This post is for those who didn't take 'Shop' in High School (or anywhere else for that matter).
It started just to warn folks about buying that 'super good deal' at the hardware store but the more I thought about it, the larger it became so if you don't understand how to make threads, or you are just hard up for something to read then read on...
Of course most folks know what a thread looks like and what it does so I won't get into that too much. There are a few things that tend to confuse some people so I will hit on some of them.
Threads are basically an inclined plane or ramp wound around a centerline.
Over the years, they became standardized and there are a lot of standards, many of them standards we gunbuilders aren't very interested in (like Light Bulb Threads, Whitney Threads, Acme Threads etc.).
For us gunbuilders, there are two standards we are interested in: The UN and the Metric Threads.
No, UN isn't that bunch of government weenies from all over the world, it stands for Unified National. Metric threads are similar to UN threads in their shape but of course they are made to the Metric System. Beyond mentioning them here and a little later, I won't be getting into them very much.
The UN threads are triangular in shape with a 60 degree included angle so both faces will be at 30 degrees from the axis of the thread diameter. This, it has been found gives a good strength for providing axial thrust without introducing excessive radial forces into the nut or other external part.
In the more common UN threads (in the U.S.A.), there are two thread series for each size. (Yes Fred, there are more but we don't really need to get into the other ones).
The two that interest us are the UNC and the UNF.
These stand for Unified National Course and Unified National Fine.
The UNC threads include: #6-32, #8-32, #10-24, #12-24, 1/4-20, 5/16-18, 3/8-16, 7/16-14, 1/2-13, 9/16-12, 5/8-11, 3/4-10, 7/8-9 and 1-8.
The UNF threads include: #6-40, #8-36, #10-32, #12-28, 1/4-28, 5/16-24, 3/8-24, 7/16-20, 1/2-20, 9/16-18, 5/8-18, 3/4-16, 7/8-14 and 1-12.
So, what do all of these numbers mean?
The first number or fraction represents the diameter. The origin of the number sizes goes beyond the scope of this post so just trust me, it represents a standard diameter.
A external #6 is .138 dia, a #8 is .164 diameter, a #10 is .190 diameter and a #12 is .216 diameter.
The fractions are pretty obvious.
These sizes all refer to the maximum outside diameter of a male thread. A female thread must be slightly larger than the male thread to provide clearance, so the tool that makes them will be larger than the thread size would at first indicate.
The second number in a thread size is the number of threads per inch so a 32 will have 32 threads per inch. The distance between these threads would be 1/32 of an inch.
If you are buying a quality tap or die you will see a few more letters in the size, for instance you might see 1/4-20UNC-2A or #10-32UNF-3B.
We know what the UNC and the UNF are now but the last number and letter indicate the thread "class" and define whether it is an external thread (A) or an internal thread (B).
The number indicates how precise the threads tolerance and fit is. The higher the number, the more precise it is. General use threads will be class 2. The threads used on aircraft for example are usually class 3.
The threads used on most muzzleloading guns are class 2 because although some of them are going to see some high stresses for the most part the size is large enough to easily do the job that's needed without compromising safety.
I almost forgot... a Metric Thread size is also given as a diameter and thread pitch but the second number (the pitch) is the distance between the threads.
For instance, a M6-1 defines a thread with a 6mm diameter (.236) and the threads are spaced 1mm (.039) apart.
If we used a similar system, a 1/4-20UNC thread would be called a .250-.050 UNC and a #8-36UNF would be a .164-.028 UNF. :grin:
OK, so now we know about threads but how are they made?
There are of course many ways to make a thread, but for us gunbuilders the old fashioned tap and die are the most common tool used.
Taps...Something they play at 'lights out'. Also, something that machines threads into a machined hole.
Dies...Something we don't want to do. Also, something that machines threads on the outside of round material.
Tap Drill...Not the licking of the lips before blowing 'Taps' on the horn nor is it the polishing of the bugle for inspection, but it is a drill sized to produce the correct minor diameter for the threads in a part.
It is very important to use exactly the size the charts specify to use for making the hole.
If it is too small, the undersize hole will most likely break the tap. If it is too large, the strength of the threaded joint will be weak and may fail or wear out prematurely.
When you are making threads a tremendous amount of heat is being created right where the tool is cutting. A lubrication made for threading is needed for anything except perhaps wood.
If you are working with steel parts, use a good sulphated oil that is made for cutting threads.
The sulfur prevents the steel chips from welding themselves to the tap or die to prevent breakage or galling. The mineral oil provides good lubrication. The stuff is cheap and it works so buy some.
When you are threading, you should stop about every 3/4 to 1 1/2 revolutions, reverse the direction of the tool at lease 1/2 turn, add a drop or two of thread cutting oil and then proceed to thread a little farther.
Why the "about" and so much tolerance in the number of revolutions? Because each size and each material will cut differently. I don't have a fixed rule to use, but if you are threading a part and the tap or die seems to suddenly become much harder to advance, that is the time! Do NOT try to go another 1/8 turn without backing up.
This allows the tool to break off the chips that are forming on each thread and it also allows the thread cutting oil to get right down to the cutting edges where it is needed.
NOTE: FAILURE TO BACK OFF THE TOOL WILL RESULT IN A BROKEN TAP OR A STUCK DIE.
Now, I get to say what I intended to say when I started this post.
About 15 years ago my wife saw a 40 PIECE TAP AND DIE SET for some unbelievable price so she bought it for me. It was made in China and the taps were coated with a black finish.
I have only tried to use this wonderous set 4 or 5 times sense getting it and the only time it seemed to work was when I was threading a hole in a piece of Maple.
All in all, this whole set is a real piece of fecal matter.
When you buy taps or dies buy the very best that you can find.
Also buy a good tap holder and a good die holder.
At least one brand of die holder has a hexagon internal shape to match their dies and it works very well.
You will regret buying anything but the very best.
Have Fun, You hear??
zonie
It started just to warn folks about buying that 'super good deal' at the hardware store but the more I thought about it, the larger it became so if you don't understand how to make threads, or you are just hard up for something to read then read on...
Of course most folks know what a thread looks like and what it does so I won't get into that too much. There are a few things that tend to confuse some people so I will hit on some of them.
Threads are basically an inclined plane or ramp wound around a centerline.
Over the years, they became standardized and there are a lot of standards, many of them standards we gunbuilders aren't very interested in (like Light Bulb Threads, Whitney Threads, Acme Threads etc.).
For us gunbuilders, there are two standards we are interested in: The UN and the Metric Threads.
No, UN isn't that bunch of government weenies from all over the world, it stands for Unified National. Metric threads are similar to UN threads in their shape but of course they are made to the Metric System. Beyond mentioning them here and a little later, I won't be getting into them very much.
The UN threads are triangular in shape with a 60 degree included angle so both faces will be at 30 degrees from the axis of the thread diameter. This, it has been found gives a good strength for providing axial thrust without introducing excessive radial forces into the nut or other external part.
In the more common UN threads (in the U.S.A.), there are two thread series for each size. (Yes Fred, there are more but we don't really need to get into the other ones).
The two that interest us are the UNC and the UNF.
These stand for Unified National Course and Unified National Fine.
The UNC threads include: #6-32, #8-32, #10-24, #12-24, 1/4-20, 5/16-18, 3/8-16, 7/16-14, 1/2-13, 9/16-12, 5/8-11, 3/4-10, 7/8-9 and 1-8.
The UNF threads include: #6-40, #8-36, #10-32, #12-28, 1/4-28, 5/16-24, 3/8-24, 7/16-20, 1/2-20, 9/16-18, 5/8-18, 3/4-16, 7/8-14 and 1-12.
So, what do all of these numbers mean?
The first number or fraction represents the diameter. The origin of the number sizes goes beyond the scope of this post so just trust me, it represents a standard diameter.
A external #6 is .138 dia, a #8 is .164 diameter, a #10 is .190 diameter and a #12 is .216 diameter.
The fractions are pretty obvious.
These sizes all refer to the maximum outside diameter of a male thread. A female thread must be slightly larger than the male thread to provide clearance, so the tool that makes them will be larger than the thread size would at first indicate.
The second number in a thread size is the number of threads per inch so a 32 will have 32 threads per inch. The distance between these threads would be 1/32 of an inch.
If you are buying a quality tap or die you will see a few more letters in the size, for instance you might see 1/4-20UNC-2A or #10-32UNF-3B.
We know what the UNC and the UNF are now but the last number and letter indicate the thread "class" and define whether it is an external thread (A) or an internal thread (B).
The number indicates how precise the threads tolerance and fit is. The higher the number, the more precise it is. General use threads will be class 2. The threads used on aircraft for example are usually class 3.
The threads used on most muzzleloading guns are class 2 because although some of them are going to see some high stresses for the most part the size is large enough to easily do the job that's needed without compromising safety.
I almost forgot... a Metric Thread size is also given as a diameter and thread pitch but the second number (the pitch) is the distance between the threads.
For instance, a M6-1 defines a thread with a 6mm diameter (.236) and the threads are spaced 1mm (.039) apart.
If we used a similar system, a 1/4-20UNC thread would be called a .250-.050 UNC and a #8-36UNF would be a .164-.028 UNF. :grin:
OK, so now we know about threads but how are they made?
There are of course many ways to make a thread, but for us gunbuilders the old fashioned tap and die are the most common tool used.
Taps...Something they play at 'lights out'. Also, something that machines threads into a machined hole.
Dies...Something we don't want to do. Also, something that machines threads on the outside of round material.
Tap Drill...Not the licking of the lips before blowing 'Taps' on the horn nor is it the polishing of the bugle for inspection, but it is a drill sized to produce the correct minor diameter for the threads in a part.
It is very important to use exactly the size the charts specify to use for making the hole.
If it is too small, the undersize hole will most likely break the tap. If it is too large, the strength of the threaded joint will be weak and may fail or wear out prematurely.
When you are making threads a tremendous amount of heat is being created right where the tool is cutting. A lubrication made for threading is needed for anything except perhaps wood.
If you are working with steel parts, use a good sulphated oil that is made for cutting threads.
The sulfur prevents the steel chips from welding themselves to the tap or die to prevent breakage or galling. The mineral oil provides good lubrication. The stuff is cheap and it works so buy some.
When you are threading, you should stop about every 3/4 to 1 1/2 revolutions, reverse the direction of the tool at lease 1/2 turn, add a drop or two of thread cutting oil and then proceed to thread a little farther.
Why the "about" and so much tolerance in the number of revolutions? Because each size and each material will cut differently. I don't have a fixed rule to use, but if you are threading a part and the tap or die seems to suddenly become much harder to advance, that is the time! Do NOT try to go another 1/8 turn without backing up.
This allows the tool to break off the chips that are forming on each thread and it also allows the thread cutting oil to get right down to the cutting edges where it is needed.
NOTE: FAILURE TO BACK OFF THE TOOL WILL RESULT IN A BROKEN TAP OR A STUCK DIE.
Now, I get to say what I intended to say when I started this post.
About 15 years ago my wife saw a 40 PIECE TAP AND DIE SET for some unbelievable price so she bought it for me. It was made in China and the taps were coated with a black finish.
I have only tried to use this wonderous set 4 or 5 times sense getting it and the only time it seemed to work was when I was threading a hole in a piece of Maple.
All in all, this whole set is a real piece of fecal matter.
When you buy taps or dies buy the very best that you can find.
Also buy a good tap holder and a good die holder.
At least one brand of die holder has a hexagon internal shape to match their dies and it works very well.
You will regret buying anything but the very best.
Have Fun, You hear??
zonie
