Author Topic: Beginners guide to nuts, bolts and threading  (Read 70474 times)

Offline ohio oz

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Beginners guide to nuts, bolts and threading
« on: June 12, 2010, 06:01:17 PM »
Hi everyone, new listener to TSP, I took it to heart when Jack said to start talking about the things you are passionate about.  I am a machinist and maybe even an all around handyman, and I'm finding myself frustrated that many people I meet can't figure out a lot of seemingly basic things (nobody on here, of course). Here's my contribution to some of the DIY projects I see some of you doing.  While you can't eat nuts, bolts or drills, you might save a few trips to the hardware store, or the repairman, and that money saved can feed the family.

If you like this, let me know, I have some other subjects in mind.

Identifying nuts and bolts for those odd projects can be confusing for the beginner, so I wanted to do a brief tutorial on nuts and bolts basics.  I also wanted to show how a simple threaded hole is made and a repair that might give new life to something that is broken or worn out.  For many of you, these will be things you already know, but I’ve found it difficult to get good basic information on things like this without lots of jargon and digression  into specialized cases.
The following images will look at a grade 5 3 inch 3/8-16NC hex bolt.  What does all that mean?
The length of a bolt is measured from under the head to the end of the threaded shank; in this case, we have a 3 inch bolt.



The diameter of the bolt is measured across the largest part of the threads.  Bolts are generally made slightly smaller than their nominal diameter for ease of installation.  Here we have a 3/8 inch bolt, and as you can see, it measures .370”.  In theory this bolt would measure .375” there is a difference of .005, about the thickness of a hair.

 
The hex head of this bolt measures 9/16”.  This is the size wrench or socket you would need to turn this bolt. There are a huge variety of heads (square, socket, 12-point), so it is necessary to specify that this bolt has a hex head.



This is a bit hard to show due to the small size and some camera parallax, but this bolt has 16 threads per inch.  The NC in 3/8-16NC stands for National Course, which refers to the angle and shape of the threads.  We could also go to the hardware store and pick up a 3/8-24NF bolt, where the NF means National Fine.  There are other standardized thread angles and shapes for special cases but for 99% of common uses, you will see NC and NF threads. 



Some further inspection of the bolt head shows us three radial marks, and the manufacturers stamp.  Strangely, if a bolt or nut shows no markings it tells us the bolt is grade 2, three marks means the bolt is a grade 5, and five marks indicate that the bolt is grade 8.  The grade is basically a measure of the strength of the steel used to make the bolt. There are specific industry standards for each grade, and even standards above and beyond grade 8.  The fasteners you will pick up at the local hardware store will probably   be grades 2, 5 or 8.  The three marks indicate that that this particular example is a grade 5 bolt.



Now that we have identified our bolt as a grade 5 3 inch 3/8-16NC bolt, what can we do with it?  Well if we were boring, we could find the corresponding nut and screw them together, but we need to fix or create something. 
For this I will need:
A hammer
A center punch
A center drill
A 5/16” drill bit
A 3/8-16 tap
A tap handle
I also used my cordless drill to drill the holes.  If you happen to have a drill press, even better!

As an example, I’m going to make a hole to fit this particular bolt.  Since you can’t just buy the widget I happen to need with the correctly threaded hole in the correct place at the hardware store, I’m going to drill and tap it to fit my needs.  The first step is to center punch the location of the hole.



A sharp whack with a hammer and I have marked the center of my hole.  Why not just start drilling you ask?  Because I need this hole to be exactly in this location, if I try to drill the hole right away the drill can move around as it spins.  Once the drill gets started it is nearly impossible to correct its course.



The next step is to drill a small center hole.  Unless you are making a very small hole, your drill can still move away from the center punch mark.  In comes the center drill.  The center drill is very short, with a small drill point on the end, followed by a taper to guide the correct sized drill into place.  You can see the center drill to the left of the center hole.



Now that we have a center hole in location, we drill with the correct sized bit.  How do we determine the correct size?  We could start with the bolt diameter, the number of threads per inch and the angle of the threads and do some math, but the easiest way is to refer to a handy little chart put together by any of several tool companies. According to the chart we need a 5/16” drill.  I’ve highlighted the pertinent information.


 
The 5/16” drill fits snugly through the corresponding nut, so it stands to reason that this is the correct size.
 


Our drill makes quick work of the hole.  I should note, it is important to get each bit perpendicular to the surface you are drilling.
 


This is a 3/8-16 tap; imagine it as a really hard bolt with some areas cut away for the chips made by cutting the threads to fall through.  If you look closely, you will see that there is a taper on the end to gradually cut each thread.
 


A tap has a square shank and is loaded into a tap handle.



We tap (cut internal threads in) the hole by applying downward pressure while twisting the tap handle in a clockwise direction.  Tap handles are shaped the way they are so you can apply force on both sides at the same time.  If you only pull on one side of the tap handle it will try to bend and possibly break the tap.  Because taps are so hard, they are brittle and will break easily.  A broken tap is one of the most difficult things to remove from a threaded hole, so take your time and twist the handle-- don’t bend.



And we have the perfectly threaded hole.



Our bolt fits in with no problems.


 
Let’s suppose our widget has served us well for 5 or 10 years, but our bolt hole is getting worn out from putting in and removing our bolt many times or maybe the threads stripped out altogether.  What can we do now?  The easiest answer is to drill our hole out to a larger size and re-thread it.  Let’s take our 3/8-16 hole and expand it out to a 1/2-13.  The procedure is exactly the same, only the sizes change.
For this I will only need:
A 27/64” drill
A 1/2-13 tap
The same tap handle as before
First we look at our handy little chart again, it tells us for a 1/2-13 threaded hole, we need to drill a 27/64” hole.  As a decimal this comes out to approximately .422” so we know we will have a clean hole with none of the left over threads from our (.375” outside diameter) 3/8-16 hole to get in our way.
 


So we select a 27/64 drill, and re-drill our worn out hole.  To the left you can see the smaller drill we used to make the initial 3/8-16 tapped hole.
 


Remember when I said that the threads on a tap start at a smaller diameter and gradually get bigger?  Well sometimes you need to thread as far as possible down a hole that doesn’t pass all the way through a part.  In that case, you select a bottoming tap.  You start with a tap with more taper and then finish off with the bottoming tap to fully cut all the threads.  If you look closely you will see the difference, the tap on the left is a bottoming tap.  A bottoming tap is much harder to turn and to get started threading perpendicular to your work piece, so if possible use a tapered tap.



Back at our broken widget, we have drilled the hole with a 27/64” or .422 drill bit.  If you measure a drilled hole it is likely to be several thousandths of an inch larger than the drill.  We can see that this hole measures between .423” and .424”.  It’s nothing to worry about for our purposes, but if your drilled hole is much bigger, the drill bit may need resharpening.



Now we tap the hole with a 1/2-13 tap.  As you tap larger holes,  it is often necessary to go clockwise a fraction of a turn, then backwards.  This breaks the chips formed while cutting the threads.



And here we have our refreshed tapped hole.  Our old bolt is laying next to the new one to show the size difference.


Offline Mr. Bill

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Re: Beginners guide to nuts, bolts and threading
« Reply #1 on: June 12, 2010, 06:57:24 PM »
Wow!

Welcome to TSP Forum, ohio oz!  That was certainly the best first post I've seen in a long time!  Very useful info, very clearly presented.

Offline TwoBluesMama

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Re: Beginners guide to nuts, bolts and threading
« Reply #2 on: June 12, 2010, 07:09:54 PM »
+1 from me!  Great post - appreciate the time it took to put it together.  Thanks & welcome!

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Re: Beginners guide to nuts, bolts and threading
« Reply #3 on: June 12, 2010, 08:37:07 PM »
Great post!
I think this may be a candidate for the Save Our Skills pages.

Offline Roknrandy

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Re: Beginners guide to nuts, bolts and threading
« Reply #4 on: June 13, 2010, 04:31:49 AM »
Nicely done! Great info you posted

Offline ryerle23

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Re: Beginners guide to nuts, bolts and threading
« Reply #5 on: June 13, 2010, 09:10:26 AM »
Great write-up, thank you for your hard work.

Offline ncjeeper

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Re: Beginners guide to nuts, bolts and threading
« Reply #6 on: June 13, 2010, 01:58:28 PM »
I would also add to use anti-seize in the freshly tapped hole just before you install a bolt for good. Otherwise it will rust together and it will be a bear to remove.

Offline LvsChant

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Re: Beginners guide to nuts, bolts and threading
« Reply #7 on: June 13, 2010, 03:20:21 PM »
+1 from me, too, Ohio Oz. Stop by the intro thread if you get a chance! Glad to have you here.

Offline ohio oz

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Re: Beginners guide to nuts, bolts and threading
« Reply #8 on: June 13, 2010, 04:21:29 PM »
Thanks for all the kind words guys, I'm glad you liked it.  It took much longer to do the writing and editing than to do the little project and photography!  I hope someone will read this and be inspired to repair that old "whatever" in the back of the garage, just like grampa used to do.

Is there interest in a similar article on metric hardware and/or pipe fittings?

I would also add to use anti-seize in the freshly tapped hole just before you install a bolt for good. Otherwise it will rust together and it will be a bear to remove.

Good call!
Even if you don't use anti seize, it's important to use some kind of lubricant on threads, even a dip in engine oil or a squirt of WD-40 helps.  A bolted joint is used to compress two things together enough that they don't move in relation to one another.  In other words you are adding more force to assure the friction between the two parts is enough that the bolt(s) never try to bend or ideally don't even try to shear the bolt in two.  If you thread a bolt in a dry hole, most of the effort you put into torquing the bolt goes into overcoming the force of friction between the threads and under the head of the bolt.  It may seem nice and tight, but it may not apply enough force between the two parts to do it's job properly. 

That's why important assemblies specify one torque to be used with a specific lubricant, and another torque value with a different lubricant. A better lube allows the right force to be developed at a lower torque.

I work in an engine rebuilding shop, and just the other day we had a customer with a very expensive engine (a 540ci Merlin BBC for you gearheads, more $$$ than a few entire new cars!) with all the best in aftermarket parts.  A connecting rod bolt had broken, and after disassembling the engine it was clear that the original builder hadn't used any assembly lube on the bolt.  As the bolt was tightened, the force of friction caused the bolt's threads to constantly weld to and tear the base metal on a microscopic level.  All this welding and tearing takes a lot of force, so the builders torque wrench said everything was tight enough, though it wasn't compressing the parts like it needed to.  Less than 1300 miles later it's back in the shop being fixed...

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Re: Beginners guide to nuts, bolts and threading
« Reply #9 on: June 13, 2010, 05:17:31 PM »
Great, informative thread! Outstanding! +1

Offline phargolf

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Re: Beginners guide to nuts, bolts and threading
« Reply #10 on: June 13, 2010, 08:44:20 PM »
great post! welcome! ;)

Offline millwright

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Re: Beginners guide to nuts, bolts and threading
« Reply #11 on: June 17, 2010, 10:42:17 PM »
Very good post!
I feel guilty now. I assume that everybody knows skills like this, because I do it every day.
Basic machining, welding, electrical, fabrication, are things that should be shared on the forum.
For people that do it everyday, it's just a grind. With a little shared insight to someone who wants to learn, black-magic turns into a useful ability.

The hard part for me is documenting a job (changing wheel bearings, welding a whatever, wiring a widget, etc,) and putting it in a useful format that can be posted here. Any particular task that I could teach in 30 min. would take me hours to figure out how to make a useful video/pic lesson.

I think there may be a forum section to be started here, I just worry about the liability aspect.



Offline ohio oz

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Re: Beginners guide to nuts, bolts and threading
« Reply #12 on: June 18, 2010, 05:04:36 AM »
I know what you mean about assuming everyone knows xyz skills.  Unfortunately it's not like that anymore.  I just spoke with my twenty-something cousin who was quite proud she learned to change a flat tire.

Like Jack said on a recent show, just take pictures of something you were going to do anyway.  I've worked with hundreds of different machinists, and if you asked them all show you how to do the same thing, you'd be seeing new methods and learning new things each time. 

The taking pictures and writing part isn't all that hard.  Each time you pick up a new tool show what it is and explain what it does and after you have used it, snap a pic of the completed step. 

Offline joeinwv

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Re: Beginners guide to nuts, bolts and threading
« Reply #13 on: June 18, 2010, 08:01:19 AM »
If I could go back to HS, I would have skipped some college prep classes and taken machine shop, welding and auto body classes.

I'll take a machinist over an engineer 90% of the time.

Offline radtke

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Re: Beginners guide to nuts, bolts and threading
« Reply #14 on: June 27, 2010, 12:01:52 AM »
tery overlooked skill +1

Offline Morning Sunshine

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Re: Beginners guide to nuts, bolts and threading
« Reply #15 on: June 27, 2010, 07:31:32 AM »
very good - thank you for the detailed explanation.  just what I needed to learn this morning

Offline soupbone

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Re: Beginners guide to nuts, bolts and threading
« Reply #16 on: August 13, 2010, 09:32:58 AM »
TO ALL YOU GUYS WHO CAN HAND SHARPEN A DRILL OR CAN DO A SPARK TEST:

Check out the American Precision Museum in Windsor VT. Beautiful region, beautiful town and wonderful museum. I was there several years ago in early fall.......(sigh)

Reminds you that really working metal (not just programming a CNC) is an art. Some folks have the touch, and others don't.

Like underhammer rifles? Best collection of them them that I've ever seen.

Check out their website.

soupbone

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Re: Beginners guide to nuts, bolts and threading
« Reply #17 on: August 13, 2010, 11:04:25 AM »
Now is a good time to buy tap & die sets.  Young people don't know what they are for, so don't value them.  Old people who own them are dying off, making these sets available for purchase at garage and estate sales.

Get you one now for your preps.  I only use mine about once every two years, but when I needed it, I really needed it.

During a long Argentina-like economic meltdown you can't buy new products because either they aren't making them due to lack of demand, or you can't afford them.  You gotta be able to repair your stuff without replacement parts.

Offline mike77

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Re: Beginners guide to nuts, bolts and threading
« Reply #18 on: August 13, 2010, 12:12:51 PM »
Great post! A quick question: Do you use oil of any type when cutting the threads? That's how I was taught, but that was also middle school shop class.

Offline ohio oz

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Re: Beginners guide to nuts, bolts and threading
« Reply #19 on: August 13, 2010, 12:42:53 PM »
Sometimes you use oil, sometimes it is ok not to. When tapping deep holes in steel, the friction of the already cut threads rubbing on the tap can be overcome by a few drops of oil.  For aluminum, the chips formed while cutting can stick to the tap, a few drops of WD-40 or similar will prevent this.  In my example it was thin steel so I didn't bother.  Many things you "have to do" for high production or to please a shop teacher aren't necessary, they just make the tools last a little longer. 

Offline Zef_66

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Re: Beginners guide to nuts, bolts and threading
« Reply #20 on: August 13, 2010, 02:37:02 PM »
Great post! This is a skill that many these days don't have.

Two things that you may want to expand on in the future. How to tell the difference between metric and standard bolts and helicoils.

Offline ohio oz

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Re: Beginners guide to nuts, bolts and threading
« Reply #21 on: August 13, 2010, 04:24:31 PM »
Now is a good time to buy tap & die sets.  Young people don't know what they are for, so don't value them.  Old people who own them are dying off, making these sets available for purchase at garage and estate sales.

Get you one now for your preps.  I only use mine about once every two years, but when I needed it, I really needed it.

During a long Argentina-like economic meltdown you can't buy new products because either they aren't making them due to lack of demand, or you can't afford them.  You gotta be able to repair your stuff without replacement parts.
Good point, there are lots of tools to be had very cheaply at yard sales and so forth.  These days you can also get a passably good new tap and die set from any number of places for not too much money.  I use mine every day at work, and a second set maybe once a week at home. 

I consider tools the ultimate prep.  If you can't use tools to build, repair or salvage a solution to your problems, you are just a smart monkey ;D

Offline ohio oz

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Re: Beginners guide to nuts, bolts and threading
« Reply #22 on: August 13, 2010, 04:26:27 PM »
Great post! This is a skill that many these days don't have.

Two things that you may want to expand on in the future. How to tell the difference between metric and standard bolts and helicoils.

I will work on that shortly, I couldn't find a suitable helicoil today

Offline soupbone

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Re: Beginners guide to nuts, bolts and threading
« Reply #23 on: August 14, 2010, 10:01:07 AM »
THE MACHINIST'S CREED

Give me a rock, and I have a hammer.

Give me a hammer and a piece of metal, and I have a chisel.

Give me a hammer, a chisel and a piece of metal, and I have a file.

Give me a hammer, a chisel, a file and a piece of metal, and I have a drill.

Give me a hammer, a chisel, a file and a drill, and I'll build you any damned thing you want!

soupbone

Offline Amator

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Re: Beginners guide to nuts, bolts and threading
« Reply #24 on: August 23, 2010, 01:26:11 PM »
Great stuff.  I just started my first machining classes last week, and this thread has given me lots of great information.  I humbly look forward to more of your articles sir!

Offline DeltaEchoVictor

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Re: Beginners guide to nuts, bolts and threading
« Reply #25 on: August 23, 2010, 02:32:53 PM »
Pinned to the top.  ;)

Offline ncjeeper

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Re: Beginners guide to nuts, bolts and threading
« Reply #26 on: August 23, 2010, 11:05:21 PM »
THE MACHINIST'S CREED

Give me a rock, and I have a hammer.

Give me a hammer and a piece of metal, and I have a chisel.

Give me a hammer, a chisel and a piece of metal, and I have a file.

Give me a hammer, a chisel, a file and a piece of metal, and I have a drill.

Give me a hammer, a chisel, a file and a drill, and I'll build you any damned thing you want!

soupbone
And a cold "Mountain Dew" and I will work all day. :D

Offline ladieu

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Re: Beginners guide to nuts, bolts and threading
« Reply #27 on: October 01, 2010, 02:57:58 PM »
Excellent post! I will add this to the save our skills site next week!!

Offline ladieu

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Re: Beginners guide to nuts, bolts and threading
« Reply #28 on: October 01, 2010, 03:07:11 PM »
Also if y'all see threads like this please email me at nick at saveourskills dot com

or just PM me here.

Thanks guys!!

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Re: Beginners guide to nuts, bolts and threading
« Reply #29 on: December 06, 2010, 12:30:49 PM »
Some further inspection of the bolt head shows us three radial marks, and the manufacturers stamp.  Strangely, if a bolt or nut shows no markings it tells us the bolt is grade 2, three marks means the bolt is a grade 5, and five marks indicate that the bolt is grade 8.  The grade is basically a measure of the strength of the steel used to make the bolt. There are specific industry standards for each grade, and even standards above and beyond grade 8.  The fasteners you will pick up at the local hardware store will probably be grades 2, 5 or 8.  The three marks indicate that that this particular example is a grade 5 bolt.


I know this is an old thread but...
In the past I read a lot about a problem with low quality foreign made or "counterfeit" bolts on the market... meaning they were grade marked but they would vary in their strength and hardly ever were up to the grade they were marked.  Is that still an issue? I do know that most fasteners that I buy now are not finished nearly as well as they used to be in years past. (They look cheap.)