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Re: Bolt thread pitch
bigedpa #1352533 Tue Mar 31 2020 04:06 AM
Joined: May 2015
Posts: 2,498
K
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
No worries, Don! That "scared" comment was a bit tongue in cheek. wink


Kevin
First car '29 Ford Special Coupe
#2 - '29 Ford pickup restored from the ground up.
Newest Project - 51 Chevy 3100 work truck. Photos [flickr.com]
Busting rust since the mid-60's
Re: Bolt thread pitch
bigedpa #1352644 Tue Mar 31 2020 10:06 PM
Joined: Nov 2004
Posts: 1,756
J
Shop Shark
I too have read up extensively on the reasons for fine threads versus coarse. One simple reason that I didn't see mentioned was something that I read in an article awhile back. It stated that it's easier to cross-thread a course fastener than a fine thread. Maybe to some degree that in certain instances using a fine was an easy way to help prevent damaging components during assembly.

John


J Lucas





1941 Chevy 1/2-Ton
1942 Chevy 1.5-Ton SWB
1959 Chevy Apache 31 Fleetside
1959 Chevy Apache 32 Fleetside
1959 Chevy Viking 40

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Re: Bolt thread pitch
bigedpa #1352662 Wed Apr 01 2020 12:34 AM
Joined: May 2005
Posts: 7,263
B
General Purpose
John, you have it backwards.


I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


Re: Bolt thread pitch
bigedpa #1352683 Wed Apr 01 2020 01:49 AM
Joined: Nov 2004
Posts: 1,756
J
Shop Shark
Whether I do or not, I don't remember where I read it so I cannot present the article. But, that's the way I remember it. At our shop we repair threads (coarse and fine) several time a week.

I will say that I cringe whenever I see people use impact tools without starting the nut or bolt by hand first. Just a pet peeve of mine.

Johnb


J Lucas





1941 Chevy 1/2-Ton
1942 Chevy 1.5-Ton SWB
1959 Chevy Apache 31 Fleetside
1959 Chevy Apache 32 Fleetside
1959 Chevy Viking 40

My Flicker Photos!

Re: Bolt thread pitch
bigedpa #1352693 Wed Apr 01 2020 02:33 AM
Joined: May 2005
Posts: 7,263
B
General Purpose
That is a pet peeve of mine also. We ran into that with assembly line people. Mostly small hardware. They got trained to never start the screw with the driver. After a week, they were starting it with the driver. Took the driver away.

I've had to be a real butt head at Discount Tire. Explaining to the kid that one twist of his hand on a lug nut is a quarter turn. So if he does it four times it's not enough before hitting it with the impact. I finally gave up and don't watch anymore. Those are fine threads, easy to cross. With an impact, you don't know it.

When I'm working on truck bolts, I only use my impacts for removal. (except lug nuts). I remove and install small hardware (phillips) with my driver after starting threads by hand or manual screw driver.


I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


Re: Bolt thread pitch
bigedpa #1352694 Wed Apr 01 2020 02:37 AM
Joined: Aug 2019
Posts: 215
O
Shop Shark
You know you're in good company when everyone gets excited to talk about bolts!

Two things to add here:

-Course thread is recommended for tapped holes in cast iron, plastic too.

-The rule of thumb thread engagement is 1.5 (not 2.5 diameters), ie nuts.
That rule holds true for stainless screw into aluminum. 1.5D is plenty to ensure the head twists off before you strip anything.

Last edited by Ott3r; Wed Apr 01 2020 02:38 AM.

'59 Chevy Suburban, NAPCO
Re: Bolt thread pitch
bigedpa #1352700 Wed Apr 01 2020 03:29 AM
Joined: May 2005
Posts: 7,263
B
General Purpose
I noticed the 2.5 diameters also. Not sure where that came from. If it's about engagement of threads, 4 treads is as strong as the bolt.

Nuts are already designed to give the 4 threads to make them as strong as bolt. You don't have to worry about that.
If it's a tapped hole in steel, it's still 4 threads or more.
Aluminum: helicoils.

1.5D engagement on a 1/4-20 is 7.5 threads. Engineers and Designers don't use rules of thumb. They use math and testing.

Regarding the clamping force of UNC vs UNF. When properly torqued, which is very iffy, a UNF only gives 13% more force. This is not a factor in old truck design. The UNF was used for other reasons. Hinge plates don't squeeze at torque levels we use.

A hard joint is what we are all used to. A soft joint is when a gasket or spring or rubber is involved, as an example.


I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


Re: Bolt thread pitch
bigedpa #1352706 Wed Apr 01 2020 04:32 AM
Joined: Nov 2006
Posts: 238
J
J M Offline
Shop Shark
I was at a workshop a few years ago, and one of the speakers had a couple of hours to talk to us about nuts and bolts. I didn't think he would be able to fill up the first hour. He should have had all afternoon. He kept us glued to our seats, and I am sure that most of us in there still remember it today. many of these kind of workshops you go to you don't remember a month later. This was not one of them.
Jim

Re: Bolt thread pitch
bigedpa #1352711 Wed Apr 01 2020 04:52 AM
Joined: May 2005
Posts: 7,263
B
General Purpose
Like Ott said, we are all "nuts" together.


I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


Re: Bolt thread pitch
bigedpa #1352848 Thu Apr 02 2020 04:08 AM
Joined: Mar 2010
Posts: 9,309
5
Master Gabster
Here is what I have found in regards to stripping one thread over another.
When you add a little muscle to a course thread to overcome a little over-spray paint on it, it feels exactly like adding a little muscle to a fine thread which was started cross-threaded.
The coarse one ends up just fine, the fine one ends up really coarse. smile

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