How do I know what thread pitch I can use?

[cvrivcharles]

In a nutshell,... im designing a cap that screws into a tube. I dont know the EXACT diameter of the cap where it will be threaded at the moment but but lets just say for example that its 2.34375".

How do I know what thread pitch I can use for this diameter? I've seen charts all over the place with nominal diameters, basic diameters, major diameters etc. But none of them come close to what I need. The closest I saw I think was 2.250 but the threads were to coarse think.

I am thinking I want something around 18tpi. But I dont know if I can do that?!?! I dont see why not? But how do I know what the specs are for this thread? I have to draft a 3D model of this part and I need to include the threads. I know the diameter of the part, the pitch, and angle(60deg right?). What about the rest of the specs like radius etc?

Can someone please explain this to me Thanks.

 

[cvrivcharles]

Yeah thats what I was kind of thinking. We'll see Oh,... was looking through the machinery handbook again and was studying the thread basic UN form and noticed that the crest and root flats are reversed for internal and external. I could use the same bit to cut external threads too right? I am thinking yes. I mean why not? But according to the handbook int and ext threads are different.

 

[KENAT]

I think I misunderstood the follow up question a bit too, sorry for any confusion.

As to the internal & external being different, I think it comes from the tolerances required to ensure a fit.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[SincoTC]

You only need to worry about the minutiae of the int/ext profile tolerance differences if you're making something to be interchangeable with some other manufacturer's parts or vice-versa that. You're making both parts to fit, so there's no need to worry.

I was recently stuck for a suitable thread mill on a large diameter thread milled job and used a lathe threading tool with a full form insert, I held the shank in a collet on the VMC and it did a great job. The only difference being that most thread mills are designed to do the full thread in one rotation overlaid with one pitch feed, whereas in my bodge, the insert only had three teeth so I had to go around several times with the appropriate feed to cut the required length.

 

[mrainey]

Look through this.

http://closetolerancesoftware.com/Downloads/VardexThreadMillingHandbook.pdf

Software For Metalworking

http://closetolerancesoftware.com

 

[cvrivcharles]

Thanks guys Thanks for the guide. I am going to look through it soon. Also im going to read through the thread milling section of the machinery handbook.

Does anyone know if you can use a cnc router with helix interpolation to thread mill really soft materials such as aluminum, copper, brass, and plastics? I'm thinking that single tip cutters would be perfect for a cnc router. What do you think?

Maybe the routers are a bit to fast. I'm thinking that would be the only problem?

 

[SincoTC]

Regarding the use of a router for threadmilling, I have a lot of doubts!

Due to the geometry of the cutters, threadmilling tends to induce a lot of vibration, this is often exacerbated by the small diameter and extra length the job often requires. If you are forced to exceed the recommended cutter tip speed and you can't attain the required feed/rev and supply flood coolant, the tool life will suffer badly. Just take a good look at the figures in mrainey's very ggod link.

In general I would say that the spindle speed will be way too high and the whole thing will lack rigidity. However, depending on your router, you may be able to dry-cut your plastic 2-3/8 x 16 thread with a single point tool or a modified a muulti-tooth insert.

 

[Ryan19]

Hi all.
I am looking into advantages and disadvantages of different lathe tool posts. Could anyone please advise me on what i should be looking for. I have been tasked will improving the saftey and reducing the risks of our lathe tool posts at work. At the minute im trying to research different tool posts. Any help would be much appreciated.

 

[KENAT]

Ryan, I think that should probably be a new thread. I suggest you press the

Inappropriate post?
If so, Red Flag it!

Below your post and re-post as a new thread.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?