Vacuum Chamber Construction

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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Thu May 28, 2020 2:56 am

Thanks for the suggestion! I might try that if I get really desperate, but after a quote from a local tool and die maker of $263 to remove the two bolts, I've ordered some flush bolt cutters and purchased a cobalt drill bit and and am going to try and solve the problem myself.

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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull » Thu May 28, 2020 7:07 am

As I noted drill 'em out you may save the fine threads if very careful and have the thinned remnant threaded sections separate using a pick. If not, just slightly over drill and tap to the next size bolt. (consulting the bolt and tap tables for drill size and tap, of course). I do not know your clearance below for a nut, but as I originally suggested you can just clear-hole bore for a suitable pass through bolt and nut. So many ways to skin this cat and no big deal at all, of course.

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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Rich Feldman
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Re: Vacuum Chamber Construction

Post by Rich Feldman » Thu May 28, 2020 11:58 am

Thanks for sharing the quote. More money than I had guessed. For that, can we expect absolutely no new damage to the threads, and no new scratches, scuffs, or dings on the flange faces? Does the work include fixing of presently damaged threads?

Bolt cutters will leave the stub distorted more than cut-off with a hacksaw, angle grinder, or any kind of abrasive cut-off wheel.
At our local self-storage facility, the office staff has lots of practice cutting padlocks. Primary tools are long-handled bolt cutters and battery-powered cutoff wheel.

Can your milling machine help to hold the workpiece and start the drill at right spot and angle?
Other drill-jig ideas that come to mind:

1. A thick nut, screwed onto a couple of threads deliberately left on broken bolt. We know those are not co-axial with threads in flange. :-)

2. Spare Conflat flange with matching circle of through holes, and a short tubular bushing with right OD and ID.
Drill jig bushings are available in many sizes, for example 5/8 outside and drill R inside. https://www.mcmaster.com/drill-jig-bushings/

3. Any scrap of flat steel, say 1/4 to 1/2 inch thick, with guide hole (and optional counterbore) made on drill press. If made on milling machine, it could have properly placed holes for a couple of other holes in bolt circle.
All models are wrong; some models are useful. -- George Box

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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Thu Jun 04, 2020 3:20 pm

Hi everyone,

I've managed to drill out the bolts to a standard that I hope will allow me to seal the chamber. The process was a bit finicky but it went as follows, flatten the top of the bolt with a mill, drill a starter hole with a carbide spot drill, then drill through with successively larger cobalt drills. One hole went quite well, and the other not so well, part of the bolt is still stuck in the hole and almost appears welded. I'd continue to attempt to drill it out, but the 250$ drill press I bought off of Amazon is really not very rigid. I'll hold off on trying to improve things until I have access to a better workholding setup.
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Dennis P Brown
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Re: Vacuum Chamber Construction

Post by Dennis P Brown » Thu Jun 04, 2020 3:56 pm

If you have a small circular file, carefully remove the remaining bolt threads till their almost flush (the abrasive force might also help loosen the remaining threads); then lots of tap oil and re-tap the thread carefully (use a tapered end tap only!) I've cleared remaining threads that way. Just don't over force it. Running a well oiled tap through a 'rough' threaded hole is always a good idea to be certain threads are clear and uniform again. Remember, very small partial turns (1/16) and back off and repeat as needed.

Anti-seize compound (never oil) is one's friend with steel on steel bolts into threaded holes.

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Bob Reite
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Re: Vacuum Chamber Construction

Post by Bob Reite » Thu Jun 04, 2020 7:04 pm

Looking at the pix, if it were me, I'd just drill them out to clearance size and put a through bolt and nut on the back, there is more than enough clearance for a nut it looks like from the photos.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull » Thu Jun 04, 2020 10:05 pm

Thanks Bob for recommending my original quick and dirty solution. Works every time. He has plenty of clearance there for that solution.

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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Rich Feldman
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Re: Vacuum Chamber Construction

Post by Rich Feldman » Thu Jun 04, 2020 11:18 pm

Whether Nicolas ends up with threads or a through hole, it helps if it's in the right place.
This is where a drill jig, clamped to the work, is better than depending on rigidity of drills and spindles. Especially when first round drilling-out has gone so far astray. (+1 on Dennis's suggestion to first attack with a round file).

A spare Conflat flange or blank with through holes, bolted to the work, would be easy. It's all you need if drilling to that size. To use it for guiding a smaller drill, a bushing can be contrived from short metal tube and/or thin sheet metal wrapped around the drill. Thicker sheet metal formed into a tube with aid of a mandrel and hammer and anvil. Maybe even straight wires/rods in bundle parallel to drill axis, or wire wound around drill. See what's already on hand that would be not too tight, and not more than 0.010 or 0.020 too loose.
All models are wrong; some models are useful. -- George Box

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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Sat Jun 06, 2020 5:00 am

I appreciate all the suggestions posted here, I've ordered some small files off amazon and am going to try and remove the remainder of the bolt using them. In the meantime I've hacked together a bit of a crude mounting system using a hacksaw and some aluminum bar stock. I plan on cleaning up the cuts when I have access to better equipment. But for now it works.
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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Sun Jun 07, 2020 2:56 am

Just a quick update, but the files along with a small pick and a rubber mallet worked very well, and the last remaining bit of bolt has been removed.

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