Vacuum Chamber Construction

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Nicolas Krause
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Vacuum Chamber Construction

Post by Nicolas Krause »

I've finally begun machining on the hemispheres for my vacuum chamber, Andrew Seltzmann's guide on his website has been a huge help. I've taken some slightly different steps though. After the hemisphere was mounted and centered on the lathe a pilot hole was drilled with a spot drill.
image2.JPG
My first attempt used a spot drill with a 90 degree tip, when drilling out the pilot hole with a drill bit, the flutes snapped due to the angle on the drill bit being greater than that of the hole created by the spot drill. A second attempt with a different angled spot drill was successful and the hole was drilled out with two successively larger drills
image1(1).JPG
. The next step is to bore out the hole to the correct size for my vacuum port.
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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull »

Good work! I used an adjustable fly-cutter on my milling machine and a tilt table to bore all the portholes in my fusor IV. The work went fast once the tedious alignment was done. The smaller holes, of course, used drills in the mill.

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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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

My boring bar arrived in the mail this week and as a result I've been able to make a bit more progress on my chamber. The boring bar was placed in a square bar holder and then mounted in a tool holder,
image1(2).JPG
Subsequently the center hole was bored out for the top conflat nipple.
image2(1).JPG
I was a bit aggressive with my initial cuts and as a result I've damaged the tip of my boring bar. The tool still cuts, but lesson learned and I'm being a bit more cautious with my initial setup and first operations. I'm about a hundredth off of the required diameter but ran out of time to finish the job yesterday. I'll complete the boring next week, and repeat the process on my other hemisphere. Then I plan on using a tilting table on a milling machine to bore the other holes for each hemisphere.

Nick
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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

I've encountered a few problems with the continued machining of my hemispheres. They are largely due to my own ignorance and have served as useful learning experiences. I obtained a tilting table and some toe clamps with which to machine the remaining holes in the hemisphere at 45 degree angles. A first attempt at a cut created a lot of chatter in my cutting tools and two broken carbide tools later after double checking everything I noted that I'd improperly set the angle and mis-centered the hemisphere. The first cut can be viewed in the image below.
image1.jpeg
In the setup above an edge finder was used to center the hemisphere on the x and y axis of the milling machine. After doing some research online I noted that carbide tooling breaking in drilling operations is a common problem and decided to switch to HSS bits for the remaining holes. My RPM for the drilling operation was set to 600, which for a 1/4 inch diameter tool was inline with both online recommendations and the Machinery's Handbook I have on hand. However after attempting to drill the first hole, no cutting was observed and the drill bit was obviously dulled.
image2.jpeg
These drill bits were obtained from KMS Tools, the Canadian version of Hobby Freight and while they were specified as metal cutting drill bits suitable for steel I think the cheap price I paid indicates they're low quality tools from China. Going forward I hope to salvage the work piece, I think that the proper centering should take care of that chatter and any breakage with carbide tooling. However I'm a bit concerned I may have work hardened a small portion of the workpiece and am worried that may cause problems. Given the small size of the possible work hardened area if I return to using carbide tooling will I have any issues with drilling through it? Any advice is much appreciated.
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Re: Vacuum Chamber Construction

Post by John Futter »

Nicolas
first never centre punch SS for hole position this work hardens the SS straight away
If you have skidded your drill on the SS it has work hardened and you will need to use your carbide drill
I see little or no coolant on your work piece this is bad
slow your speed to below what your book says.
The correct drills for SS are cobalt drills that are much harder than HSS but not as brittle as Carbide
They are not cheap but a 1/8", 1/4" and 1/2" should be in your tool kit.
1/8' for pop rivets into SS 1/4' for use in hole saw mandrel for SS
and 1/2' is good start for milling larger holes
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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull »

It looks like you bought the same ChiCom tilt table that I bought for my mill. That table saved me many a complex operation on my hemispheres turning the operation into a snap. It has served me in many other ways since building fusors III and IV. That sucker is a heavy beast though. Those Chinese backyard blast furnaces can turn out some impressive castings.

Good work on the progress you are making. We learn as we go. Teachable moments we will keep all throughout our lives. There is nothing like the hands-on experience.

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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Re: Vacuum Chamber Construction

Post by Jerry Biehler »

Use good, name brand bits. Don't buy cheap chinese bits, they are trash.

You can use cobalt like John says but it you are just doing a few holes it wont matter much in the end. I try to get 135 degree split points. Constant pressure while drilling. Don't stop, if you let up and let the bit rub instead of cut the stainless will work harden and then you get to get out a carbide bit to get through it. You really dont need coolant for drilling though it cant hurt. Tapping, yes, you absolutely need it.

Also, spot drills are used to just make a little divot, not to drill all the way through. Try and get ones that match the drills you are using. 90 is too steep for most things. I usually use 120's which are for 118 degree drills. They are fine for 135 too.
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Rich Feldman
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Re: Vacuum Chamber Construction

Post by Rich Feldman »

Can one use a torch to locally anneal work-hardened places in a SS workpiece?
For applications (such as fusor chambers) that don't demand the best mechanical, chemical, electrical, magnetic, or aesthetic properties.
All models are wrong; some models are useful. -- George Box
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Re: Vacuum Chamber Construction

Post by Jerry Biehler »

Not really, you just have to machine through it or grind it out. People make a big deal out of stuff like stainless and titanium and they are not that big of a deal. Keep feed constant and keep your surface speed where it should be (~200sfm for 304 with carbide) and you probably wont have any problems.
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Re: Vacuum Chamber Construction

Post by Richard Hull »

Of course, the only reason you hear a big deal made of SS is that it comes from the non-machinist who thinks it ought to go like common alloy aluminum or wood. The wake up call comes with a new set of blue tipped bits that won't even do wood well any more.

A quick read in a basic machinist's book would end the issues with SS provided they heed the speed, keep up a steady pressure and use a good tool steel or carbide bit.


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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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

After a bit of a school enforced break, I've finally managed to find some time over the summer holidays to return to the machining of my vacuum chamber. Using a carbide spot drill, a pilot hole was drilled and then subsequently enlarged to 3/8 size with a number of drill bits. I now plan on using a step drill to enlarge the whole to close to its final size and finally a boring head to take the hole to the precise diameter. The second hole visible in the photos below is from an earlier machining attempt that didn't work out.
image1.JPG
image2.JPG
I do however have a question about workholding. I'm using 4 toe clamps on a tilting table to hold my workpiece in place. The hemisphere seems to come loose rather regularly with the setup. After monkeying around with it for a bit I was able to find a seemingly stable solution that held the workpiece securely, but I wanted to know if there was a better way to go about holding the hemisphere. Or if I'm simply setting up the toe clamps in a way that doesn't use them effectively.
image3.JPG
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Re: Vacuum Chamber Construction

Post by John Futter »

Toe clamps directly to mill slide bed
t bolt through the hole in the top with machined aluminium disc to fit hole now held top and bottom you will need to offset mill head to correct angle to bore hole.

enjoy
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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

Thanks for your suggestion John, I've cobbled together a better workholding solution as a result. A t-bolt in the middle of the hemisphere is connected to a long bolt, which has a couple washers on the end. I plan on adding a dab of superglue between the washers to hold them together as a unit and make assembly and disassembly of the work piece a little bit less finicky.
image1.JPG
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

Before returning to school I was able to complete the first angled port on one of my hemispheres. Now that I have the series of operations figured out I anticipate that I'll be able to complete the remaining ports much more quickly. I'll likely be able to get to it over winter break or failing that early spring once school breaks for the summer. A cheap step drill from china performed very well to rough out most of the hole and a boring bar was used to take it to final dimensions. Initially the boring bar was too long and excessive chatter resulted, but I switched to a much shorter tool and chatter was greatly reduced and surface finish improved drastically.
image1(1).JPG
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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull »

Great work! You are using the exact same tilt table I use on my milling machine to do such work.

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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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

After a school enforced break, I've managed to pass all my classes for the semester and have found some time to work a bit more on the machining of the hemispheres. I've successfully completed a second angled port on one hemisphere. What took me most of summer to finish with interruptions and mistakes in machining process took me the better part of an hour this time. I anticipate I'll be able to finish the remaining ports within the next few weeks. Then I can move on to learning to how to TIG weld!
hemisphere2.JPG
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

Machining has been completed on one hemisphere and the angled ports have been started on the second hemisphere.
small.JPG
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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull »

Gee! That is some aggressive machining with ports-a-plenty.

I trust once the flanges that hold the system halves together are welded, that you have clearances for the ports, which I assume are CF stubs.

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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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

Yes, I'm copying Andrew Seltzmann's design that he's posted on his website. I doubt my machining tolerances are as good as his though, I've been using an edge finder and tilting table instead of the precision rod and indexing head setup he used. I've got a single half nipple CF port you can see partially hidden in the photo. I've been using it to test fit as I machined out the port holes. I've checked the port against the flanges which I also have and all fit quite well.

I figured that 10 ports would allow for some flexibility, it seemed a waste to build a vacuum chamber and then not be able to reconfigure it if in the future I wanted to monkey around with sputtering or semiconductors or some other project requiring high vaccuum.

I have the following general plan mapped out for the fusor chamber.

2 On Axis Ports:
TurboPump Connector
High Voltage Feedthrough

8 Off-Axis Angle Ports:
Pressure Sensor
ViewPort
Hydrogen Ion Gun
Boron Ion Gun
Quadrupole Mass Filter - based on Rapp Instruments design posted here
3 spare ports

I view this project as a rather long term thing for educating myself and gaining useful skills, I'm not planning on attempting Deuterium based fusion, many people have succeeded at that on this forum and I would like to try something new. If at the end of this none of my ideas work out I'll merely have gained a bunch of useful skills, which I view as a pretty good deal. My plan for the next year or so is to complete the chamber, power supply and high voltage feedthrough, and pump system. This will allow me to generate a plasma, and then I can begin working on the more advanced components. While I have most of the individual components all require some work, for example I have a small turbopump however I have to design a controller for it as I don't have the funds to purchase one new.
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Re: Vacuum Chamber Construction

Post by Richard Hull »

You are doing it the right way and the best way. Do a little and learn a lot. Do a little more, read and practice the skills. You will succeed in fusing even if your ideas don't pan out. As you note, it is a win for you that will give you skills for a lifetime of future endeavors. Each skill is another tool... a tool that you can't go to the store and buy. The "hands-on imperative" is ingrained into all doers.

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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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

I've now completed machining of the ports for the vacuum chamber. Up next is an order to lds vacuum for the remaining parts I need and some practice welding.
image1.jpeg
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Re: Vacuum Chamber Construction

Post by ian_krase »

That is a lot of holes.
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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull »

I mentioned that before above....An awfully hole filled chamber. Lots of CF stubs and lots of blank offs unless you are shooting for ion guns aplenty. At least he won't be at a loss for hassle free "add ons", if needed, in future.

On page two Nicolas gives a full, optimistic, listing of what is planned for each port. Until they are all in place, that means blank offs during early work.

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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Re: Vacuum Chamber Construction

Post by ian_krase »

In the excellent but extremely grognardy and complicated Kerbal Space Program mod KSP Interstellar, we see this fusion reactor, which appears to be a fusor-type reactor with ion guns.

Image

This makes me think of it.
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

While I source the final vacuum components for my chamber I figured I could work a bit on the pressure sensor. I've got a vacuum thermocouple gauge, and a spare Tiva C series board lying around. I figured I would use one to monitor the other, I've been planning on picking up Forth for awhile and this seemed like a good project to start with. Mecrisp is a publicly available version that supports my board so I'm working on getting a connection made to the board.
image1(1).jpeg
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