Inch thread, its main parameters and characteristics
If you read the regulatory document GOST 6357-81, describing the cylindrical pipe inch thread, then you can find the following information. Its main characteristic is the pitch and diameter. The diameter should be understood as one of the following definitions:
- The outer diameter is a unit that characterizes the distance between the opposite upper points located on the tops of the threaded ridges.
- The inner diameter is a unit that characterizes the distance between the opposite bottom points located on the grooves of the thread groove.
The height of the profile is determined by finding the difference of these two diameters.
The pitch of the pipe variant is the distance between two nearby depressions or two adjacent ridges. It is always the same, since the distance between turns is stable. If this condition is not met
, it is not possible to choose a nut or bolt for such a threaded connection.
Distinctive features between metric and pipe threads
In fact, there is not much difference between an inch and a metric thread. If we talk about the most prominent, highlighting the inch version against the background of the metric, it should be said about the shape of the profile of the threaded ridge. In appearance, it seems more acute. So, the top corner of the threaded profile is equal to 55 degrees.
In addition to the shape, the distinctive feature of the metric pipe version from the inch is the calculation of the dimensions of the diameter and pitch. Thus, for metric calculation occurs in millimeters, and for tubal - in inches. However, the unit of measurement "inch", in this case, does not correspond to the usual value of 2.54 cm. For pipe threads use a special, tubing inch, which is 3.324 cm.
A detailed table can be found in the above normative document. It contains both integer and fractional values of these inches. Thus, for example, the thread marked with ¾ will be approximately 25 mm. Moreover, the step itself is usually considered not in mm, but in threads. Threads are chopped grooves, on an inch measuring segment.
To determine the step, you need to use the usual tools: a comb, a caliber, a mechanical meter, etc. Therefore, the measurement will be based on the same rules as in the metric and pipe versions.
And so, how do you measure the step:
- Take the coupling or choke, with the cut internal or external thread, knowing their parameters. Screw the bolt into the thread.
- If the bolt has sat tight, then the pitch and diameter can be considered definite. If the bolt does not fit, repeat with the next caliber.
When using a threadmaker, the process is much easier. You just need to attach the plate to the thread. If the profiles coincide, then the thread coincides with the digit indicated on the tool plate.
Using a standard caliper or micrometer, you will be able to determine only the outer diameter.
Inch carving, manual and mechanical way of cutting it
Pipe and metric threads are cut either on the outside or on the inside surface by manual or mechanical means. Let's consider each of them.
For a manual cutting method, you will need tools such as a die( for the outside) and a tap( for the inside).
To perform the thread cutting manually, follow the following instructions, based on your thread type:
- Fix the pipe in a vice, with the tap in the drawer and the insert in the plate holder.
- Put the die on the pipe, and insert the tap into it.
- Rotate the handle of the plate holder or the turntable, screw or screw the die or tap onto the pipe.
- If necessary, repeat the procedure several times.
To make the mechanical cutting, proceed as follows:
- Clamp the pipe in the chuck of the machine by placing a threaded scar in its caliper.
- Turn on the machine and make a chamfer.
- Adjust the caliper travel speed.
- Fit the cutter to the surface and turn the thread flow.
Thread forming using the cutter gives a good and qualitative result( of course, if the turner has enough skill).
Table of sizes of inch threads according to GOST
Dimensions are shown in the pictures above.
