Vacuum Chamber Construction

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Nicolas Krause
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Vacuum Chamber Construction

Post by Nicolas Krause » Thu Sep 21, 2017 7:48 pm

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 » Fri Sep 22, 2017 5:42 pm

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Thu Sep 28, 2017 8:17 pm

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 » Wed Dec 20, 2017 9:04 pm

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 » Thu Dec 21, 2017 11:12 pm

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 » Thu Dec 21, 2017 11:16 pm

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Jerry Biehler
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Re: Vacuum Chamber Construction

Post by Jerry Biehler » Sun Dec 24, 2017 6:34 am

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 » Sun Dec 24, 2017 8:27 am

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.
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Re: Vacuum Chamber Construction

Post by Jerry Biehler » Sun Dec 24, 2017 10:46 pm

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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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull » Mon Dec 25, 2017 5:58 pm

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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