How do you tell what OD and ID go together. For example, if something is threaded 5/16 - 18 ID, what size threading would you need for something to screw into it? In the same vein if something is 7/16 - 20 OD, what inside threading would fit it. Would the two i mentioned be a set or no?
Threading
- Thread starter aggromere
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The threads are always the same designation. A 5/16 -18 thread defines both the male and female pieces.
so if a piece is a female piece labeled 5/16 - 18 what does that mean exactly? The two examples I gave where how some parts where listed in a cataloge and the first one said inside diameter and the second said outside diameter.
randyrls
Member
The 18 is 18 Threads Per Inch (TPI).
Thread geometry is not difficult to figure out. If you are making a bolt, the bolt has to start out the with the 5/8" size so you can cut the threads into the outside of the bolt. If you are making a nut (female) part, the drilled hole has to be the Minor Diameter. The hole has to be drilled .5568 or 37/64". Then use a tap or single point threading tool to cut the threads.
Check out this table; it contains all the common Imperial and metric threads. In particular check out the 5/8" x 18TPI lists of sizes.
http://www.littlemachineshop.com/Reference/tapdrill.php
The reference section has a lot of good information too!
Added Later: The two sizes would not be a set. a 5/8" bolt fits a 5/8" nut.
This is a video you can rent that explains threading much better than I can!
http://smartflix.com/store/video/132/Threading-on-the-Lathe
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workinforwood
Member
Depending on your lathe, it can be a bugger to stop and restart your lathe for standard threads. Like on my lathe you have to use a manual counter guage and reset the lathe for each pass. Metric threads are far simpler to accomplish. The are simpler in many ways, the math is easy, and most lathes are built with a metric ...oh dang, can't remember the right term for it, but the acme rod bar that runs your cross slide is most likely in metric. You simply spin to the right diameter, then you set the cutter maybe half way deep for your thread, turn on that acme rod bar and then hit your threading switch. When you get to the end you quickly back the point out a bit, then you reverse the drive so the cutter drives itself back to the beginning. Now you reset your depth for the second pass. You have your toolrest at 28 degrees, so you reset the depth on the cross slide to match what you're first pass, then you move the toorest slide forward for the second pass. This way you re-cut to final depth and the cutter is taking off only one side of the first thread pass you already made. When the cross slide returns, it will automatically be aligned with where you started the first time so you don't have to worry about the cutter traveling the same line as before, just have to worry about the depth. Sounds much more complicated than it is. You can cheat by running a first line of thread at half depth and then come back over the rod using a tap, which will clean everything up and will run nice and straight over the existing thread line, as well as compensating for any human errors that can occurr, like setting the thread depth too deep or not deep enough.