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> Diy High Voltage Connectors
johansen
Posted: November 03, 2011 11:21 am
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yay or nay?

I'm thinking female banana plug at the bottom of a 3/8" pvc pipe. (ID= .493")
The male connector would be a male banana plug at the end of a 1/4" pvc pipe (nominal OD =.540, would need to be turned down to fit)
I'd probably go with 3 inches deep to be safe (50kv max)
I'm thinking if I turn the pipe down to fit snug, it would be a friction fit and a small amount of grease would provide a relatively secure dielectric seal.

Like this user posted image
but not $15 each, (i need approximately 10-20 sets of them.)


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CWB
Posted: November 03, 2011 02:32 pm
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what ya building ?


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tekwiz
Posted: November 03, 2011 09:30 pm
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A grease seal shouldn't be necessary unless operation in all weather conditions are anticipated.
You don't even have to make your male connectors...many commercial HV cables are based on(solid core) RG-8 coax with the ground shield stripped back for a considerable distance.
The coax itself is good for at least 50kV. Some connectors I've seen allow up to 12" of coax center into the connector.
I see no reason why this couldn't be used with banana hardware & gutted PL259 hardware.
One big advantage is that your HV lines are completely shielded by grounded metal, which makes them much safer.


BTW: Most common plastics can be machined in a wood lathe. This can be as simple as a drill clamped to the bench with a scrap wood tool rest clamped beside it. A hand held "tailstock" can be used for drilling, as drills tend to self center when it's the work that's rotating, as long as the drill has at least a punchmark to start it straight.


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Sch3mat1c
Posted: November 04, 2011 05:00 am
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50kV? Heh...

I once saw the hot end of a 100kV x-ray power supply. Was for verifying machined parts, looking for internal holes, cracks, density, that sort of thing. Anyway, the cable was a bit over an inch thick, and the connector is a rather long cone of white plastic coated with grease. Looked a bit more diabolical than something one might find in an adult toy store. Chatting with the tech working on it, apparently it had arced over before, hence the funny serpentine mark along it...

Tim


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johansen
Posted: November 04, 2011 09:14 am
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As to what I am making, well, attempting to make an e-beam welder, then from there sintering metal powders and making parts, layer by layer. preferably out of something like titanium. biggrin.gif
but might end up making a lot of x rays instead.


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tekwiz
Posted: November 04, 2011 09:48 pm
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QUOTE (johansen @ November 04, 2011 12:14 am)
As to what I am making, well, attempting to make an e-beam welder, then from there sintering metal powders and making parts, layer by layer. preferably out of something like titanium. biggrin.gif
but might end up making a lot of x rays instead.

What are you going to use for cathodes?

High levels of X-rays are a given with any electron beam welding. They are a natural byproduct of the process.

I think I know what your ultimate goal is. I'd think lasers would be better, as hard vacuums shouldn't be necessary at all with lasers. Even diode lasers are up to the job these days.
An interesting project, for sure. thumbsup.gif


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

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johansen
Posted: November 05, 2011 01:49 am
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Thoriated tungsten tig welding rods?
no seriously.. they have about the right amount of thorium in them, only problem with something that big is focusing it down to a point.

there's other highpower e beam guns that use a crystal of LaB6, but the datasheet on those guns specify 10^-6 torr minimum


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Sch3mat1c
Posted: November 05, 2011 07:22 pm
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Titanium requires argon or vacuum, and even if you backfill with argon, you'll probably want a vacuum purge to do it, though it doesn't necessarily need to be a microtorr vacuum. (Come to think of it, it's not economical to purge down to a vacuum much lower than the partial pressure of the impurity gasses in the argon, so that sets your lower limit.)

Suppose you might use regular arcs too (CNC TIG welded powder, essentially?), but that might have its own problems (spot size, density -- depending on if you *just* stick particles together, or if they melt into a ball much denser than the loose powder was, etc.). Not to mention electrode wear, which might be compensated by monitoring arc voltage. There are some interesting data, statistics and control work that could be done in such a project...

Man... just be sure you get *all* the combustible gasses out before the heat hits. Powdered titanium with anything other than argon in it is going to be interesting to say the least (it even burns in nitrogen and CO2, so you'll get lots of oxidation if it's not completely purged).

Note that copper, and to a lesser extent aluminum, aren't as great for lasers, though you should have no problems if you achieve an e-beam process.

Steel and copper powders should have no problems under a reducing or neutral atmosphere (N2, CO2, or if you want, a dash of CO, H2 or CH4, though I'd avoid hydrogen with steel for best results), which makes laser particularly attractive.

Besides diode, CO2 lasers should also be sufficient, just use less power (or more feedrate) than the "frickin' lazer vaporize mwahaha!!" level.

Don't forget to anneal your finished pieces (for reactive metals, still inert atmosphere). Depending on density going in, they'll probably shrink a bit, become stronger and denser (when annealed hot enough), and become less brittle (as HAZ strain is relieved).

Tim


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johansen
Posted: November 05, 2011 08:37 pm
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thanks for all the info smile.gif

Right now the goal is printing parts from an e-beam, which requires a hard vacuum. The most difficult part of this entire project is going to be getting the cathode to survive the ion bombardment, as far as I can tell. That and focusing it.

All the extra hardware lends itself to lasers of course, which I hadn't considered.

hmm CNC TIG? what about CNC arc melting with mechanical pencil lead sized carbon rods? might take some work to get the arc stable though.


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tekwiz
Posted: November 05, 2011 09:47 pm
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QUOTE (johansen @ November 05, 2011 11:37 am)
thanks for all the info smile.gif

Right now the goal is printing parts from an e-beam, which requires a hard vacuum. The most difficult part of this entire project is going to be getting the cathode to survive the ion bombardment, as far as I can tell. That and focusing it.

All the extra hardware lends itself to lasers of course, which I hadn't considered.

hmm CNC TIG? what about CNC arc melting with mechanical pencil lead sized carbon rods? might take some work to get the arc stable though.

You'd still be better off with tungsten for arc melting...carbon has too much resistance & will probably ablate too fast.
As for using tungsten TIG electrodes, the biggest challenge will be shaping them into the required sharp V shape. Conventional E beam welders use tungsten electrodes with cross sections in the small fractions of a mm. While TIG tungstens are available down to .020" dia, shaping is going to be difficult & may require heating to high temps in a controlled atmosphere, as tungsten doesn't bend without breaking until it gets well over 2000F. I'm not sure of the exact temp, but I've had TIG points sag & bend at very high current densities. Precision bending jigs will be needed for repeatability(e beam cathodes are considered consumables), & these must also withstand high temps without contaminating the tungsten. This eliminates most refractories as they are primarily composed of oxides & the extreme temps necessary will result in contamination at the slightest touch. Water cooled copper is about the only choice, AFAICS.
Lamp filaments might be another source of suitable wire, if they can be uncoiled without breakage.


BTW: Acr brazing is another possibility for 3D printing. In this process a small amount of lower meting point alloy is used to hold together a larger quantity of higher melting point material, with temps being controlled so only the lower MP stuff actually melts. A variation of this method, minus the arc heating aspect, is used for many powder metallurgy products, including the making of carbide cutters & inserts.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

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AwesomeMatt
Posted: November 05, 2011 11:38 pm
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QUOTE
Lamp filaments might be another source of suitable wire, if they can be uncoiled without breakage.


Not likely. I know a chemist who was trying to make chainmaille out of tungsten. He tried all sorts of light blubs. Even using the large, expensive bulbs, the tungsten still shattered when uncoiling, and especially when cutting.
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johansen
Posted: November 06, 2011 12:14 am
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http://esr.lib.ttu.edu/bitstream/handle/23....pdf?sequence=1

or google search DESIGN AND CONSTRUCTION OF A HIGH POWER ELECTRON if that link don't work


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Sch3mat1c
Posted: November 06, 2011 01:04 am
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It's my understanding the brittle-ductile transition temperature varies by alloy; very pure tungsten can be bent at moderately elevated temperatures with leather gloves.

Tim


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Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.
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tekwiz
Posted: November 06, 2011 08:51 pm
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QUOTE (Sch3mat1c @ November 05, 2011 04:04 pm)
It's my understanding the brittle-ductile transition temperature varies by alloy; very pure tungsten can be bent at moderately elevated temperatures with leather gloves.

Tim

That's my impression as well, except I'm not sure what the temperature is.
TIG electrodes are available in pure tungsten...that's the standard formulation for aluminum welding.


@AM: Now you see why your friend has had so little success. Tungsten can't be worked at normal ambient temps.


@johansen: Link works fine. Some interesting stuff.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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