Threading logic check
Threading logic check
I thought I Understood this but I'm seeing some vastly different data in different calculators so figured I'd lay it out.
I have some thick walled tubing I need to internally thread. Its ID is 1.320
I want to create a 20tpi thread.
When I look at my handy lathe threading chart (this is the classic one out of the atlas manual I think) I follow over to the 20 tpi line and see a single depth of thread at .0379. So by using the correct compound depth I feed to .043. When I finish I indeed have a good thread that has a depth of thread at .0379.
So thinking this through I now have a Minor diameter of 1.320 and a major at 1.3579 ?
None of the calculators I've checked seem to produce this Major diameter. I must of messed up something basic here, can some one educate me a little ?
Thanks in advance!
I have some thick walled tubing I need to internally thread. Its ID is 1.320
I want to create a 20tpi thread.
When I look at my handy lathe threading chart (this is the classic one out of the atlas manual I think) I follow over to the 20 tpi line and see a single depth of thread at .0379. So by using the correct compound depth I feed to .043. When I finish I indeed have a good thread that has a depth of thread at .0379.
So thinking this through I now have a Minor diameter of 1.320 and a major at 1.3579 ?
None of the calculators I've checked seem to produce this Major diameter. I must of messed up something basic here, can some one educate me a little ?
Thanks in advance!
Re: Threading logic check
Look in the Machinery' handbook under American Standard Unified Thread Form Data. It is a chart in the Threading section.
Therein you will find that the depth of thread for a 20tpi internal thread is .02706. So if you start with your minor bored diameter and add 2x the thread depth you will get an overall OD of the male thread of 1.374. That is nearly 1-3/8-20 which is going to be a special as 1-3/8-18 is the UNEF series.
Most people making an odd sized internal thread make an externally threaded 'master' and then fit the internal thread to the 'master'.
Let us know how you measured your results.
--earlgo
Therein you will find that the depth of thread for a 20tpi internal thread is .02706. So if you start with your minor bored diameter and add 2x the thread depth you will get an overall OD of the male thread of 1.374. That is nearly 1-3/8-20 which is going to be a special as 1-3/8-18 is the UNEF series.
Most people making an odd sized internal thread make an externally threaded 'master' and then fit the internal thread to the 'master'.
Let us know how you measured your results.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
Re: Threading logic check
That's why I went the calculator route, none of the charts fit the sizes exactly. Was using this tool http://theoreticalmachinist.com/Threads ... erial.aspx
I have only measured the depth of thread on my DRO so far. Original ID was with a set of internal calipers. I really need to get something to do internal threads......and a copy of the handbook.
My next step, once I figure out my dimensions will be to make the male portion. Need to know what the major needs to be to start that of course.
I have only measured the depth of thread on my DRO so far. Original ID was with a set of internal calipers. I really need to get something to do internal threads......and a copy of the handbook.
My next step, once I figure out my dimensions will be to make the male portion. Need to know what the major needs to be to start that of course.
Re: Threading logic check
You are neglecting the fact that you are working with a sharp V tool.
The proper major diameter is calculated using a 1/8p flat, (which is what the calculators are doing) not a sharp V, so your major diameter as cut will be larger.
Also keep in mind that the chart above reflects COMPOUND infeed which is normally roughly at 29 degrees.
The proper major diameter is calculated using a 1/8p flat, (which is what the calculators are doing) not a sharp V, so your major diameter as cut will be larger.
Also keep in mind that the chart above reflects COMPOUND infeed which is normally roughly at 29 degrees.
Glenn
Operating machines is perfectly safe......until you forget how dangerous it really is!
Operating machines is perfectly safe......until you forget how dangerous it really is!
Re: Threading logic check
Ah ok that makes sense. So the chart I posted with the 20 tpi Single Depth on a V form of .0379, and a compound feed of .043 may be correct ? Is the data in the handbook based on the sharp v or the 1/8p flat ?GlennW wrote:You are neglecting the fact that you are working with a sharp V tool.
The proper major diameter is calculated using a 1/8p flat, (which is what the calculators are doing) not a sharp V, so your major diameter as cut will be larger.
Also keep in mind that the chart above reflects COMPOUND infeed which is normally roughly at 29 degrees.
Re: Threading logic check
Data in the Handbook should be based on a 1/8p flat at root for internal thread major diameter.
Glenn
Operating machines is perfectly safe......until you forget how dangerous it really is!
Operating machines is perfectly safe......until you forget how dangerous it really is!
Re: Threading logic check
Hmm. This could be a challenge. Wish I had a set of calipers with the right anvils to measure this to the root. All Ive seen so far just support external threadsGlennW wrote:Data in the Handbook should be based on a 1/8p flat at root for internal thread major diameter.
Re: Threading logic check
I'm at a loss to understand why ANYONE would attempt a thread----any thread--- by judging pitch diameter based on charts, using tool pickup as the reference point. There's more room for error (size of flat, variations in major or minor diameters, error in compound angle) to make the possibility of hitting the desired size nothing more than random. If it matters, use the charts to create a plug gauge, using wires to determine pitch diameter. That way you aren't working blindly.
I've been single pointing threads since 1957 and have never relied upon thread depth as a means of determining size. I practice what I preach. To be fair, I do use that information in determining the depth of a thread relief, assuming one is permissible.
Harold
I've been single pointing threads since 1957 and have never relied upon thread depth as a means of determining size. I practice what I preach. To be fair, I do use that information in determining the depth of a thread relief, assuming one is permissible.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Re: Threading logic check
Calipers?heavyg603 wrote:Hmm. This could be a challenge. Wish I had a set of calipers with the right anvils to measure this to the root. All Ive seen so far just support external threadsGlennW wrote:Data in the Handbook should be based on a 1/8p flat at root for internal thread major diameter.
You've already lost the battle. Calipers do not provide the degree of precision that would make any readings you might establish of value. Tolerance on threads, especially small threads, is quite tight.
Why are you so obsessed with the root diameter? Its tolerance is likely far greater than the pitch diameter, which should be your concern.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Re: Threading logic check
I'm just explaining why you're calculated numbers don't match up to other published numbers.
The answer to cutting an internal thread to size was already mentioned here:
The answer to cutting an internal thread to size was already mentioned here:
earlgo wrote:Most people making an odd sized internal thread make an externally threaded 'master' and then fit the internal thread to the 'master'.
Glenn
Operating machines is perfectly safe......until you forget how dangerous it really is!
Operating machines is perfectly safe......until you forget how dangerous it really is!
Re: Threading logic check
Oooook, haven't been doing this for 50 years so trying to figure it out? Not obsessed with the root diameter but all I could grasp to figure out a major diameter for my male part. I have micrometers as well but not internals.Harold_V wrote:Calipers?heavyg603 wrote:Hmm. This could be a challenge. Wish I had a set of calipers with the right anvils to measure this to the root. All Ive seen so far just support external threadsGlennW wrote:Data in the Handbook should be based on a 1/8p flat at root for internal thread major diameter.
You've already lost the battle. Calipers do not provide the degree of precision that would make any readings you might establish of value. Tolerance on threads, especially small threads, is quite tight.
Why are you so obsessed with the root diameter? Its tolerance is likely far greater than the pitch diameter, which should be your concern.
Harold
Or maybe I should ask it this way, given I have a internal threaded part, and I want to make a male part to fit, how would you go about it? Or if I go back to the beginning. I have an ID of 1.320 I need to thread and make a male part for.
Re: Threading logic check
Use thread wires for pitch diameter measurement and turn an external threaded plug to use as a gauge, and then cut the internal thread until the plug screws in nicely, or as desired.
Glenn
Operating machines is perfectly safe......until you forget how dangerous it really is!
Operating machines is perfectly safe......until you forget how dangerous it really is!