Thread: Information Chart for Threading on a Lathe.....

There seems to always be questions from time to time regarding threading and related problems, so I thought I would post this chart showing the depth and double depth of National Form Threads.

Yeah, I know, you experts out there don't need this but perhaps it will benefit someone new to turning threads on their new lathe. This covers the info needed to turn threads from 4 TPI to 96 TPI.
Newbies may want to keep a copy nailed on the wall above their machines........pg

Thank you VERY MUCH for that post, pg. Those last two columns in this chart are pure gold. I have seen charts that gave the thread depth and other specs, but never one that gave the ACTUAL COMPOUND MICROMETER DIAL FEED for the proper thread depth the compound set at 29 1/2 degrees. That pretty well removes the guess work.

I was just about to launch into cutting a 1" thread for a shell mill arbor I have built, so I'll be able to put this to use immediately. BTW, I'll try to post pics of this arbor when I get finished... it's a 2" shell mill arbor in Kwik Switch 300, heheh. It's to hold big 6-8" facemills on my bridge mill.

Wow, that's cool, I like it! That's going to get printed, laminated, and stuck right to the backsplash of my lathes. It's such a GREAT idea to convert the cut depths to the total feed for the compound. Thank you for that!

So: Is National Form current? Last I heard we were working with Unified (UNF/UNC). Any difference?

Good question John. I'll wait for an answer before copying and tacking up.

Paul

That table does NOT agree with the table in Machinery's Handbook #27 page 1734 Table 1 American Standard Unified Inch Screw Thread Form Data. The thread depths for "sharp Vee", for example, are completely different. It might be better to re-work the table from MH and calculate the compound travel for each depth.

compound travel = depth/(cos 30*)

Put it all in a spreadsheet and print.
Might be better to even just calculate all the stuff you need for a given thread... just make up a script or form in Excel (or whatever). Nice thing would be to have the compound travel, wire size and dimension-over-wires for a given thread pop out of the calculations. In other words... the dimensions one has to cut to and the values one should measure for a given thread.

Doesn't someone already make such a program?

-DU-

Is the chart correct?
That I cannot answer, but I can say that I have used it since the early 1970's and the threads I turn fit the standard nuts and bolts I buy at the hardware store. What more can I ask for?

The chart comes from the Atlas Lathe 'Manual of Lathe Operation and Machinists Tables'- sixteenth edition 1955, published by the Atlas Press Company. Out of date? Yes, 1955 is a bit dated.

However, this is the only publication that I have ever seen that gives one the amount of compound advance for a given thread. Note too that this info has the compound set at 29 degrees. Now, where else have you seen that? I will also note that if your lathe has direct reading dials then you want to double the figure in that far right column. Example, for a 5/16-18 the figure is .047. With direct reading dials this becomes .094. I also use only the V form tool....a sharp 60 degree.

As far as the Machinery Handbook saying 'compound travel = depth/(cos 30*)'. I certainly will not argue with that.
But what am I to do if my compound is set at 29 degrees? Pull out the calculator, or in the old days my Smoley's manual?
Granted the difference is small, but it is still a difference.
So I'm left wondering.....it would seem that threads are not such a cut and dried science in my opinion, but it sure makes for an interesting subject.......pg

John, if nothing else, this will let me make spindle nose tooling for the L&S. I know it's National Form. 5 1/2x 6tpi I think is the thread.

" Yes, 1955 is a bit dated."

Hey, I resemble that remark! Gary P. Hansen

Here is my take on setting the compound at 29* for threading. This is my opinion and I guess I'm entitled to it. I suggest you do it the way you want to. This has served me well for over 40 years (most of the time anyway) and I'm not about to change now.

The way I understand it, the purpose of putting the compound on 29* or so is so the tool will be fed in on an angle enabling the tool to cut mostly on one edge thus eliminating the form tool effect which is prone to chatter. However the last 2 or 3 passes should be fed straight in with the cross slide to ensure a 60* thread. Now if it's ever gonna chatter it will be at full depth or nearly so and taking a very light cut. With that thought in mind, why not just do it all straight in with the cross slide. This way you can tighten up the gib in the compound to the point where you can't move it which in itself can do wonders in elimnating chatter. This makes life so much simpler. You can get the depth of most threads off a fishtail and never give a thought to cos 30*.

I know it's National Form. 5 1/2x 6tpi I think is the thread.

Thanks for reminding me Mike!

[QUOTE=garyphansen;829504]" Yes, 1955 is a bit dated.

So I guess I should stop using my 13th edition Machinerys Handbook and just use the new 28th edition?