Chamber Design

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Chamber Design

Post by Colt_Reid » Sat Jul 14, 2007 3:29 am

This is my design for the chamber. The pictures show the top hemisphere. The bottom hemisphere will be similar but will not have the hole for the view port. But will instead have the hole for the vacuum, gas and HV lines.
What do you guys think of this design?
fusor chamber.JPG
fusor chambertop.JPG

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Re: Chamber Design

Post by drmike » Sat Jul 14, 2007 3:41 am

Nice graphics!

How are you going to seal? The groove for O-rings needs to be placed carefully. I'm not sure you need that many bolt holes either, I bet you can make it work fine with half as many.

How will you fabricate it? I can see several different processes that would work, but I usually pick the hardest way possible :-)

Very nice start of a design, good luck with making it work!

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Re: Chamber Design

Post by Chris Trent » Sat Jul 14, 2007 3:56 am

Very nice work. That would make a truly beautiful fusor.

Just based off of what I see in the pictures: You will want to study various flanges; conflat, KF, etc, and see how they fit together before you actually make this. You will notice a sharp ridge called a "Knife Edge" on the conflats for the gasket to seat against, it actually bites in and makes a better seal. You might want to accommodate such a seal in your design; as I understand it, flat gaskets tend to leak a bit in high vacuum applications, "O" rings are usually better, knife edge seals are better still. (For all I know you might already know this, but then again you might not)

Also be sure that none of the bolt holes penetrate to the interior of the chamber, bolts don't seal very well.

I'm curious; is this intended to be milled out of a billet, cast, or do you have a source of thick hemispherical blanks (If so, can I have some)?


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Re: Chamber Design

Post by UG! » Sat Jul 14, 2007 9:05 am

a few comments:
you want to make shour the recessed for the bolts are large enough to get a hex socket over the nut and bolt heads to tighten them up! they don;t look big enough to me.

you need to decide that sealing type you'r going to use, you don't appear to have much space for o-rings etc.

also for a ~4" chanber, far fewer bolts are needed. look at conflat flanges to see how many they use on 4". (probably about 8)


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Re: Chamber Design

Post by Colt_Reid » Sun Jul 15, 2007 2:59 am

-I will study the conflat Seals and try to intergrate the ideas into the design. if i am not successful wil put an o-ring groove.

-I now see that the number of hole is exessive. I was planning to use a hex socket head cap screws. the holes for the view port will be blind hole and taped not through like shown.

-It will be machined out a solid piece of 6" dia round stock. Most of the work will be done on a CNC lathe. Though first it i will drill and bore or mill the 3" hole on a mill to allow the chuck to hold it on the inside of the hole. Then profile the outside. Flip it and bore the inside. The holes will be drilled on a CNC mill.

-As i thought about it i found that i dont have to even use mastercam to make the shape. I have written it manually in less than 100 lines of code. Whole thing being spherical in nature makes it easier to do on a lathe. Even with really small stepovers a ball endmill cant beat the lathe.

-Thanks for the info

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Re: Chamber Design

Post by Nanos » Sun Jul 15, 2007 5:57 am

How much does a piece of 6" dia round stock cost ?

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Re: Chamber Design

Post by Colt_Reid » Mon Jul 16, 2007 3:01 am

-For now to do the fact I now no money I am using a piece of aluminum that a friend had from a pervious project.

-Which is far and away not optimal. But for it to fit the design criteria to will have to work. It is going to be project in one of my classes. I am a machining technology student thus it needs to have significant machining done to it. if I do it as a project I can borrow vacuum equipment from the sci and chem labs thus eliminating a major cost.

-If you go to this site they have the same thing for $100 for a foot. (They have Stainless in 4" for about the same price. For Stainless in 6" dia the best i have found is about $500!! But i am not the best at finding good deals. There are a lot of places to look here

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Donald McKinley
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Re: Chamber Design

Post by Donald McKinley » Mon Jul 16, 2007 6:03 am

Since you will use a CNC lathe, looks like you might want to try a wire seal arrangement for your chamber gasket. You can only do it though if you use stainless for the hemispheres. IMO the conflat are expensive if you plan to do any amount of disassembly and changing setup within the chamber. You can make a whole bunch of wire gaskets with a spool of #12 house wire annealed in pieces in a flame, quick, with a torch (maybe not necessary to anneal). One gasket is only 18" for a 6" chamber. The male female arrangement on the chamber would be a snap on the CNC.

You can jig up and make your rings precision with even a board and a few positioning blocks. Saw the wire to length, silver solder a butt joint on the ring and bolt it together. You want enough cold flow to squeeze the wire into the pits. Here's a few illustrations for inspiration from a web search for "wire seal vacuum". ... ay?

Wire Seal.JPG
Wire Seal.JPG (32.77 KiB) Viewed 3928 times

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Re: Chamber Design

Post by tonybarry » Mon Jul 16, 2007 10:45 am

Hello Colt_Reid,
I had a look at your hemisphere. Nice drawings. The bolt holes to
secure the top to the bottom seem a bit questionable though. Since it's a
vacuum inside, you don't need quite so many I think; and the killer is that
you are going to have to machine each hole with an end mill to get the bolt
head seating, whereas you could just put down a plain flange round the
periphery and bolt through that. Much less milling, and much less likely to
break cutters as you don't have to mill into a tangent surface.
However, if it's a uni assignment, and the instructors want some serious
machining, then it's a good job, for that reason. In your writeup you can
say that it is done as an exhibition piece and not a production piece, and
they'll love you because all good machinists secretly love cool milling like
this, but they have to follow the rules and keep costs to a minimum.


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