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I like it! Some Questions.

Posted by John Meacham 
I like it! Some Questions.
March 10, 2011 10:06PM
Hi, I find the ideas behind the metalicarap really interesting. I built a plastic printing reprap a while ago and am very happy with it, but always wondered if there was a good path to printing in metal.

It just so happens I had the idea of building a farnsworth fusor in the back of my head for a while, and the set-up has a lot in common between the two.

A few questions,

what sort of vacuum do you think is needed? you can get cheap pumps that will bring you down to about 50 microns, which is enough for a nice plasma ball in a farnsworth fusor, but you need to get to about 10-4 torr for fusion to occur, so I am assuming somewhere between the two? There is a pretty big jump in complexity between high vacuum and ultra high vacuum, so I was hoping I could get by with an inexpensive vacuum pump that can get down to 75 micron like [www.amazon.com]

For my initial experiments I am thinking of just setting up a small desktop vacuum chamber with an ebeam in it to point at various metals measuring temperature change, testing my HV power supply and whatnot. not trying to build a full MetalicaRap or an axis or any of that.

for the X-Y axis, do you think it is possible to use electrostatic or magnetic control of the beam rather than actual physical movement of the gun?

So, this also seems like it will produce a prodigous amount of Bremsstrahlung x-rays, how much of a concern is that, since they would mainly be in the axis of the gun, it seems that as long as I don't sit underneath it, I will be fine, but of course that isn't something I want to take on faith. (I have an x/gamma-ray detector, so will definitely measure it, but perhaps someone here knows from experience what to expect)

It seems that if you have a lot of the mechanics inside of the vacuum chamber, outgassing from oils/plastics will be a problem, but if you don't need an UHV I guess that won't be an issue.

Can you elaborate on why you need 2 guns? is the one that is far away just to keep the surface near the melting point so the melting gun doesn't have to do much work?
Re: I like it! Some Questions.
March 11, 2011 07:36AM
Good to hear from you,
In MetalicaRaps case to keep a defined beam for more than 2cm you need high vacuum
achieved with 2 pumps; roughing pump and turbo pump (/ or oil diffusion pump) See below.

Turbo pump for High Vacuum 10 -4 Torr only works after using a roughing pump ( see below),
Leybold TW 400-300-25 or Leybold 700 700 litre/S

Vane pump roughing pump
Varian DS102

you can get them second hand on ebay.

For X-ray issues see [www.icrp.org] cover most aspects,
see for ebeam melting applicationreprap sls vs ebm discussion

Materials need to be chosen from the [www.ece.ualberta.ca]
to limit outgasing.

In the future we hope to combine the 2 guns in MetlaicaRap in to one, but for now, so we replicate existing working systems our vision system need to be close to the target just like a normal scanning electron microscope in a cartesian XY format to reach the whole print area, and our magnetically deflected melting beam needs to be far enough away (1m) from target to cover the whole build area while limiting the beam deflection to 8 degrees.

Sounds an exciting project,

p.s. I stick to solar cell printer and keep any fusion 93 million miles away its warm enough for me at that distance.
Re: I like it! Some Questions.
March 14, 2011 09:48PM
I think I will probably be much less ambitious than you for my initial attempts smiling smiley

I have a suitable roughing pump, and a small vacuum chamber (2 cubic feet more or less), I think I will simply start by getting a relatively weak e-beam working and some suitable deflector grids running pointed at a phosphor target.

Over my small chamber, I'd only expect a small amount of deflection, but it should be enough to validate calculations. A homebrew CRT is a far cry from a MetalicaRap, but it seems like a good first step and more importantly. can be done with what I already have at home. smiling smiley

I am worried about the high voltages you are planning, at 150kV, the 100pF capacitor that is a person wearing rubber soled shoes can build up enough charge to kill if they are particularly unlucky.

In any case, I'm going to do my experimenting at about 10kV to avoid having to worry about x-ray shielding or electrostatic induction hazards for now. Since I am only interested in targeting/focusing and not melting, a glowing dot on a target I can see visibly and manipulate is a goal I can set for myself that can justify me breaking out more money for the heavier equipment if successful.

I'm going to have to start thinking about a bigger vacuum chamber (converted gas/propane cylinder?) and an eye on eBay for a suitable turbopump.
Re: I like it! Some Questions.
March 15, 2011 03:54AM
This may be of interest, teralab

Random Precision
Re: I like it! Some Questions.
March 16, 2011 08:00AM
kind regards
MetalicaRap team
Re: I like it! Some Questions.
March 16, 2011 06:13PM
I've always wondered if it was possible to use a "liquid ring pump" to achieve a high vacuum at low prices. Of course, instead of using water as the middle, you should use an oil similar to those used in a diffusion pump so you do not have a vapor pressure at 20 torr.

This type of pump is incredibly strong and demand little maintenance, simply check the level of liquid inside the pump to ensure maximum efficiency.
Re: I like it! Some Questions.
March 17, 2011 03:14AM
Apparently a diffusion pump is pretty easy to make, here is one made of glass:


It certainly looks 3d printable, probably want to do it upside down unless you can print a support material. perhaps with a steel cup at the bottom for heating until a reprap that can print in metal is made.

Then all you need is a roughing pump, the liquid ring pump certainly looks like it might work. worth checking out! I am not sure the current gen of repraps have enough precision for this sort of thing, but a version that can can't be far away.
Re: I like it! Some Questions.
April 24, 2011 03:37PM
I just seen this short vid that explain EBM http://blog.netfabb.com/index.php?bid=36 it help me to grasp the concept... thus I share it here, even if it's based on a commercial machine it may inspire something (or to add on the wiki) smiling smiley
Re: I like it! Some Questions.
April 25, 2011 08:20AM
great its done
kind regards
MetalicaRap team
Re: I like it! Some Questions.
April 25, 2011 08:50AM
I think this project is quite amazing and I'd like to point you to this cad software as is you still seem to be looking for good trial or free electron beam modelling software.


I haven't worked with it but from what I've read it should be useful.

Keep up the good work
Nice Work!

I want one! This is the sort of project that should be listed on kickstarter.com. The reprap community as well as makers everywhere will surely donate to this project to get it off the ground faster. Sadly experts in the fields you are working in are harder to come by than the money for it.

Thanks for being awesome.
When I read through the current status of the wiki i can't tell exactly where you guys are at.
Have you got working prototypes for the different parts, or are you hung up somewhere? You needing help to figure something out or to buy some equipment?
I also had a question. I have heard of the cost of the metal powder and wonder if an approach that is more like automated TIG welding would be more appropriate. The obvious thing that comes to my mind is that TIG welding will have power regulation issues and will be difficult to make fine work, but it avoids the magnetic focusing and vacuum requirement. TIG essentially is an electron beam process, but less focused and uses only electrical potential across air/gas to cause electrons to flow.

I just wanted to hear your take on why this is not the preferred plan as of now. Thanks
Re: I like it! Some Questions.
May 18, 2011 09:51AM

As you said, "it will be difficult to make fine work" this is critical as you may need all the other machines as well,

If you want to look at nasa's metalurgy lecture on metal forming in a vacuum you will see its advantages; [www.aeronautics.nasa.gov]# see this video podcast

have a look at the following section;


You might want to add a TIG section with your ideas.

the sub section below gives some guidance on metal attributes to research and quantify to asses TIGS pros/cons.

sub section
General guidance on comparison with the production of metal parts.
Re: I like it! Some Questions.
May 18, 2011 03:37PM
The above link to the subsection did not work

You can find it in the usefull links section of metalicarap site ( near the bottom)
Its called "Discussion of Advantages and Disadvantages of different Tool head processes" good luck

We had bad news today we had an electron microscope donated to us from a university for vision system development
they said they would keep it for us, but when we turned up to collect they had just thrown the 100,000 euro microscope in the skip.We checked the skip but it was gone. Damm!!!

thats open source hardware ups and downs for you!

If any one offers you one and is flogging it on the cheap, then I bet its ours!!
I hope in a few years time I see it at a opensource day covered in lots of leds blink blink

oh well try agaian tommorrow!

keep up the power!!

kind regards
MetalicaRap team.
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