Fusor2_DMS

For posts specifically relating to fusor design, construction, and operation.
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Richard Hull
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Re: Fusor2_DMS

Post by Richard Hull »

Circular or as you say "stir" welds are always recommended for no filler rod welds. I would never join pipe sections like that as there is no filler metal in the joint on so thin a material wall. All of my welds are machined welds with excess "lip" that can supply what a rod would supply, (extra metal to flow into the joint during welding). For vacuum piping, no welding should be used to make pipe mating joints like in the video. (auto motive exhaust) Turns and odd sections should be joined by proper vacuum rated flanges like CF or KF ending pipe sections. It is abysmally easy to cut a pipe to desired system length requirements and then add via welding with no rod in the weld any form of flange as the extra metal or lip is there. As such, as the "lip" metal melts, the circular motion of the TIG tungsten electrode mixes the lip metal into the flange for a good seal.

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
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russssellcrow
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Re: Fusor2_DMS

Post by russssellcrow »

Wait, I'm not quite understanding this "lip" you speak of, for providing the welding material for the joint.

I have cut and practiced autogenous TIG Welding on thin walled steel pipe for a while. The tolerance seems to be the main factor, and it would be nice to have some extra material around the joint to melt and stir, but if one cuts the pipe with a straight saw, there is no "lip".

I have created a lip by drilling through a vacuum blank; it leaves a thin protrusion on the backside where the hot stainless was pierced by the bit. This would be an outside weld, I would have to drill it backwards to put the lip on the inside of the weld (ideas).

What do you mean by "lip", and how do you create it?
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Richard Hull
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Re: Fusor2_DMS

Post by Richard Hull »

Again, I would never attempt under any circustances to join pipe to pipe! I indicated in my last post that would demand filler rod.

I could never imagine the need for a pipe to pipe straight-on butt joint in any build of my own design.

I tend to do only pipe to flange and flange direct to sphere with no pipe. These are easy if you own a lathe and can make lips for these joint with zero need for filler.

I supply crude drawings.

Richard Hull
Attachments
pipe to flange lip.jpg
Flange to sphere lip.jpg
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
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russssellcrow
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Re: Fusor2_DMS

Post by russssellcrow »

I was thinking "filler lip", and used a KF25 Blank. We drilled a 0.600" hole in the center (outer diameter of backside port on the Diffusion Pump), and left a 1/16" tall lip, about 0.035" thick.

We fitted the blank over the port, bringing the port tube to the same level as the trough in the KF25 Flange. Then we cut a big washer to a proper diameter to protect the sealing surface (where the O-ring presses).

I used our Miller to TiG tack the flange at 3 points. The lip melted almost instantly, and the flange side needed more attention to accept wetting because it has a lot more mass than the pipe to which it is mated.

This weld is only about 2.5 mm wide, but I have seen finer from Kurt Lesker or MDC.

The sealing surface may need a little dressing up, but it appears pretty good. I'll report back the vacuum test results.
Attachments
20220703_202756.jpg
20220703_193325.jpg
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Richard Hull
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Re: Fusor2_DMS

Post by Richard Hull »

The weld looks OK. I would test it by blanking off the diff stack. (Might take a while to get rid of outgassing items.) Never assemble a system completely that personal welds are done on parts of it. Test as you go.

I tend to leave a machined, .125 lip as a minimum on a conflat against a sphere I tend to leave a .20 lip I want plenty of flange or pipe metal to flow into the weld. All of my lips are very tight fits to the work and are often tapped into place with a mallet.

Richard Hull
Attachments
Typical lip welds done via machining mating components.  These are my first welds after much practice on scrap pieces of SS back in 1998.
Typical lip welds done via machining mating components. These are my first welds after much practice on scrap pieces of SS back in 1998.
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
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russssellcrow
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Re: Fusor2_DMS

Post by russssellcrow »

This is the 2nd practice pipe, the 1st is in the trash. It's 3/4 inch thin walled steel. The pipe was numbered on each side of the cut line so it could be re-aligned, then cut in several places.

I then used a piece of angle iron as an alignment trough, and TIG welded them back together using no filler rod. The main trick is making sure the gap is VERY TIGHT between pieces (0.005"), and it is manditory to tack before putting a bead all the way round. Autogenic welding is possible for pipe, but mechanically demanding in preparation.
20220412_181252.jpg
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Richard Hull
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Re: Fusor2_DMS

Post by Richard Hull »

Still, as you note and show, practice makes one better by degrees. Lots of practice over and over again, leads to confidence at each chosen task. This leads to becoming a master at the task over time. I see and applaud your efforts. You have what it takes.

The trouble is if you don't do something every day the skill level falls away. I would not give a Nickle for my TIG welding skills now! I haven't fired up my big Lincoln TIG machine here for 3 years! While the basics of setup and procedure never leave you, once learned; all skills that demand precision and active participation are indeed perishable. Re-acquisition demands drill and practice all over again.

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
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