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Tool Talk Discussion Forum

Coarse or Fine threads

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Pandora 504

01-27-2008 16:44:40




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Whats stronger for holding power, coarse or fine threads in steel.Working on stump grinder wheel,bolts to hold two of the teeth cannot go all the way through the wheel(poor planning on my part). Bolts will be5/8 grade 8.Wheel is 1 1/4 thick,high carbon.




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Kevin Schmidt

01-29-2008 18:38:14




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 Re: Coarse or Fine threads in reply to Pandora 504, 01-27-2008 16:44:40  
I think most of you missed the obvious, lube the bolts properly, and torque them properly. That will do more to hold them than anything. That and maybe some removable locktight in your application



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Slowpoke

01-29-2008 00:35:52




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 Re: Coarse or Fine threads in reply to Pandora 504, 01-27-2008 16:44:40  
The wheel already has the correct threads. If you cut new threads it will weaken the original hole and the bolts will tear out. There's lots of pressure on the teeth when the machine is cutting to the side. Go to the dealer or a rental outfit and get the correct type and length bolts that fit in the recess of the tooth. This is not a place to re-engineer the mounting. If the teeth come off they will hit you or something else.

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dr sportster

01-28-2008 13:41:13




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 Re: Coarse or Fine threads in reply to Pandora 504, 01-27-2008 16:44:40  
Generally a fine pitch is used with a nut to squeeze parts together tightly,however in a casting a coarse thread is more desirable because it resists being pulled out more.If you really want pressure and ease of turning then an Acme or square thread:like on a jack.



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Pandora 504

01-28-2008 05:57:35




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 Re: Coarse or Fine threads in reply to Pandora 504, 01-27-2008 16:44:40  
Thanks to all for your advice,fine threads it will be..... ....



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Eric in IL

01-27-2008 20:35:07




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 Re: Coarse or Fine threads in reply to Pandora 504, 01-27-2008 16:44:40  
Fine threads are stronger. I remember learning this in trade school because it just didn"t seem right to me. I also just looked in my Machinery"s Handbook to see if my memory was correct. Sure enough, the tensile stress area for a 5/8-11 is .226 compared to a 5/8-18 with .256 . So if you are wanting the strongest thread go with the fine. Also remember you need 1 1/2 times the diameter for length of thread engagement. So for a 5/8 bolt you need 15/16 worth of thread length. It sounds like that will not be a problem if you have an 1 1/4 thick plate.

If you need some stumps to try it out on, come on over I"ve got a few.

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JimAg

01-27-2008 19:29:11




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 Re: Coarse or Fine threads in reply to Pandora 504, 01-27-2008 16:44:40  
Fine threads are stronger. For one reason, the coarse threads are cut deeper into the bolt which makes the bolt diameter smaller than the shallower cut fine threads.
Jim



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135 Fan

01-27-2008 16:49:27




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 Re: Coarse or Fine threads in reply to Pandora 504, 01-27-2008 16:44:40  
Fine thread is usually specified on high torque applications. The threads aren't as deep but there is more of them. I think the deeper cut threads on course thread bolts create more of a notch effect which could lead to breaking. Dave



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cactus farmer

01-27-2008 17:00:01




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 Re: Coarse or Fine threads in reply to 135 Fan, 01-27-2008 16:49:27  
Fine threads are more vibration resistant. strength is about the same.



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