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imsmooth

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Joined: 07/02/2008
Location: United States
Posts: 214

Posted: 03:44pm 29 Mar 2013

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I thought someone here might have a solution for me:

I have a stainless steel vacuum bottle (thermos). There are grooves on the inside of the mouth for screwing in a plastic cap. The outside of the bottle neck is smooth. I am using this for a project where I am going to turn a piece of teflon to fit on the outside. The top of the teflon will be below the top of the bottle mouth. I need to secure this teflon from sliding as the nature of the project will want to cause it to slide off.

I would like to make a metal (stainless, copper, brass) cap to replace the plastic one. This cap will have a diameter slightly larger than the mouth's diameter, so the teflon can not come off the neck. I need to know how to mimimick the groove pattern so I can screw this metal cap on. Any ideas?

I though of making a mold, making a negative and casting the cap. However, I don't have this capability. I didn't know if there was an easy method or a trick to get something to work.

I also though of slighly enlarding and deforming the mouth's rim, trapping the teflon below it.

yahoo2

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Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 03:16am 30 Mar 2013

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What options you have depends on a couple of things.

How much force is levering on the cap from the teflon sleeve.

and do you need to remove the cap to put liquid in the thermos?

The threads on a thermos are a very course pitch it probably wont stay tight without the taper on the bottom or the o-ring on the top creating some friction to hold it from unscrewing.

The easiest material to work with would be brass or perhaps a tough machinable plastic, only catch is that brass conducts heat extremely well.

You could machine the basic shape of the stopper then carefully scribe the outline and centreline of the thread then use a triangular file to cut a V along the centreline about half the depth of the original thread, then switch to a round file the same radius as the stoppers thread to complete the job.

If you are looking for something really solid you could drill the centre of the new stopper to a standard size and tap a thread in it to take a brass plug. Then cut a thread on the stopper's lip to fit a large nut and washer (spacer) to hold the teflon ring on. If you do this then the new stopper doesn't need a coarse thread hand cut to hold it in, it can be fixed in the neck of the thermos with a two part epoxy, like Devcon. (that stuff is almost indestructible).

I don't like your chances of rolling the rim very far, it's likely to split. You could fit a two piece collar/clamp, there should be enough flare on the rim to hold something provided it is machined for a tight fit.

Not much else I can suggest without seeing the job.

I'm confused, no wait... maybe I'm not...

isaiah

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Joined: 25/12/2009
Location: United States
Posts: 303

Posted: 06:52pm 30 Mar 2013

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See how many threads per inch you can get close with a scale or tape measure for this then see if you can find some one with a lathe to turn it for you. have him also cut a "o" ring surface (AND POSSIBLY A TAPER ) on it so you'll get a good seal.
Be careful if you are going to have much pressure.
I hope its not one of those Chinese stainless steel thermoses if it is throw it away and look at good will and flee markets and find one made in U.S.A. They will hold the heat or cold better.

Isaiah

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