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firbikrhd1
03-31-2014, 09:00 AM
In reading my Atlas "Lathe Operation" book I came across a gauge that is designed to be used as a guide to grind HSS tool bits to the proper form for the National Thread form. After searching for one on the web, Starrett's online catalog and eBay I came up empty. Anyone have an idea where to get such a tool? The one illustrated in the Atlas book on page 96, Figure 130 is round with 60 degree "V" shapes cut around it's circumference. At the bottom of each "V" is the appropriate sized flat for the thread pitch being cut. Such a gauge would be handy for grinding HSS tool bits to the proper shape for true to form National Form threads.
Unfortunately the picture in Figure 130 is too small to see a manufacturer's name or number on the tool shown.
Thanks in advance!
Steve

chucketn
03-31-2014, 09:06 AM
Are you asking about a "Fishtail" or Centering gage? Google those names, you'll find lots of examples and explanations.

Chuck

loose nut
03-31-2014, 09:22 AM
You would have a hard time finding a round one. They are call a "fish" because they look like a fish and are actually more useful because they are used to align the threading tool to the work.

TGTool
03-31-2014, 09:33 AM
The OP is asking about a way to gauge the flats at the roots of threads that the National form calls out. A fishtail won't do that, it's made with a sharp V, though that also means it will fit any thread pitch.

loose nut
03-31-2014, 09:50 AM
Do they make a gauge like that anmore???

Haven't seen one, most people just eye ball it. If you are doing critical work then something better would be needed, like a comparator. If the big online tool companies like McMasters, Production tool etc. don't have it it probably isn't available.

Willy
03-31-2014, 09:58 AM
I believe that the OP is refering to a gage like the one pictured in fig.160 of this page (http://www.hnsa.org/doc/tools/part3.htm). I haven't seen one like that for quite some time not sure if they are still available or not.

Have you thought about using a thread pitch gauge? Lots of those around.

plow boy
03-31-2014, 11:28 AM
I believe it is fig. 170 in Willy's link. If so I got one off e-bay a week or so ago. The ones i have seen were made by Brown&Sharpe

loose nut
03-31-2014, 11:34 AM
When was it made.

plow boy
03-31-2014, 11:46 AM
I don"t know when they were made but I could not find a new one.

firbikrhd1
03-31-2014, 02:56 PM
TG and Willy have it right, I'm looking for the gauge they are referring to, not the fishtail gauge.

plow boy
03-31-2014, 04:04 PM
Yes Willy is right. I was looking at the page number not the fig#. Sorry about that. but that is the type I bought. so keep a watch on E-bay

andywander
03-31-2014, 04:41 PM
Bear in mind that these days, you would need 2 of these gages, one for internal thread tools, and one for external thread tools.

RussZHC
03-31-2014, 05:05 PM
Looking and looking and looking...so far the closest thing I can find is "thread profile gauge" and there are a few companies that make those (appear to be mostly oil field related work) some of which list nearly all thread profiles you could think of, "problem" would be you would need to get/order a gauge for each thread you planned to make (the gauges I saw could be several inches long, depending on profile) and then work backward by grinding to fit a given profile. I have a pretty old Starrett catalog and there is nothing I could see in there (its old enough to have several pages of wire gauge gages, piano, spoke etc.).

No joy so far finding an "all in one" sort of gauge you saw (had to look in my copy of "Lathe Operation" to see exactly which one you meant)...oh and while I found some Brown and Sharpe, round, those were for Acme thread form.

Edit: On page 75 of my copy HTRAL, there is a similar photo and its clear enough to see that it is a Brown and Sharpe made gage, "Standard Screw Thread Tool Gauge" and they go on to state, "...finer than 10tpi the point is usually left sharp or with a very small flat...for coarser pitches and when maximum strength is desired, the flat on the point should be one-eighth (1/8) of the pitch."
Further, based on a PM thread, it's a #724 http://www.practicalmachinist.com/vb/tooling-parts-accessories-sale-wanted/wtb-brown-sharpe-thread-gauge-217003/

Carld
03-31-2014, 07:45 PM
Be careful with a flat on the end of the V. If you don't cut the V deep enough, that is, have to wide a flat on the V of the cutter tool, the internal and external threads will interfere with each other. I have found it best to just stone a small flat on the end of the V rather than try to get the specified flat on the V. If your cutting a class thread all those dimensions are critical if you want the thread to actually fit. Better a small flat than to wide a flat.

Paul Alciatore
03-31-2014, 07:48 PM
If you are going to use a gauge to check a thread cutting tool, I would wonder why you would want a gauge with the flat at the point of the Vee. The flat, at the 10 or 12.5% point on the thread form drawings represents the limit of that feature. In practice, that feature on the cut or otherwise produced thread can be at ANY location and of any shape (arc, flat, oval section, whatever) between the single point of a sharp Vee to the flat shown in the specification. This "feature" of a screw thread is included in the specification to allow a certain amount of wear on the tool that is cutting the thread before it must be resharpened or replaced. It is not producing an out of spec thread until it wears PAST that point. So notice that a tool that is worn out of spec would fit in the flat bottomed Vee gauge while one that is in spec would NOT.

Therefore, if you had a Vee gauge with that flat on the apex of the Vee, a properly sharpened tool would either just barely fit that gauge or would NOT fully seat in it. This is because the tip of the in spec tool would be longer than the depth of the Vee. And even if it just fits or if it has only a small amount of interference with the flat of the gauge, if the tool has an arc shape (a radius instead of a flat) then that tool would NOT be in spec because the edges of that arc would be outside of the profile.

A thread cutting tool that is made to that flat shape would not last long in use. All practical tools would be sharpened with a smaller flat or radius to allow for wear as it is used.

When I sharpen a threading tool I first sharpen it to a sharp Vee and then lap it on a stone to both improve the sharpness of the edges and also to give it a small radius at the tip. The size of that radius is perhaps 1/4 to 1/2 the size that would just fit under the flat shown in the thread specs. An arc will produce a stronger thread by avoiding the two stress risers that a flat would produce and is a lot easier to make. It does NOT have to be any precise size, just within a range for the desired thread pitch. And actually, most of the time I will sharpen such a tool with a radius on the small end of a particular thread size so it can also cut several smaller threads (and one or two larger ones too).

I think that such a gauge would be a waste of money. Get the fish gauge with sharp Vees that others have described above If you want more precision in making these tools, I would look at optical comparators with the appropriate scales. Or a zoom microscope so one scale can serve for several thread sizes.

On the other hand, if you are inspecting the threads that have been cut, a standard, high quality, thread pitch gauge would be the thing. If they are well made, they should have the proper sized flats and with appropriate magnification, would be good for inspecting the cut threads. Check on this feature BEFORE buying them.

becksmachine
04-01-2014, 11:27 AM
The flat, at the 10 or 12.5% point on the thread form drawings represents the limit of that feature. In practice, that feature on the cut or otherwise produced thread can be at ANY location and of any shape (arc, flat, oval section, whatever) between the single point of a sharp Vee to the flat shown in the specification. This "feature" of a screw thread is included in the specification to allow a certain amount of wear on the tool that is cutting the thread before it must be resharpened or replaced. It is not producing an out of spec thread until it wears PAST that point. So notice that a tool that is worn out of spec would fit in the flat bottomed Vee gauge while one that is in spec would NOT.


As a general rule for HSM use I would agree, but this seems to indicate otherwise in the rarified atmosphere of thread specifications. It seems that I recall something about an API standard that also specifies a minimum flat/radius at the root diameter.

Dave

http://www.ring-plug-thread-gages.com/ti-UN-BACD-2086.htm

90LX_Notch
04-01-2014, 09:10 PM
You don't need a guage you can measure the flat with a mic and a scale.


To measure the width of the flat:

Measure the diameter of your micrometer spindle.

Lay a scale against the sides of both the spindle and the anvil of the micrometer.

Place the point/flat of the threading tool against the scale.

Measure the width of the threading tool with the micrometer while continuing to hold the flat against the scale. This is the width across part of the 60 degree angle.

Width of flat= width of tool - (2 X spindle diameter X tan 30)

This gives you what the flat actually measures. You grind the flat until this measurement equals 1/8 of the thread pitch.

-Bob

firbikrhd1
04-01-2014, 09:16 PM
Thank you to all for your input and suggestions. I'll watch eBay for a gauge, although I know I don't really have to have one. I just thought it would be an easy way to grind a proper tool. Until I get one I'll just cut sharp V threads to 75% of the depth and leave the tops flat.

andywander
04-01-2014, 09:26 PM
You don't need a guage you can measure the flat with a mic and a scale.


To measure the width of the flat:

Measure the diameter of your micrometer spindle.

Lay a scale against the sides of both the spindle and the anvil of the micrometer.

Place the point/flat of the threading tool against the scale.

Measure the width of the threading tool with the micrometer while continuing to hold the flat against the scale. This is the width across part of the 60 degree angle.

Width of flat= width of tool - (2 X spindle diameter X tan 30)

This gives you what the flat actually measures. You grind the flat until this measurement equals 1/8 of the thread pitch.

-Bob

1/8 of the thread pitch is only good for an internal threading tool.

For an external threading tool, you want the flat at the tip of the tool(which will be the root of the external thread( to be 1/4 of the pitch.

andywander
04-01-2014, 09:29 PM
Thank you to all for your input and suggestions. I'll watch eBay for a gauge, although I know I don't really have to have one. I just thought it would be an easy way to grind a proper tool. Until I get one I'll just cut sharp V threads to 75% of the depth and leave the tops flat.

With a sharp tool you would cut to 75% depth of the theoretical sharp thread depth on an internal thread.

For an external thread you would have to cut to 7/8 (or 87.5%)of the theoretical sharp thread depth.

garyhlucas
04-01-2014, 10:12 PM
I believe that the OP is refering to a gage like the one pictured in fig.160 of this page (http://www.hnsa.org/doc/tools/part3.htm). I haven't seen one like that for quite some time not sure if they are still available or not.

Have you thought about using a thread pitch gauge? Lots of those around.

Interesting link, I think I have every tool tool pictured except the snap gauges. A friend gave me the contents of a machinists tool chest he bought at a yard sale. He wanted the box!

andywander
04-02-2014, 12:35 AM
Here is a shot of the No. 724 gauge in a 1916 Brown & Sharpe Catalog.

Note that the flats are 1/8 of the pitch, and would only be usable today for an internal threading tool.
http://i1369.photobucket.com/albums/ag204/andywander/BampS724_zps17b6adbb.jpg

I am not sure what year the standard was changed from using the 1/8 pitch flat at roots of both internal and external threads, to using 1/4 pitch flat at root of external threads, and 1/8 pitch flat at root of internal threads.

firbikrhd1
04-02-2014, 08:25 AM
Well shoot! Now that I've asked the question I've learned just how dumb I am. All of my references are older, such as the Atlas lathe book, South Bend book etc. Even my copy of the Machinist's Handbook is ancient. So, apparently part of my problem is that I don't know what the current standards are. Anyone have any suggestions of a book that explains current standards in SIMPLE terms so even an idiot like me can understand them?

Up until now I've been able to single point threads that work using a sharp V ground tool bit with the tip touched to a stone. I just wanted to be able to cut threads that were more proper in form, hence the reason for wanting the gauge.
Now I need an understanding of modern current thread standards in order to do that. Maybe I'll just go back to my old method and forget it.

90LX_Notch
04-02-2014, 09:32 AM
andywander is correct about the .25P for external and .125P for internal being current and textbook. However, .125P works fine for both in the homeshop. If you want to be textbook, you still can do it. What I posted earlier still applies; just grind the threading tool until you reach .25P for the width of the flat.

-Bob