# Threading via Machinist Handbook (measuring)



## GunsOfNavarone (Oct 29, 2020)

I picked this metrology section for a reason. Though this is about threading, the questions are more about measuring than the process of threading.
As the ELS is up and running in my lathe, I really wanted to start to finish use the Machinist Handbook parameters and do lots of measuring from begining to end to come to the final product rather than grabbing a manufactured nut and do the old go/no go technique.
I took the outside diameter to 24.07mm as the hand book show a 24mm x 2 Major diameter to be 24.00 to 24.513
I did many passes with a 60 degree carbide threading tool to end up with a minor diameter of 22.108mm (M.H show max of 21.835 to 22.210)
Using the 3 wire technique, it shows I need to use the "45" wires. Now I hate using these, but this is about measuring so... I used a piece of foam to hold and came up with 24.408mm subtracting 1.7mm (card in 3 wire said this is the "constant") so I end up with 22.708mm. M.H says the pitch diameter should be between 22.701 and 22.925)
When I go to put the nut on the final product, I can only get on about 1 turn. I Dykem'd the threads and hit it with the nut again. It pretty much was removing ink from all places. This says to me everything is right...but just too large and I would need to take the major and minor down equally. Doing all the same measuring, I now had a pitch diameter of 22.563mm (the MINIMUM per M.H. is 22.701) but it now fit great....Maybe SLIGHTLY on the snug side, that is, there is zero wiggle from 2 turns in to all the way down. I will post the reference page just to show what I went off of (24x2). Now this is 6h tolerance class, not sure if that plays, but I only saw that or 4h. I would think 2a would have been more ideal but I would expect it to fit (?)
Any ideas based on measurements I used and the results? I wouldn't think the "best" home shop technique is trying a nut until it fits...? If your doing a 10mm thread, you pretty much turn that diameter and just thread what ever pitch until you nut goes on. BUT, if like me, you want to try doing it to "the Books" specs, well I didn't have spectacular initial results.


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## extropic (Oct 29, 2020)

The book is "Machinery's Handbook", not "Machinist Handbook".

The table you posted is for the INTERNAL thread (nut). Since you say you checked your workpiece with a nut, it seems you're trying to cut an EXTERNAL thread. The good news is that, you can find the correct table and there is still material left to finish your workpiece.

TIP: The major diameter of a standard external machine screw thread is never allowed to be larger than the nominal (24mm in this case) major diameter.


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## benmychree (Oct 29, 2020)

And, most of the time you need to file the OD smaller after threading is complete.  so far as measuring is concerned, a thread mike is a good investment, they can be had on e bay fairly cheaply.


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## GunsOfNavarone (Oct 29, 2020)

Sorry Extropic I get this a sensitive subject for you.. 
It says right there...internal threads...super. I don't need to save the work, I'm just wanting to use another method other than the testing a nut for fit. That now makes sense why the tolerance was allowed to be larger that the nut I was threading to work with!
As the usual, I can get to the end goal by having this conversation with folks here. Sometimes the answers are RIGHT THERE but you need a 2nd, 3rd, 4thset of eye on it. I'll try again when I come to the right table in the MACHINERY'S HANDBOOK (tm) and hope to get better results right off the bat. Sure does take longer with all the measuring...truthfully this is the first time it did it to specs...wrong specs, but still specs.
We'll see how the next one works out.


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## GunsOfNavarone (Oct 29, 2020)

Ok, before I just in head first, I was again looking for a table for a 2a threading chart. That's when I hit the 4h/6h and just went back to the 6h (wrong internal thread chart) This chart is that one. Am I missing something obvious again?


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## JRaut (Oct 29, 2020)

Those designations are the tolerance classes.

For SAE fasteners, the thread classes are as follows:
1A -- loose bolt*
2A -- normal bolt
3A -- tight-tolerance bolt

1B -- loose nut*
2B -- normal nut
3B -- tight-tolerance nut

*Thread classes 1A and 1B are super loose, and I don't think they're ever really used unless it's a special circumstance.


The thread classes for metric fasteners follow similar logic, but have different designations:
   General purpose fit --- 6g bolt and 6H nut
   Close fit -- 5g6g bolt and 6H nut

A quick googling brought up this PDF, which has a bunch of additional information


			https://mae.ufl.edu/designlab/Online%20Resources_files/fastener_handout.pdf


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## jaek (Oct 29, 2020)

Is your major diameter too big from the initial use of the internal thread chart?

The official thread form has flats on the crest and root, and fit happens at the pitch line  If the threads are sharp at the crest and the PD is max allowable, the crest may interfere with the minor diameter of the female thread.

But yes, you have the right chart now. 22.562 PD is solidly within the tolerances.


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## GunsOfNavarone (Oct 29, 2020)

@JRaut      Yeah, I've been reading through the M.H. man it's dry and hard to stay focused but I did come the different classes but I only found the 4H/6H, not 5g/6g...I'll keep looking and I'll take a look at your PDF
@jaek  yes, it was too big which makes sense as that would be slight loose fit as an internal thread. I keep the Maj/Minor the same ratios and just took them down evenly and it fits very snug but nice. I was just lost as to why all the measuring and end up winging it. My focus just is a bit muddled right now.
I have no pressing reason to do it by the book, but I'd like the learning experience. Press on!


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## JRaut (Oct 29, 2020)

It's quite satisfying to cut a thread by the book, so to speak. Certainly worth pressing on.

One suggestion I have: if you're cutting an external thread (bolt), DO NOT PAY ATTENTION TO THE MINOR DIAMETER.

All you should have to care about is the *major diameter* and the *pitch diameter*. Assuming you've got your tool ground at 60* and your feed setting correct on your lathe, those are (just about) the only two variables that matter for the thread.

(Well, you can pay attention to minor diameter in a general sense, to see if you're getting close. But never rely on it as a factor in determining when you're done cutting.)


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## mickri (Oct 29, 2020)

I have been trying to use the 3 wire method too.  My 1915 Machinery's Handbook gives formulas for metric, imperial and whitworth threads.  Simple to use because it gives you the micrometer measurement over the wires. The formula for metric threads and imperial threads is the same because they are both 60 degree threads.  The formula is  M = D- 1.5155P +( 3 W).   M is the measurement over the wires.  D is the outside diameter of the screw in inches ( major diameter).  P is the pitch of the thread in inches.  For metric threads you have to convert the metric diameter and pitch to inches.  W is the diameter of the wires.  Plugging your numbers in M = .9449 - 1.5155 * .0787 + (3 * .045).  M= .9606 or 24.4000 mm.  This is the measurement over the wires.


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## GunsOfNavarone (Oct 29, 2020)

@mickri  my 3wire set has a booklet with it. I was doing 2 threads per mm so I just take the whole value (M) and subtract 1.7mm (it was actually something like 1.698) and that number should fall within the allowance of the pitch diameter. I almost want to pop for a thread micrometer, if I can find one that covers a large range and isn't a grand.
@JRaut  it does make sense to at least consider the minor diameter last for sure. I have threading down but my technique could use some cleaning up, hence the metrology.


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## mickri (Oct 29, 2020)

Thread micrometers are nice but just like a regular micrometer each thread micrometer only covers 1".  You need a 0 - 1, 1- 2, 2- 3, and so on.  With the wires there is no limit to the diameter that you can measure.  My set of wires also came with an instruction card.  The instructions work off of the pitch diameter which you either have to calculate or look up in a table.  Using the formula in my old Machinery's Handbook all you need is the major diameter.  Both methods will get you to the same place.  I just find the old formula easier to use because it gives me the measurement over the wires and that is what I shoot for.

Holding the wires is a pain.  I found using rubber bands really helped to keep the wires in place.


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## GunsOfNavarone (Oct 30, 2020)

Yeah, that rubber band method looks better than the form block I was using, what a pain.
To clarify, you’re just comparing the number you get from measuring with wire against the books Major diameter? I was taking that number, subtracting the constant from the wires cheat sheet and comparing that to the pitch diameter in the handbook. As long as I was within the allowance I was good (?)


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## mickri (Oct 30, 2020)

What we are both doing will get us to the same result.  I have some odd ball threads that I need to cut where there is no table where I can look up the pitch diameter.  I would have to calculate the pitch diameter.  So it is easier for me to use the major diameter.  Both methods get the same measurement over the wires. 24.400 mm.  When I am cutting a thread I keep cutting until the micrometer measurement equals the calculated measurement over the wires.  I don't do the math to see how the micrometer measurement over the wires compares to the major diameter.  If you really want to know if your are within the min/max pitch diameter range I would do the calculations at the min and max diameters.  Using your numbers that range would be 24.231 mm to 24.400 mm based on the min/max numbers in the table you posted.

I invariably overshoot my target diameters.  To try to avoid this I have started doing two things.  One thing is that when I get within 0.010 to 0.015 of my target diameter this is where I take my cleanup/spring cuts.  Then say I am still 0.008 over diameter for example.  I now take two 0.004 cuts and just two 0.004 cuts.  I have found that by doing this I am spot on to 0.0005 larger than my target diameter.  The other thing I am doing is instead of taking my cleanup/spring cuts at the last position of the tool bit I back the tool bit out 0.005 to 0.010 for the cleanup cuts.


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## pacifica (Oct 30, 2020)

If you use full profile threading inserts, each insert is only for  one tpi(for example 13 UN). With this type of inserts it is hard to cut too deep of a thread. the downside is you need a separate insert for each TPI.


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## mikey (Oct 30, 2020)

mickri said:


> Thread micrometers are nice but just like a regular micrometer each thread micrometer only covers 1".  You need a 0 - 1, 1- 2, 2- 3, and so on.  With the wires there is no limit to the diameter that you can measure.



Just guessing here but a 0-1" and 1-2" thread mic will cover maybe 99.9% of the threads most of us cut. Above 2", just use your wires.

Thread mics are faster, quite accurate enough for a hobby shop and are direct reading so no calculations to do or mess up. Plus, you spend zero time looking for the wire you dropped in the chip pan or that rolled under the lathe. 

Nowadays, import thread mics are so cheap and come with changeable anvils to cover a wide range of threads. Shars sells some for a decent price.


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## Jim F (Oct 30, 2020)

mickri said:


> I have been trying to use the 3 wire method too.  My 1915 Machinery's Handbook gives formulas for metric, imperial and whitworth threads.  Simple to use because it gives you the micrometer measurement over the wires. The formula for metric threads and imperial threads is the same because they are both 60 degree threads.  The formula is  M = D- 1.5155P +( 3 W).   M is the measurement over the wires.  D is the outside diameter of the screw in inches ( major diameter).  P is the pitch of the thread in inches.  For metric threads you have to convert the metric diameter and pitch to inches.  W is the diameter of the wires.  Plugging your numbers in M = .9449 - 1.5155 * .0787 + (3 * .045).  M= .9606 or 24.4000 mm.  This is the measurement over the wires.


Finally found someone with an older version than mine.
My copy of M.H. is a 6th edition, 1924.


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## GunsOfNavarone (Oct 31, 2020)

Man...I respect the old/vintage tools....but guys, a lot has been invented and changed since the 1920's! 
Seriously though, I would dig having an old piece of history like that.


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## GunsOfNavarone (Oct 31, 2020)

mikey said:


> Just guessing here but a 0-1" and 1-2" thread mic will cover maybe 99.9% of the threads most of us cut. Above 2", just use your wires.
> 
> Thread mics are faster, quite accurate enough for a hobby shop and are direct reading so no calculations to do or mess up. Plus, you spend zero time looking for the wire you dropped in the chip pan or that rolled under the lathe.
> 
> Nowadays, import thread mics are so cheap and come with changeable anvils to cover a wide range of threads. Shars sells some for a decent price.


For sure, after trying to do it by the book, I REALLY want a thread mic. Wires are so frustrating. I have no idea how long I fiddled with those to get a solid, repeat reading


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## mickri (Oct 31, 2020)

Because I do everything manually I specifically wanted an older version of the Machinery Handbook.  Those guys were just as smart as today's machinists.  They just didn't have all of the newfangled equipment.  I have do things like they did.  My copy is a pdf.  I would like to have a hardcover because I could keep it out in the shop rather than having to go back and forth to look something up on the computer.


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## GunsOfNavarone (Oct 31, 2020)

Mine is 30th edition...Ironically, I want an old version print version.
I am looking at the Shars thread micrometer, it does cover about anything I might need. Feel like that's taking the easy way out, but not much wrong about that i suppose. THOUGH that have the manual version and the digital version..going digital as it is a MUCH easier and faster way to go as well. Here's too lazy! HAZAA!


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## Asm109 (Oct 31, 2020)

I love the old versions of the handbook, but thread standards have evolved a lot since before the first world war.  I would only use a thread chart published some time after WWII. Preferrably since the 70's (That is still over 40 years old)


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## mickri (Oct 31, 2020)

There are hundreds for sale on Ebay.  Every vintage from the early 1900's to the latest new edition.  Search for "Machinery's Handbook" and take your pick.

I don't have anything that is digital.  The batteries go dead so quickly that you need to keep a supply of spare batteries on hand.  No thanks.


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## mikey (Oct 31, 2020)

GunsOfNavarone said:


> Mine is 30th edition...Ironically, I want an old version print version.
> I am looking at the Shars thread micrometer, it does cover about anything I might need. Feel like that's taking the easy way out, but not much wrong about that i suppose. THOUGH that have the manual version and the digital version..going digital as it is a MUCH easier and faster way to go as well. Here's too lazy! HAZAA!



I used a Fowler analog thread mic for about a decade and I think it was Chinese; it went back to its owner after I bought my Tesa mics. Before I sent it back to my friend, I checked the Tesa's against that Fowler and there was essentially no difference in the readings. The differences were in the quality of the mic and anvils but in terms of accuracy, I saw none. This is why I suggest the import thread mics like Shars. You won't use it that often but when you do, you'll be glad you have it.


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## GunsOfNavarone (Oct 31, 2020)

Interesting, I honestly wouldn't have thought that thread standards have changed. I'm thinking, carbide tools, CNC and speeds/feeds I would still love a 1957 or '59 version, just because I love that time period. Not that I lived it, but wish I dd.


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## GunsOfNavarone (Oct 31, 2020)

@mikey I'm a fan of Shars and Accusize if I'm honest. I'll probably go that route, just have to decide, easy (digital) or work for it (manual...err analog? You know what I mean.)


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## mikey (Oct 31, 2020)

Either will work but you have to keep spare batteries on hand if you go digital. The nice thing about modern thread mics is that they read in tenths, unlike the older analog ones that read in thousandths and you have to interpolate. For those of us who have been using mics for a very long time, interpolating within a tenth is no big thing but a direct reading is more accurate. If I was starting out today, I would buy a Shars 0-1" thread mic and only buy larger when I really needed it. And given my aging eyes, I might just go digital.


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## Jim F (Oct 31, 2020)

mickri said:


> Because I do everything manually I specifically wanted an older version of the Machinery Handbook.  Those guys were just as smart as today's machinists.  They just didn't have all of the newfangled equipment.  I have do things like they did.  My copy is a pdf.  I would like to have a hardcover because I could keep it out in the shop rather than having to go back and forth to look something up on the computer.


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## ThinWoodsman (Nov 1, 2020)

mickri said:


> Because I do everything manually I specifically wanted an older version of the Machinery Handbook. Those guys were just as smart as today's machinists.



There is a lot of good stuff in those old books. Fred Colvin has the "Kinks" series (e.g. Screw Machine Kinks, 1923) and the American Machinist's Handbook, Starrett has their Machinist's Apprentice book, Suverkrop has The American Machinist's Shop Notebook, and there's a ton on forgottenbooks. 

Back on-topic, does anyone know of a better way to identify thread form than using a magnifying glass and eyeballing it? I have a threaded rod on an old Stanley 55 plane that a thread gauge (not wires or micrometer, admittedly) showed to be 28 TPI, but a 1/2-28 TPI nut binds on the second turn. At that TPI, all fastener thread forms kinda look the same.


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## mickri (Nov 1, 2020)

Depending on how old the plane is it might be an old style "V" thread.  I am just guessing.


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## devils4ever (Nov 1, 2020)

I started with the thread wires and decided to switch to a Shars thread mic. Great decision! Those wires are tricky to handle. I can get a reading much quicker than with the wires.

I use the MH for reference, but most of the time I use an online thread calculator. This gives all the parameters you need for the thread you are cutting. MH is great but it's easy to misread the table with all those entries. Plus, I print out the page and keep my MH pages clean.

For cutting an external thread, I turn down the diameter to within the range listed. Then, I cut the thread until the pitch diameter is within the range listed.


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## ThinWoodsman (Nov 1, 2020)

mickri said:


> Depending on how old the plane is it might be an old style "V" thread.



Plane is somewhere between 1930s and 1950s. I'm guessing Whitworth, which Stanley was rather fond of back then.

Looks like there is a gage for whitworth; the problem with the gage is false positives. The 27-TPI American/Unified gage seemed almost right, the 28 TPI seemed spot on.

The only way I know of to determine the thread form is to magnify it with a stark background, snap a photo, and then measure the angles and examine the crest manually.


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## mickri (Nov 1, 2020)

I have both imperial and whitworth thread gauges.  Put a piece of white paper behind the threaded rod with good lighting.  If the threads are whitworth you should be able to see the white paper between the 60 degree imperial thread gauge and the side of the 55 degree whitworth thread.


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