Threading question

[fishingreg]

Hello Again,

As anyone who saw my parting off question, you know I am very new at this. I have probably only had 3 or so hours of play time on my lathe. I have been playing with 1.5" steel rod. I have been doing test external threads and they have been going well. I would turn some threads, smooth them off, do another set of another Tpi and repeat the process. I stayed within the TPI range of my tool. So far so good. My question is as far as I can tell one of the last steps is to just touch off the sharp crown of the treads with a file. I have been doing that. If the specs call for say .500 majors, is that before or after I touch a file to them? If after, how much do most of you allow to be filed off when you do the initial turn to major OD?

Also, what do you use to measure the minors/root or do you go off how deep you run the tool in? I am using dial calipers but I know they can not get all the way down into the root due to how narrow it is so I am not sure my minor reading is accurate. I do have some thread wires on the way so maybe that solves that question but I thought I would ask. I have tested nuts on my threads and they work just fine but I am sure by spec they are either a little sloppy or tight due to my lack of knowledge and just playing around so far.

Thanks,
Greg

 

[Bob Korves]

The important part of the thread is the pitch diameter, which can be measured with thread wires or a thread micrometer. For all but the fussiest threads, the root size can just be what remains after hitting the pitch diameter. Filing the thread is just to remove any burs, don't get carried away and try to stop at the turned size before threading. Ultimately, for a home shop thread, what matters most is how it fits the female thread it will be used with, not too loose, not too tight, Goldilocks...

 

[fishingreg]

The important part of the thread is the pitch diameter, which can be measured with thread wires or a thread micrometer. For all but the fussiest threads, the root size can just be what remains after hitting the pitch diameter. Filing the thread is just to remove any burs, don't get carried away and try to stop at the turned size before threading. Ultimately, for a home shop thread, what matters most is how it fits the female thread it will be used with, not too loose, not too tight, Goldilocks...

Thanks and that makes sense, some of my threading will have multiple items that will be threaded on to it though that are factory made and I could test them all but who knows might buy more attachments so I wanted to kind of make sure I hit the standard fairly well.

It sounds like at least for now the thread wires I have coming should help with that.

I have one other question, I have read many posts on threading and some use the cross slide and some use the compound slide to advance. Why one vs. the other?

Thanks,
Greg

 

[cathead]

Advancing with the compound allows a person to cut with one side of the cutter. This makes for a smoother cut. I have a stop on
my cross slide so use that at the end of the cut to quickly pull back the cutter.

 

[fishingreg]

Advancing with the compound allows a person to cut with one side of the cutter. This makes for a smoother cut. I have a stop on
my cross slide so use that at the end of the cut to quickly pull back the cutter.

Ok, that makes sense. I have played with a cheap piece of rod from Home Depot and it turns fine but my threads look like crap so maybe if I used the compound it would work better since it is just cutting with one side. The same tool does well on another piece of steel I have. I will try that. Thanks for the explanation. Since I am new and don't know any other way, I am threading in reverse with a left hand tool so I am pulling away from the piece to thread so I won't have to sweat the stop but I do know what you are saying to pull back quick.

 

[benmychree]

You do not say anything about using a cutting fluid when threading; with steel, it is essential, I use TapMagic. I normally just fit threads to a ring gage or a nut that I have passed a tap through to eliminate burrs that effect fit. Infeeding should (nearly always) be done with the compound, it begs for mistakes to be made if infeeding with the cross feed due to remembering the setting at each subsequent infeed. There is no downside to filing off the crests of the threads to eliminate burrs, the material at the crests has little effect on thread strength, if diameter is reduced in doing so.
Also, this applies to the roots as well, and it is a good practice to grind a small flat on the point of the tool in accordance with specifications published, and gages are made to show the amount of flat for differing thread pitches; the flat, for one thing, strengthens the tool tip so that it is not so easily dulled in use. The tools sold by Aloris have a flat ground on them in accordance for the smallest TPI they are intended to cut.
Thread wires are a PITA to use, generally, the only time I would use them is for making a thread plug gage, and that if I did not have a suitable thread micrometer.

 

[fishingreg]

You do not say anything about using a cutting fluid when threading; with steel, it is essential, I use TapMagic. I normally just fit threads to a ring gage or a nut that I have passed a tap through to eliminate burrs that effect fit. Infeeding should (nearly always) be done with the compound, it begs for mistakes to be made if infeeding with the cross feed due to remembering the setting at each subsequent infeed. There is no downside to filing off the crests of the threads to eliminate burrs, the material at the crests has little effect on thread strength, if diameter is reduced in doing so.
Also, this applies to the roots as well, and it is a good practice to grind a small flat on the point of the tool in accordance with specifications published, and gages are made to show the amount of flat for differing thread pitches; the flat, for one thing, strengthens the tool tip so that it is not so easily dulled in use. The tools sold by Aloris have a flat ground on them in accordance for the smallest TPI they are intended to cut.
Thread wires are a PITA to use, generally, the only time I would use them is for making a thread plug gage, and that if I did not have a suitable thread micrometer.

Thanks for the info, I am using some lube, just cutting/treading fluid from home depot since I just started playing a week ago. I forgot to mention the fluid though. That makes sense about remembering the settings. I made probably 8-10 different sets of threads in an hour or so and I did find myself having a tough time remembering what number to go back to to clear the treads and then what number to put it back to in order to make the next cut. That alone would be a good reason to use the compound. I will try that this weekend. I'm not sure I am understanding the "flat ground on the tool" and what it does. I am using a Mesa threading tool right now and for internal I plan to use the Micro 100 tools since I will be doing some fairly tight openings like 1/2 X 28 and such. I have not tried my first internal thread yet but plan to try that this weekend as well. It sounds like the wires my not be much fun, I might have to look into something else but I would think if you repeat the same thread often if you always started with the same major and you always advanced to the same depth, there would be very little to change except maybe tool wear. Would that sound accurate?

 

[benmychree]

The flat that I refer to takes odd the sharp point of the tool, this creates a flat at the root of the thread, which strengthens the thread and reduces the tendency of cracks to propergate from a sharp angle at the bottom of the thread; all commercial threads are made to that specification. To my experience, having a sharp vee tools does not lead to accuracy of the fit of a thread cut that way; yes, there tables of compound depth of cut for sharp vee threads, but tools made with the flat hold up much better, and just fitting the thread to a ring gage or nut or thread mike generally results in a more accurate fit than the compound dial depth. A depth of cut measurement gives (at least) twice the error of a pitch diameter measurement.

 

[pacifica]

There are a number of ways to cut threads , but to get an accurate, consistent thread you need to measure the pitch diameter(wires or a thread mike) and cross reference to the numbers in the Machinery's Handbook. Then you can see how your technique is for consistently hitting a class 3 , class 2 or class 1 thread. If you can get threads approaching those on a starrett micrometer then you are doing very well.

 

[RJSakowski]

There is a less cumbersome way to measure pitch diameter that is only slightly less accurate. It involves using a single wire. First measure the major diameter of the thread. It doesn't have to be geometrically correct but it should be uniform across the thread. Then insert one wire and measure across the thread and the wire. The pitch diameter is equal to 2 x the second measurement minus the first measurement.

Edit: It is not the pitch diameter but the diameter that you would measure with three pitch wires (labeled M in the Pee Dee chart and Machinery's Handbook). You still have to go back to the table that is furnished with the pitch wires or to Machinery's Handbook to determine the actual pitch diameter based on the thread pitch, the value of M and the diameter of the wire.