Proposal to remain flexible and keep costs low

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Rob Pope
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Proposal to remain flexible and keep costs low

Post by Rob Pope »

OK, I had a thought-
The standard procedure for creating a fusion chamber is to either buy hemisperes and do a lot of expensive machining and welding, or to buy a cross with flanges at the ends.

I lack the tooling, skill, and desire to go the hemisphere route, which leaves me with a cross.
Buying a large enough (4") cross with attached flanges means I'm going to be going with ConFlat, which is quite expensive. They don't readily make KF crosses that large.
In addition, once purchasing, you are constantly looking for adapters and correct sized flanges and that always adds up to time and money

So, my idea. Buy a stainless steel cross, with no flanges. When you need to attach something, weld on a blank (which are cheap), drill a hole in the blank, and weld on the flange of the size and type you need to connect!

Does anyone think this is a bad idea?
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Carl Willis
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Re: Proposal to remain flexible and keep costs low

Post by Carl Willis »

It sounds like false economy to me. It seems you're proposing to avoid machining and welding of standard parts by doing machining and welding of less-standard parts.

In my opinion the best way to keep costs down is to be an opportunist (willing to wait for something suitable in scrapyards or eBay) and stick with standard, mass-manufactured components. Yes, you can make your own flange adapters, but I don't see you competing with mass-produced ConFlat or ISO flanges, particularly the frequent second-hand bargains on eBay.

The costs of having professional machining and welding work done on a vacuum chamber range so significantly that I can only suggest you talk to a number of shops before deciding something is beyond the budget. You might be charged $200 for the work on a 6" fusor with a few ports at one shop, and another shop might quote $1000 for the exact same thing. All this depends on how much time they think they need on the work and how comfortable they are with it, and that is quite subjective based on the machinist and their fixturing and tool arsenals. You need to make clear that you're a local student, your tolerances are loose, your materials are all customer-supplied, you're not on a deadline, and you're willing to take suggestions on how to make it cheaper (changes that are insignificant to you may shed a lot of expense in the machinist's eyes). You might also seek out a mentor in a university, where access to the inexpensive in-house machine shop is but one of many possible benefits.

-Carl
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Richard Hull
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Re: Proposal to remain flexible and keep costs low

Post by Richard Hull »

Carl is right.......Work the system, don't let the system work you and don't try and create a new system or you'll usually find the old system worked pretty well and was the best choice all along.

Carl is talking about working the system at every turn. Not just in hardware selection and scrounging, but in the art of begging and appearing as a supplicant, as well as a knowledgable and determined young person. It's an art.

Make sure to utilize teachers, friends of friends, etc. People who know the right people can save you a lot of time, effort and money.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Brandon.Abshire
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Re: Proposal to remain flexible and keep costs low

Post by Brandon.Abshire »

this is what i did and i think you should too.

I used two stainless steel hemispheres, and two correspoding conflat-flanges (8" flanges in my case). I bore out holes for accessory flanges, and then TIG welded it all together. since your using conflat, only weld it on the inside, never on the outside. you dont want to weld both sides because virtual leaks can be formed if you weld both sides.

Brandon Abshire
Rob Pope
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Re: Proposal to remain flexible and keep costs low

Post by Rob Pope »

Alright, Thankyou all for your input, probably should have checked for flangeless crosses online first, apparently they don't exist

Regarding the hemisphere route, did you do the welding yourself, or have it done?
My main thing with hemispheres is, how to machine the end of the flange being inserted.

Also, are there advantages to welding the inside as opposed to the outside?
John Futter
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Re: Proposal to remain flexible and keep costs low

Post by John Futter »

Rob
read your replies carefully
you have been already given the reason why you weld the inside to avoid virtual leaks

a bit of web searching will explain why.
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