Cheffy
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| posted on 22/4/05 at 11:12 PM |
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Application differences between fine and coarse thread
Could somebody please tell me why the different thread pitches? Is fine thread stronger or weaker than normal/coarse thread? Where on the car, and
why, would you use one instead of the other?
Thanks in advance for any help/advice,
Cheers chaps,
Martin.
Farts are like Rock'n'Roll. You love your own but you hate everybody else's. Lemmy, Motorhead.
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Rorty
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| posted on 23/4/05 at 06:06 AM |
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It's a very complex subject, all too frequently overlooked by the inexperienced. There are so many variables that it's not easy to give
straightforward answers to your questions. Two bolts the same diameter and length, one in tension, the other in shear, can be vastly different. Also,
the material of the female thread can determine whether coarse or fine threads are appropriate.
Best you have a read of some theory and specifications. The following may get you started:
Bolt Science.
Earnest.
IF.
Maryland Metrics.
ARP.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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907
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| posted on 23/4/05 at 07:11 AM |
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Hi.
One application of fine threads (IMHO) is when adjustment is needed.
I'm thinking in particular of suspension joints.
I have used rod ends on my rear bones that have a coarse thread.
I wish I'd have used fine threads as this would give me finer adjustment
of wheel alignment and camber.
At least a rod end can be screwed in or out half a turn at a time so they may be OK.
I can but hope.
Paul G
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flak monkey
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| posted on 23/4/05 at 07:51 AM |
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As mentioned finer threads are better when small adjustments are needed.
As for materials, bolts etc fitted in to soft materials (eg aluminium) are less likely to pull out or rip the threads if they are fine as there are
more threads engaged. But as Rorty says this gets quite complicated on which thread to chose for a cretain application.
I tend to use fine threads for the above anyway.
David 
Sera
http://www.motosera.com
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Rorty
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| posted on 23/4/05 at 08:39 AM |
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quote:
Originally posted by flak monkey
...bolts etc fitted in to soft materials (eg aluminium) are less likely to pull out or rip the threads if they are fine as there are more threads
engaged.
It's the other way around actually. Coarse threads for soft materials like aluminium; think of rocker studs in aluminium heads etc.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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flak monkey
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| posted on 23/4/05 at 09:11 AM |
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OK...I'll shoot the guy that told me that then.... 
Sera
http://www.motosera.com
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Fifer
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| posted on 23/4/05 at 11:18 AM |
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Aggree wit the above and would add the following.
If you think of the thread as working like a wedge, the course thread is a thick wedge and the finer ones would be a very thin wedge.
Drive a thin wedge into a gap and the force is huge, therfore, the fine threads apply much more force and generally can be torqued to higher
amounts.
the materials of the female thread is very important though as stated above.
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David Jenkins
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| posted on 23/4/05 at 03:23 PM |
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Also, the core of the fine-thread bolt is thicker than that of the coarse-thread one, so is stronger.
To say a bit in favour of the coarse thread, the thread itself is stronger, and also it is much more suitable where the thread is likely to get muddy
or dirty - it's less likely to jam up solid.
But, as said above, it's a complex subject.
David
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tks
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| posted on 23/4/05 at 04:49 PM |
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Loossening
Think also on the bolt loosing part....
To undo a fine thread nut you need to turn it much more revs then the other one...
as about of strengt you need the middle way, because a strong thread with a week inner body isn't usefull soow same for strong body with weak
thread..
then you have to compare the 2 bolts wo weight the same (more material more strenght)
also you need to think that a bolt with much more thread (finer) has a bigger contact surface with the other one
soow loosening is also overthere braked (more resistance)
TKS
The above comments are always meant to be from the above persons perspective.
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britishtrident
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| posted on 23/4/05 at 05:34 PM |
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Coarse threads apart from use in light alloys and cast iron coarse threads are excellent for bolts exposed to road muck and salt such as on exhausts.
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Cheffy
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| posted on 23/4/05 at 06:42 PM |
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Cheers guys, thanks for all the input. Much appreciated.
Martin.
Farts are like Rock'n'Roll. You love your own but you hate everybody else's. Lemmy, Motorhead.
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Rorty
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| posted on 24/4/05 at 07:59 AM |
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If you want to get seriously into bolts and bolted joints then this is THE bolt
bible.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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