Approximate internal dimensions of 20 lbs/5 gal propane cylinder?

[WilCo]

Does anyone have the internal dimensions of a 20 lbs/5 gal propane cylinder? I have found the external dimensions, 12" diameter & 18" height (and more precise measures by manufacturer), but the height I presume includes the collar and foot, and I have no idea how thick the material is, so I am not confident that I could get a reasonable estimate even with the bottle on hand until I have opened. Given the level of detail that I see people recording here, surely someone has measured and actually recorded for posterity these figures, but I am unable to find them, using either the board/forum's built-in search or Google with (and without) the `site:` operator.

I am asking for the dimensions, rather than waiting until I've opened my tank and measuring it myself, because I am planning several forges and want to work out how much of the various insulating/refractory materials I need. "Several" because I am using a 3 lbs coffee can now with a torch but without any insulation, so it's really just a wind-break, and I want to get it insulated before I melt a hole in it. With a coffee can forge and a torch I can work out the process for installing the insulation without at the same time having to figure out cleaning and marking and cutting and fabricating the propane cylinder for shell and building the burner(s). Limiting the number of unrelated aspects that I have to work out before I have something I can test usually increases my chance of success (much like a "spike" or "tracer bullet" in certain agile software development practices).

[Jealdi]

A quick google search shows somewhere in the 2.27 to 2.44 mm range. I did not measure my tank when I cut it for thickness, but I have a 30 or 40 lb tank I cut up, so it may differ slightly.

[ThomasPowers]

I have a number of propane cylinders of that size and they vary slightly with manufacturer and age making a difference. However I can tell you the wall thickness is quite thin and how much you compress the kaowool installing it and how thick a layer of covering refractory you will be using is a much larger factor than wall thickness of the tank!

Seem more like a "Measure with a micrometer, mark with chalk and cut with a torch" situation.  Just measure the outside and you should be close enough.

[Frosty]

I'm afraid you've made a common beginner's mistake. There is nothing precise about building a propane tank forge. If you don't buy more than you need you'll short yourself. 

This is blacksmithing, you aren't building a moon rocket and the Sistine Chapel is still good.

Frosty The Lucky.

[WilCo]

27 minutes ago, Jealdi said:

A quick google search shows somewhere in the 2.27 to 2.44 mm range. I did not measure my tank when I cut it for thickness, but I have a 30 or 40 lb tank I cut up, so it may differ slightly.

About 3/32" thick, or 3/16" of the diameter cross-section, then.

Estimating the body of the tank is 15", taking 3" off for the collar & foot from an approximate 18" height, we get: The internal surface area is 5.38772 ft^2. The external surface area (which just ignores the thickness) is 5.49779 ft^2. Given that the measurements of the tank are approximations in the first place, it is probably just as well to ignore the thickness, both for simplicity and building in a buffer of required materials by over-estimating.

(I will update this as I collect data and work it out the calculations, reigning in some of my over-thinking as I go.)

[Frosty]

Oy vey! You are not only over thinking this, you're over thinking something that doesn't really matter. 

Have you allowed for the thickness of what you're applying to the cylinder? How about the effects of compression on the more elastic materials? First, second, or, ply? How many plies? 

Tank dimensions NEVER include the base, handles or valves unless specifically stated. Say you needed to know how much clearance necessary to fit one. 

Why don't you calculate the dimensions by the tank capacity? A 20lb. tank has a 5 gal capacity plus 10% volume for expansion. 

The problem with you running on about this kind of thing, especially offering to keep us updated is it really confuses other beginners making them think it matters. It really doesn't, cut the tank if you want exact measurements but approximation is about as precise as these things require.  FIVE DECIMAL PLACES!        !!!

Frosty The Lucky.

[ThomasPowers]

The tanks I have cut have not been over 1/8" thick.  If you must know exactly; the tank will have to be cut to make a forge, do so (*SAFELY*) and measure!

If 4+ digit accuracy is important to you; drop blacksmithing and take up machining---there you you will be praised for it!

[WilCo]

1 hour ago, Frosty said:

I'm afraid you've made a common beginner's mistake. There is nothing precise about building a propane tank forge. If you don't buy more than you need you'll short yourself. 

Yeah, it might seem like that, but I can have a painfully literal mind, which, coupled with a terrible sense of proportions, can lead to ridiculous disasters... Like when I was in charge of buying the sausage for Oktoberfest in college... well, we ate well for many months afterwards. And then there was the time my friend and I were shopping for cranberries to make sauce fro Thanksgiving.  If you wanted a good laugh, I could list a few things that I have been surprised by the dimensions of.

If I miscalculated, say, 10x the amount of materials I need (don't think I can't screw up that badly!), I might throw up my hands at the cost or, worse, actually buy it and then felt like I had to hoard it "just in case", and add more junk to my already overcrowded-with-junk garage.

1 hour ago, Frosty said:

Tank dimensions NEVER include the base, handles or valves unless specifically stated. Say you needed to know how much clearance necessary to fit one. 

Ah ha! This is the kind of thing I would have never known if you hadn't told me. Sometimes I miss the things that are obvious to other people. If I had gone out to measure it, I probably would have had to try several measuring tapes and sticks before deciding that everything was wrong, then another week for that obvious factoid to pop into my head.

2 hours ago, ThomasPowers said:

If 4+ digit accuracy is important to you; drop blacksmithing and take up machining---there you you will be praised for it!

I try to be precise in planning, partly, because I know I will be sloppy in execution; I don't think that goes well with machining.

You folks have gotten hung up on the number of decimal places I included, but that's just because that's what WolframAlpha gave me; rounding it would have been another step, which I cannot convince WA to do directly with the other calculation and with interruptions from kids coming in and messages from work, etc., it's safest to do the easiest, which is just copy the data as-is, and make adjustments later.

1 hour ago, Frosty said:

The problem with you running on about this kind of thing, especially offering to keep us updated is it really confuses other beginners making them think it matters.

In fact, the point of updating it is to not leave my foolishness on the floor where anyone can trip over it.

[Frosty]

Okay, I think you'll fit right in here if you're not irritated by people pointing out the obvious all the time you're more patient than I am and I REALLY NEED the obvious pointed out to me and frequently. 

I need a little clarification. Why do you want to make several forges? One propane tank forge is too large enough for most folks and the rems from building one should be plenty to line a small forge, bean can or coffee can sized.

I'm assuming you aren't talking about making several propane tank forges. That's a slap you with a rubber chicken obviously obsessive silly, so I  assume the benefit.

Besides lining the circumference of the tank you'll need to line the ends, whatever you decide on. Leaving the ends open just spills heat and costs extra fuel money for a cooler forge. You don't close a forge completely but you want to hit the happy medium of closed enough to contain the heat as much as reasonably possible and still have room for exhaust gasses to exit. 

Check out the posts regarding "thermal baffles" and how they work by Mikey. They work much better than doors and there are a number of methods for mounting them. 

Back to lining the forge, current consensus is a multiple liner. Starting with the shell: propane tank, coffee can, box, whatever. You'll want two layers of 1" 8lb. ceramic blanket, I just call it Kaowool because it's what I have available and it's easier to remember as a generic term, there are lots of brands. You can calculate the exact circumference but it works better to just use the ID of the tank, the extra kaowool will compress and hold itself in place. Using two layers of 1" kaowool rather than One layer of 2"  kaowool is for a very good reason. Rolling 2" thick ceramic refractory blanket around the inside of a round tank WILL result in impressive wrinkles. Wrinkles make heat shadows and disrupt the swirl and like square dancers everywhere nobody likes their swirl messed up. Two 1" layer are more flexible and roll into smoother tubes. 

Next step is to "butter" it. In this context buttering is simply wetting it with a spritzer. Buttering is a mason's term and has solid reasoning behind it. Applying mortar, plaster or other cement to a dry surface flash dries it and leaves a layer of dry mortar against whatever it's been applied to. It doesn't bond to the surface properly. Applying a mortar or rigidizer to a wet surface dilutes it on contact with the surface, the dilute cement is then drawn into all the nooks and crannies in the surface down to the particle size of the mortar. When it sets or dries (depends on the cement or application) it is in as full contact as is possible forming the best bond possible. This is why you see brick layers brush the wall with a wet brush and dip bricks in a bucket of water before troweling on the mortar.

So once buttered you spritz on the rigidizer. Don't do what I did and buy a gallon from the masonry supply, it's good stuff and works well but is expensive and has a limited shelf life, especially after opening the can and you only  need maybe 1.5 pints. What works very well is inexpensive and easy. Fumed silica also called colloidal silica works a treat. Mixed with clean fresh water with a couple drops of food coloring, it spritzes easily, the food coloring lets you see how evenly and complete the cover. How buttering works for rigidizing is the wet fibers would normally flash dry the mix at and just below the surface but the wet fibers will draw the rigidizer well into the kaowool, concentrating where fibers make contact. Once dried and heat cured the kaowool will be well rigidized and better still the fibers will be encapsulated so they won't break free and drift around your breathable air.

A Bernzmatic torch or a minute or so of run time on your burner will fuse the rigidizer to refractory the blanket. Step 2 is a repeat for the second layer of Kaowool.

If you decide to make a "vault" or D shaped forge the easy way to make a flat floor is to cut a strip of Kaowool the width of floor you'd like and length of the forge interior. Feather the edges where it will meet the forge wall. Feathering is just thinning the long sides of the floor strip so it meets the cylindrical wall reasonably smoothly and the strip lays flat. Kaowool can be thinned by pealing it in layers, it's pretty easy a little practice is all you  need. The center of the strip may have an open space under it so lay the kaowool you pealed for the feather in the space. 

This will be the floor of your forge and will take more weight and mechanical abrasion so it deserves to be a little tougher than the walls and lid/ceiling. So, I recommend rigidizing the floor heavily on both sides and don't forget the fill. It doesn't need to be sopping wet and dripping but if that happens it won't hurt anything, the rigidizer will just seep deeper in the liner.

Dry and heat cure the second layer. 

Next step is to make your burner ports. This is where my love of hole saws turns into a recommendation, if you don't have a hole saw large enough to accept your burner's flare then you need one. Yeah, some guys can make a reasonably round hole with a cutting disk on a grinder but holy moley it's a lot more work and considerably more dangerous. If a hole saw binds the drill stalls or maybe twists out of your hand, maybe painfully but if a cutting disk binds it usually breaks and sheds shrapnel off a wheel spinning what? 20-30 k rpm? 

Once you have the hole in the shell you're looking at the kaowool liner from the shell side. Yes? How to make a nice smooth hole into the forge's interior? . . . Hole saw? Ayup, just don't get in a hurry or it might leave an odd shaped shaggy burner port. If you have a flare on the burner you only want to make the hole through the liner a little larger than the OD of your flare. However if you didn't put a flare on your burner you can shape the burner port into the ideal taper for a flare.

A sharp knife carves rigidized Kaowool nicely, steak knife serrations are nice but not a big improvement. A 1:12 ratio is the MAX taper you want for the flare, that means the diameter will increase one time in 12 times that in length. As an example a 1" burner taper should NOT exceed a 1" increase in 12" length. so after 12" the D should be 2". The same ratio applied to a 1/2" burner would make it 1" ID in 6" length. 

1:12 is the max increase of the taper That will produce a smooth flow. I cheat laying these things out, I just draw it out on paper and measure the width at the smallest dia. measure the length and the diameter there. In this case it would be at the 2" mark. By draw, that's two lines in a truncated V, I don't draw cones or try calculating things like that, I'm lousy at math so I cheat if I can.

Anyway, once you have your burner port hole cut and shaped, rigidize and heat cure it then apply a layer of the hard refractory you're going to use for the flame face, inner liner of your forge. Kastolite 30 li is a good performer and has earned a high shelf in preferred home shop forge liners.

I didn't mention it above, I forgot but the burner port needs to be cut enough oversize to allow for the flame face refractory and oh baby YES the burner ports need the flame face and kiln wash, it's likely to be the hottest part of your forge in operation.

About Kastolite 30 li. It does NOT dry, it sets and cures in the same manner Portland cement concrete does. Water combines with the calcite compound binder in the refractory forming crystals that set it like stone. While they're different this is what happens when your concrete sidewalk sets and cures. The cure is semi tricky but has positive effects on the finished product. Once it sets, gets too stiff to work anymore, it needs a 100% humidity environment to cure to full strength and heat capacity. We don't need it's 100% strength and heat rating but close is a nice touch. I seal my forge and the NARBs in a plastic tote with a few inches of water in the bottom. Once set you could put completely under water for a week and it'd be happy. Honest it LOVES the available moisture as it cures.

Once you've cured it let it dry out, the Kaowool will be saturated and take some time to dry out, a light bulb in the chamber will speed it up. Oh DRATS, something else I forgot to mention earlier. Drilling a couple holes in the bottom of the shell as the forge stands in use will allow water to escape, either drain or as steam. 

Yeah put legs under it, it's a pure PITA to use a forge as it rolls around the shop. They don't need to be long or really heavy duty so long as they're stable and get the forge a couple few inches off whatever you put it on. 

That sort of covers the basics and some of the reasons for lining a basic propane forge. I'm sure I've forgotten parts and gone on to boring detail in others but hopefully it'll give you an idea why precision isn't really a thing. Making burners is a whole different matter though but we aren't going there just yet.

Frosty The Lucky.

[WilCo]

Blah. Apparently I cannot edit my previous comment after some period, so I can't actually fix anything like I thought I could.

I have ultimately realized the actual surface area of the inside does not matter, regardless of precision, because the insulating blanket is a sheet, so the circumference is what matters. I calculate <38" for a 12" circle, but now that I've gotten my hands on a copy of Mikey98118's book via inter-library loan, I see his build calls for 35", which I understand now because a 10" circle (which is 1" from both ends of the diameter) is ~31.5", so 35" is about the middle, which accounts for fact that the blanket is 1" thick.

Another way to think about it is that  the middle of a 1" blanket would be an 11" circle, which is a 34.5" circumference, so 35" adds a little padding, no doubt compensating for the >= 1.7% shrinkage of the blanket.

I do, however, need to work out the volume for the Kast-o-lite, since Mikey98118's book does not cover that in the propane bottle build (and I haven't looked closely enough at the jeweler's furnace to compare volumes); he uses blanket cut to 11"-13" wide, because of the round ends, so if I assume 13" "height" for the cylinder shell, inner diameter 10", outer diameter 9" (1/2" thickness), I get 0 cu ft, rounding to the nearest integer :-) Seriously, ≈0.112265 cu ft (sorry, I don't what level of precision is appropriate here, so I'm just going to keep it all). 90lbs/cu ft * 0.112265 cu ft = 10.1 lbs just for the sides; plus some for the ends.

 

 

[ThomasPowers]

Have you checked out Wayne's propane bottle forge build instructions?

Frosty didn't mention another reason to use 2 1" layers:  when the inner layer degrades, you can then just replace it leaving the outer layer in place. (Pretty much everything in a blacksmith's shop is a "consumable" some items just have longer use lives than others!)

[WilCo]

21 minutes ago, Frosty said:

I need a little clarification. Why do you want to make several forges? One propane tank forge is too large enough for most folks and the rems from building one should be plenty to line a small forge, bean can or coffee can sized.

My neighbor wants to build one too; he used to do stock-removal knives and has a roll of 1" insulating blanket (I don't know if it's 6# or 8# and, while I know the difference is non-trivial, my guess is that it's not great enough to warrant spending extra when there is material on-hand).

The coffee can I am speaking of is the Costco-size, which 3 lbs, not the <1 lbs grocery store size; I think 7" height, 6" diameter. Zoeller's coffee can is a 2 lbs. I'm not sure which size you're imagining since you mention bean cans. (I guess warehouse stores sell beans in sizes comparable to the big coffee cans, but that's not want comes to mind immediately.)

Partly, I am also trying to decide where to source my materials -- there is a local outfit called High Temp Inc that has everything but kiln wash and a local potter's supply place that might have that (their site doesn't mention the brand). The former sells to the public but they're mainly oriented towards industry -- if I were just building one, certainly not, but building 2 -- maybe? For example, they sell Kast-o-lite 30 LI in 55 lbs bags. If I need 13-15 lbs per propane cylinder, then 55 lbs might not be crazy. Shipping cost for 30lbs would probably outweigh the savings of buying less quantity from elsewhere (i.e. Glenn).

Thanks for the detailed instructions; I am sure I will have further questions of things that I am either totally missing or totally overthinking.

I've been reading "Forges 101" and "Burners 101", and as I mentioned I now have a copy of Mikey's book (which, I understand based on his comments and differences from the threads, is dated in some ways) and a couple kiln-building books from my local library (which have proven to be a little useful but not as much as I hoped).

[WilCo]

1 hour ago, ThomasPowers said:

Have you checked out Wayne's propane bottle forge build instructions?

Yes, I have; this one, right? While I like the idea of being able to open it to make the casting easier, I don't quite understand how the blanket is supposed to stay in the top. It also makes me nervous because it's a little different than the other descriptions and after all the mistakes I've seen people make and admonitions to follow well-tested designs and procedures by the participant here, I am hesitant to go with something like that.

[Frosty]

There are other blacksmiths in and around Portland and the NWBA is an active ABANA affiliate. Hook up with other smiths within visiting distance and you'll probably meet guys willing to split a sack or have a partial they'd like someone help pay for. Same for all the materials, tools, equipment, etc. involved in the craft. Networking is a good thing. Besides you'll want to keep some on hand. Kastolite can be patched simply by mixing some up and troweling it on the damaged spot, let it dry and fire it up. Commercially they use Kastolite to repair furnace liners without letting them cool off much. Guys in aluminized HOT suits, literally gunnite (spray) it on red hot furnace walls.

How good are your shop and fabrication skills? If you're a competent fabricator the clam shell propane tank forge plans on Wayne's site are pretty straight forward easy. We're not talking journeyman skill level, we're talking high school shop class competent. Keeping the blanket in the lid is as easy as running some screws in through the shell and the natural compression caused friction. 

6lb. will work but will need replacing sooner than 8lb. The liner if a propane forge is a consumable, it will wear out eventually. This is one of the reasons the evacuated silica spheres (bubbles) in Kastolite 30 make it so attractive. It is not only rated for prolonged 3,000f. temperatures it is an insulator and shields the blanket from a portion of heat. 

For kiln washes, do NOT buy ITC 100ht. it is not only darned expensive stuff it isn't particularly suited for propane forges. Sure it contains zirconium but as a release agent so glazes and such don't weld pottery to the kiln furniture. What we want is another layer of armor and a strong IR re-radiator.

Plistex 900 and Matrikote both fire hard like a coffee cup and resist mechanical abrasion and are poor thermal conductors, meaning heat doesn't pass through very fast so it stores more energy from the flame and sheds it in 360 x 360 (a sphere) but one whole plane is blocked by the Kastolite so it can't shed heat as quickly that direction. Another slice it's trying to shed heat to is directly connected to itself so nothing is going that way. That leaves the interior of the forge as the easiest route to shed energy as IR radiation. Energy ALWAYS takes the path of least resistance so the heat shines back on your work. Kiln wash good, Hmm?

Frosty The Lucky.

[ThomasPowers]

Quibble: energy always takes *ALL* paths possible to it.  The "easy" ones just get more going out that way.

[WilCo]

14 hours ago, Frosty said:

There are other blacksmiths in and around Portland and the NWBA is an active ABANA affiliate. Hook up with other smiths within visiting distance and you'll probably meet guys willing to split a sack or have a partial they'd like someone help pay for. Same for all the materials, tools, equipment, etc. involved in the craft. Networking is a good thing.

Yeah, unless I'm missing something, the NWBA forum is... quiet. And the rest of the stuff on the site requires membership, which would be worthwhile except that everything is closed at the moment. In fact, were it not for this shut down, I'd probably still be content with 2hrs/wk at Trackers, at my skill level. 

15 hours ago, Frosty said:

6lb. will work but will need replacing sooner than 8lb

Right, and barring some other significant thermal difference, that's why I figured it better to use whatever is on-hand. I have assumed because that is the durability is the only difference I have read about, the thermal difference is negligible.

14 hours ago, Frosty said:

How good are your shop and fabrication skills? If you're a competent fabricator the clam shell propane tank forge plans on Wayne's site are pretty straight forward easy. We're not talking journeyman skill level, we're talking high school shop class competent.

For metalwork, practically non-existent. Prior to a couple years ago when I started restoring hand tools for woodworking, I had mostly sharpened knives and opened and closed computer cases. I have taken to heart the admonitions of yours and others here not to rely YouTube for forge-building, although I have paid attention to it for fabrication, since that is rather less specialized and (I hope) likely to be wrong (and to be amused when they make mistakes that even I can see--like putting teflon tape on brass propane fittings).

2 hours ago, ThomasPowers said:

Quibble: energy always takes *ALL* paths possible to it.  The "easy" ones just get more going out that way.

That reminds me of something I learned from my father that took me years to un-learn: "Heat rises"... What he was misunderstood is that hot air rises. Like the difference in weight and mass, the distinction is rarely important for most everyday applications. For years I was confused and annoyed by the fact that most refrigerators had the freezer on top.

[ThomasPowers]

I don't know about that; I live in a passive solar house and so for us, "Heat Rises" in the east and sets in the west.  Overnight we can use stored heat in the form of wood.

[Frosty]

You're right, I didn't think of NWBA and dang near everybody being at a really low ebb right now. Once things get going again, membership is worth the price, especially when you're breaking into the craft.

If you don't have the skill sets then fabricating a . . . thing that requires them is not recommended procedure. There are other options that don't require more than drilling holes and assembly or just stacking bricks.

Valid quibble Thomas, I retract the statement. 

Cool, I get to interject my own quibble! 

Heat doesn't rise, cool sinks. Convection is driven by the weight of colder gas/liquid's greater weight per volume taking up the space formerly occupied by the warmer less heavy, gas/liquid. 

Thinking about all power being solar, raises the argument for nuclear not being solar. I just realized I use Big Bang power, it's just less direct. 

Frosty The Lucky.

[ThomasPowers]

BBP:   Yes with multiple supernovas or neutron star mergers as intermediate processing.

My local ABANA Affiliate will not be charging 2021 dues for any member whose dues are currant as of September 2020.  I've told my wife to start planning for Quad-State 2021 as I want to make it a less hurried trip out and back as vacation time is building up!

[SLAG]

Lieber Herr Frosty,

I thought the energy from the sun was due to a fusion thermonuclear reaction.

Mein Gott!

Could I be wrong?

SLAG.

[Frosty]

Most of it probably I suppose, if you discount heavier element reactions from impurities in it's accretion disk. See rest of solar system for list.

Deb and I are hoping to be able to take to the road in 21 for the steelwool combo. Speaking of elemental explosions I made a pork roast last night. Simple fare: seared roast, salt, pepper, bit of sage, bit of thyme, onion, celery, carrots, new and finger potatoes, slow braised at 275f. I didn't carve of course, pulled it apart and dished up the spuds, and veggies, with some of the pan juices. It came out just about like I wanted, a Super Nova.

Frosty The Lucky.

[cleatusj]

I paid 72.00 for 55lb's of KOL from a local company, which saved me 40,00 in shipping.