I've never even tried to cut threads on my lathe, I've always used taps and dies and am familiar with what size drill to use for say an M6 and what size a piece of stock should be turned down to to take that die for example. Looking at those charts, I were trying to work out the formula/figure that you could apply to any size of diameter of stock but I don't think there is? This must be down to the differences in the depth of the teeth between the coarse and fine sizes I'm thinking?? I want to have a go at making a capsule with screw on lid, let's say you have a thick walled tube with a 17mm inner diameter for example, how deep would you cut a thread into that for a start? Then what would you turn the lid down to before you start to cut the thread onto that? I have to change/swap out cogs on my lathe for thread cutting, would I be right in saying that it wouldn't really matter which size I actually went for, 0.5 pitch for example because at the end of the day, only that lid and body of capsule needs to fit together.
You can invent any thread you want, I regularly repair very old parts that don’t conform to standard threads. Working away from any standard is also a good way to build confidence in screw cutting. firstly I would chose a thread that is as easy as possible for you to cut, is your lathe metric or imperial?
You can have any diameter, Choose your pitch and work backwards from there. make the male threAd first and then make the female to suit.
Thanks,...probably a silly question to you but how deep you make those male threads in the first place? Do you just look at the depth of the cutter or go in by X amount by turning the wheel? And then how do you work out the size of the hole before cutting those threads??
So the only constant you have is the tube i/d being 17mm, given that for a metric thread you subtract the thread pitch from the thread o/d to give the tapping drill (bore size) you could choose M18x1, M18.5x1.5 and so forth or if you where to bore the tube I/d if you have enough thickness you could bore it to 18.5 and go for a standard m20x1.5 thread.
I use a reference book, but this online calculator works well, set the first box to custom and you can put any pitch on any diameter https://www.amesweb.info/Screws/IsoMetricScrewThread.aspx edit:all the tolerances are listed for your selected thread, but for a simplified depth of thread you can use the fundamental triangle hieght ‘H’
If you are cutting with a standard 60 degree threading tools, in other words not a full profile insert, then you will just be more or less approximating things anyway. You will not have exactly the correct root and you will not have exactly the correct crests. Because of that you are just making up a thread to suit your own needs so just add the pitch (0.5mm) to the internal diameter and you get 17.5mm, so cut your internal threads to 17.5mm dia and you will close enough for your purposes. Then when doing the external thread just keep trying your already cut internal thread on it until it fits.
BTW if doing the above I would go slightly smaller on the external threads uncut diameter before starting to thread as this will approximate the crest, so for a 17.5mm thread maybe start with a 17.4 OD for the external.
Er, no not really, I just used 17 as an example. I am thinking of using the shell of an 1860 battery to hold ear plugs, that's around that size but the wall is too thin obviously so I'd need to make a spacer/piece to go inside but then the larger section of the ear plugs probably wouldn't pass through it. Lol Just got me thinking of any diameter/size of such capsules/containers.
Thanks,.....I'm not even sure about the threading tools I have, the rest seems like the sort of guide I were hoping for, like all these types of containers, threads ain't gotta be perfect/strong I guess.
the idea is you find what fixed size you have to work with, then develop the thread you use from there.
If you're just doing your own thing the rules don't matter to much , as long as the bits fit each other . If you were making the male thread and some bloke in Italy was making the female thread then the rules matter . A lot !
Ah right, so every capsule/container from a £ coin holder to a jar size or larger, a dedicated fixed size would have already been worked out by someone?
Yes, that's my situation, just not sure how to go about matching both parts size wise before attempting to put threads on them.
Look at engineering tables for a list of thread sizes. Forget the diameter, look at pitch and depth of cut. Just apply this to your diameter. So if you wanted to use a standard M6 thread pitch on a 50mm dia, just cut the thread to the pitch and depth for M6 listed in the tables. I would make the hardest part of the thread first and just make the two threads go together.
exactly, you just need that starting point to work from. No different to cutting threads with a tap and die. The male part will be the same or a shade under the thread o/d your aiming for and the female will be the same as you would drill a tapping hole as I explained above.
