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PostPosted: Sat Apr 16, 2011 8:19 pm 
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Yay For Hay!
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Location: Wodonga - Vic/NSW border
mickmini wrote:
simon k wrote:
yes, talk to an engineer, but it's not the bolt heads that do the holding, it's the bolt shanks acting as dowels, and the friction of the two mating faces


Sorry Simon, this is the engineer in me talking, based on some very good texts that I consult when I am designing stuff for the race cars.

NO, NO and NO. NEVER use the bolts as the locating device. That is what dowels are for. They are designed to very tight tolerances for the holes to prevent fretting, misalignment and have no threads to act as stress raisers. They transmit the load in single shear very well, unlike bolts.

ONLY use the bolts for clamping. End of story.


cheers
michael


oh! ok!! :D

Just thinking about with my wife's subaru, I don't remember any dowels in it's flywheel


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PostPosted: Sat Apr 16, 2011 9:08 pm 
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1275cc
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Location: Sydney - strangely, I am glad of the sight of hills!!
Don't mistake designing to a cost with engineering it properly :roll:

Using dowels on a one off job like this one will cost the same as using bolts. This is not the case in a production line.

A mate of mine who is a software geek always used to question why we would change the cast iron manifold for some nice tubular extractors. His argument was always " but the factory used the cast iron one, so it must be good ". I am sure that your Mini does not still have it's cast iron manifold designed to the cost price that the BMC accountants set in 1957.

cheers
michael

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PostPosted: Sat Apr 16, 2011 10:00 pm 
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Location: Wodonga - Vic/NSW border
mickmini wrote:
Don't mistake designing to a cost with engineering it properly :roll:

Using dowels on a one off job like this one will cost the same as using bolts. This is not the case in a production line.


very true - I'm with you ;)

If, in this case, there is no room to add dowels to the flange on the crank, or adding dowels would remove enough material to weaken the flange, what would be the sensible approach?


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PostPosted: Sat Apr 16, 2011 11:08 pm 
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1275cc
1275cc
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Joined: Mon Apr 26, 2004 6:31 pm
Posts: 4663
Location: Sydney - strangely, I am glad of the sight of hills!!
I have seen a kind of dowel sleeve used where the location is done by a sleeve and the bolt passes through to clamp. I still don't like it though.

Best idea IMHO is to dowel four locations and clamp four locations with bolts. Four dowels will easily transmit the drive load and four bolts will easily provide sufficient clamping. Just because there are eight holes does not mean that they should all be filled in with the same thing.

If you have a look at a racing wheel and hub arrangement, usually you will see dowels and bolts/studs+nuts. In this arrangement you transmit the drive with the dowels and clamp with the studs+nuts. Ever wonder how the drive can be transmitted to the wheels on an F1 car that only has one big nut? It sure as hell is not by friction!

cheers
michael

_________________
the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates ;-)


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