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Mike Thompson
Prolific User
Username: vroomrr

Post Number: 1178
Registered: 04-2019
Posted on Sunday, 05 January, 2020 - 17:17:   Edit PostDelete PostView Post/Check IP

I was so impressed with the ease of the plasma cutter in the video of swapping car frames, that I want to get one. (Not right now, I'm running out of money, and the 64 Imperial is not running well enough to sell.) The question is, what should I look for in a plasma cutter? (I would rather to not need to buy gas for it.)
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David Gore
Moderator
Username: david_gore

Post Number: 3549
Registered: 04-2003
Posted on Monday, 06 January, 2020 - 06:23:   Edit PostDelete PostView Post/Check IP

Mike,

Unfortunately for you, the gas is the most important component in the whole set-up.

The gas is electrically excited by the cutter electronics to form a "plasma" and it is this excitation that is the key to the whole process. The plasma is the best way to cut materials that are resistant to traditional oxy-acetylene and other methods requiring oxidation of the metal during the cutting process.

https://en.wikipedia.org/wiki/Plasma_cutting

.
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ross kowalski
Prolific User
Username: cdfpw

Post Number: 1299
Registered: 11-2015
Posted on Monday, 06 January, 2020 - 09:39:   Edit PostDelete PostView Post/Check IP

Mike,

The cheapest one on Amazon, you supply 110v and air. I don't know the cfm consumption because my compressor is 15 scfm at maybe 100psi and doesn't strain it but I doubt it's that bad.

They are cheaper on eBay, but at that price point you might want Amazon because of the return policy.
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Mike Thompson
Prolific User
Username: vroomrr

Post Number: 1179
Registered: 04-2019
Posted on Monday, 06 January, 2020 - 09:55:   Edit PostDelete PostView Post/Check IP

I might be wrong, but in the video of the little English Ford, I think the cutter had some sort of fan built in. I have an old Sears air compressor that sat for years (out doors, and with the water inside) bought it for $25 dollars and got it working. But the tank has a leak due to rust (scary) and will only get up to 60 psi. I never stand close to it. Needless to say I need to fix it.
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Trevor Hodgekinson
Experienced User
Username: wm20

Post Number: 139
Registered: 11-2006
Posted on Monday, 06 January, 2020 - 11:22:   Edit PostDelete PostView Post/Check IP

I have a Dillon low pressure oxy-acetylne system and it cuts beautifully.
I can slice up cylinder heads to use as feed for my little foundry.

Being the cuting torch is part of the welding kit it cutting is essentially free.
They are now called "Cobra or DCH 2000"
Apart from that you can weld aluminium up to around 1/2 " thick and steel as thin as a beer can.
I use it regularly to repair aluminium mower base plates with blade / rock holes through them.
Uses about 1/3 of the gas as a std Oxy system so becomes very cheap if you buy the bottles rather than hire them.
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Mike Thompson
Prolific User
Username: vroomrr

Post Number: 1180
Registered: 04-2019
Posted on Tuesday, 07 January, 2020 - 09:09:   Edit PostDelete PostView Post/Check IP

I have been passing by this place everyday and seeing they have pallets and what not. So I went in to ask what I could take, all these things they said no to, but then said you can take as many bad fire extinguishers as you like, out back. At the moment I could not think of a use for them. But walking back to the truck I thought of this thread, and that I need air tanks. Fire extinguishers are essentially air tanks with a bunch of powder in them. So I got four of them and I will plumb them together to form one much bigger tank than I now have. They sound thicker than the original compressor air tank. Does anyone know how much psi a large fire extinguisher can hold? (They are 2 feet tall.)

fire extinguishers
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David Gore
Moderator
Username: david_gore

Post Number: 3552
Registered: 04-2003
Posted on Tuesday, 07 January, 2020 - 17:42:   Edit PostDelete PostView Post/Check IP

Mike,

There should be a Standard Compliance stamp somewhere on the tank if it is classified as a pressure vessel. I checked my workshop Dry Powder extinguisher and the base is stamped with a compliance to an Australian/New Zealand Standard which I cannot access as it is behind a pay wall.

No stamp; DO NOT use as a pressurised storage tank under any circumstances. The same rule applies if visible corrosion is evident inside or outside the tank. Your life is worth far more than the saving achieved from using an uncertified/untested tank.
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Omar M. Shams
Prolific User
Username: omar

Post Number: 1925
Registered: 04-2009
Posted on Wednesday, 08 January, 2020 - 02:42:   Edit PostDelete PostView Post/Check IP

I cannot emphasize the point that David has made above more.
Thank you David for your post.
Cylinders are small bombs.
Unknown cylinders are even more deadly.
Please Mike - be very very careful.
It is not worth the risk mate. Leave them be and walk away from them.


Omar
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Trevor Hodgekinson
Experienced User
Username: wm20

Post Number: 140
Registered: 11-2006
Posted on Wednesday, 08 January, 2020 - 10:34:   Edit PostDelete PostView Post/Check IP

One of the reasons why they had so many is there are very few processors that will recycle them.
We used to pt them in a big press and bail them before being committed to the furnaces
We knew when they were doing
Fire extingusher or gas bottles cause the floor would shake due to all of the explosions.
If you want a good cheap air receiver then keep an eye on receivers auctions. Lots of them come up and because of OH & S reasons very few go for much.
I bought a massive hydrovane compressor and a 2000 gallon vertical receiver from a service station that was being converted to a mini mart for about a days wages.

On a similar path back when i as a technician we tried in vain to get the method of testing pressure vessels changed .
Even now in the 21st century the accepted method is to put them in a tank of water then pump them up with water.
If the water level i the tank rises the pressure vessel is condemmed.
A better method is to fix a transonder to the vessel then pump it up to it's working pressure + whatever the safety extension is for it.
The transponder will start to click if there is any damage to the tank on subsequent testing or you can have it hooked up real time. When over pressurizing a tank you can actually induce internal failures and make lattice inconsistancies that are sessile become glissile .
So a tank that is passed as safe can can fail in service in a very short time.
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David Gore
Moderator
Username: david_gore

Post Number: 3553
Registered: 04-2003
Posted on Wednesday, 08 January, 2020 - 16:01:   Edit PostDelete PostView Post/Check IP

Trevor,

Bloody hell mate - what are you doing to me?

Sessile and Glissile - haven't heard these words since our atomic crystallography and lattice dislocation lectures in room G10 50 years ago. {Explanation: these are terms to describe atom behaviour and the resulting structural configurations after being subjected to external forces}.

Yes, you are absolutely correct about pressure vessels that pass hydrostatic testing subsequently failing at lower pressures than the hydrostatic test pressure [especially when adverse environmental conditions are involved].

I would expect Omar may have experienced this type of failure in the oil industry and this is one of the reasons for his advice above.
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Patrick Ryan
Grand Master
Username: patrick_r

Post Number: 2198
Registered: 04-2016
Posted on Wednesday, 08 January, 2020 - 16:39:   Edit PostDelete PostView Post/Check IP

Considering trucks of all types that run a full air brake system run up to 8 tanks per truck and run pressures between 110 -150 psi, I rarely see tank failures.

When I am inspecting our Volvo workshops, the only tank failures I have seen have either been caused during an accident, or something has flown up into them off the road and holed them.

I guess what I am getting at is I find truck air tanks very stable.
Most these days are made from aluminium for weight saving.
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Mike Thompson
Prolific User
Username: vroomrr

Post Number: 1185
Registered: 04-2019
Posted on Wednesday, 08 January, 2020 - 19:12:   Edit PostDelete PostView Post/Check IP

Since the bottom of my air compressor tank was repaired with Permatex Liquid Metal Filler (glue, by someone else). I'm pretty sure anything is safer than the tank I am using now, albeit at a distance. I will keep it top secret whether I actually use another alternative or not (for site liability concerns). (But I could point out that the tanks are rated to 240 psi, well above the cutout at 100 psi.)

(I'm not that confident in my welding ability to repair an air tank.)

Stuff others have said on this subject.

https://www.s10forum.com/threads/fire-extinguisher-as-air-tank.336596/
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Trevor Hodgekinson
Experienced User
Username: wm20

Post Number: 141
Registered: 11-2006
Posted on Thursday, 09 January, 2020 - 08:03:   Edit PostDelete PostView Post/Check IP

David,
Sorry but there is really no other way to describe it without writing a text book.
Did you ever encounter Vince Manners from the Defense Standards Lab ?
One of their jobs was to certify rocket & missile bodies.
He showed me several that had passed the standard over pressure test and the actual testing had compromised their structure to a point that they were actually screaming at loads substantially lower than the actual operating pressure.
The failure of industry to embrace acoustic emissions has always been perplexing to me particularly as you get real time warning a very long time before failure .
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David Gore
Moderator
Username: david_gore

Post Number: 3555
Registered: 04-2003
Posted on Thursday, 09 January, 2020 - 18:03:   Edit PostDelete PostView Post/Check IP

Trevor,

I was trying to provide a concise comprehensible definition and, yes, even the text books find this difficult. Have been trying to remember our lecturer, I think it was either Peter MacDougal or Mike McGurr who ruled the 1st Floor X-ray Diffraction Laboratory at the time but I could be mistaken. I remember spending more time watching the girls walk by on their way to the upper campus than doing the diffraction experiments.

I never had any contact with DSL in Alexandria in the 1970's other than one visit to drop off some samples they had requested from Comsteel Waratah and then I didn't get past the front desk as I didn't have clearance.
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Mike Thompson
Prolific User
Username: vroomrr

Post Number: 1189
Registered: 04-2019
Posted on Thursday, 09 January, 2020 - 19:20:   Edit PostDelete PostView Post/Check IP

Of course the opposite of cutting is welding. To get a title for a custom car one must have the welds of the kit body, in this case a 1957 Chevy attached to a Cadillac, to under go an inspection by a ASE master mechanic. When it comes to welding sheet metal so far the best I can do is blast it away as a plasma cutter with my equipment. What do they use to weld thin metal?
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Trevor Hodgekinson
Experienced User
Username: wm20

Post Number: 143
Registered: 11-2006
Posted on Friday, 10 January, 2020 - 16:15:   Edit PostDelete PostView Post/Check IP

You have already been told
Use a Henrob - Dillion -DHC 2000 oxy set.
As previously welds aluminium up to 1 " thick
Cuts through steel up to 4" thick
Welds steel as thin as a beer can.

Old man DIllion came to the yard cut a pair of steel beer cans in half.
He then welded the 2 bottom 1/2s together and immersed it in water to prove it was a good weld .
he then did the same thing with 2 aluminium soft drink cans.
Changed tips and sliced railway lines into 1/4 slices.
Very impressive kit.
However Simsmetal was CIG's biggest customer and as such only paid for the actual gas used at a substantial discount and got it delivered for free.

I got into deep poo because I showed interest and latter on bought one.
The single best investment in tooling I have ever made.
That was just under 50 years ago, i still have it and it works perfectly. only has to replace 2 tips and do hundreds of welds a year with it from stainless steel to aluminium.

Now with respect to your hilbilly cheap nature, you can make a reasonable spot welder out of the transformer in an old microwave.
lots of boob tube videos on how to do it.
Really easy and cheap but f you do please discharge the cap , from a safe distance as they can and do go bang very big time.
I am currently collecting them to see if I can make a high energy press by vapourising a length of wire .
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ross kowalski
Prolific User
Username: cdfpw

Post Number: 1300
Registered: 11-2015
Posted on Monday, 13 January, 2020 - 11:13:   Edit PostDelete PostView Post/Check IP

Mike,

Working with 50's sheet metal is a pleasure. It's thick and low carbon. The only problem is they were not shy leading seams.

The cadillac will have galvanized bits for a good dose of zinc fever, thin high carbon sheet metal with no shortage of spray on sound deadening / seam sealer / paint.

Good luck.

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