Three wire notes part one

B

Boyd Allen

Active member
Really precise sets of thread measuring wires cost a ton. Cheap sets are not precise but they are affordable. The question that comes to mind is whether I can I come up with a formula to tell me what the over the wires measurement of a given thread would have been with perfect wires, if I know the diameter of my cheap wires.

After some head scratching, and drawing (It has been a long time since plane geometry and trig.) I think that I have an answer.

The correction factor is three times the difference between the wires used and their proper size.

For instance, if my wires measure .0317, .0003 short of perfection (.032) I would need to add three times .0003 to the measurement taken with my wires to get what the measurement would have been with perfect wires. In other words, to calculate the over the wire measurement of any given thread would be with perfect wires, I would have to add .0009 to whatever measurement I get with mine.

With this corrected over over wires diameter I should be able to use the standard constant to calculate pitch diameter, if that is called for.

Added later: All of this is based on a 60 degree V thread.

After looking at many web pages on the subject of the three wire method, I found this one to be the easiest for me to understand. http://littlemachineshop.com/instructions/ThreeWireMethod.pdf
 
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I bought the cheap wire set, and me fumbling and dropping them on the concrete made me start looking for some thread micrometers, I tell you I have been really liking those.
 
for those who dont like fumbling the thread wires stick them in a couple small pieces of elastic. The elastic hold them perfectly in line how they should be. I know this is a little off topic but i am pretty proud of my discovery. LOL!! Lee
 
Boyd,

Check out the link below. I think it will get you the info that you are looking for.

"Approximate Formulas for Measured Pitch Diameter
The following approximate formulas for computing the pitch diameter, from the measurement over wires, should be used only for screws having lead angles from 0° to 5°. These formulas neglect the effect of lead angle and give results which show the screw to be larger than the true condition. The formulas are for any wire size which will fit in the thread."

http://http://www.threadcheck.com/the-three-wire-method-of-measuring-pitch-diameter/technicalinfo/

Looks like will get you very close. Very close meaning it should put you only a couple/few tenths on the safe side for a male thread.

Jerry
 
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skeetlee said:
for those who dont like fumbling the thread wires stick them in a couple small pieces of elastic. The elastic hold them perfectly in line how they should be. I know this is a little off topic but i am pretty proud of my discovery. LOL!! Lee
Click to expand...

What Lee posted will work. A small hunk of squishy foam works as well. I use a small blob of grease on top and bottom of thread to hold the wires when they are small.

Here'e a tip.......when you drop a thread wire into your chip pan, don't touch anything! Look down for the wire. If you cannot see it, get a flashlight and keep looking without disturbing the chips in the pan. Just before you are ready to give up and empty the chip pan, take another thread wire and your flashlight and drop it in the same way that the first pin dropped. Follow the pin while it falls and viola!...it will have fallen right where the first one landed. Has worked for me bunches of times. To the point that I have given up searching first and just drop the second wire before bothering to look.

Jerry
 
Since your link didn't work for me, I did a little looking and found what I think is your document, and this is my try at posting a link to it. Is this the page that your link was supposed to lead to? I appreciate your tips. What I was trying to do was come up with the simplest conversion to get what a measurement would be with the precise best wire diameter, when imperfect wires are used to take the measurement. I think that I did that. If everyone was to measure his wires, and if they are off, apply the proper conversion factor, we could all be on the same page.
http://www.threadcheck.com/technical-documents/thread-measuring-wire-formulas.pdf


 
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Boyd Allen said:
Since your link didn't work for me, I did a little looking and found what I think is your document, and this is my try at posting a link to it. Is this the page that your link was supposed to lead to? I appreciate your tips. What I was trying to do was come up with the simplest conversion to get what a measurement would be with the precise best wire diameter, when imperfect wires are used to take the measurement. I think that I did that. If everyone was to measure his wires, and if they are off, apply the proper conversion factor, we could all be on the same page.
http://www.threadcheck.com/technical-documents/thread-measuring-wire-formulas.pdf
Click to expand...

Boyd,

Thanks for pointing out that my link did not work. It is fixed now.

Both of our links contain the same formulas for using wires that are not the "best wire diameter" for measuring a particular thread. It looks to me that using the "Approximate Formulas for Measured Pitch Diameter" allows you to calculate for wires of "imperfect" diameter for your thread. Is this the info you are seeking?

Jerry
 
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Tclaunch said:
I bought the cheap wire set, and me fumbling and dropping them on the concrete made me start looking for some thread micrometers, I tell you I have been really liking those.
Click to expand...

Second the thread mikes. I have two a 0-1" and a 1-2" both the same make so I only need one set of anvils.
 
Drumcorpschamp,
The page that you shared a link to is a good one, but what I WAS looking for, was not found on any site that I looked on, so I drew the problem, and characterized the dimensions in terms of the radius of the wire, and trigonometric functions. Using the general case, I made a table, showing the results of several wire diameters. Using this, I was able to come up with the formula which I expressed in words, in my first post. If I have an over the wire measurement that I have taken with wires that while labeled as the ideal diameter, are not. I can easily convert the measurement to what it would be if perfect wires of the correct size were used. I did not find this conversion factor, I calculated it, for 60 degree V threads. I solved my problem, I just thought that since the conversion turned out to be so simple, that I would share it. My next step will be to buy some piano wire that is supposed to be .032, and measure it to see, what its actual diameter is, and how uniform it is. The goal is to be able to accurately communicate the size of a thread, at the least cost, and fewest number of variables. As it stands, if the piano wire is uniform enough, the simplest approach will be to cut a set of wires, use them too measure the thread that I want duplicated, and send the wires to the person who will be doing the work. Of course this still leaves the issue of differences in micrometers. I am working on that.
Boyd
 
Boyd Allen said:
Drumcorpschamp,
The goal is to be able to accurately communicate the size of a thread, at the least cost, and fewest number of variables. As it stands, if the piano wire is uniform enough, the simplest approach will be to cut a set of wires, use them too measure the thread that I want duplicated, and send the wires to the person who will be doing the work. Of course this still leaves the issue of differences in micrometers. I am working on that.
Boyd
Click to expand...

Boyd,

Understand what you want. Great work on your part.

If you are not happy with the piano wire (good idea, by the way) I have a link below for gauge pins.

Going back to your post from several days ago about calibrating your micrometers, I put in links for a micrometer standard and a gauge block.


Class ZZ .0320" minus gauge pins. The tolerance is minus .0002" so they'll be very close. My experience with these is that if you order 2 or 20 of the same size, they all measure within .00005" of one another. Good product at a good price.
http://www1.mscdirect.com/cgi/NNSRIT2?PMAKA=89003206&PMPXNO=2257746&cm_re=ItemDetail-_-ResultListing-_-SearchResults

1.000" micrometer standard. =/- .00008" tolerance.
http://www1.mscdirect.com/cgi/NNSRIT2?PMAKA=06407019&PMPXNO=1755254&cm_re=ItemDetail-_-ResultListing-_-SearchResults

1.000" gauge block. I have purchased many of these affordable gauge blocks to use as standards and set-up aids for some very precise work. Tolerance is +/- a couple bazillionths.
http://www1.mscdirect.com/cgi/NNSRIT2?PMAKA=86295706&PMPXNO=2221435&cm_re=ItemDetail-_-ResultListing-_-SearchResults

I do this stuff for a living (toolmaker) and know when one needs to spend a ton of money to get where one needs to be. I think the items linked above will get you very precise results.

Jerry
 
Tclaunch said:
I bought the cheap wire set, and me fumbling and dropping them on the concrete made me start looking for some thread micrometers, I tell you I have been really liking those.
Click to expand...

Tim, stick with wires. Buy jobbers length twist drills and measure over the unfluted shank.
Buy a copy of Machinerys Handbook, even if it is a 50 year old version.
 
Thread chart

This is an old chart from a thread set I have used for about 40 years and it has always worked for me.
Denton
 
ever run into an uncommon/non std./xtra.fine internal thread.....then scratch your head on bore size..... Here`s the formula they taught us in the Navy..... and it gets you real close...
Bore Size= Major Diameter-1/number of threads per inch.....
divide 1 by the number of T.P.I.... and subtract that from the M.D.
I`ve used it a few times over the years....
bill larson
 
Boy, am I ever glad that I started this thread. You guys have a wealth of useful information, and I thank you all. Chet, my next stop is to pick up some piano wire, measure it, and bend it into one of those.
 
You've probably already thought of this.

If you're still concerned about differences in micrometers-----why not just send your piano wire and your micrometer to the person doing your work.

A. Weldy
 
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