PDA

View Full Version : Tap and Die Dimensions For 1-1/4 - 10

John Buffum
11-09-2014, 09:11 PM
I tried hard to understand Machinery's Handbook's treatment of tap dimensions. Fail!

What should be the maximum diameter of the thread on the tap? 1.25" 1.28" ??
For the die, the OD cut should be ?? 1.23" 1.22?

Will be making out of mystery tool found at my friendly neighborhood industrial surplus store.

Will be making these to use in cutting lathe accessories for my 1885 F.E. Reed lathe.

J Tiers
11-09-2014, 09:35 PM
I make it 1.228 max diameter on bolt, , based on the flat of 1/8 pitch on the thread crest.

Tap should clear that, the spec has a flat or equivalent at 1/4 pitch. so the nut ID would be 1.033 or so.

That's based on thread specs that your lathe is dated well before. It wasn't made to them. So you may be looking at sharp V threads in most places on your machine.

Arthur.Marks
11-09-2014, 10:31 PM
1 1/4" x 10 tpi UNS tap tolerances to produce a class 2B thread.
Max Major Diameter: 1.2630"
Min Major Diameter: 1.2565"
Max Pitch Diameter: 1.1875"
Min Pitch Diameter: 1.1865"

These figures were calculated using Handbook For The Metalworking Industries, 1st Ed. by Modern Machine Shop. I'll admit to giving up on Machinery's Handbook for almost everything lately. I could go on a rant, but I won't ;) Here is how I arrived at the above dimensions.

Max. Major Dia. = Basic + A
Min. Major Dia. = Max. Major Dia. - B
Max. Pitch Dia. = Min. Pitch Dia. + D
Min. Pitch Dia. = Basic Pitch Dia. + C

A, B, C and D are tabulated above these formulas. They correspond as follows for a 1 1/4" x 10 tpi tap: A = .0130" B = .0065" C = .0015" D = .001" The Basic Pitch Diameter was referenced under Table 6, "Unified Screw Threads. Internal Dimensions" on page 1417. Under Class 2B, the Minimum Pitch Diameter is 1.1850". This was the figure used in my calculations as it accounts for Maximum Material Condition. For clarity, though, the Maximum Pitch Diameter is 1.1932" for a 2B thread.

I hope that was helpful :) It would take me a bit more work to look up, calculate and transcribe the die dimensions...

J Tiers
11-10-2014, 01:21 AM
That brings up a question....

If the PD is the same as for a sharp V, but the thread is made with the flats, should not the actual as-made part with flats be smaller than the major diameter listed?

If the flatted crest is made at the major diameter, it seems the PD must be different than with sharp V and they would not be compatible.

The major diameter you show is for the theoretical sharp crest. That may indeed be more in-period for the machine, so might be what the OP wants.

But to be generally useful AND fit that machine, the use of the modern profile seems best. Then the flat would be 0.866 x 1/8 pitch smaller on the radius, double that as a reduction for the diameter.

Paul Alciatore
11-10-2014, 04:13 AM
I can't go back any further, but I have a copy of Machinery's Handbook, 14th Edition, 1952. It does not list a 1 1/4 - 10.

1 1/4 - 7 Cut Thread TAP sizes:
Major Dia, Basic: 1.2500"
Major Dia, Min: 1.2587"
Major Dia, Max: 1.2632"
Pitch Dia, Basic: 1.1572"
Pitch Dia, Min: 1.1582"
Pitch Dia, Max: 1.1617"

1 1/4 - 12 Cut Thread TAP sizes:
Major Dia, Basic: 1.2500"
Major Dia, Min: 1.2555"
Major Dia, Max: 1.2600"
Pitch Dia, Basic: 1.1959"
Pitch Dia, Min: 1.1969"
Pitch Dia, Max: 1.1999"

1 1/4 - 7 Ground Thread TAP sizes:
Major Dia, Basic: 1.2500"
Major Dia, Min: 1.2600"
Major Dia, Max: 1.2620"
Pitch Dia, Basic: 1.1572"
Pitch Dia, Min: 1.1582"
Pitch Dia, Max: 1.1597"

1 1/4 - 12 Ground Thread TAP sizes:
Major Dia, Basic: 1.2500"
Major Dia, Min: 1.2565"
Major Dia, Max: 1.2575"
Pitch Dia, Basic: 1.1959"
Pitch Dia, Min: 1.1969"
Pitch Dia, Max: 1.1979"

The minimum and maximum diameters are all greater than the basic diameters. This would be to allow an allowance for proper fit. The ground taps are held to a tighter standard than the cut taps.

This edition of the handbook does not list tables for the limits on die sizes. My assumption would be that they are the same as that for the external screw threads. It is the taps that are a bit over-sized to product the needed clearance between an external thread and a tapped hole. If I am wrong on this, please do correct me.

I checked that above, 1952 numbers against those in Edition 26, 2000. The cut thread numbers are identical but some of the ground thread numbers have been changed.

I think your best bet is to measure the pitch diameter of the threads you have and go from that.

I tried hard to understand Machinery's Handbook's treatment of tap dimensions. Fail!

What should be the maximum diameter of the thread on the tap? 1.25" 1.28" ??
For the die, the OD cut should be ?? 1.23" 1.22?

Will be making out of mystery tool found at my friendly neighborhood industrial surplus store.

Will be making these to use in cutting lathe accessories for my 1885 F.E. Reed lathe.

John Buffum
11-10-2014, 07:40 AM
I produced a collar as a basis for a face plate. Just kept cutting the threads deeper until it became a snug fit. I started with a TT carbide with a 1/64th radius in a homemade boring bar. I finished with a homemade SS internal thread cutter with a sharp point. The sharp point removed VERY little, deep in the groove, but made a big difference. I'll then weld a piece of 1/4" plate, and finish grind on the lathe.

Today, I'll remove and measure the collar's minor diameter and report.

Yeah, try 5/16-20 threads for accessory brackets. 1/2-12 holding the legs on, and machine screw size holes I can't get the thread pitch gage into. Square heads on all original bolts.

The bearings are GREASED, not oiled.

The threads on the spindle were badly damaged, the first 3 threads, but the rest are OK, I CAREFULLY restored them with a triangular file. Seems to work, and, using that collar to measure, the runout of the spindle thread nose is way under a thou.

I was going to be working on a 1911 Rumely Model E, 1/5 scale, but this is taking most of my time. Still, it DIDN'T end up in a scrap yard. It makes me feel SICK thinking of how many fine, old lathes end up in scrap yards so someone can have cast iron legs on dining room tables, HIDDEN BY THE TABLE CLOTHS, so no one even SEES them! Grrr! :mad:

J Tiers
11-10-2014, 08:22 AM
I produced a collar as a basis for a face plate. Just kept cutting the threads deeper until it became a snug fit. I started with a TT carbide with a 1/64th radius in a homemade boring bar. I finished with a homemade SS internal thread cutter with a sharp point. The sharp point removed VERY little, deep in the groove, but made a big difference.

Typical of sharp V threads. Had teh same issue with a Logan spindle and SB faceplate. Had to scrape out the tips to fit, one was sharp V, the other had the newer flatted tip profile.

Video Man
11-10-2014, 12:54 PM
A lathe that old could not have Unified threads, probably National Form, back then probably called U.S. Standard thread. Some info that might be helpful:

From a very old Atlas lathe manual: External National form 10 thread single depth of thread 0.0650 for a flat crest thread, 0.0758 for a v-form (sharp trough but leaving the top with the proper amount of flat) thread. It shows the major diameter for either thread as the same as the nominal diameter, in this case, 1.25 inches.

1.25-10 is not listed, but for guidance, 1.25-7 is listed as major diameter 1.250, minor diameter 1.0644, pitch diameter 1.1572. A 0.75-10 National form thread is listed as major diameter 0.750, minor diameter 0.6201, pitch diameter 0.6850 if that's any help.

About the flat crest thread form the manual says: "These threads for 60 degree Vee threads with the points cut off so that the depth is 75% of the depth of a Vee thread of the same pitch." Depth of thread is given by pitch *.64952 for the flat crest and trough, and pitch * 0.866 for the sharp-v form ( in this case, sharp v at top and bottom both).

FWIW a program I have calculates a UNC 1.25-10 thread tap drill at 1.150 inches, if that's any help. All this info, of course, is about the thread size, not the tap size specs.

Paul Alciatore
11-10-2014, 02:05 PM
I think there is way too much concern here about an exact, theoretical thread size. The beauty of a Vee thread for mounting a lathe chuck is that it is self centering.

I cut chuck back plates by test fitting them on the spindle. You can mount your stock in a chuck or on an existing face plate and face and bore it. Then start threading and take it off the spindle, STILL MOUNTED IN/ON THE CHUCK OR FACEPLATE and do a trial fit on the spindle. Remount it for cutting and cut the thread a bit deeper and test again. Continue until it fits properly. Both the existing faceplate/chuck and the new plate you are making will recenter on the spindle the same way each time they are mounted.

And, because the threads are a Vee form, THERE CAN BE SOME CLEARANCE BETWEEN THEM AND THE SPINDLE while still maintaining that self centering feature. In fact, there MUST be some clearance for self centering to actually work. So don't get too worked up about a precise thread fit.

Some have advised that you need to make a precise copy of your spindle threads to test new accessory threads while you are cutting them. The fact that you can remove the work and test it on the actual spindle negates this idea. You CAN test them on the actual spindle itself.

Oh, a bit of an inspection with a magnifier (10X?) should be done to determine if the existing thread is a sharp Vee or a more modern form with flats and fills. Incorporate this knowledge in your thread cutting.

John Buffum
11-10-2014, 03:49 PM
OK. The collar internal was 1.135" and the spindle thread external was 1.235. The bottom is SHARP, and the top is, indeed, rounded, but is that from over a century and a half of use?

I'm making a 12" face plate, and my South Bend maxes at 9". Creativity and a lot of measurement.

I'll weld on 5 webs from the hub to very near the edge, then roll a piece of 1/4 x 1/2 to weld to the rim. I then let is sit a week, then mount it on the Reed, and use my Home Shop Machinist article tool post grinder to grind it. If I was reasonably competent, there shouldn't be that much to grind.

A 10" aluminum face plate comes next with T-slots. After that, a steady rest. Waiting for word back from T de G about the chuck jaws.

Yes, I definitely plan to make a copy of the spindle threads for a thread gage. Probably out of machinable stainless. I am, today, working a piece of scrap S-7 to make a tap. This thread is about that process. Egad but S-7 is tough. Can't do hog cuts with the South Bend. Later comes a 2-1/2" x 2-1/2" scrap S-7 to make the die. Should I make the tap and die to the spindle, or to the 1-1/4" "standard"?

Off to the races, here.

Scored a 1-1/2 -8 tap for \$10 at a flea market! Scored a 1-1/2 -8 die for \$25 at Acme Industrial Surplus, where Wiley Coyote shops!

Paul Alciatore
11-10-2014, 08:54 PM
Because you do not know the exact size of the flat/round at the top of the threads, you can not use the OD measurement to make the tap. You really do need to measure the PITCH diameter of the spindle thread.

If the spindle pitch diameter is greater than that shown in the tables, then you need to use the actual pitch diameter of your spindle to specify the tap. On the other hand, if it is smaller, then you can use either one: I would use the standard one from the tables in MH. The pitch diameter of the tap should be a bit larger than the one you choose above, perhaps 0.001" to 0.002" larger. Making it larger than that, within reason, will be OK. By going from the pitch diameter you will ensure that the threads will fit. If you go from the OD, you may discover that your tap cuts a thread that is too small and there is no way to increase it's diameter after it has been made. You would have to start from scratch and make another one.

You seem to indicate that the threads were probably a sharp Vee when it was made. I would go with a very small flat on the tap's threads, perhaps 0.002" or 0.003". No more. In the valleys of the tap, I would use a more generous flat or radius, perhaps 0.005" to 0.010". Both of these choices will cause the tap to remove more material in the hole and the sharp Vee thread will not interfere with the female thread it cuts.

John Buffum
11-10-2014, 09:19 PM
I finished cutting the threads on the new tap. 1.249" with sharp points. Sharp valleys. The sleeve I made for the spindle test is too snug and won't fit on the tap, but is an easy, tho not sloppy fit on the spindle. Wear on the spindle, or a thread size made up as they went along? I don't know. I'm going to sleep on it. If I want this tap for the lathe, alone, it must be sized for it, not a standard created a quarter century later. As you say, once cut, no going back.

As has been stated, sometimes taps are made a bit large to allow the tapped hole to be an easy slip fit on the bolt, almost a wobbling fit.

Does S-7 expand when it's fired and tempered?

andywander
11-10-2014, 10:23 PM
This is a common misconception; the flatted crest has nothing to do with the OD that you should start with. In fact, for the tightest tolerance and allowance, I believe that the OD of a rod to be threaded(and also it's OD after threading) is the nominal size of the thread, in this case 1.25".

The nominal size of a 1-1/4" external thread is 1.25" TO THE FLATTED CREST, not to the theoretical sharp V thread.

I make it 1.228 max diameter on bolt, , based on the flat of 1/8 pitch on the thread crest.

Tap should clear that, the spec has a flat or equivalent at 1/4 pitch. so the nut ID would be 1.033 or so.

That's based on thread specs that your lathe is dated well before. It wasn't made to them. So you may be looking at sharp V threads in most places on your machine.

J Tiers
11-11-2014, 01:03 AM
This is a common misconception; ............................

The nominal size of a 1-1/4" external thread is 1.25" TO THE FLATTED CREST, not to the theoretical sharp V thread.

Considering that my copy of H28 SHOWS the flat as being cut below the major diameter...... which is shown as the V crest, it seems that the theoretical V crest is still the major diameter. The V form is referred to as the "basic profile" and the location and slope of the thread flanks are shown as identical for both the basic and the flatted profiles.

I suspect the "misconception" is the other way round.

If that were not the case, and the "crest" or major diameter were actually made to the flat, then the PD of the sharp V and the PD of the flatted standard thread would be different for the same nominal size bolt, and the flatted profile would be the larger PD.

But they are not different. The flatted will always screw into a nut of that size, although the sharp V may not screw in due to interference of the sharp crest and the nut profile.

andywander
11-11-2014, 01:40 AM
Considering that my copy of H28 SHOWS the flat as being cut below the major diameter...... which is shown as the V crest, it seems that the theoretical V crest is still the major diameter. The V form is referred to as the "basic profile" and the location and slope of the thread flanks are shown as identical for both the basic and the flatted profiles.

I suspect the "misconception" is the other way round.

If that were not the case, and the "crest" or major diameter were actually made to the flat, then the PD of the sharp V and the PD of the flatted standard thread would be different for the same nominal size bolt, and the flatted profile would be the larger PD.

But they are not different. The flatted will always screw into a nut of that size, although the sharp V may not screw in due to interference of the sharp crest and the nut profile.

I'd like to see what you are looking at, J. :confused: The picture below is from p.1706 of MH26, and it is pretty clear that the Major Diameter is at the flat, NOT at the theoretical sharp point. The only thing that goes to the points is "H", which is the theoretical full depth of a sharp V thread, which is only used to calculate the actual depth of the thread(5/8H). The "Basic Profile" of the thread is the heavy line which moves along the flats and the flanks, NOT the construction lines that go to the points. And the pitch diameter is still at the "halfway" point of the theoretical sharp thread, even with the asymmetrical flats at root and crest.

Take a look; I think you'll see what I mean.

If you have a reference that shows something else, I would be very interested in seeing it!

J Tiers
11-11-2014, 08:30 AM
Oh, of course.... It has been mentioned many times that it is the flat. And, the tables of course give the 1" to the flats.

I think it's goofy, though. It's a sort of misconception from the beginning....

Given that, the standard 1" bolt has been changed in dimension, with the PD corresponding to, not the old 1" bolt, but now a 1" bolt is really a 1.021" bolt.

There should be some trouble getting a new 1.021" bolt into an old 1" sharp thread nut. But for some reason I have never had any particular trouble getting any combination of hardware to assemble, old, new, etc, even though there ought to be a problem..

andywander
11-11-2014, 09:21 AM
Oh, of course.... It has been mentioned many times that it is the flat. And, the tables of course give the 1" to the flats.

I think it's goofy, though. It's a sort of misconception from the beginning....

Given that, the standard 1" bolt has been changed in dimension, with the PD corresponding to, not the old 1" bolt, but now a 1" bolt is really a 1.021" bolt.

There should be some trouble getting a new 1.021" bolt into an old 1" sharp thread nut. But for some reason I have never had any particular trouble getting any combination of hardware to assemble, old, new, etc, even though there ought to be a problem..

Well, PD may correspond to what it would be if you made a sharp-crested bolt of 1.021".....but why would you ever do that?

It's not like you need to start with a 1.021" diameter piece of stock, thread it until the crests are sharp, and then "take it down" to 1", thereby creating the flats.

Just start with a piece of 1", and cut the threads until it is the correct depth, leaving the proper flats at the crests.

George Bulliss
11-11-2014, 09:43 AM
Does S-7 expand when it's fired and tempered?

Yes, it does expand and move a bit, though it is one of the more stable tool steels. I've cut things finished before heat treat and allowed for the growth. Can't remember the exact numbers, but it was something in the range of a couple of ten thousandths per inch of stock – I think.

J Tiers
11-11-2014, 10:44 AM
Well, PD may correspond to what it would be if you made a sharp-crested bolt of 1.021".....but why would you ever do that?

It's not like you need to start with a 1.021" diameter piece of stock, thread it until the crests are sharp, and then "take it down" to 1", thereby creating the flats.

Just start with a piece of 1", and cut the threads until it is the correct depth, leaving the proper flats at the crests.

Means the two have different PDs sharp vs national for SAME sized nominal bolt. You missed the point of the comment.

National 1" has the PD of a 1.021" sharp.

Toolguy
11-11-2014, 11:14 AM
I would just use calipers to measure the spindle threads by putting the jaws in the grooves of the thread. Record that number. Make the tap so it is .002 -.005 above that number when measured the same way. Not much math needed. You will more or less be measuring the pitch diameter, not worrying about all the theoretical stuff. The caliper will be angled 1/2 the pitch when doing the measurement. It is an accurate and simple way to do a comparative thread measurement for a job such as this.

You can also make a copy of the spindle thread for a thread gage for a die this way too, just make it the same size as the spindle.

sarge41
11-11-2014, 11:42 AM
John: In post #6, you mentioned that you had some machine screw sized holes that were mystery size, if you haven't worked it out already, a trick I use on something like that is to turn a wooden dowell rod down to a size about .010 to .015" bigger than the minor dia. Screw it in by hand and then out. This will show you the pitch and minor dia. Good luck.

Sarge

Rosco-P
11-11-2014, 02:27 PM
A lathe that old could not have Unified threads, probably National Form, back then probably called U.S. Standard thread. Some info that might be helpful:

From a very old Atlas lathe manual: External National form 10 thread single depth of thread 0.0650 for a flat crest thread, 0.0758 for a v-form (sharp trough but leaving the top with the proper amount of flat) thread. It shows the major diameter for either thread as the same as the nominal diameter, in this case, 1.25 inches.

1.25-10 is not listed, but for guidance, 1.25-7 is listed as major diameter 1.250, minor diameter 1.0644, pitch diameter 1.1572. A 0.75-10 National form thread is listed as major diameter 0.750, minor diameter 0.6201, pitch diameter 0.6850 if that's any help.

About the flat crest thread form the manual says: "These threads for 60 degree Vee threads with the points cut off so that the depth is 75% of the depth of a Vee thread of the same pitch." Depth of thread is given by pitch *.64952 for the flat crest and trough, and pitch * 0.866 for the sharp-v form ( in this case, sharp v at top and bottom both).

FWIW a program I have calculates a UNC 1.25-10 thread tap drill at 1.150 inches, if that's any help. All this info, of course, is about the thread size, not the tap size specs.

John Buffum
11-11-2014, 03:13 PM
Decided to make the tap to support lathe accessory building. Everything fits. Next door neighbor wrapped it in tool wrap and is cooking it. The oil bath awaits. Final dimension of pointy threads 2.245". Again, the spindle threads is 2.235, but with rounding. I'm holding my breath. A snug fit in the test collar.

If the tap works well, we do the die - adjustable!;)

More tomorrow.

cameron
11-11-2014, 03:32 PM
Means the two have different PDs sharp vs national for SAME sized nominal bolt. You missed the point of the comment.

National 1" has the PD of a 1.021" sharp.

What is the point of the comment? Of course a nominal 1" sharp thread would have a different PD than a 1" standard national of the same pitch.

Paul Alciatore
11-11-2014, 03:34 PM
The numbers I posted here ARE from the old US Standard but it was not a sharp Vee thread. Unfortunately the 1 1/4 - 10 was not a standard thread under that standard and was not included. So it is a special thread, then and now, and all numbers would have been at the discretion of the lathe manufacturer.

RE: All the discussion about the OD and flat vs. sharp. The OD is indeed measured to the flat, not to the missing Vee point which would have been higher. This does indeed increase the PD (pitch diameter). But, as my 1952 edition of MH shoes, the pitch diameters of the American Standard threads AT THAT TIME were exactly the same as they are today. Not even a tenth difference. So, the American Standard at that time was essentially the same as the Unified Thread Form of today. That, 1952 edition of MH shows the sharp vee thread as a reference the past and does not show any numbers for it. My point is that the change from sharp Vee to UNS was made a lot earlier in time and I doubt that anybody here today was ever able to go out and buy any sharp Vee hardware.

Some sharp Vee hardware probably existed and I do not doubt that it probably caused some problems when those screws and nuts were no longer available. Tapped holes were probably "cleaned out" with a new tap. Old nuts would fit the new bolts so no problem there. Other problems also had to be dealt with, like the 3/16" vs #12 thing. And now we have inch vs metric.

John says he has already made a tap to the present standard. I can not be sure, but I fear that if the lathe's threads are sharp Vee, that tap will be too small and the internal threads it cuts will not fit on his spindle. I hope this is wrong.

In a situation like this, you really do have to go by the pitch diameter. Or some other method of measure on the sides of the thread, as Toolguy suggests. It is going to be hard to keep a tap of that diameter straight and concentric. Personally, I would single point the threads on the back plates or face plates I was making and just test them on the spindle itself. Been there. Done that. It works. Tee shirts on order.

I can't go back any further, but I have a copy of Machinery's Handbook, 14th Edition, 1952. It does not list a 1 1/4 - 10.

1 1/4 - 7 Cut Thread TAP sizes:
Major Dia, Basic: 1.2500"
Major Dia, Min: 1.2587"
Major Dia, Max: 1.2632"
Pitch Dia, Basic: 1.1572"
Pitch Dia, Min: 1.1582"
Pitch Dia, Max: 1.1617"

1 1/4 - 12 Cut Thread TAP sizes:
Major Dia, Basic: 1.2500"
Major Dia, Min: 1.2555"
Major Dia, Max: 1.2600"
Pitch Dia, Basic: 1.1959"
Pitch Dia, Min: 1.1969"
Pitch Dia, Max: 1.1999"

1 1/4 - 7 Ground Thread TAP sizes:
Major Dia, Basic: 1.2500"
Major Dia, Min: 1.2600"
Major Dia, Max: 1.2620"
Pitch Dia, Basic: 1.1572"
Pitch Dia, Min: 1.1582"
Pitch Dia, Max: 1.1597"

1 1/4 - 12 Ground Thread TAP sizes:
Major Dia, Basic: 1.2500"
Major Dia, Min: 1.2565"
Major Dia, Max: 1.2575"
Pitch Dia, Basic: 1.1959"
Pitch Dia, Min: 1.1969"
Pitch Dia, Max: 1.1979"

The minimum and maximum diameters are all greater than the basic diameters. This would be to allow an allowance for proper fit. The ground taps are held to a tighter standard than the cut taps.

This edition of the handbook does not list tables for the limits on die sizes. My assumption would be that they are the same as that for the external screw threads. It is the taps that are a bit over-sized to product the needed clearance between an external thread and a tapped hole. If I am wrong on this, please do correct me.

I checked that above, 1952 numbers against those in Edition 26, 2000. The cut thread numbers are identical but some of the ground thread numbers have been changed.

I think your best bet is to measure the pitch diameter of the threads you have and go from that.

J Tiers
11-11-2014, 07:30 PM
What is the point of the comment? Of course a nominal 1" sharp thread would have a different PD than a 1" standard national of the same pitch.

(Edited to be some what polite)

The point is that the two would be totally incompatible, yet that is not what is seen, at least aside from the sharp V interfering, they actually screw together, but they logically should not.

And, there is ABSOLUTELY NO "of course" whatsoever involved.

One would expect that a 1"-8 screw would be generally compatible with a 1"-8 nut. It's not at all like a total makeover to metric or whatever..... it's all V-threads, 60 deg, with substantially the same pitches involved.... pretty much the same stuff.

But a 1"-8 NS should not be in any way compatible with a 1"-8 sharp V nut, based on the PD differences.

The other odd thing is that that seems to not be the case. I have old sharp V hardware, and it appears to fit whenever the "direction" is old nut on new bolt. The reverse is not so easy, since the crest hits the nut.

In other words the behavior does not seem to fit the differences that are actually in the tables in the book (and at least one diagram is messed up, appearing to disagree with the tables)

I have to assume that the old stuff was so sloppy as to not matter.

Paul Alciatore
11-11-2014, 10:57 PM
J, the secret is allowances. There is an allowance between the bolt size and the nut size. The thread in the nut is larger than the largest allowable one for a matching bolt. I am sure that when they adopted the US Standard and then the Unified Thread Form they were WELL aware of the sizes of the older, sharp Vee threads and of the allowances that were specified for them. AND for the amount of allowance that the manufacturers were using at that time, which was probably larger than the required amount in the spec. In short, they probably leaned on a generous amount of allowance being present in the older nuts and the manufacturers of the new standard bolts probably leaned toward the smaller side of the tolerance range.

I would imagine that there were probably some, perhaps many instances where this did not work and a tapped hole had to be "cleaned out" or an older, sharp vee nut had to be tossed and a newer one substituted. The fact that you have one or a limited number of instances where the old and the new can properly mate does not mean that is the case in all instances.

John Buffum
11-12-2014, 08:28 AM
WOW! Threading is as gnarly a topic as religion and politics!

Last night was the "drawdown". 500 degrees for an hour, then the oven turned off and allowed to cool. Today, the polish and test.

After I change shocks on the Saturn, it's on to the motor lift lever for the Reed lathe. Pull the lever, change which pulley the belt is in, release the lever. Will have a pawl to hold it. Neat stuff!

Thank you all for the depth of advice on threading. If I was producing landing gear bolts for heavy lifter aircraft, I'm sure your information would have been absolutely critical, particularly for something like a "Connie".

I'm going to save these exchanges. They were certainly more informative than Machinery's Handbook, which just crossed my eyes, and made me dizzy.

Just an idea. Tho a crazy one. If one of the threaded parts can be spared, carefully saw it, and microscope a section. Bounce it against the information you so generously provided. That would tell most. In this case, I couldn't do that. I COULD put mold release on the best part of the threads, near the collar, then build a frame of clay, then pour epoxy. When the epoxy is hard, remove and cut, then microscope.

Can you post pictures on this forum? My Nikon d5100 takes EXCELLENT macro (close-up) shots.

RichR
11-12-2014, 09:41 AM
Hi John
You can post pictures but you have to upload them first to a hosting site. I use Tinypic.com because there is no signup or logging in required, just an
occasional captha to make sure you're not a bot. After your picture is uploaded, it provides you with four links. Copy the one labeled Forum and