Harold,
Re. Measuring threads using wires.
After reading your posts I did some asking around.
The idea of being able to more accurately measure thread pitch is interesting.
I had heard of using wires to measure threads before, but had never seen them available for sale in Australia.
After asking a lot of people I'm unable to find anyone who did an apprenticeship for fitting and turning or tool and die making prior to approx 1980 who received training with regards to the use of wires.
I was also unable to find anyone who still actually uses them.
I was also unable to find anyone with new thread wires for sale. A couple of my local machinery dealers had second hand kits with certification dates dating from the 40's.
They seem to have been largely been replace in this part of the world by thread mic's and go/no go style thread ring gauges. Thread mics are the most popular and is what I was taught to use.
Questions:
1. Can you give us some hints, tips for using wires. It seams to me that holding thread wires in places and measuring with a micrometer would be quite difficult?
2. Do you use the wires when cutting the thread to measure for correct pitch dia and thread depth or only afterwards to check thread has been cut correctly?
3. what are the advantages of using wires over a Screw Thread Micrometer?
thanks
PS. With regards to the large thread wire string on this board, I don't think anyone disagrees with regards to what your saying, just I suspect that most folks don't have a need to cut threads to an accuracy that needs to be checked to such a high level for home use.
Respectfully submitted
Mike
Question for Harold V.
-
Doug_Edwards
- Posts: 612
- Joined: Thu Apr 10, 2003 8:06 pm
- Location: No. Idaho
- Contact:
Re: Question for Harold V.
Harold,
Re. Measuring threads using wires.
After reading your posts I did some asking around.
The idea of being able to more accurately measure thread pitch is interesting.
I had heard of using wires to measure threads before, but had never seen them available for sale in Australia.
After asking a lot of people I'm unable to find anyone who did an apprenticeship for fitting and turning or tool and die making prior to approx 1980 who received training with regards to the use of wires.
I was also unable to find anyone who still actually uses them.
I was also unable to find anyone with new thread wires for sale. A couple of my local machinery dealers had second hand kits with certification dates dating from the 40's.
They seem to have been largely been replace in this part of the world by thread mic's and go/no go style thread ring gauges. Thread mics are the most popular and is what I was taught to use.
Questions:
1. Can you give us some hints, tips for using wires. It seams to me that holding thread wires in places and measuring with a micrometer would be quite difficult?
2. Do you use the wires when cutting the thread to measure for correct pitch dia and thread depth or only afterwards to check thread has been cut correctly?
3. what are the advantages of using wires over a Screw Thread Micrometer?
thanks
PS. With regards to the large thread wire string on this board, I don't think anyone disagrees with regards to what your saying, just I suspect that most folks don't have a need to cut threads to an accuracy that needs to be checked to such a high level for home use.
Respectfully submitted
Mike
Mike,
I'll throw some stuff in the hat for your consideration.
I am a moldmaker, younger than Harold (he's old enough to be my dad ; )), and
am a second generation toolmaker. My dad used thread wires, although I
don't know how far back. Technical schools in this country were still training
to use them in the early 80's. I still use mine. I don't have a thread mike, although
if I did production on threads, I might consider it.
Some people put tape on their wires to hold the two together. If you use them
enough, you will figure out how to hold them loose with out too much problem.
I personally use mine to check before and after the final cuts.
Wires give you an accurate measurement with out any adjustments. Thread
mikes need different anvils for different thread pitches. If you have a thread
standard to check the mike against, you are miles ahead. The wires
by themselves are more adaptable to odd threads, as they don't need
anything for adjustments. Thread wires are also cheap to buy compared
to mikes.
I'm with Harold on anyone making the effort to do good work. It will seem
much slower in the beginning, but you can go much farther than if one gets
in the habit if machining "just good enough". My $.02 worth.
Doug
http://www.precisionlocomotivecastings.com/
Building a 70 ton Willamette in 1.6"
Building a 80 ton Climax in 1.6"
"Aim to improve!"
"Mine is not to question why, mine is just to tool and die"
Building a 70 ton Willamette in 1.6"
Building a 80 ton Climax in 1.6"
"Aim to improve!"
"Mine is not to question why, mine is just to tool and die"
Re: Question for Harold V.
I know...... I'm not Harold either, but I can offer a few things to your questions.
It is not as much a matter of high accuracy as it is a known dimension reference. Basic thread wires are not that great at high precision, due to variables in the tool forms if hand ground and perpendicularity alignment to the pitch centerline. For the sake of comparison reference. They work acceptibly well when it is unrealistic to check fit with its actual mating part or a thread ring.
Considering 2 solid objects have difficulty when trying to occupy the same space, at the same time. It is feasible that a pitch diameter measurement could appear correct, but the mismatched thread forms could causes interference.
A screw thread mic covers more of the thread form than just merely 2 tangent points. The thing that has always bothered me about thread mics is that the anvils are directly aligned but checking a thread they are tilted in relation to the part centerline by one half the pitch. That just seems goofy!
I have used some foam rubber strip to hold the pins or tape them to some tag board folded about the middle. My hands get charley horse cramps if I take too long having trouble getting them in position. My patience grows thin if I keep dropping them dumb things into the chip tray too.
DC
It is not as much a matter of high accuracy as it is a known dimension reference. Basic thread wires are not that great at high precision, due to variables in the tool forms if hand ground and perpendicularity alignment to the pitch centerline. For the sake of comparison reference. They work acceptibly well when it is unrealistic to check fit with its actual mating part or a thread ring.
Considering 2 solid objects have difficulty when trying to occupy the same space, at the same time. It is feasible that a pitch diameter measurement could appear correct, but the mismatched thread forms could causes interference.
A screw thread mic covers more of the thread form than just merely 2 tangent points. The thing that has always bothered me about thread mics is that the anvils are directly aligned but checking a thread they are tilted in relation to the part centerline by one half the pitch. That just seems goofy!
I have used some foam rubber strip to hold the pins or tape them to some tag board folded about the middle. My hands get charley horse cramps if I take too long having trouble getting them in position. My patience grows thin if I keep dropping them dumb things into the chip tray too.
DC
-
Jon_Bohlander
- Posts: 18
- Joined: Sat Jan 04, 2003 3:53 pm
Re: Question for Harold V.
Hi,
I was taught to poke the wires through pieces of rubber band to help hold them
Harold- I would like to hear the correct way to use wires (I haven't used them since vo-tech-1996) and I know those who haven't used them could really use it.
I usually just lurk on this board but I would like to say I really learned alot from the thread on threading. i was also glad to see everyone could have a discussion and in the end still be "board mates". My vo-tech teacher always said you could be a machinist a hundred years abd never learn it all.
Thanks, Jon Bohlander
I was taught to poke the wires through pieces of rubber band to help hold them
Harold- I would like to hear the correct way to use wires (I haven't used them since vo-tech-1996) and I know those who haven't used them could really use it.
I usually just lurk on this board but I would like to say I really learned alot from the thread on threading. i was also glad to see everyone could have a discussion and in the end still be "board mates". My vo-tech teacher always said you could be a machinist a hundred years abd never learn it all.
Thanks, Jon Bohlander
Re: Question for Harold V.
All the single lead thread mics I have used have jaws that nest together when the mic is zeroed. The thread mics with directly opposing points were made for 2 and 4 lead threads and had to be set to a calibration standard.
-
Michael_Az
- Posts: 407
- Joined: Sat Jan 04, 2003 10:07 am
- Location: Southeastern Az
Re: Question for Harold V.
I started 40 years ago as a machinist and ended up in a tool and die shop. Then changed professions through no desire of mine but just economics. Anyway, every shop I worked in used thread wires and I have always used them in my home shop. My experience has always been, when the wires say its right, it works.
Michael
Michael
Saimp 2 HP 10 X 44 mill, #2 Cin Horz Mill, Cholchester 13" lathe, LeBlond 15" Dual Drive.
Re: Question for Harold V.
Mike,
Regards your comments of the use, or lack thereof, of thread wires.
I've been away from the industry for 20 years now, so I have not been mandated to produce anything that would be subject to stringent inspection. That is not to say that I haven't been on my machines, however. Still, not having to work to stringent standards, I may be out of touch with what is common practice today, but I don't think so.
I was trained in a missile facility, but briefly spent time in commercial industry after leaving, and before starting my own shop.
My first job was for a manufacturing firm that had some degree of quality control, so it was not uncommon to find the odd set of ring gages or snap gages to aid in cutting threads. I don't recall every seeing thread wires used at that job, which was of short duration (only 5 months) due to the business being sold to Japan and the shop folding.
The following job was the real eye opener. The company was engaged in manufacturing large pumps and floatation mills for the extraction of metals from their ores. Not only did we not have gages, but this company had no QC, so the accepted practice in this instance was to machine to fit. Anything that would assemble was assumed to be good. Needless to say, I never saw thread wires there, either.
I think that one can conclude that the environment in which you spend your time will flavor your concepts of what constitutes acceptable procedures. I can't imagine not using thread wires, yet I've run into more than a few people that can't begin to understand why you'd want to. "What's wrong with a nut? That's what's going to fit the thread, isn't it?"
Hard to argue with that logic, so in defense all I can say is that the nut has the necessary allowance to provide for that rare case when the male component may be on top tolerance, and the nut on low tolerance, so the part might not fit all threads that have been generated using a nut that is on top tolerance, plus the allowance, as a gage.
By resorting to the charts, and the application of wires, you reduce the chance for accumulated error. The pitch diameters that are published reflect the allowance, so it doesn't work against you. It keeps industry, and those of us that care to conform to accepted standards, from deviating from accepted dimensions and tolerances. The other reason to use wires is that wire sets will measure any diameter of thread, so long as it is within the pitch of the wire (assuming you already have the proper micrometer for the diameter in question). The proper use of wires can eliminate the need for a multitude of ring or snap gages. I guess that's about as close as I can come to suggesting a reason to use wires, when the obvious reasons (to me, anyway) may not be so apparent to others.
There has been a little talk about the PeeDee wires. The real problem with them, and it's minor as compared to not measuring, is that the formula provided with the wires tells you that you add a constant to the theoretical major diameter, and that provides the right pitch diameter. Unfortunately, it doesn't tell you where you fall within the tolerance of the pitch diameter, which is not a single figure. Pitch diameters are listed by two numbers, the maximum and minimum diameters. When using the cheap wire sets, you have no idea where you stand relative to either of those numbers.
Proper thread wires do not relate to the major diameter. You are provided a constant that is then applied to the published pitch diameters of the thread, which are the maximum and minimum dimensions, as mentioned above.
I think my first comment would be that when one is first introduced to a micrometer and instructed as to the "proper" method to hold it, it appears to be somewhat cumbersome. Sort of clumsy. Not long afterwards, however, it would seem unnatural to hold it in any other fashion. Most of us pick up a mic and automatically grasp it as we've learned, with the little finger wrapped around the frame. One can conclude that it's just a matter of becoming familiar with the routine, at which time it is no longer difficult, nor clumsy.
I'm from the old school. I do nothing to aid the use of thread wires. I detest the use of tape, which can influence your measurement under adverse conditions, and find it is more difficult to work with than free wires. I am also not fond of other methods of holding the wires, and for the same reason. One important thing to note: When you use thread wires on your lathe, it's important to clean out the chip pan before you begin. If you drop wires, it's nearly impossible to see them in the pan when they're mixed with chips.
You always have an idea of the diameter you expect to measure, so one sets the mic slightly larger than the measurement desired (over the wires), places the mic on the part, and installs the top two wires, with the wire centered on the part such that they are balanced on their centerline, and spread such that they will not be beyond the width of the spindle of the mic. With light pressure on the mic, once installed, the wires will stay in position with no trouble. One then installs the bottom wire, centered as near as possible, between the two wires on top. With the gap of the mic set appropriately, the wire can't slide out sideways, and if the wire is centered on the part, it won't slide out either front or back. One then feels for dead center with the mic as it is closed for measurement. All of the wires will remain captive as long as you keep the mic over them.
The wires, while being installed, are kept in your lips. They are within easy reach, and you don't have to take your eyes off the procedure.
The wires are used no differently than one would use a micrometer when turning a diameter. If you're running more than one-off, and make setups where you work by dial marks, which is the common practice in light production shops pre-CNC days, once you've established the relationship between the cross slide, compound and the thread pitch diameter, you can start measuring when you're near final size, so the number of repetitions can be minimized. On a one-off, my typical procedure is to chase the thread near size, judging by the appearance, then start measuring.
In production, it's not uncommon to check each part several times. It's all a matter of the degree of precision you desire, or the level of quality demanded by the application. If your thread must meet standards, you inspect as much as is necessary to achieve the required pitch diameter. With a marked dial and a machine that can repeat, you can often measure only a couple times to achieve the finished thread. It's a good idea to not trust dial marks alone because of the higher risk of tool damage in threading, and the relatively narrow band of tolerance in threads.
I'm not sure there are any particular advantages from the perspective of a guy making parts. Thread mics should not be construed as a method to verify the proper pitch of a plug gage, but they tend towards more than enough precision for production work and are certainly easier to handle than wires. They measure the pitch from the high points of the thread form being generated, so they may or may not be measuring the pitch diameter. The effect is to measure the maximum diameter, which may not be at the pitch line, although it translates to a reading as if it is. By using a thread mic, a thread won't be found to not fit a mating part should the thread form be slightly off.
By their nature, wires are not effected by thread form, unlike thread mics or triangles. They measure at the pitch diameter, even when the form is wrong. That is why triangles or thread mics are not used in gage calibration, aside from the lack of an equal level of precision that comes from the proper wires.
Personally, I don't like thread mics. I wouldn't be interested in owning one, even as a gift, and have never counted one in my tool collection. Yes, I have used one. That's why I don't like them.
Measuring by thread wires is the ultimate procedure. As long as the correct thread wires are used for the given pitch, the degree of precision of the measurement is adequate for the calibration of thread gages, and is, indeed the correct procedure for the calibration of such, coupled with the use of a supermike. To my knowledge, no other method lends the same degree of precision.
It stands to reason that the wire procedure is not mandatory for thread measuring in most instances. The proper use of ring or snap gages would certainly be better suited to the production environment. We used a combination of all methods when I worked in the missile facility.
Perhaps the most important features here would be the fact that if a thread is in dispute, wires could be the ultimate inspection procedure. Assuming all conditions and features are correct, a thread would be accepted (or rejected) on the strength of the wire measurement. The other thing to consider is that a complete set of thread wires equates to every conceivable thread size that can be machined. That set of wires could effectively be replacing literally tons of gages, although at the expense of slower inspection procedures.
Measuring by wires is very difficult if you don't have the piece being measured held by some means. You just don't have enough hands. It likely goes without saying that the wires want to be parallel with the ground, too. Otherwise you can't keep them in position while applying the mic. [img]/ubb/images/graemlins/smile.gif"%20alt="[/img]
Perhaps a mention of a negative attribute of wire measuring.
Wires do not disclose any lead errors. A part with lead error, drunkenness, or a slightly modified pitch, such a when chasing a metric thread in error when one is not intended, would not be disclosed by thread wires unless the error was severe. A few thou would not be apparent. (Please don't ask!) [img]/ubb/images/graemlins/blush.gif"%20alt="[/img]
While I agree in principle, it's difficult for me to come to terms with the idea that any manufacturing process should be endorsed when it leaves the maker in the position of not knowing the size of the part, especially if more work, or future work may be involved. It's not so much about attempting to achieve some theoretical level of excellence, but more one of knowing what the size is so you can do work in keeping with the known dimension, which is discovered by measuring. Certainly, making one-off threaded parts eliminates the necessity, so long as parts are made to fit one another. The problem with that, though, is that if a repair part is necessary at some date in the future, it can't be successfully made without the mating part. By working to a known standard, even if the standard being used doesn't comply with accepted standards, you can make parts by print. That's one of the more important features of measuring. Again, it provides missing information.
Harold
Regards your comments of the use, or lack thereof, of thread wires.
I've been away from the industry for 20 years now, so I have not been mandated to produce anything that would be subject to stringent inspection. That is not to say that I haven't been on my machines, however. Still, not having to work to stringent standards, I may be out of touch with what is common practice today, but I don't think so.
I was trained in a missile facility, but briefly spent time in commercial industry after leaving, and before starting my own shop.
My first job was for a manufacturing firm that had some degree of quality control, so it was not uncommon to find the odd set of ring gages or snap gages to aid in cutting threads. I don't recall every seeing thread wires used at that job, which was of short duration (only 5 months) due to the business being sold to Japan and the shop folding.
The following job was the real eye opener. The company was engaged in manufacturing large pumps and floatation mills for the extraction of metals from their ores. Not only did we not have gages, but this company had no QC, so the accepted practice in this instance was to machine to fit. Anything that would assemble was assumed to be good. Needless to say, I never saw thread wires there, either.
I think that one can conclude that the environment in which you spend your time will flavor your concepts of what constitutes acceptable procedures. I can't imagine not using thread wires, yet I've run into more than a few people that can't begin to understand why you'd want to. "What's wrong with a nut? That's what's going to fit the thread, isn't it?"
Hard to argue with that logic, so in defense all I can say is that the nut has the necessary allowance to provide for that rare case when the male component may be on top tolerance, and the nut on low tolerance, so the part might not fit all threads that have been generated using a nut that is on top tolerance, plus the allowance, as a gage.
By resorting to the charts, and the application of wires, you reduce the chance for accumulated error. The pitch diameters that are published reflect the allowance, so it doesn't work against you. It keeps industry, and those of us that care to conform to accepted standards, from deviating from accepted dimensions and tolerances. The other reason to use wires is that wire sets will measure any diameter of thread, so long as it is within the pitch of the wire (assuming you already have the proper micrometer for the diameter in question). The proper use of wires can eliminate the need for a multitude of ring or snap gages. I guess that's about as close as I can come to suggesting a reason to use wires, when the obvious reasons (to me, anyway) may not be so apparent to others.
There has been a little talk about the PeeDee wires. The real problem with them, and it's minor as compared to not measuring, is that the formula provided with the wires tells you that you add a constant to the theoretical major diameter, and that provides the right pitch diameter. Unfortunately, it doesn't tell you where you fall within the tolerance of the pitch diameter, which is not a single figure. Pitch diameters are listed by two numbers, the maximum and minimum diameters. When using the cheap wire sets, you have no idea where you stand relative to either of those numbers.
Proper thread wires do not relate to the major diameter. You are provided a constant that is then applied to the published pitch diameters of the thread, which are the maximum and minimum dimensions, as mentioned above.
1. Can you give us some hints, tips for using wires. It seams to me that holding thread wires in places and measuring with a micrometer would be quite difficult?
I think my first comment would be that when one is first introduced to a micrometer and instructed as to the "proper" method to hold it, it appears to be somewhat cumbersome. Sort of clumsy. Not long afterwards, however, it would seem unnatural to hold it in any other fashion. Most of us pick up a mic and automatically grasp it as we've learned, with the little finger wrapped around the frame. One can conclude that it's just a matter of becoming familiar with the routine, at which time it is no longer difficult, nor clumsy.
I'm from the old school. I do nothing to aid the use of thread wires. I detest the use of tape, which can influence your measurement under adverse conditions, and find it is more difficult to work with than free wires. I am also not fond of other methods of holding the wires, and for the same reason. One important thing to note: When you use thread wires on your lathe, it's important to clean out the chip pan before you begin. If you drop wires, it's nearly impossible to see them in the pan when they're mixed with chips.
You always have an idea of the diameter you expect to measure, so one sets the mic slightly larger than the measurement desired (over the wires), places the mic on the part, and installs the top two wires, with the wire centered on the part such that they are balanced on their centerline, and spread such that they will not be beyond the width of the spindle of the mic. With light pressure on the mic, once installed, the wires will stay in position with no trouble. One then installs the bottom wire, centered as near as possible, between the two wires on top. With the gap of the mic set appropriately, the wire can't slide out sideways, and if the wire is centered on the part, it won't slide out either front or back. One then feels for dead center with the mic as it is closed for measurement. All of the wires will remain captive as long as you keep the mic over them.
The wires, while being installed, are kept in your lips. They are within easy reach, and you don't have to take your eyes off the procedure.
2. Do you use the wires when cutting the thread to measure for correct pitch dial. and thread depth or only afterwards to check thread has been cut correctly?
The wires are used no differently than one would use a micrometer when turning a diameter. If you're running more than one-off, and make setups where you work by dial marks, which is the common practice in light production shops pre-CNC days, once you've established the relationship between the cross slide, compound and the thread pitch diameter, you can start measuring when you're near final size, so the number of repetitions can be minimized. On a one-off, my typical procedure is to chase the thread near size, judging by the appearance, then start measuring.
In production, it's not uncommon to check each part several times. It's all a matter of the degree of precision you desire, or the level of quality demanded by the application. If your thread must meet standards, you inspect as much as is necessary to achieve the required pitch diameter. With a marked dial and a machine that can repeat, you can often measure only a couple times to achieve the finished thread. It's a good idea to not trust dial marks alone because of the higher risk of tool damage in threading, and the relatively narrow band of tolerance in threads.
3. what are the advantages of using wires over a Screw Thread Micrometer?
I'm not sure there are any particular advantages from the perspective of a guy making parts. Thread mics should not be construed as a method to verify the proper pitch of a plug gage, but they tend towards more than enough precision for production work and are certainly easier to handle than wires. They measure the pitch from the high points of the thread form being generated, so they may or may not be measuring the pitch diameter. The effect is to measure the maximum diameter, which may not be at the pitch line, although it translates to a reading as if it is. By using a thread mic, a thread won't be found to not fit a mating part should the thread form be slightly off.
By their nature, wires are not effected by thread form, unlike thread mics or triangles. They measure at the pitch diameter, even when the form is wrong. That is why triangles or thread mics are not used in gage calibration, aside from the lack of an equal level of precision that comes from the proper wires.
Personally, I don't like thread mics. I wouldn't be interested in owning one, even as a gift, and have never counted one in my tool collection. Yes, I have used one. That's why I don't like them.
Measuring by thread wires is the ultimate procedure. As long as the correct thread wires are used for the given pitch, the degree of precision of the measurement is adequate for the calibration of thread gages, and is, indeed the correct procedure for the calibration of such, coupled with the use of a supermike. To my knowledge, no other method lends the same degree of precision.
It stands to reason that the wire procedure is not mandatory for thread measuring in most instances. The proper use of ring or snap gages would certainly be better suited to the production environment. We used a combination of all methods when I worked in the missile facility.
Perhaps the most important features here would be the fact that if a thread is in dispute, wires could be the ultimate inspection procedure. Assuming all conditions and features are correct, a thread would be accepted (or rejected) on the strength of the wire measurement. The other thing to consider is that a complete set of thread wires equates to every conceivable thread size that can be machined. That set of wires could effectively be replacing literally tons of gages, although at the expense of slower inspection procedures.
Measuring by wires is very difficult if you don't have the piece being measured held by some means. You just don't have enough hands. It likely goes without saying that the wires want to be parallel with the ground, too. Otherwise you can't keep them in position while applying the mic. [img]/ubb/images/graemlins/smile.gif"%20alt="[/img]
Perhaps a mention of a negative attribute of wire measuring.
Wires do not disclose any lead errors. A part with lead error, drunkenness, or a slightly modified pitch, such a when chasing a metric thread in error when one is not intended, would not be disclosed by thread wires unless the error was severe. A few thou would not be apparent. (Please don't ask!) [img]/ubb/images/graemlins/blush.gif"%20alt="[/img]
PS. With regards to the large thread wire string on this board, I don't think anyone disagrees with regards to what your saying, just I suspect that most folks don't have a need to cut threads to an accuracy that needs to be checked to such a high level for home use.
While I agree in principle, it's difficult for me to come to terms with the idea that any manufacturing process should be endorsed when it leaves the maker in the position of not knowing the size of the part, especially if more work, or future work may be involved. It's not so much about attempting to achieve some theoretical level of excellence, but more one of knowing what the size is so you can do work in keeping with the known dimension, which is discovered by measuring. Certainly, making one-off threaded parts eliminates the necessity, so long as parts are made to fit one another. The problem with that, though, is that if a repair part is necessary at some date in the future, it can't be successfully made without the mating part. By working to a known standard, even if the standard being used doesn't comply with accepted standards, you can make parts by print. That's one of the more important features of measuring. Again, it provides missing information.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Re: Question for Harold V.
Hi Mike,
Nope, I'm not Harold either. I figured he'd have answered by now, but perhaps he's all typed out for now. I know I would be if I posted as much as he has this past week. Since I'm familiar with using them many times, I'll tell you how I do it. And it probably won't be too far off from the way Harold does it. And I begin measuring with them when I'm about 3/4 of the way toward finishing (maybe even closer) and keep measuring right to the final pass.
Since I'm right handed it'll be from that perspective. And this is for an item in the lathe where the threads are horizontal. First you must have an outside micrometer of the proper size which is big enough to span the diameter of your threads. I have never seen anyone try to use a vernier caliper for this either. The object is to place two wires on one side, and one wire on the opposite side. At the lathe I prefer to put two wires on the top and the remaining wire in the bottom. I position the two top wires midway of their length so that they balance horizontally by themselves. No tape and no rubber bands holding them. I also tend to use the mid point in the thread to measure on. Of course if the thread is long you'd want to measure in several places along the way.
Now for the fun part. With my left hand I place the third wire on the underside of the thread making sure that it is between the upper two that are sitting there. And it is important that you have it in the this correct position on the bottom side of the thread. You must not have it skewed one thread over left or right. Now, holding the wire in place with my left hand finger(s), I pick up the micrometer that is opened wide enough with my right hand, and holding it by the body near the spindle, I guide the anvil over the lower wire I'm holding. At the same time I'm careful not to disturb the two upper wires sitting there.
As the micrometer anvil reaches the lower wire and my fingers, I shift them to hold both the anvil and wire in place. At almost the same time I position the spindle of the mike over the upper two wires and begin closing the micrometer against them to take my reading. I use a very gentle rocking motion (front to back) along with my "feel" on the mike to be certain I'm centered. I take my reading right there in position and do not remove the mike first.
After I've gotten my reading, I loosen the mike a little and carefully pull it away trying not to jar the upper wires off and down into the black hole that is in most every chip pan. Harold says you should always clean the chip pan first, and he's right of course. But sometimes I just don't. Although a rag or something across the ways to catch them would help.
I have never cut such a course thread that when using wires the micrometer spindle wouldn't span across the two on top. I guess one could use a standard ware block or something between the wires and mike spindle and subtract the difference.
So that is how I measure with thread wires. Perhaps holding the bottom wire (or wires, makes no difference if you do it vice versa) and juggling with the top ones may seem tedious and awkward at first, but it becomes real easy in just a short time. One only needs a normal amount of dexterity to master this.
Victor
Nope, I'm not Harold either. I figured he'd have answered by now, but perhaps he's all typed out for now. I know I would be if I posted as much as he has this past week. Since I'm familiar with using them many times, I'll tell you how I do it. And it probably won't be too far off from the way Harold does it. And I begin measuring with them when I'm about 3/4 of the way toward finishing (maybe even closer) and keep measuring right to the final pass.
Since I'm right handed it'll be from that perspective. And this is for an item in the lathe where the threads are horizontal. First you must have an outside micrometer of the proper size which is big enough to span the diameter of your threads. I have never seen anyone try to use a vernier caliper for this either. The object is to place two wires on one side, and one wire on the opposite side. At the lathe I prefer to put two wires on the top and the remaining wire in the bottom. I position the two top wires midway of their length so that they balance horizontally by themselves. No tape and no rubber bands holding them. I also tend to use the mid point in the thread to measure on. Of course if the thread is long you'd want to measure in several places along the way.
Now for the fun part. With my left hand I place the third wire on the underside of the thread making sure that it is between the upper two that are sitting there. And it is important that you have it in the this correct position on the bottom side of the thread. You must not have it skewed one thread over left or right. Now, holding the wire in place with my left hand finger(s), I pick up the micrometer that is opened wide enough with my right hand, and holding it by the body near the spindle, I guide the anvil over the lower wire I'm holding. At the same time I'm careful not to disturb the two upper wires sitting there.
As the micrometer anvil reaches the lower wire and my fingers, I shift them to hold both the anvil and wire in place. At almost the same time I position the spindle of the mike over the upper two wires and begin closing the micrometer against them to take my reading. I use a very gentle rocking motion (front to back) along with my "feel" on the mike to be certain I'm centered. I take my reading right there in position and do not remove the mike first.
After I've gotten my reading, I loosen the mike a little and carefully pull it away trying not to jar the upper wires off and down into the black hole that is in most every chip pan. Harold says you should always clean the chip pan first, and he's right of course. But sometimes I just don't. Although a rag or something across the ways to catch them would help.
I have never cut such a course thread that when using wires the micrometer spindle wouldn't span across the two on top. I guess one could use a standard ware block or something between the wires and mike spindle and subtract the difference.
So that is how I measure with thread wires. Perhaps holding the bottom wire (or wires, makes no difference if you do it vice versa) and juggling with the top ones may seem tedious and awkward at first, but it becomes real easy in just a short time. One only needs a normal amount of dexterity to master this.
Victor
"The machines are gaining ground upon us; day by day we are becoming more subservient to them" ~ Samuel Butler (1863)
Re: Question for Harold V.
Victor,
You did an excellent job of explaining the procedure of using thread wires. But for me who never heard of them, what is the theory of their use? In other words, do the wires come in different diameters depending on the thread size, are there tables used after you get the mlke reading that tell you if the thread is correct or not, etc. etc.? [img]/ubb/images/graemlins/confused.gif"%20alt="[/img] Also, what is the difference between regular thread wires and PeeDee wires?
This whole discussion has really got my curiosity going!
Thanks,
Jay
You did an excellent job of explaining the procedure of using thread wires. But for me who never heard of them, what is the theory of their use? In other words, do the wires come in different diameters depending on the thread size, are there tables used after you get the mlke reading that tell you if the thread is correct or not, etc. etc.? [img]/ubb/images/graemlins/confused.gif"%20alt="[/img] Also, what is the difference between regular thread wires and PeeDee wires?
This whole discussion has really got my curiosity going!
Thanks,
Jay
Re: Question for Harold V.
Thanks for the informative reply Harold.
The guy that I buy most of my tooling from has a real nice set of thread wires sitting out the back that he showed me the other day. From memory there was some 40 odd vials of wires in the kit in a felt lined lather bound case.
After actually seeing them I can see what you mean about dropping them.
It funny that this post on wores came up cause I had a job last week that called for a 3/8 UNEF 32 TPI thread on a fitting for a hydralic unit for something in an aircraft and the thread to be checked for pitch dia with wires (with copies of cetificates to be provided).
Checked with the customer and he was ok with a thread mic, as long as it had an in date calibration certificate from an outside source. I was going to borrow a thread mic from a mate who has ISO 9000 cet. and has to have all of his stuff calibrated, but I think I might give the wires a try after all.
Thanks
Mike
The guy that I buy most of my tooling from has a real nice set of thread wires sitting out the back that he showed me the other day. From memory there was some 40 odd vials of wires in the kit in a felt lined lather bound case.
After actually seeing them I can see what you mean about dropping them.
It funny that this post on wores came up cause I had a job last week that called for a 3/8 UNEF 32 TPI thread on a fitting for a hydralic unit for something in an aircraft and the thread to be checked for pitch dia with wires (with copies of cetificates to be provided).
Checked with the customer and he was ok with a thread mic, as long as it had an in date calibration certificate from an outside source. I was going to borrow a thread mic from a mate who has ISO 9000 cet. and has to have all of his stuff calibrated, but I think I might give the wires a try after all.
Thanks
Mike
Re: Question for Harold V.
Thanks for the informative reply Harold.
The guy that I buy most of my tooling from has a real nice set of thread wires sitting out the back that he showed me the other day. From memory there was some 40 odd vials of wires in the kit in a felt lined lather bound case.
I think I might give the wires a try after all. Thanks
Mike
Wish they were here for me to buy. They fetch a pretty penny when they come up on eBay.
Make sure each of the vials contains three wires, and the constant is provided. They are useless without the constant, and two wires can't be used, you must have three.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
-
J Tiers
Re: Question for Harold V.
All this talk about "constants" and not having a measurement from the pitch line with some wire set, etc, seems a little odd.
If I have the geometry visualized right, it should be relatively easily calculable for any wire.
The geometry is a given....always (in our case) two lines 60 deg apart, touching a circle in two places.
Therefore, the contact point on the circle will be the same regardless of the actual PD, so long as there is a 60 deg angle. The contact point on the thread flank will be different from the PD if the wire isn't the correct size for that pitch.
So, for any perfect size wire, a constant will indeed be added to the PD to find the measurement over. This will be the radius of the wire, plus the distance from center line to the chord between the contact points, doubled. That is a direct adder to the PD.
If you are at the wrong PD, the wire will still contact at the same points on its circumference (constant angle) but the contact with the thread flank won't be at the desired PD. You should be able to subtract the constant and find your PD error.
In the case where you have non-perfect wire size for that pitch, the "constant" for any given pitch is made up of two portions.
First, the radius and distance to chord, doubled, as above, which is a wire characteristic. Second, there is an error of the contact point on the flank above or below the actual PD.
So the actual "effective wire constant" for that wire and pitch is the sum of the above, the true wire constant plus a pitch-dependent error term.
For any given pitch, and any given wire diameter, the error is also calculable, since you know the distance between the contact points on the wire (chord length).
So, it should be possible to take any set of Pee-Dee wires, carefully measure their diameters, and then calculate both the true constant and the pitch-dependent error term for each wire size and possible pitch.
Futzy details would have to be considered as to the actual desired PD for the fit class, etc. But that isn't relevant to the actual measurement.
The real PD of the part at any pitch should be findable by subtracting the "effective wire constant" for that pitch from the measurement you get over the wires.
Obviously if you are not contacting the actual PD line, you are "inferring" the measurement at the PD from a measurement made elsewhere on the thread flank. The assumption is that the thread flank angle is constant and correct.
If the flank angle is wrong, or is not constant, the PD measurement will be off, because you don't know the "real" error term for the incorrect thread angle you cut.
My logic wrong anywhere?
If I have the geometry visualized right, it should be relatively easily calculable for any wire.
The geometry is a given....always (in our case) two lines 60 deg apart, touching a circle in two places.
Therefore, the contact point on the circle will be the same regardless of the actual PD, so long as there is a 60 deg angle. The contact point on the thread flank will be different from the PD if the wire isn't the correct size for that pitch.
So, for any perfect size wire, a constant will indeed be added to the PD to find the measurement over. This will be the radius of the wire, plus the distance from center line to the chord between the contact points, doubled. That is a direct adder to the PD.
If you are at the wrong PD, the wire will still contact at the same points on its circumference (constant angle) but the contact with the thread flank won't be at the desired PD. You should be able to subtract the constant and find your PD error.
In the case where you have non-perfect wire size for that pitch, the "constant" for any given pitch is made up of two portions.
First, the radius and distance to chord, doubled, as above, which is a wire characteristic. Second, there is an error of the contact point on the flank above or below the actual PD.
So the actual "effective wire constant" for that wire and pitch is the sum of the above, the true wire constant plus a pitch-dependent error term.
For any given pitch, and any given wire diameter, the error is also calculable, since you know the distance between the contact points on the wire (chord length).
So, it should be possible to take any set of Pee-Dee wires, carefully measure their diameters, and then calculate both the true constant and the pitch-dependent error term for each wire size and possible pitch.
Futzy details would have to be considered as to the actual desired PD for the fit class, etc. But that isn't relevant to the actual measurement.
The real PD of the part at any pitch should be findable by subtracting the "effective wire constant" for that pitch from the measurement you get over the wires.
Obviously if you are not contacting the actual PD line, you are "inferring" the measurement at the PD from a measurement made elsewhere on the thread flank. The assumption is that the thread flank angle is constant and correct.
If the flank angle is wrong, or is not constant, the PD measurement will be off, because you don't know the "real" error term for the incorrect thread angle you cut.
My logic wrong anywhere?