectations, I don't know how much axial space you have to play with, and I don't know your material or environmental requirements.

RE: The Impossible Rod Coupling - Does it exist?

The "phishing" pole idea by jon286 is the right path. With the radial stress distributed throughout the whole taper and perhaps a "thru" as an additional measure you have basically all the elements required in the post.

RE: The Impossible Rod Coupling - Does it exist?

Hi DistressedNerd.

Posted a day or 2 ago by OP, DistressedNerd.
"Design constraints, details, and specifications halt creativity - open ended parameters help creativity. I need at least a few ideas, answers and hyperlinks before we dig into the details.

Posted by DistressedNerd back in January in his own different thread in response to a few replies by others -
"can you help me find (some paper/fabric holding commercial product on line) so I am not taking shots in the dark making 100 prototypes to figure out design principles."

===============================

OP feels A 1/16 inch pin in double shear is " near equivalent strength to 1/4" steel rod itself ." in tension ?
I think a few design constraints and specifications would speed this thread along nicely.

RE: The Impossible Rod Coupling - Does it exist?

I am getting very suspicious .... Based on the conversation and responses above, are we dealing with an MBA here ?

MJCronin
Sr. Process Engineer

RE: The Impossible Rod Coupling - Does it exist?

(OP)
All,

The democracy has spoken - here are additional design details

Product: Collapsing Sand Auger
Environment: Marine
Material: T316 Stainless Steel
Action: Ascending & descending through 32" worth of sand via rotational motion of auge
r

wannabeSE - sewer pipe connection requires tool and violates #2
2. Hand operated Quick connect/disconnect

IRstuff +Great Post!
Pneumatic Quick Connect was my original idea, however I could not find one that is "rigid" they all seem to freely rotate or spin.

One step closer,

Edison

RE: The Impossible Rod Coupling - Does it exist?

Posted June 3: "Any specific end prep of the rods? Threading? Grooving? Upsetting?"
ditto. I have something in mind.

Per your last post, I'm sure my idea will work. I'm thinking of the sand retainers we used in pile driving back in the 70's - are you sure this is not a reinvention?

RE: The Impossible Rod Coupling - Does it exist?

(OP)
BUGGAR - Anything goes keeping in mind #4
4. The catch all - practical to incorporate in mass produced product

Lets here it

Thanks,

Edison

RE: The Impossible Rod Coupling - Does it exist?

So, rigidity is the the same a rotation, since rigidity usually refers to a bending stress situation.

So, what's the issue with the coupling rotating? If this is a real problem, then you can simple have defined circular detents for the balls, which would keep the rods from rotating relative to each other, but that presumes that there's sufficient rotational freedom to get the balls to align with the detents.

TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: The Impossible Rod Coupling - Does it exist?

(OP)
IRStuff
In order to screw the sand auger into the ground the coupling must satisfy 5. Rigid when coupled in all planes of motion To include radial planes.

Circular indentations for the balls makes sense - my idea was to fill the void of the air channel (they are all pneumatic couplings) with a hexagonal female/male connections to prevent rotation - it's got to be filled anyway for structural integrity. What's your counter argument?

Thanks,

Edison

RE: The Impossible Rod Coupling - Does it exist?

DistressedNerd, I don't think you can get all your requirements wrt strength satisfied, that is full strength in axial, bending and torsion, and in both directions.
You should start to release some of them: e.g. full strength in pushing (easy to achieve), but reduced strength (by how much?) in pulling. Or: same strength in torsion in both directions, but, when inverting the direction of torsion, the joint could disengage if pulled at the same time. Or you could ask for a rigid coupling in pushing when turning clockwise, and in pulling only when turning anti clockwise.
What else can you release?
This is the same argument as by others: you need to narrow down more your specifications, if you want a solution. And don't say you don't know, you must fully know the functional requirements of your device, otherwise 'what the hell are you looking for?'

prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads

RE: The Impossible Rod Coupling - Does it exist?

Driving a "sand auger" (whatever that is) w/ a 1/4" dia. rod? Well, OK.

All kinds of real drill strings are coupled with threads, one male, one female.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: The Impossible Rod Coupling - Does it exist?

Please see below a quick section view mockup of the coupling I had been trying to describe earlier. You can see in the middle a double ended collet, and on the left hand side is a sleeve with matching taper to drive up it to close it up. You have a second one of these sleeves on the other side. The rods to be joined go inside.

This can be made as long as you want in theory - in reality it is limited by machining tolerances, particularly as that taper becomes extremely fine.

Link

RE: The Impossible Rod Coupling - Does it exist?

i suspect that the design is impossible as first posited.

to make a joint as strong at the connecting elements,
(this design constraint kills any idea at the get go; none of the suggestions achieve this),
that is hand installable, mass producible,
that fits within a very tight envelop.

The best solution seems to be your original idea, 'cept i'd do it with three pins (matching the hex. shape suggested). Mind you a hex profile fitting within a 3/8" diameter with a 1/4" bore doesn't provide much thickness in the coulping.

I assume you can't thicken the rod locally, so that if you cut both sides to be mating semi-circles (or mating 1/2s) and pin them together.

unfortunately all these ideas fail to retain the pins in any acceptable manner.

another day in paradise, or is paradise one day closer ?

RE: The Impossible Rod Coupling - Does it exist?

Buy a rifle cleaning kit :)

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: The Impossible Rod Coupling - Does it exist?

doubt that meets the strength and stiffness requirements

another day in paradise, or is paradise one day closer ?

RE: The Impossible Rod Coupling - Does it exist?

I can't believe you guys are still playing his game.

RE: The Impossible Rod Coupling - Does it exist?

I like games on a slow day. Something similar to this might work.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies to make the best use of these Forums?

RE: The Impossible Rod Coupling - Does it exist?

is the coupling as strong as the typical rod section ?

in tension ? in bending ?

how big is the circlip ?

another day in paradise, or is paradise one day closer ?

RE: The Impossible Rod Coupling - Does it exist?

Seriously, the pin part is the easiest aspect of this use an R pin or similar - bit too small for a pit/pip pin.

Hard part may be making the socket in cost effective manner depending on volumes etc.

Any concern of stress corrosion cracking?


Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: The Impossible Rod Coupling - Does it exist?

MadMango, your drawing shows promise, but it has two flaws:
1. The typical E-ring will not meet the diameter requirement.
2. Because the E-ring has three teeth and three gaps, the assembly can be disassembled axially if the E-ring is aligned rotationally with either set of jaws. If each rod had two jaws instead of three, it would sort of work, but probably be a little wobbly.


Perhaps it could be improved by threading the OD of the rod ends instead of grooving them.
One rod threaded a little more than the length of the jaws, and equipped with an upset shoulder at the proximal end of the thread.
The other rod threaded for a little more than twice that distance, allowing withdrawal of:
A sleeve, threaded internally, knurled externally, length roughly equal to the jaw lengths.
Spin the sleeve away from the jaws to allow disengagement.
Spin the sleeve over the jaws and tighten it against the shoulder to secure the joint.

I might further enhance the joint, getting rid of the sharp corners, by giving the jaws roughly the same shape as the finger joint used in woodwork. ... and maybe reduce the number of jaws, perhaps as far as two jaws on one rod and a complementary tongue on the other, again with the finger joint profile. ... given that, the central pin and socket may not be required.


Mike Halloran
Pembroke Pines, FL, USA

RE: The Impossible Rod Coupling - Does it exist?

I wasn't trying to engineer the OP's solution, only offering a suggestion. A snap ring would be better than the e-clip shown, and sharp corners should be removed to reduce stresses. The 3-lug features could be made with rotary broaching or standard CNC.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies to make the best use of these Forums?

RE: The Impossible Rod Coupling - Does it exist?

Seems there may be a US/rest of the world naming discrepancy related to the infamous cotter pin confusion.

This is what I'm talking about.



http://www.mcmaster.com/#pins/=12skwej has a whole bunch of pins that may work.

One assumes you've spent a bunch of time googling similar items to see what worked for them? Obviously make sure not to intentionally violate any IP.

https://www.google.com/search?q=collapsible+auger&...



Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: The Impossible Rod Coupling - Does it exist?

I question the requirement of no tool being needed. It's really not inconvenient or risky if it's integrated into the overall product, like a drill chuck key on some portable or cordless drill motors.


Overall, I'm a big fan of rigid mechanical couplers like @MadMango modeled in the post a few spaces up. It's a semi-common strategy for such situations. When you /do/ want flex in the line, then I'd design something akin to your average automotive universal joint, so long as the angle of flexure isn't great. Without the flex though, you minimize clearance between mating lugs/fingers and come up with whatever manner of retention is practical. Using a 4-lug mate would be easier to make, but less rigid than the tri-lug coupler @MadMango suggests.

I believe that's generally the wisest approach, until someone else comes up with something better ;)

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