Vacuum Chamber Construction

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John Myers
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Re: Vacuum Chamber Construction

Post by John Myers »

An online tap & drill calculator shows it should be 21/64 (.3281) which is close to the Q drill bit size (.3320)
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Rich Feldman
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Re: Vacuum Chamber Construction

Post by Rich Feldman »

Yes, drill Q seems to be what they say, except McMaster-Carr's economy carbon steel tap calls for drill R (0.339). If you go a little large and don't get full height internal threads at the small end of taper, would a bad thing happen?

Machinists argue about the value of tapering the hole before tapping pipe threads.
https://www.practicalmachinist.com/vb/g ... ap-151341/
With a straight hole, the big end of the tap does a lot more work than the little end.
I like to use a tapered reamer from the hardware store, with a T handle.
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 »

Thanks for the clarification! I'd seen Q and R mentioned as well online, but had decided to go with the 5/16 since if it was a mistake I could always make the hole bigger!
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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

I have some successes and failures to report by way of an update. I've successfully sourced some valves via eBay for my fusor, a ball valve is now attached to my roughing pump and I've obtained a manually operated butterfly valve. With regards to the butterfly valve, the lip for the seal seems different from the knife edge I've got on all my other conflats. Is this just due to a manufacturing difference or does it mean it can't take a copper gasket?
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Secondly I've successfully tapped a blank and put in a bike valve. It took a bit of work but pleased with that effort.
IMG_1057[1].JPG
Finally the failure, while assembling the chamber for a leak test, I accidentally cross-threaded two bolts on one of my half nipples. This is the only nipple on the chamber that has threaded holes, I purchased it at a cheap price off of eBay, all others were ordered new and didn't have threaded holes. While trying to remove the cross-threaded bolts both snapped. I'm now wondering what the best course of action for removing them is and repairing the damage. Can I just drill out the holes with a slightly larger drill bit and remove the threads? Or is it better to get a tap and re-thread them?
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John Futter
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Re: Vacuum Chamber Construction

Post by John Futter »

Take it to a tool making house that has a spark eroder
my local one charged $25 per bolt removal and they did such a good job that putting a tap back down the hole removed no material and the correct bolts worked fine mixup between 5/16 and 8mm bolts
you now need to buy a tub of no sieze grease i prefer the nickel based one as the copper one is a nasty color
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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull »

I'm cheap and opt for Q&D, (quick and dirty)....If it were mine I would flush cut the bolts and bore 5/16 holes through the old bolts, then use mixed proper threaded bolts on the other 4 holes and use 1/4" bolts and nuts in the two bored holes. You just have to be very careful flush cutting the bolts against the flange face. While scratching the flange face is no big deal, the knife edges must be kept pristine. Pretty and proper is nice and fine if you have the bucks and people who can do the work to keep pretty in place. I tend to just want stuff to work as planned when sealed up.

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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Dennis P Brown
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Re: Vacuum Chamber Construction

Post by Dennis P Brown »

Have you considered differential thermal expansion heating/cooling? That is, heat the assembly in a regular oven to four hundred Fahrenheit or so, then use ice to chill the bolts. Next, using vice grips locked on to the bolts try and rotate them?

Failing that, I've had luck drilling such bolts nearly out and then extracting.
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Rich Feldman
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Re: Vacuum Chamber Construction

Post by Rich Feldman »

We know you enjoy cutting metal & getting hands dirty, but you don't have to for this.
Broken-off bolts have been dealt with millions of times in the last 150 or 200 years.
There are people not far from you, with proper tools and experience, who do it all the time.

I like Dennis's shrink idea, but am skeptical about this particular geometry.
Because of the time for temperature changes to diffuse into and along the bolt, whose thermal contact with internal thread was increased by the mechanical abuse, and then the time to switch from ice to vise-grip connection. Can't hurt to try.
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 »

Hi Dennis,

I've given the heating/cooling idea the old college try and haven't had any luck. I'm going to look around town for some people with bolt removal experience
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Dennis P Brown
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Re: Vacuum Chamber Construction

Post by Dennis P Brown »

One method (used on rusted and/or seized bolts) is a torch. Heat the bolt to red heat, then vice grips (rapid cooling of bolt) and a powerful twist. The extreme thermal expansion/contraction can breack the bond between metals. This often allows removal. But it is drastic and not something I'd attempt except as an extreme measure.
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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

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 »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Rich Feldman
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Re: Vacuum Chamber Construction

Post by Rich Feldman »

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 »

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.
IMG_1080[1].JPG
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IMG_1084[1].JPG
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Dennis P Brown
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Re: Vacuum Chamber Construction

Post by Dennis P Brown »

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 »

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 »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Rich Feldman
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Re: Vacuum Chamber Construction

Post by Rich Feldman »

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 »

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.
IMG_1086[1].JPG
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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

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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Dennis P Brown
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Re: Vacuum Chamber Construction

Post by Dennis P Brown »

Very pleased to hear it all worked out - both literally and figuratively.
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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause »

Just a quick update. I've got the chamber all assembled, and sitting on its frame. While I'm sure in the future I'll like having so many ports, at the moment it's mostly a lot of tedium anytime I try and put it all together. This is the second time putting it together today as earlier I was nearly done, but ran into some problems again with bolts biting into threads on the top port. Rather than fuss about with it, I disassembled the top half and drilled out the threads on every hole up top. Don't have to worry about that problem again! Tomorrow I plan on tightening up all the bolts, and pressurizing the chamber with a bike pump I have handy. I'll use a soap and water solution on the joints to check for any major leaks.
IMG_1104[1].JPG
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Dennis P Brown
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Re: Vacuum Chamber Construction

Post by Dennis P Brown »

Your system looks absolutely professional and you've obviously become an expert machinist, as well. I'd find it hard to believe that you'll see any leakage using pressure/soap because that system is too well made to exhibit any significant leaks. Look forward to your further posts.
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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull »

I'm glad you took my advice on just drilling out those threads to make it thru-hole. Threads are great and even demanded in tight or ill-designed conflat mountings, but plain holes with clearance warrants that a bolt that is snapped off in no problem. A messed up nut just be cut off without having the hassles you have had with stripped or damaged threaded flange holes. In addition, thru-holed flanges are cheaper.

My motto is design with clearances so you can use common hardware bolts, if you can, and use thru-hole flanges.

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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Rich Feldman
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Re: Vacuum Chamber Construction

Post by Rich Feldman »

Anybody here using nut plates instead of single nuts, to use fewer wrenches and lockwashers?
CF-Flange-Plate-Nuts.png
CF-Flange-Plate-Nuts.png (75.69 KiB) Viewed 10045 times
https://apexvacuum.com/product/conflat- ... late-nuts/
All models are wrong; some models are useful. -- George Box
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