3D Printed Ceramic Calibration Piece

26 09 2012

All Photos.

Received a 3D printed ceramic calibrations piece from shapeways. As you can see the glazing adds about 0.11mm to the surface:

By Mark Suppes





Polywell Assembly Overhaul

26 08 2012

It’s clear from the inconclusive results of the symmetry test that our experimental apparatus isn’t durable enough. It needs to for a long period of time over the course of many trials, without breaking. Every time it breaks, we need to open up the chamber and fix it. In doing so, we inevitably make some slight change to the alignment of the components, the material makeup of the assembly, etc. Each of these changes introduces unknowns. This makes it difficult to compare the results of one set of trials to another, and thus difficult to accumulate the date we need to actually demonstrate something conclusively. To make matters worse, we aren’t getting deep vacuums because the much of the plastic and rubber components of the assembly are out-gassing.

It’s as though instead of running one experiment a thousand times, we run a hundred slightly different experiments ten times each.

In a word, the three main problems with the old polywell assembly are alignment, structural integrity, and vacuum compatibility. I designed a new assembly which should remedy these problems. instead of multiple separate components, it will be one solid piece of 3D printed ceramic which include a core, acclerator anode, hot cathode, and langmuir probe, all bolted to the 8” conflat flange:

The two feet (bottom left) will be bolted to the conflat flange.

Close-up of the hot cathode holder:

The cathode holder is actually two pieces which sandwich two 2o mm lengths of 10-gauge solid copper wire between them into the inside grooves (A). The grooves on the outside of the cathode holder accept zip ties which will hold the copper wires firmly in place (B). Once the wires are secured, the whole thing is put into place against the left column, and another zip tie is slipped through the hole (C) on the extreme left of the cathode holder and looped around the column. This connection will be strong  enough to prevent the cathode holder from moving during setup/normal operation.  A light bulb filament, serving as the cathode itself, is soldered to the ends of the copper wires.

Close-up of the anode holder:

The anode, a copper cylinder,  is put into the crescent moon shaped space (A), and a zip tie goes around it and through the hole (B), and secures it to the assembly.

Langmuir probe holder:

The langmuir probe fits int the groove in the cylinder (A), and attached with a zip tie or perhaps teflon tape. It extends into the center of the core, indicated by the blue sphere (B). The cylinder is oriented and positioned such that the langmuir probe will extend into the center of the core.

Here’s the new langmuir probe:

The new langmuir probe is a strand of wire inside a very thin ceramic tube. The 9-volt battery on the right is for scale.

Core

The coils fit into the cavities in the core, and then covers go over them. The covers will be secured with zip ties or perhaps hose clamps.

Other than the zip ties and wires, all of this will be made of ceramic. The zip ties will be made of tefzel, a strong, heat tolerant, and highly vacuum compatible material similar to teflon. All wire insulation will be teflon.  This assembly will be heat resistant, electrically insulating, and much more rugged than previous designs. Ideally, we will be able to put it together, put it into the chamber, pump down to much deeper vacuum, and do hundreds of trails without anything breaking. moving, or changing shape.

In order to work at all, this design has to be compatible with the vaccum chamber and conflats that we already had. If one dimension is even slightly off, then the whole thing fails. To prevent that, I first took measnurements of the chamber and flange, and maodeled exact copies of them in OpenSCAD, and built this assembly inside the chamber :

Here you can see the conflat flange (left) and the chamber. Notice that the blue sphere, which indicate the center of the polywell is not centered in the chamber. By offsetting the core slightly, I was able to get more clearance between the walls of the chamber and the core, which in turn allowed for a larger coil radius.

Another pic of the whole thing:

While I have uploaded these models to shapeways, they will probebly not be the ones we actually have printed. This is more of a first draft.

The source code is here

Domenick Bauer





Electron Gun Trial Run Setup

31 05 2012

While the armature is approaching completion, we have yet to test the electron gun which it holds.  As described in earlier posts, it will consist of the cathode from an electron beam welder, a piece of copper tube for an accelerator anode, and a shard of phospher screen so that we can be sure it is actually shooting electrons.

This weekend, we will test a simplified version of this design. Instead of using the welder cathode, we use the tungsten filament from a broken light bulb, as suggested by Rehan:

Instead of using the phosphor screen, we will use the langmuir probe to detect the electrons.

In preparation, I have printed holders for the ceramic light bulb socket, and the accelerator anode so that the filament and the axis of the accelerator anode  are on the same line with each other and with the tip of the langmuir probe.

light bulb socket holder

ccelerator anode holder

both pieces together

Hopefully, this will work as a rudimentary way to inject electrons into the center of the reactor, deepening the potential well. If it does work, and we decide that we want an even deeper well, we will continue work on the original electron gun design.

Domenick Bauer





Electron Gun Progress

29 05 2012

The work on the electron gun armature is progressing nicely. Shapeways is currently printing this version:

Similar to the last one, but this time with a phosphor screen holder in the right shape for our phosphor shard.

This project demands a high level level of precision for its components. Everything needs to be exactly the right size and shape, and so in order to  use 3D printing effectively, we need to understand its limitations and work around them.

In all likelihood, there will be a problem with the armature above. Possible problems include:

1) The holes in the first column which are supposed to accept the hot cathode are smaller than they should be.

2) the columns are warped by the kiln-firing process.

3) Some unforeseen problem.

To address problem 1, We have also printed a hole-gauge:

The holes have a range of diameters, all clustered around 1.28 mm, the right size for the holes in the hot cathode holder.

The range of diameters in the gauge will give us a good idea of the relationship between the hole diameters in the OpenSCAD files, and the hole diameters in the printed part. If the holes in the printed armature are smaller(or bigger) than they should be, then this will tell us how to compensate in the next printing. Source code

Here’s the hole gauge in plastic

The hole into which the cathode is inserted was designed to have a diameter of 3mm, but as you can see, it tightly holds the cathode foot, which has a diameter of about 1.3 mm, which means that the diameter of the plastic version of the hole is 1.7mm bigger than that of the OpenSCAD version.

with further measurements, it might be possible to find a formula which converts OpenSCAD dimensions to real dimensions for this material and MakerBot setting, but that’s not important right now.

Another concern (problem 2), is keeping the columns straight. I’ve been in correspondence with the Shapeways, and according to them,  long thin pieces like the armature columns sometimes warp unpredictably when fired. This is problematic because a straight line of sight from the cathode, to the center of the accelerator, to the phosphor screen is integral to the electron gun’s operation.

If they don’t warp, great.
If they do, then we must alter the design so that this doesn’t happen, and reprint. Here’s a candidate:

In this version, the columns are buttressed in the x and y dimensions, so they shouldn’t warp. If they do anyway, or if something else goes wrong, then it’s back to the drawing board for another armature design, but that’s OK, because OpenSCAD and 3D printing make the prototyping process fast and inexpensive. Source code

Domenick Bauer





Electron Gun Armature

21 05 2012

One of the components of the electron gun is an armature which will hold the hot cathode, accelerator anode, and phosphor screen all in the same line with the center of the reactor.

This is a challenge because the armature must be an excellent electrical insulator and have a  high heat tolerance. The ideal material is ceramic.

The problem with ceramic is that it we cannot machine it into the unique shapes required, but we can 3D print it! I’ve modeled the armature shape in OpenSCAD:

Here’s a link to the source code

The three curved “feet” have the same curvature as the inside of the reactor chamber, so it will fit nicely and sit still in the bottom of it.

the first column on the left holds the cathode, the middle column, the accelerator anode, and the last, the phosphor screen. the black line will be the path of the electrons to the center of the reactor. Everything here is pretty much how it’s going to be on the final armature, except the phosphor screen will have a different shape, and the distances between the columns will be different as well.

The MakerBot wouldn’t be able to print this all in one shot, so I printed it in sections, and glued them together to get a feel for the final one.

The accelerator cradle

Column for hot cathode

Base of the armature

Earlier version of the base

Assembled armature with cathode and accelerator

Hopefully when I send this file out to be printed in ceramic, they will be able to do it all in one piece. If not, I’l have to find some way of gluing pieces together

Domenick Bauer





MakerBot

13 11 2011

All photos.

The Makerbot is up and running. It was fun to put together.

I was able to do a few test prints:





3D Printed Bronze

9 11 2011

All photos.

Years ago I looked into Prometal’s 3D metal printing process. The results were impressive but the stainless steel is magnetic:

This disqualified them as magnet holders!

Recently Prometal let me know about an experimental bronze process they are developing. Bronze is totally non-magnetic. BINGO!

Prometal donated a test part to see if I could make an airtight braze with a TIG welder:

The part was to be brazed to a Swagelok VCR fitting like this:

Prometal is still adjusting the process. This test part is a bit oversize so it was difficult to braze, but we got something:

The bronze attaches to the stainless nicely.

I was excited to put it in the chamber like this:

But I screwed up. I welded on the wrong VCR cajon. This one is two short to catch the male thread once the gasket is added.

Dammit.

I had the right part here all along; shown on the left:

So no vaccum check for now. But it looks like the 3D printed bronze parts braze nicely.

I count that as a win. Think of the parts I can make with 3D printed bronze + brazing.








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