Tolerancing and measuring full thread depth

[Gordon B. Clarke]

Will this help make life easier for anyone? The door is wide open

http://www.f-m-s.dk/Tolerancing%20an...ad%20depth.pdf

Gordon

[Gordon B. Clarke]

The lack of responce to my post can mean (at least ) one of two things. All agree or all disagree so much that any comment would be felt to be a waste of time

Gordon

[+ or - Zero]

Actually I just noticed it because of your bump. I suspect that finding much to disagree with there would be difficult.

[Gordon B. Clarke]

Actually I just noticed it because of your bump. I suspect that finding much to disagree with there would be difficult.

But can anything be added to make it better?

Like your aka BTW Accuracy doesn't get much better than that LOL

Gordon

Wonder if ±0 would be accepted? (ALT 241 and 0)

[luthor]

Gordon, the only thing I can suggest to help make it more technically correct is that you change this statement - "a thread with a pitch of 5 TPI". The thread actually has a pitch of .20" or 1/5".

[Gordon B. Clarke]

Gordon, the only thing I can suggest to help make it more technically correct is that you change this statement - "a thread with a pitch of 5 TPI". The thread actually has a pitch of .20" or 1/5".

Now I'm curious I've never seen an "inch" pitch written or described like that, have you? You are correct of course but giving a pitch as a single distance or as so many in an inch is one of the main differences between metric and imperial. I even gave an example as how to calculate and chose 5 TPI because it was so simple. OK, 10 TPI would have been even easier.

5 TPI is easy to work with but how about 6 or 7 TPI or any other number that isn't easily divided into 1? I can imagine endless discussions on how many decimals should be used.

Gordon

[Glenn Wegman]

"Pitch" defined:

p=pitch=1/n

PITCH. This is the distance from a point on the screw thread to a corresponding point on the next thread measured parallel to the axis of the thread. It is represented by the letter p.

I have never seen it defined in any other way, but I haven't seen everything yet...

[Gordon B. Clarke]

"Pitch" defined:

p=pitch=1/n

PITCH. This is the distance from a point on the screw thread to a corresponding point on the next thread measured parallel to the axis of the thread. It is represented by the letter p.

I have never seen it defined in any other way, but I haven't seen everything yet...

With TPI then yes 1/n not with metric

The OP was about drawings and not so much definitions though.

Gordon

[Glenn Wegman]

I was addressing this:

Now I'm curious I've never seen an "inch" pitch written or described like that, have you?

...in regard to luthors comment.

Both were in reference to Imperial threads, not metric.

Even though, pitch is the distance from point to a corresponding point, whether metric or imperial.

Stating "a thread with a pitch of 5 TPI" is incorrect. It should be "a thread with a pitch of .20", or "a thread of 20 TPI".

[The real Leigh]

Now I'm curious I've never seen an "inch" pitch written or described like that, have you?

Luthor's statement is correct.

While common usage gives thread count in turns per inch (TPI), the pitch, being the reciprocal of TPI, can also be used and will be understood.

That occurs frequently in very large diameters where the TPI may be less than one, and it may be easier to measure the pitch than the count.

- Leigh

[Gordon B. Clarke]

Luthor's statement is correct.

While common usage gives thread count in turns per inch (TPI), the pitch, being the reciprocal of TPI, can also be used and will be understood.

That occurs frequently in very large diameters where the TPI may be less than one, and it may be easier to measure the pitch than the count.

- Leigh

I stand by what I wrote in post #8 and never implied he wasn't correct with his definition. However the thread is (was?) about drawings and how depth should/could be stipulated.

I don't think I've ever seen a thread depth on a drawing given as so and so many "full thread" turns so perhaps this is an American phenomina?
I have seen it a few times as part of an inspection routine even with metric threads.

Gordon

[The real Leigh]

... perhaps this is an American phenomina?

This is an American board.

We have a number of standards and customs with which you seem unfamiliar.

- Leigh

[Gordon B. Clarke]

Stating "a thread with a pitch of 5 TPI" is incorrect. It should be "a thread with a pitch of .20", or "a thread of 20 TPI".

I've no problem admitting you are correct but I doubt if I'd be corrected by a machinist on a shop floor.

If it helps I'll apologize and state that pitch P is in fact the distance of one single thread.

I did get it right when I wrote this:

http://www.f-m-s.dk/1.01.pdf

[CarbideBob]

Now I'm curious I've never seen an "inch" pitch written or described like that, have you? ....

Gordon

Really?????
How do you check an English pitch on a comparator or toolmakers microscope? (I mean actually measure a thread not just screw some silly go/no-go gauge on the part.)
I learned these numbers way before I knew how to calculate feeds and speeds.
Bob

[luthor]

This description of Pitch from (http://www.f-m-s.dk/1.01.pdf)

"When the pitch is given in mm (millimetres) it is the distance
a screw or a nut moves in one rotation. When the pitch is
given in T.P.I. (Threads Per Inch) it is the number of turns
necessary to move the screw or nut one inch (25.4 mm)"

There are a few errors here as well Gordon, your description of Pitch above is not technically correct and is more a description of "Lead" and would only apply to a single start thread.
You have also made the same mistake here confusing Pitch and TPI.
I have to ask why you would bother to write these documents when all of this information is already freely available in thousands of text books and other referances worldwide.

[Glenn Wegman]

I guess the only other suggestion I would have would be to eliminate this from the bottom of the page.

"Note: Any that feel something should be added to this or if the premises are incorrect are more than
welcome to give suggestions"

The woman that asks "Does this dress make me look fat?" come to mind...

[Gordon B. Clarke]

This description of Pitch from (http://www.f-m-s.dk/1.01.pdf)

"When the pitch is given in mm (millimetres) it is the distance a screw or a nut moves in one rotation. When the pitch is given in T.P.I. (Threads Per Inch) it is the number of turns necessary to move the screw or nut one inch (25.4 mm)"

There are a few errors here as well Gordon, your description of Pitch above is not technically correct and is more a description of "Lead" and would only apply to a single start thread.
You have also made the same mistake here confusing Pitch and TPI.
I have to ask why you would bother to write these documents when all of this information is already freely available in thousands of text books and other referances worldwide.

I've changed the text in http://www.f-m-s.dk/1.01.pdf and I thank you for the input.

However with, "I have to ask why you would bother to write these documents when all of this information is already freely available in thousands of text books and other referances worldwide." in your post then I will give an explanation although you are on the right track.

The information I give is in fact in "thousands of text books and on the internet" but how many know how to search for this material and sift through the relevant information from what are often lengthy and complicated documents?

I don't think it is any secret that I manufacture inserts that measure, among other things, external and internal pitch diameter. Writing the thread manual that the link represents took months and most of it is relevant information on thread pitch diameters and tolerances. I also, whenever possible, give a reference to the standard I have used and recommend that if more information is required that it be read.

I didn't need to make my thread manual but but I have over the years been asked so many questions on just about everything under the sun about threads that I thought that to most makers of threads it would be useful. I've never as yet had anyone say they didn't find it useful. Of course I've made mistakes and when they have been pointed out to me I have corrected them. Most mistakes I've made is by "hitting" the wrong key when writing hundreds of numbers.

"My" thread manual isn't intended as a scientific work for specialists and experts but as a tool for those that machine threads and either don't read or have access to the "thousands of text books and other referances worldwide."
I also write in the manual that any person or company wishing to make their own manual (as I doubt many will need all pages) can just print the pages they feel necessary. I could also have the wish that I've kept it simple enough so that people (users) want to read more from actual standards.

This might help explain http://www.f-m-s.dk/0.03%20Introduction.pdf

Wow did this thread ever get side tracked?

To avoid any possible misunderstanding then I do appreciate all input that makes the manual better. Please bear in mind though that the target group is machinists and they usually as such have more interest in being practical rather than theoretical. Excelling at both is of course the ultimate goal

Gordon

[+ or - Zero]

I suspect in many ways I'm the exact person Gordon is writing for --notice my comment was that I didn't see much to disagree with in the OP.

The odd thing is I've had no problem with understanding any posters description or definition of TPI/Pitch/lead/etc., even the ones that were new to me.

Now I freely admit I'm quite literately a *practical* machinist --like "Farmer John's backwoods/neighborhood machine shop".

Actually the OP seemed to be covering rather obvious things about thread fit and depth tolerance, especially as related to deep or long internal threads. The drawings do express what I believed was the point --it costs more to do deeper threads with great accuracy, and why.

I have had a customer come in and ask me to make him a 'special' thread that is used on camera mounts so he could mount his camera in an unusual location. When I said those are just common 1/4-20 bolts available almost anywhere, all I got was a blank stare. He was a budding amateur photographer who's day job was as a CPA. He wasn't a stupid man, just how one described a bolt in that way meant nothing to him.

Well I'm practical --I just gave him the bolt he was after in the length he needed, didn't charge him or go into massive explanations about screw threads, etc., and he will be back if he ever has a real paying project.

What I have found out is that it seems accuracy is set at 4 significant decimal places in the published standards, metric or imperial.

Which brings up cumulative error if one was searching for perfection. Like on a long deep thread. Which is likely why it would cost more to do.

Yes I own Machinery's Handbook and other works, but in truth I don't use them much --as a practical matter I can usually have the job done faster then I could look up how and why to do it some particular way. When I do need to know something I'm still not likely to dig into the large tomb of a book like Machinery's Handbook --I'll go let Google be my friend and find a solution.

Maybe not the most precise or even the best solution, but a practical one, non-the-less.

So I see that I just don't know enough to critique Gordon's work in the OP, but I didn't seem to have any trouble understanding it either. So it would be useful in a practical way to me, if I needed that bit of knowledge --about the cost of ever more precise threads as one goes deeper, and why that is so.

Zero.

[MichaelP]

"...and a thread with a pitch of 5 TPI a tolerance of at least 1/5 x 2 = 0.2x2 0.4".

...and a 5 TPI thread a tolerance of at least 1/5" x 2 = 0.2" x 2 = 0.4".

[Gordon B. Clarke]

I suspect in many ways I'm the exact person Gordon is writing for --notice my comment was that I didn't see much to disagree with in the OP.

Zero.

I gave you a "like" but I'll expand on what you wrote - from my point of view.

I don't know if you are the "exact" type I'm writing for but you certainly come very close My basic education is as machinist but also college. I've taught in subjects that have to do with both metrology, statistics and mathematics (mainly trigonometry) in my free time.

None of those I've dealt with were stupid but to some those subjects were foreign territory or were of no previous interest. T knew that if I swamped them with theory they would close down almost immediately. The trick was to come up with "funny" methods to illustrate the points and subjects.
People had as much fun learning as I had teaching and I also learned a great deal too along the way because of many of the questions I was asked.

I still remember one machinist I just happened to talk to about threads during a company visit and my jaw dropped when I realised he knew just about as much about threads as I think I do. I'm really glad I didn't make any patronising remarks when I first started talking to him as he might have run rings around me. When I asked how he knew so much about threads his reply was refreshingly simple, "It interests me".

As Luthor mentioned, reading standards and searching the internet can give a great deal of information, but you have to be pretty sure you know what you're looking for. Those that really want to know the whys and buts and ifs will take the time but they are a minority.

For those that don't quite get what I mean then take a look at some of the threads and the posts in other sub forums in PM and you'd be surprised (or maybe not) how often the answer can be found with a very simple search on the internet.

When my son was younger he started to ask me to help him with maths or something and I gladly did so. When he started watching the TV or playing on his computer while I was doing his homework I asked why he was wanting me to help. His reply? "It's easier just asking you". That was that and I told him that he had to work it out for himself and I'd have a look at it afterwards. That didn't happen often. He ended up top of his class without my help LOL

Gordon