Random machining question

[JoeFahey]

My knowledge is somewhat limited in terms of machining. I know how to tap a metal hole to create threads, but only for the limited diameters that most workshop taps have. How are larger holes threaded? I am interested in how this is done on the inside of a round metal barrel as well as the exterior of it.

I am curious because I want to thread the interior and exterior of the parts of a metal pot. So if a metal pot were to be cut in half, the bottom half could screw into the top half.

Thanks

 

[MedicBob]

Larger taps and dies.

They also could use a lathe to cut the threads.

 

[Eli]

Yep, larger taps and dies.

Or a lathe. Making threads with a lathe is a bit more complicated, unless its a CNC setup. It takes talent to do it by hand.

 

[JoeFahey]

Any idea where I can find larger taps/dies? I can't seem to find anything over an inch.

 

[Jeff7]

Yep, larger taps and dies.

Or a lathe. Making threads with a lathe is a bit more complicated, unless its a CNC setup. It takes talent to do it by hand.

Yeah, it depends on the lathe.

The ones I worked with on campus were engine lathes. I don't think they were CNC; they did have a numeric readout, but I don't think anything was guided by computer. There was a lever somewhere that controlled the feed speed of the tool carriage, and you could set that to the right speed, along with the proper spindle rotational speed, and it would cut the thread you needed. The operator was responsible though for stopping the automatic feeding action before the tool crashed into something.
I think it was all manual gearing though, as all speeds and actions were controlled by lever, not buttons.

But yes, a CNC lathe would definitely do the trick much more easily.

Any idea where I can find larger taps/dies? I can't seem to find anything over an inch.

What size? McMaster lists taps up to 2.5" diameter. Expensive, though.

 

[JoeFahey]

What size? McMaster lists taps up to 2.5" diameter. Expensive, though.

Yeah I managed to find some slightly larger ones, but what I am talking about would be more around the 12" of a pot or bowl. This seems awfully large for a tap/die which is why I asked the question of whether there are alternative methods.

 

[Howard]

Turn the thread on a lathe.

 

[Rubycon]

Yep, larger taps and dies.

Or a lathe. Making threads with a lathe is a bit more complicated, unless its a CNC setup. It takes talent to do it by hand.

Lead screw.

Four jaw chucks were always a PIA to get dead centered. 3 jaw chucks for the lazy - quick to go but can be too sloppy for real work.

2.5" tap? I could not imagine the torque to twist that sucker! Perhaps threading soft metals or plastic but something hard? Yikes!

 

[HappyPuppy]

My knowledge is somewhat limited in terms of machining. I know how to tap a metal hole to create threads, but only for the limited diameters that most workshop taps have. How are larger holes threaded? I am interested in how this is done on the inside of a round metal barrel as well as the exterior of it.

I am curious because I want to thread the interior and exterior of the parts of a metal pot. So if a metal pot were to be cut in half, the bottom half could screw into the top half.

Thanks

I think all previous responders to your thread should rethink their answers.

 

[Howard]

Do you HAVE to use threads to fasten the two halves?

 

[Colt45]

They make big ones for pipe, but I can't see thread working on a pot anyway - it's too thin.
I think you'd have to roll thread onto it, so you need some sort of thread roller, with dies on either side, and deforms the material to fit the thread, rather than cutting it... not sure if I've ever seen a thread roller like that, though.

time for plan B. Can't you just by a pressure cooker or something?

 

[Rubycon]

For a pot it would be spun with a flange that could be bolted together. Interlocking ridges with a circular clamp, etc. Depends on how strong it needs to be.

 

[boomerang]

Assuming you can get this to work, which sounds questionable because the wall thickness is not going to allow for threads, what is the intended use?

You realize it's going to leak, right? The first thing that came to my mind is a teapot or something for boiling liquid in which case you're going to want to thread the upper half into the lower half which is the opposite of how you described it. Condensation on the walls will run down instead of coming out through the threads. You'll get some wicking action anyway. It'll be a mess.

If whatever it's holding is above the level of the threads, it will be running out all over the place.

 

[WHAMPOM]

My knowledge is somewhat limited in terms of machining. I know how to tap a metal hole to create threads, but only for the limited diameters that most workshop taps have. How are larger holes threaded? I am interested in how this is done on the inside of a round metal barrel as well as the exterior of it.

I am curious because I want to thread the interior and exterior of the parts of a metal pot. So if a metal pot were to be cut in half, the bottom half could screw into the top half.

Thanks

On thin metal, threads are formed using a mold(like jar lids). Thick pieces (have to cut the thread depth)use lathes and threading machines. Why not make it a taper fit?

 

[iGas]

It is going to be difficult at getting taps & dies that is greater than 2.5". There are taps & dies that go up to 4" but 36" wrench is not going to cut the muster at that size. And, I doubt it that you can handle a 48" chain ratchet wrench by yourself.

 

[JoeFahey]

Assuming you can get this to work, which sounds questionable because the wall thickness is not going to allow for threads, what is the intended use?

You realize it's going to leak, right? The first thing that came to my mind is a teapot or something for boiling liquid in which case you're going to want to thread the upper half into the lower half which is the opposite of how you described it. Condensation on the walls will run down instead of coming out through the threads. You'll get some wicking action anyway. It'll be a mess.

If whatever it's holding is above the level of the threads, it will be running out all over the place.

I think that I'll go with some kind of locking guide milled into one of the sides of the pot instead. I can mill a guided path on one half of the pot and put in something to stick out of the other half to lock into place.

Since this will not hold the water very well I'll need to find something to keep it sealed. I guess I'll just need to find a polymer that I can use which has a melting point over 210*F, and have this lining the space between the halves.

 

[jaha2000]

are you trying to boil something in a sealed container?
You do realize how dangerous that is correct?

 

[JoeFahey]

are you trying to boil something in a sealed container?
You do realize how dangerous that is correct?

I'm not making my own pressure cooker. I value my life.

I am taking a regular cooking pot with an open lid and finding a way to reattach its two halves once it has been cut.

 

[iGas]

I'm not making my own pressure cooker. I value my life.

I am taking a regular cooking pot with an open lid and finding a way to reattach its two halves once it has been cut.

Why don't you design one with groves lid & bottom and use gasket that can handle up to 600~1000C ++ screws & bolts?

 

[JoeFahey]

Why don't you design one with groves lid & bottom and use gasket ++ that can handle up to 600~1000C ++ screws & bolts?

I would but I will need to be able to connect the pieces for boiling water and disconnect for storage multiple times.

 

[boomerang]

An O-ring will suit your purposes very well I believe. Some sort of cam lock system 180 degrees apart should seal that up just fine. Or, mill a dovetail slot in each side with a corresponding piece to hold the halves together. If it's round, wall thickness may preclude you doing that.

Re-read your post, I think we're on the same page in regards to holding the halves together.

 

[iGas]

I would but I will need to be able to connect the pieces for boiling water and disconnect for storage multiple times.

You know it is hard enough to seal leaks on large screw fittings specially greater than 2" with even temperature. What you are proposing is almost impossible because the pressure that you need to tighten the fittings is huge, unless you have a gasket (IMHO an O-ring or double O-rings would be best for such large surface that require repeated disassemble & reassemble). And, then apply uneven heat that change the shape of the threads.

It is time to give it a rest because you are way over your head in this.

 

[JoeFahey]

An O-ring will suit your purposes very well I believe. Some sort of cam lock system 180 degrees apart should seal that up just fine. Or, mill a dovetail slot in each side with a corresponding piece to hold the halves together. If it's round, wall thickness may preclude you doing that.

Re-read your post, I think we're on the same page in regards to holding the halves together.

This all seems much more reasonable and easier to make than trying to thread the sides of a pot. I can figure out a way to hold them together since the O-ring will act as a good seal.

I am doing this to reduce the bulk size of pots I would be bringing on backpacking trips. Typically you can just stuff your extra gear inside the pot to not waste the space it takes up, but it would be better if I could make a large cooking pot into a flatter disk like is already done with dishes that aren't used for cooking:
http://www.ems.com/product/index.jsp?productId=3662440&cp=3677338.3737364

 

[iGas]

An O-ring will suit your purposes very well I believe. Some sort of cam lock system 180 degrees apart should seal that up just fine. Or, mill a dovetail slot in each side with a corresponding piece to hold the halves together. If it's round, wall thickness may preclude you doing that.

Re-read your post, I think we're on the same page in regards to holding the halves together.

It would be funny to see the OP screwing around with his pinched o-rings while other enjoy their meal that cooked from a traditional pot, or a simple single use cooking bag.