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TPF to Degrees?

WarpToken

Plastic
Joined
Aug 12, 2006
Location
Utah
Hi,

Sorry if this has been answered here somewhere already.

Is there a simple formula to convert taper-per-foot to degrees?

For example, if I wanted to cut a 3" TPF thread, what would I enter for the angle?

Thanks,

-Wes
 
To figure out any angle if you have the 2 sides,you need a trig function calculator with the tangent key.
Then divide 3 by 12 and hit Inverse Tangent. That will be your angle. The answer is 14.036 degrees.
NPT thread is 3/4" per foot and to use the Fanuc G76 you have to program the amount of taper over the distance travelled and it comes to 1.79 degrees. Dont forget the value you get as the taper is usually given as a diameter, so to figure the actual taper, you have to take half to figure the angle.
(From "Simplified Math for CNC" on the website.)
Heinz.
http://home.columbus.rr.com/hputz
 
So is it possible to use those numbers and cross multiply with your other disired tapers?

Like a 1.5 TPF would equal 7.018?

-Wes
 
I just cross multiplied. 1.5(new taper per foot) X 14.036 (angle of the 3" TPF)and then divided that by 3 to get the new angle =7.018

Actually in this case it's just half of the other angle since the TPF is half too =)

But you're telling me that won't work? Why not?

-Wes
 
It won't work because trig functions aren't that simple. If you graph them, they form almost an S shape. For example, the tangent of 20 is .36397, the tangent of 40 is .8391, and the tangent of 80 is 5.67128.

There's no easy way around learning trig.
 
To figure out any angle if you have the 2 sides,you need a trig function calculator with the tangent key.
Then divide 3 by 12 and hit Inverse Tangent. That will be your angle. The answer is 14.036 degrees.
NPT thread is 3/4" per foot and to use the Fanuc G76 you have to program the amount of taper over the distance travelled and it comes to 1.79 degrees. Dont forget the value you get as the taper is usually given as a diameter, so to figure the actual taper, you have to take half to figure the angle.
(From "Simplified Math for CNC" on the website.)
Heinz.
http://home.columbus.rr.com/hputz
For a tapered connection on a lathe. Once you divide 3/12, you then divide that by 2, then inverse tangent of that number gives you the angle in degrees.
 
For a tapered connection on a lathe. Once you divide 3/12, you then divide that by 2, then inverse tangent of that number gives you the angle in degrees.
This is correct.

Taper/foot is understood to be an included angle. If you draw the taper you will see there are no right angles, hence no simple trig solution will work. Add the centerline of the taper to the drawing and you will see two right triangles each with a base of 1.5" and height of 12". The formula for the 1/2 the taper angle is inverse tangent (1.5÷12)=7.125 degrees. So the included taper angle is 14.25 degrees.
 
Yeah, the error if you don't do it Tyler337's way is very, very recognizable. There are at least 2 or 3 threads here on PM where somebody asked why the handbook angle for some taper doesn't match up with the D:L ratio, and we've been able to diagnose and correct their procedure just from the specific wrong results they ask about.
Take the arc tangent of half the taper on diameter, then double the result. That's the included angle of the full taper. Just taking the arc tangent of the full taper on diameter does not give the same answer.
 
For a tapered connection on a lathe. Once you divide 3/12, you then divide that by 2, then inverse tangent of that number gives you the angle in degrees.
You resurrected a 16 year old thread to give us this nugget of wisdom?
 
You resurrected a 16 year old thread to give us this nugget of wisdom?
I responded and didn't see the original thread was that old. Sometimes i forget to look.

16 years is pretty old but what is the de facto age to not rankle? I've seen guys bashed for atarting new hares instead of chasing old ones.

You can't have it both ways. What is the thread age limit to remain acceptable?
 
My personal opinion is that no thread is ever too old for useful info or additional experience to be added. Not everybody agrees, and a lot of "social media" automatically lock threads after some set amount of time. I think PM is more of a real and persistent resource, and less of an idle chit-chat bulletin board.
On the other hand, adding a new flame to some chain of rants that petered out years ago is just pointless, as well as annoying.
 
C 'mon, it takes some guys a little longer than others to figure stuff out :D
I run a Mazak in Lafayette La. A lot of API connections and we have a big binder with all the blank out dimensions and taper angles already printed out. I’m learning more trig and always wanted to know how to use the inverse buttons on the calculator, and in what ways I could use them. No one out here knew how to figure out how to do the trig to calculate the taper angle in degrees so I decided to figure it out on my own. Machinist down here tend to get lazy bc the Mazak calculates everything for us at the screen.
 
The math for taper calculations is really simple. That said the results are less than user friendly at least on an engine lathe. 3/4 tpf (common for lots of stuff) works out to 1.79 degrees not all that easy to set a compound slide to.
 
I run a Mazak in Lafayette La. A lot of API connections and we have a big binder with all the blank out dimensions and taper angles already printed out. I’m learning more trig and always wanted to know how to use the inverse buttons on the calculator, and in what ways I could use them. No one out here knew how to figure out how to do the trig to calculate the taper angle in degrees so I decided to figure it out on my own. Machinist down here tend to get lazy bc the Mazak calculates everything for us at machinists don't want to leatn much.

LA doesn't have a lock on machinists that don't want to learn anything. For 15 years we said we'd pay college tuition for anybody that wanted to take classes related to their job, even a whole degree. The only employee that took classes was the office manager. She took a few accounting classes.

There are those that will tell you with CAD/CAM you don't need to know a thing. My worst teacher ever taught civics, and he was proud he told his kids he didn't care if the failed math, because they could just get a calculator. I wonder how they came out? More knowledge doesn't hurt when using a computer, but less knowledge certainly doesn't help.

Bottom line is if you really wanna excel it takes some elbow grease and some time off the clock. Cudos to you for being one of those guys. Time to learn can be hard to find, but just keep trying. Leave those other fellas behind!

Sounds like you aren't lucky enough to have a mentor at work. A mentor can be extremely helpful. But, with all the free web help you can teach yourself algebra, trig, and geometry if you are motivated enough.

Check this out. It has helped more guys to learn trig than anything else I know.


And always sketch out your problem, even if you are the only one that will see it! A good sketch is a great tool. I've never understood why guys won't sketch out a problem and label their knowns and unknowns. You'd think you asked them to get a tooth pulled. Show your work, step by step. After a while you won't always need to, but at first it really is essential.

Before you know it you may be able to be a mentor.
 
The math for taper calculations is really simple. That said the results are less than user friendly at least on an engine lathe. 3/4 tpf (common for lots of stuff) works out to 1.79 degrees not all that easy to set a compound slide to.
Very true. You can't effectively use the protractor divisions.You can always use a sine bar but it's usually kind of cumbersome.

You can use a travel indicator and get very close. Set the compound as close as you can with the protractor. Turn a reference journal you are sure has no taper somewhat over an inch long. In the horizontal plane, zero the indicator on the reference surface with the stem as close to perpendicular as you can and as close to the centerline of the ref surface as you can. Assume a triangle with a 1" side adjacent to the 1.79* angle. Move the cross slide through 1/(cos(1.79*)) =1.0005, as you are traveling on the hypotenuse. The indicator should read tan(1.79*) which is 1/32. This makes sense since the npt taper is 3/4 per foot which is 1/16 taper per inch and you are setting the half angle.

Of course you can use a triangle with any length side adjacent you want. Also note for small angles the tangent and the cosine are very nearly equal. Try it on your calculator. This approximation is sometimes used to expedite engineering problem solutions.

This can help you make a quicker, closer setup to cut small angles. Just like a sine bar, the bigger the angle the less precision. You'll still have to use a taper attachment or tracer to cut an npt thread, but you can top it with the compound.
 








 
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