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 Post subject: Torque Specs ?
PostPosted: Mon Sep 28, 2015 5:12 pm 
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The support rep where I bought my AI says that there are no torque specs for the bolts used on the AI.

I have a hard time believing that.

For starters, the production people have to have some standard besides "This tight".

Plus steel bolts into brass inserts just cry out for a spec on how hard they can be tightened without stripping.

I'm no engineer, but specifying torques for bolts sounds like Engineering 101 to me.


So: Does anybody know what the torque specs are ?

I would think there are at least two:

  • The bolts holding the caps on the Xbars
    .
  • Any other bolt that goes into a brass fitting.

??

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 Post subject: Re: Torque Specs ?
PostPosted: Mon Sep 28, 2015 6:41 pm 
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Interesting question Pete.
I wondered how mast step bolts come loose and wonder if your first guess is right.


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 Post subject: Re: Torque Specs ?
PostPosted: Mon Sep 28, 2015 7:54 pm 
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ChangeMan wrote:
Interesting question Pete.
I wondered how mast step bolts come loose and wonder if your first guess is right.
One of the things that got me going on this was the realization on that my rear xbar was protruding two more inches on one side than the other.....after six times total on the water.

Assembled that way ? ......bolts not tight enough?......... How tight is enough ? .....Who knows ?

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 Post subject: Re: Torque Specs ?
PostPosted: Mon Sep 28, 2015 8:27 pm 
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Of course, you can always put some sandpaper between the xbar and brackets, so the pressure needed to prevent the xbar slipping, as is used by Railblaza in its fittings designed to attach to the akas, is much lower..

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 Post subject: Re: Torque Specs ?
PostPosted: Mon Sep 28, 2015 9:13 pm 
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Yes there probably are torque specs on all the fasteners used on the Hobies, however Hobie would not establish those specs. Those types of specs are established by the hardware manufacturer or by common standards used by everyone (ie... SAE, DIN, etc). For example the manufacturer of the brass inserts would have a torque spec.
Hope this helps
FE


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 Post subject: Re: Torque Specs ?
PostPosted: Tue Sep 29, 2015 1:31 am 
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Pete, I recall reading here that a good guide is to take the supplied Allen key and tighten the bolts are hard as you can usng a single finger on the end of the long end of the Allen key

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 Post subject: Re: Torque Specs ?
PostPosted: Tue Sep 29, 2015 6:35 am 
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tonystott wrote:
Pete, I recall reading here that a good guide is to take the supplied Allen key and tighten the bolts are hard as you can usng a single finger on the end of the long end of the Allen key
Sounds reasonable, but with two of the xbar saddle bolts I wouldn't even be able to turn them using one finger..... dunno if it's Hobie's application of thread locking compound or what..... but the other two are totally free and easy-turning.

I'm warming up to the sandpaper idea - but would still like to know the specs at least for the inserts and unencumbered bolts.

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 Post subject: Re: Torque Specs ?
PostPosted: Tue Sep 29, 2015 10:37 am 
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There are no torque specifications used in Hobie production. Never has been. I suppose because we are not dealing with consistent materials like on an engine block bolting aluminum or steel parts together. Plastics and fiberglass compress differently from boat to boat. Snug and loc tite are all I know.

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 Post subject: Re: Torque Specs ?
PostPosted: Tue Sep 29, 2015 7:51 pm 
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OK so which Loctite Matt, or does it vary?


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 Post subject: Re: Torque Specs ?
PostPosted: Wed Sep 30, 2015 12:08 am 
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Blue loctite is the more benign. and IMHO has a higher initial grip but "breaks" more easily than red, which (again IMHO) has a higher final "break point"

Please note, I have absolutely zero qualifications on this subject, but am relying 100% on my own observations.

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 Post subject: Re: Torque Specs ?
PostPosted: Wed Sep 30, 2015 5:03 am 
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Or you can just read the bottle/tube, it tells you the application purposes. I read the tubes and selected locktite blue. The locktite actually serves two purposes, the first being to make the bolt a little less likely to work out on it's own, and the second it helps prevent corrosion on the threads themselves. Anyone who has tried to get old rusty bolts out of anything swears by the stuff (things like trailer lug nuts, U bolts on axles, leaf spring cross bolts, etc). In our case with boats we are typically joining dissimilar metals (aluminum/stainless, stainless/brass, cadmium plated steel (V-frame for mast bracing). All prime candidates for galvanic corrosion.
As far as torque recommendations on screws and bolts, thats all just common sense, if you tighten a bolt and it snaps in half, the next time you know better. Same with locktite, if you assemble something, and three weeks later it works loose, you know to add a little locktite and tighten it a little tighter, you also need to look at the joint, the bolt itself should never be what holds anything together, it's the contact area around the bolt that takes all the force ( bolts are not designed to withstand side force or flexing forces at all). This applies to all bolts, on all applications on everything in use today, not just boats.
The easiest way to get a feel for how tight to tighten things is to take a scrap piece of metal and thread in a bunch of different threads, then take your cordless drill put allen wrenches into the chuck, now drive a screw into the hole, if the screw snaps off, you know it's too much. All the drills have a torque dial, turn the torque dial down and try it again. When you get down to a torque that doesnt snap the bolt, take a sharpie and mark on the drill "6/32", then on the next size screw the screw in until it breaks, then keep turning the torque down until it no longer snaps the bolt, mark on the drill that setting "8-32". Keep going thru all the sizes and mark on the drill housing with your sharpie. When done take your phone and take a pic of the drill, if the drill ever breaks, you can copy the numbers over to the new drill, for example if your "6/32" mark is close to the 8 on the dial, you can safely mark the new drill on the same number (it's all standard torque stuff on most drills).
Now you have the torque specs you requested, these specs apply to everything on the planet (boats, cars, bikes, tv's, toys. swing sets, etc) as long as you follow the correct diameter to length ratio for threads for that particular material. For example steel might be 1.5 to 1, aluminum might be 2.5 to 1, plastic might be 4 to 1. With the first number being the length of thread and the second number being the diameter of the bolt. Every bolt made and every material out there has a different ratio, it's easiest to just memorize them all rather than having to look it up in the machine shop guide (which is a 3 1/2 inch thick book, that you should memorize also), if you don't memorize it, you will wear the book out every 6 months leafing thru the pages. You can forego all the testing if you just refer to the book it has all torque specs for all bolts and fasteners , all materials, all thread types all on nice little charts, the same exact charts are used on cars, boats, wind mills, space shuttles, airplanes, toys, electronics, etc, basically everything on and off the planet. The easiest way is to just memorize it all.
Or you can just ask an Engineer (torque specs are universal and apply to everything in all industries, all products in use today), most can calculate in their head the torque requirements of any material and application based on the tensile strength of the selected material and the desired FOS), if they can't, and they design bridges and sky scrapers, I would find out what bridges they designed and avoid those bridges (just sayin). Look at things like the Brooklyn bridge, which was built in 1870, it's still standing and doing fine, all those calculations were made with slide rules and logarithmic math (before calculators, and computers) so they must know what they are doing.
Hope this helps
FE


Last edited by fusioneng on Wed Sep 30, 2015 6:58 am, edited 1 time in total.

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 Post subject: Re: Torque Specs ?
PostPosted: Wed Sep 30, 2015 6:20 am 
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fusioneng wrote:
... if you tighten a bolt and it snaps in half, the next time you know better.
All true.... But it's not shearing of bolts that I am obsessing about - rather the stripping of threads in those brass inserts.

Seems to me like the problem with the AI is that experimental determination can leave one in a world of hurt..... once the threads are stripped in one of the brass inserts under an xbar cap it seems to me like Game Over.

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 Post subject: Re: Torque Specs ?
PostPosted: Wed Sep 30, 2015 6:35 am 
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mmiller wrote:
There are no torque specifications used in Hobie production. Never has been. I suppose because we are not dealing with consistent materials like on an engine block bolting aluminum or steel parts together. Plastics and fiberglass compress differently from boat to boat. Snug and loc tite are all I know.
But a steel bolt into a brass insert (as on the xbar caps) does not fit that model.

Considering both the tendency of xbars to migrate side-to-side (requiring corrective action in the form of making the bolts tighter) and the dire consequences of stripping one of those inserts I am even more surprised to hear that there are no specs for how hard the bolts should be tightened.

One more point for the sandpaper workaround....... I guess....

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 Post subject: Re: Torque Specs ?
PostPosted: Wed Sep 30, 2015 7:34 am 
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Pete you are incorrect, the maker of that brass insert has already calculated the number of threads and length of thread required to hold in all conditions, any industry, any product on or off the planet, you will likely find the same brass inserts on space stations, lunar rovers, in cars, toys, electronics, boats, etc basically everything in use today, and over the last 150 yrs or so (including the Brooklyn bridge).
Hobie (and everyone else) just buys and uses the stuff. If you go to Home depot you can select the class bolts that you need for your application, just select from the right drawer, here is a chart ( https://www.engineersedge.com/hex_bolt_ ... cation.htm), it's all really simple stuff and standardized globally. Every bolt, every fastener made has similar charts (including your brass inserts), just pick the one you need based on the required loads and class then design around it. Obviously if you put a class 8 bolt into a class 4 brass insert, the insert will fail, but nobody would ever do that.
Any engineer can tell you the correct torque requirement on any fastener of any type if they know the material specs and class requirements (most can tell you off the top of their head), just go to engineering school they teach you all that useless crap in the first semester.
FE


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 Post subject: Re: Torque Specs ?
PostPosted: Wed Sep 30, 2015 8:06 am 
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fusioneng wrote:
Pete you are incorrect, the maker of that brass insert has already calculated the number of threads and length of thread required to hold in all conditions, any industry, any product on or off the planet, you will likely find the same brass inserts on space stations, lunar rovers, in cars, toys, electronics, boats, etc basically everything in use today, and over the last 150 yrs or so (including the Brooklyn bridge).
Hobie (and everyone else) just buys and uses the stuff. If you go to Home depot you can select the class bolts that you need for your application, just select from the right drawer, here is a chart ( https://www.engineersedge.com/hex_bolt_ ... cation.htm), it's all really simple stuff and standardized globally. Every bolt, every fastener made has similar charts (including your brass inserts), just pick the one you need based on the required loads and class then design around it. Obviously if you put a class 8 bolt into a class 4 brass insert, the insert will fail, but nobody would ever do that.
Any engineer can tell you the correct torque requirement on any fastener of any type if they know the material specs and class requirements (most can tell you off the top of their head), just go to engineering school they teach you all that useless crap in the first semester.
FE

Great stuff.... and maybe it's even starting to soak in:

  • I determine the Class of the bolts used for the xbar caps. Probably a raised number at the bottom of the allen key hole.
    .
  • I determine the Class of the brass insert - probably a raised number on the face of the insert.... boat's not available or I'd just go look.
    .
  • I verify that the two numbers are the same or choose the lesser of the two if they are not.
    .
  • I determine which of Proof Load,, Yield Strength Min (psi), or Tensile Strength Min (psi) is the relevant number.
    .
  • I figure out how to convert that number into torque in Newton-Meters, Foot-Pounds, or Inch-Pounds
    .
  • I assume that the torque calculated above will not strip the threads in said brass insert.
    .
  • I assume further that the torque calculated above will not strip the insert out of the surrounding polyethelene.
    .
  • I decide on a CYA/Fudge factor to be subtracted from that supposedly-safe number.
    .
  • I set my torque wrench accordingly.


Sheesh!..... No wonder Hobie's assemblers are doing this on a wing and a prayer......-)


But, seriously, I am still having with the guys who assemble things not being given torque wrenches and instructed accordingly.....

I believe it, now that it's been said, but still find it troublesome.

It's too simple/obvious and the consequences of failure on the high side are too severe.

..... And then there is the nuisance value of failure on the low side - which I (and who knows how many others.....) seem to have experienced recently.


Edit 2015 09-30 12:54:

.... Not to mention mechanics at dealer locations across the country..... Even if company policy were that users don't mess with the product, I would think those guys would benefit by having a number.

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Last edited by PeteCress on Wed Sep 30, 2015 10:01 am, edited 1 time in total.

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