Help needed with a design 2

[Bounty3153]

To start, I am not an engineer. However my company has put me on a project that requires knowledge above mine. I have worked on many design projects but none where the physical characteristics of the parts have been so crucial to the success or failure of the design.

I will attempt to explain the project, but there is an attachment of what I have came up with so far.

It is a clamping style fixture that needs to be secured around a 1" rod while 10,000lbf will be applied to the ears in a vertical pull. The plates are 1" thick with 1" Socket head bolts to pull the 2 plates together.

Ideally, the plates will be bolted together with enough force from the 1" bolts to basically crimp around the rod and hold it secure while cables are hooked to shackles in each hole on the end. It will be used to tension cables that will be pulled at 10000lbf.

My questions are:
1. Will the 1"-13 UNC Bolts apply enough pressure to secure the clamp to the rod and allow no slipping when the force is applied.
2. If the amount of torque needed to actually "crimp" the plates can be reached with the 1" bolts, will the socket head type bolts be the best route? Or would regular hex head bolts be more sufficient in reaching the amount of torque needed?

Thanks ahead for any response at all...

 

[MikeHalloran]

Don't bother building what you've got yet.
To find out why, you definitely need to rent an engineer locally.
Relative to project failure, engineers are pretty cheap.



Mike Halloran
Pembroke Pines, FL, USA

 

[miningman]

Reminds me an incident on one of my job sites many years ago where someone needed to install 800 feet of sched 80 2 inch pipe in an almost vertical hole that had been drilled by a conventional diamond drill. These drills use hi strength light weight drill rods and have holding mechanisms designed for light loads. Someone made the decision to use the diamond drill to lower the 2 inch sched 80 pipe, 20 feet at a time with a high pressure welder sitting there running a bead as necessary. Every thing went fine untill the approx 500 feet of pipe in the hole overcame the hoding capacity of the drill and the 500 foot string airmailed itself the remaining 300 feet. Have you any idea how well a string of sched 80 pipe can resemble a pile of spaghetti when it hits the bottom??? Get an engineer!!!

 

[LittleInch]

There are so many things wrong with the situation you describe I don't know where to start. Your company has asked you to design something you say you have no experience or knowledge, apparently without it being checked by others or any guidance offered - looks wrong to me.

Design of clamps is a specialism and the thoughts of nearly 5 tons hanging off this thing look wrong to me. Getting 1" plate to mold exactly to a 1" bar will not be easy. Even if you welded the thing it just looks wrong.

The fact you've come on here knowing your limitations and looking for help is admirable. Now you need to go the next step and tell your superior in writing the exact same thing and that you cannot take design responsibility. Amazing what a written communication can do sometimes.

Good luck.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[LittleInch]

If you want some background into calculations and safety factors, search "clamp design" on this site and also look at asme VIII, appendix 24. Will give you some food for thought as to whether you know all the data and can do the calcs. Manufacturing tolerance is a key factor as well as your safety factor. 1.5 is minimum meaning your clamp would need to hold over 7 tons without moving.....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[dhengr]

Bounty3153:
It never ceases to amaze me, that once a company gets a CAD program and/or a FEA program too, they immediately assume that anyone can do any type of engineering problem without being an engineer or having any engineering experience. They seem to think that all you gotta do is CAD a couple nice pitchers, rotate a view or two, and you’ve got an engineered design. I’m all for my drafters helping me with the engineering and detailing, to the best of their experience and ability, as long as they have my guidance. You need an in-house engineer as a mentor and to help you with this design, and if your company can’t supply that or doesn’t have any engineers, they probably shouldn’t be doing this kind of work. As LittleInch suggests, don’t let your boss push you into doing engineering design which you don’t have the experience to do, just to save a few bucks on proper engineering. You could really hurt someone in the process.

It isn’t particularly clear if the 1" rod has a 10k tension, or if each cable has a 10k tension, for a total of 20k on the rod. You have to explain in more detail what you are actually trying to do. Are you trying to pre-stretch the cables to 10k, or are you pulling on the cables to put a 20k load on the 1" rod? And, then what do you do with it, and how is the load applied, and the various ends tied off? These might all influence how you design that gripper, but at the moment it is likely not an adequate or safe design.

 

[JohnRBaker]

It's just as true today as it was 35+ years ago when I sat down in front of a CAD 'workstation' for the first time. Management needs to understand that any sort of CAx system is simply an 'amplifier' and they must decide who do they wish to spend their money 'amplifying', their best people with the highest skills or someone holding an entry level position.

On second thought, I don't think it's as true today as it was back then, at least not in the sense of what you'd expect management to do since a typical 'seat' of CAD cost about $100,000 (hardware and software) each (and those were 1977 dollars) and so it was a much easier argument to make that the company should put their best people on the system. With today's prices and this idea that everyone comes to a job already 'trained', even that entry level guy you just hired, to use a computer since he has one at home that he plays video games on or he's been surfing the net buying stuff on Amazon.com or EBAY, that anyone can just sit down, run through a few 'tutorials', log onto an on-line help site like E-Tips, and before you know it, you're cranking out complete, fully engineered, designs ready to be fabricated and put into production.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[Cockroach]

You know what? I'm going to take this on and develop it. What is the required centre-to-centre distance for the thru holes (i.e. ears) and those of the bolts? Safe working load is 10 kips, but the design will be tested to 30 kips, FOS=3.

I hope those set screw looking fasteners in the front of the face are not thru to the rod! Rather, you need something more like a pawl on a Rope Socket to hold the rod. Infact, you need something exactly like a Rope Socket to hold the rod. Then with the greater the tension, the more it will grip.

Sounds good? How do I contact you outside this forum?

Regards,
Cockroach

 

[Bounty3153]

Hey guys,

Thanks for all the input. There hasn't been any more talk about this project since the day I posted this thread, but after reading some of these opinions I'm very relieved that there hasn't been. To those of you that are asking for more details, for what I assume is just to satisfy a personal curiosity that comes with all engineers I have known being "natural fixers", I will try to give you the information to help you better understand.

The rods are currently and permanently in the ground. At the end of the rod there is an eye (approximately 2-1/2" O.D.) capturing the cables that are to be tensioned. The cables are stretched from the rod in the ground, to what was referred to as a "tower". I have no specs or any more information on this "tower".

The total amount of force is 10,000lbf. That is what the cables will be tensioned to. The way that they are being tensioned now is by using some sort of mass produced cable clamp. It was described to me to be something like a U-bolt, but I'm not sure exactly what it is they are referencing. However, during the tensioning process of using these U-bolts, the force isn't being evenly distributed on the rod via the clamps and the rods are being distorted.

So, the clamp must be a 2-piece design in order to be positioned on the rod. The only limitations on the clamp itself is that it must clamp around a 1" dia. rod and the lifting holes must be spaced enough for the chain or cable to clear the eye at the end of the rod while pressure is applied. The hole size will be determined by the pin size of whichever lifting shackle has an inside width large enough to clear the plates. Right now I have it at 1 5/8".

 

[MintJulep]

Something based on a split Taper-loc or QD hub perhaps.

 

[MJCronin]

OK..... my two cents worth on this discussion.

Amen to MikeHalloran and LittleInch....... 3D CAD designing is not engineering....and we all know how much responsibility the boss will take if anything breaks or someone gets hurt...

1) Your design seems to need a shear to ensure that it doesn't slip along the rod. How about a nice double-welded coupling placed just below the device ?

2) Any chance to increase the rod diameter to 1.5 inches and use a threaded rod coupling ?

http://www.anvilintl.com/productsearch/productthumbnailview.aspx?plid=106&ptid=600

(check the load rating on these things.....I do not thing you will get your 10,000 lbs on threaded 1" inch mild steel rod

3) Does your boss have an MBA ?

 

[Compositepro]

It sounds as though you are searching for sucker rod clamps.

http://www.hfpumps.com/catalog/harbison-fischer-polished-rod-clamps

 

[Bounty3153]

I do believe that is exactly what I need, Compositero!! Thank you so much for the link. My purchasing manager is calling for a quote this morning. Thanks again to you all