Cutting Steel Rings from an 8.5kg gas cylinder

[BigWave]

Looking for advise here.
I have an old 8.5 kg gas cylinder which I'd like to cut 5 to 6mm rings from the main body.
Clearly I'd need to flush the cylinder with water first to clear any residual gas.
I could use an angle grinder I suppose, but was wondering if anyone could suggest another way to get a "cleaner" and more accurate cut.
I am planning on using these rings for circular sundials.
Cheers All

 

[Banjo68]

Maybe make up an adjustable jig for both the grinder and bottle
The jig would take longer to make but at least the cuts would
be consistent

 

[OzzieAu]

Yep, without a jig, youd need a steady hand with a angle grinder or better still a plasma cutter:
https://www.totaltools.com.au/welding/welding-machines/plasma-cutters

 

[Dihusky]

5-6mm, fairly narrow bands, I'd be setting up a pair of rollers with a bar to steady your hand. Cut with a 125 x 1.2mm cutting disc, the type used for cutting stainless, bit of care and should do the job fine, just don't push the blade, allow it to cut at the rate it wants to cut.

 

[Manpa]

Do you know anyone with a power hacksaw?

 

[Nightjar]

Why get some 6mm aluminium/steel and roll your own rings?
No sharp edges to clean up and perfect sizes?
You would save hours of frustration and time.

 

[Ded Driver]

I would use an old air tank before a gas cylinder. I know it can be/has been done, but ...
As for the cutting, a metal saw bench would be the way to go (horizontal band saw with clamp), if you can locate a fab shop that has one

 

[aussiefarmer]

Go the thinnest disc you can , 125mm angle grinder

 

[aussiefarmer]

You may be better off buying 5x2 flat bar and rolling circles.

 

[BigWave]

Sorry, I meant ~6cm width.
Based on the above kind responses, I'll likely use my 125mm angle grinder.
The main pieces I want are +/- 3cm on either side of the central weld, so that I can have an inscribed centre line for the time circle imitating the picture below:

I'll hacksaw groove and number stamp times into this ring (the one shown nearly horizontal).
The other ring (almost vertical) holds the Gnomon (pointing to celestial South - adjusted to my latitude). The Gnomon is normally a rod casting a shadow, but as you can see in the picture, an Analemma pattern - ready to drill (a plate sheet with holes drilled in it) has been substituted which contains the Equation of Time (EOT) which casts light onto the sundial. I need to the exact inner radius of the gas cylinder though (I think roughly 29.4cm) so that I can accurately scale the Analemma.
I have calculated the Analemma pattern (a figure of 8 as the sun rises in altitude with the seasons, but is also early or late depending on its elliptical orbit around our sun).
By interpolating between sun light dots on the sundial and the centre line, I'll have a fairly accurate sundial (normal sundials are up to +/-16 mins early or late). It may look like it, but the Alanemma it's not symmetrical about its longitudinal axis and is a very complex shape.
What else can us Melbournians do during this lockdown?
Thanks again all.

 

[Gilly47]

band saw and fence

 

[Dignit]

BigWave
My work has a bandsaw for cutting lengths of RHS steel.
I can take a closer look at it on Monday to see if it could accomodate cutting the bottle.
Its an old machine but it does the job we need it to do.
No doubt wed need some form of jig to hold the bottle.
Id be concerned whether flushing the bottle with water would be sufficient to remove dangerous flammable/explosive residue. You being an Engineer Im confident you know that you need to be absolutely sure the bottle content residue is inert before doing a cut.
Let me know if youd like me to take a look.
Cheers

 

[reynard]

Run a hose from your car exhaust into the bottle and fill it with carbon monoxide ,
it can't blow up without oxygen.
Jim erfect: :/

 

[Gpx5000]

BigWave
My work has a bandsaw for cutting lengths of RHS steel.
I can take a closer look at it on Monday to see if it could accomodate cutting the bottle.
Its an old machine but it does the job we need it to do.
No doubt wed need some form of jig to hold the bottle.
Id be concerned whether flushing the bottle with water would be sufficient to remove dangerous flammable/explosive residue. You being an Engineer Im confident you know that you need to be absolutely sure the bottle content residue is inert before doing a cut.
Let me know if youd like me to take a look.
Cheers

If you fill the cylinder with water and leave it for 48hrs, this will be enough to clear impregnated gas out of the cylinder.
I do this all the time making fire pits on legs.

Cheers.

 

[Tathradj]

A piece of paper then wrap it around the bottle over lapping.
Line up the straight edge of the paper overlap then using a suitable sharpie pen, Draw a line around the bottle.

Second one is a jig made out of 3 x 4 timber set at a right angle. Drill a hole centered taking
into consideration the amount of material removed when cutting.
stick a pencil or similar in the hole then rotate the cylinder.

Use a thin cut off wheel on a grinder. Don't take a large bite with the grinder.
You will be fine.

That is the method I use.

Mild soapy warm water and rinse the day lights out of the bottle before cutting.
I also use the exhaust trick if not sure.

Have not been caught yet and do not plan on it. oop: :bomb:

 

[CreviceSucker]

A piece of paper then wrap it around the bottle over lapping.
Line up the straight edge of the paper overlap then using a suitable sharpie pen, Draw a line around the bottle.

Second one is a jig made out of 3 x 4 timber set at a right angle. Drill a hole centered taking
into consideration the amount of material removed when cutting.
stick a pencil or similar in the hole then rotate the cylinder.

Use a thin cut off wheel on a grinder. Don't take a large bite with the grinder.
You will be fine.

That is the method I use.

Mild soapy warm water and rinse the day lights out of the bottle before cutting.
I also use the exhaust trick if not sure.

Have not been caught yet and do not plan on it. oop: :bomb:

When I am welding fuel tanks or petroleum pipeline there are chemicals to neutralise the VOC (volatile organic crap) and odours but after steam cleaning we also purge the space inside with inert gas such as argon or CO2 , the problem with using exhaust fumes is they can have unburnt fuel vapour in them so its no guarantee.

 

[CreviceSucker]

BigWave
My work has a bandsaw for cutting lengths of RHS steel.
I can take a closer look at it on Monday to see if it could accomodate cutting the bottle.
Its an old machine but it does the job we need it to do.
No doubt wed need some form of jig to hold the bottle.
Id be concerned whether flushing the bottle with water would be sufficient to remove dangerous flammable/explosive residue. You being an Engineer Im confident you know that you need to be absolutely sure the bottle content residue is inert before doing a cut.
Let me know if youd like me to take a look.
Cheers

If you fill the cylinder with water and leave it for 48hrs, this will be enough to clear impregnated gas out of the cylinder.
I do this all the time making fire pits on legs.

Cheers.

Some people have been caught out due to rust inside fuel tanks , petrol soaks under the rust flakes and even if they washed out the tank , when the tank sits for a while the fumes fill the tank again and it goes boom when ignited.

44 gallon drums also have rolled seams which trap fuel causing the same phenomenon as above , I think its been at least 5 years since someone took their face off with a 44 explosion.

 

[user 12139]

first flush with water a few times, then get some HCL from your local hardware (used for cleaning bricks). Soak overnight a mix of about 5% HCL to water, be sure to flush well with water again after soaking with HCL... won't hurt to put a bit of bicarb soda in the final flush to neutralise any residual acid.

If it were me I use a plasma cutter.. easier, cleaner and faster. Should be able to hire one easily enough if you or ya buddies dont have one

 

[Mike678]

Get the rings rolled up at your local fab. shop , cheaper in the long run .

 

[crustydog]

Sit the tank on an upturned skateboard, so you can rotate the tank easily and cut with a thin wheel on the grinder.
P.s carbon monoxide is explosive between 12.5 and 74%
Id be using water myself.