Sanitary TIG Welding 101: Flask Fabrication

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About: Diving headfirst into metalworking. Mostly just making tools to make more tools, occasionally ending up with a finished product along the way. check out what i have been building on my instagram over at ht...

In this instructable I will share my love of welding with you as we build a stainless steel flask together. I have built a lot of different flasks, they are a great alternative to the very boring, poor quality ones you can get at the store. Picture this: you are at a black-tie wedding and you find yourself hanging out with the bride and groom enjoying a super fancy single barrel Bourbon in a $3.99 flask from Walmart.... not fun! I will explain what you need to know so that you too can learn how to preform food-grade TIG welding and make a super steller stainless steel flask of your very own.

There is a lot to know about sanitary welding. There are many different kinds or levels of sanitary welding that you need to pass very strict tests in order to be certified or allowed to weld on certain products. Some examples are welding on nuclear reactors, oil refineries, fighter jet engines, pharmaceutical production facilities, food production factories. almost every one of these fields has their own certification, standards, and guidelines that need to be followed exactly as it is written in the codes . Not only do the people performing these welds need to be certified but each and every inch of weld they lay down must also pass strict parameters often times being x-rayed to make sure they are sound, strong, and safe welds free of any inclusions or contaminants deep inside the welds of... lets say a nuclear reactor radiator core.

For this instructable I'll be going over basic food grade stainless steel TIG welding, I am not going to go over every thing in this instructable. in fact i am barely scratching the surface on the subject. there is waaaay more to it than I would ever want to learn. Here is a basic overview of the TIG welding process for those who are unfamiliar with it.

TIG Welding

TIG welding stands for Tungsten Inert Gas welding. a TIG welder machine uses an arc of electricity that is shot off a (T)tungsten electrode through the (I)inert argon shielding (G)gas and into the metal you are welding on. The argon being a noble gas protects the molten weld puddle from any harmful atmospheric gasses in the room. Our atmosphere contains 78 percent nitrogen and 21 percent oxygen among many other gasses. Without the protective barrier of the inert gas the nitrogen will get sucked into the liquid metal as it tries to equalize the concentration of nitrogen between the two solutions. it is just like how saltwater mixes with freshwater to equalize the salt content between the two solutions. As the metal freezes and turns back to solid it now will have air bubbles stuck in it and will no longer be a strong solid piece of metal but rather a fluffy or foamy metallic structure full of tiny holes on the surface and hollow spaces inside. This makes for a weld that is very likely to be the weakest part of the object and most susceptible to rust, oxidation, decay and eventually failure.

TIG welding stainless steel

You can use TIG welding on a wide variety of metals such as steel, copper, brass, bronze, gold, silver, aluminum titanium, nickle, inconel, monel, and stainless steel. There are over 150 different types of stainless steel, each alloy has a different compositions of elements. Some of the most important elements to consider include: iron, carbon, nickle, chromium, manganese, molybdenum, silicon, niobium. Each element has a profound impact on the properties of the metal for different applications in aerospace, nuclear, marine, and food grade aplications. For this instructable ill be using 304 stainless steel. 304 is the most commonly used food-grade type of stainless. Unlike mild steel which is just iron and very small amount of carbon (0.20%) type 304 stainless steel has two very important elements added into the iron and carbon alloy, they are 8% nickle and 18% chromium (chrome). These elements adjust the microscopic grain structure of the alloy. Chromium adds corrosion resistance and the nickle makes the stainless alloy much tougher and more resistant to abrasion than regular carbon steel. These elements can burn out of the stainless steel if you over heat it with the welder or if you expose the metal to atmospheric air while it is heated. if you burn the stainless the chromium turns to chromium carbide (commonly called "sugar") which is a very tough crystal like structure that will grow out away from the weld. Chromium carbide is harder than most abrasives so its best to be avoided in the first place rather than trying to remove it once it grows. If it grown inside a pipe where you cant get to it an entire section of pipe must be cut and and replaced. This chromium carbide is a bad thing to have around food processing equipment for many reasons. One reason is because it provides spaces for the food to get physically trapped. This prevents the pipes in a factory from being able to be rinsed and cleaned between production runs, this provides lots of spaces to trap food and let bacteria grow. Another reason it is bad is because once the chromium burns out of the weld zone the weld is no longer stainless steel, it is now very prone to oxidation and corrosion especially around acidic foods such as pasta sauce, vinegar, and even more importantly around solvents like industrial ammonia based cleaners, or in our case alcohol.

Argon purging

While tacking up the stainless pieces the TIG welding torch will sufficiently provide enough inert argon shielding gas to keep the atmospheric air away. however as you add more parts (like the six sides of a flask) you will physically start to block the argon provided by the torch from reaching inside. You will need to add extra inert argon gas to purge the atmospheric air out of the inside leaving behind an argon layer to shield the backside of the weld. there are many ways to purge the air out with argon. if you didn't have the inside purged with inert gas the welds inside would be burnt up and no longer stainless steel. they would eventually dissolve from the ethanol in the liquor and start to effect the taste of the liquor. eventually the flask will start to leak or maybe even start to fall apart.

Step 1: Tools and Materials

    Welding

    • TIG Welder with 3/32 Ceriated Tungsten (orange)
    • (TIG welder gas lense optional) helps disperse argon more evenly
    • welding PPE - Personal Protection Equipment: helmet, gloves, leather shoes, safety glasses,etc
    • extra argon regulator
    • T 92 argon fitting
    • argon hose with brass tube

    Turning/ Machining

    • Lathe
    • cutting bits
    • 3/8"HSS twist drill bit
    • coconut oil

    Hand Tools

    • Beverly Shear or angle grinder with cutoff wheel
    • combination square
    • dividers
    • center punch
    • hammer
    • drill
    • 1/8" HSS twist drill bit
    • 1/4" to 3/4" step drill (uni-bit)
    • scribe
    • hacksaw
    • file
    • sandpaper about 80 to 120 grit
    • non woven abrasive pad (scotch brite pad)
    • jewelers saw w/ #2 blade

    Materials

    • 20ga 304 Stainless Steel Sheet
    • 16ga 304 Stainless Steel Sheet
    • 5/8-16UNC 304 Stainless Steel Threaded Rod (or bolt)
    • 5/8-16UNC 304 Stainless Steel Nut
    • 0.045" diameter type 308L Stainless Steel TIG Filler Wire

    Argon purging

    For my shielding gas purger I used a brass T fitting (T-92)that allows for
    two regulators to be used on one argon bottle. one regulator is for the welder/torch it is set at 15cfpm and the other one is to be hooked up to an argon hose with a brass fitting on it set at 5cfpm . This way i can insert it into the flask without melting the hose from the heat of the welder. I made the brass fitting many years ago by taking the argon hose to the hardware store and finding an adapter fitting in the plumbing department that fit the threads on the argon hose. i then found a section of brass tubing that was a close fit inside the adapter.

    • soldering an end cap on to a brass tube.
    • drill 4 small holes into the cap.
    • flare out other end of the tube by bonking it lightly over a ball bearing
    • slide the adapter over the tube until the flare catches and then tighten onto the fitting on the argon hose.

    Step 2: Layout and Cutting

    Metal and in particular stainless steel is a very unforgiving material to work with. As a fabricator you will need every advantage on your side. When fabricating small intricate fine objects out of thin gauge stainless steel. One of the most important steps is the layout. It is very important to spend a lot of time on the layout and prepping of the materials, it will make the welding easier aka actually possible when working with thin stainless.

    Layout

    • decide how big you want to make your flask. For this particular one I choose to make the body 3 x 4-1/2 x 1-1/4 for these final dimensions you need six pieces of stainless steel.

    2@ 3x4-1/2 for the front and back

    2@ 4-1/2x1-1/4 for the sides

    2@ 3x1-1/4 for the top and bottom

    • when trying to precisely cut metal it is best to use a single very fine and crisp line to follow.
    • test out the scribe on a scrap of material to find the correct setting.
    • layout the six sides accordingly on the stainless steel sheet using the combination square and scribe.
    • it is very convenient to hold the sheet over the edge of a table using either a non marring clamp or to put something heavy on the metal to hold it down while you slide the square and scribe along the edge of the stainless to make a uniform parallel mark down the material edge.

    Cutting

    there are many ways to accurately cut sheet metal. each has its own perks and disadvantages. a very efficient and fairly inexpensive option is to use a 4-1/2 angle grinder with an abrasive cut off wheel attached. it is very loud and make a lot of stinky dust both from the abrasive wheel being consumed and also from the kerf (material being removed from the sheet metal) in the form of 1500+ degree glowing red hot sparks. A much more peaceful route is to use the Beverly Shears, a hand powered shear to cut out the metal. the Beverly Shear utilize a very well thought out tool design from the 1930's that has not changed at all, it is a throat-less style shear used to cut straight or curved lines in a variety of metal thicknesses. Due to its shearing nature it will curl the metal a bit which can be easily remedied using an anvil and a flat faced hammer or mallet.

    • either way you cut the metal out you are going to want to pick one side of the scribe line to stay on and pay a lot of attention to try and stay on that side of it. it is very very easy to stray off your original line and end up with a not straight line and or a not very square piece of metal.
    • After you cut out the sheet metal there will most likely be sharp burs on the metal. it is a very good idea to gently file them down or sand them off to avoid getting cut.
    • after you shear the metal straighten the metal with the hammer and anvil.

    *** I did not take any pictures here because it was just flat pieces of metal that are all in the next step!

    Step 3: Tack Welding

    when tack welding stainless it is best to use slightly more amperage than mild steel of the same thickness. a quick blast of heat is best. it may seem counter intuitive to blast the heat in however less heat overall is pulled in to the metal. you will want to practice a lot on some scrap stainless first because this can be difficult on the thin stainless. i have found that masking tape is a good way to hold the parts in place. be sure to only do a few tacks per piece then remove the tape otherwise it will burn on... stinky sticky mess.

    • using the masking tape to hold the the first two sides(front and left side) of the metal into the shape of L . you want to try and line up the you edges to be open corner type of welds. this will allow for the easiest corner welds.
    • Tape and tack the corners together squaring them up and removing the tape as you go take your time on the tacking as it will help when you are welding
    • Tape and tack weld the back piece on to the L to make a U. it helps if you stack some metal to hold the front and back pieces parallel to each other. if you can find a nice solid piece of copper it works very well for this. copper is very nice to have when welding. you can put copper behind a large hole in thin sheet metal and fill it in much easier. it acts like a heat sink preventing the thin sheet metal from melting away and it is difficult for steel or stainless steel to stick to copper.
    • Tape and tack weld the final side piece onto the U shape. here I used a large piece of one inch square steel to help hold the flask into a comfortable location and act as a heat sink to prevent the thin stainless from melting away.

    before you tack the top piece onto the flask you have to make the threaded spout on the next step.

    • center punch where ever you want the center of your spout to be in the top piece of the flask

    • drill a 1/8" pilot hole in the centerpunch mark

    • securely clamp the top piece of flask and a piece of wood under it onto your work bench

    • drill out pilot hole with the step drill until it is the correct size that corresponds with the lip you machined onto the spout.

    • deburr the hole with round rat tail file or a piece of rolled up sandpaper
    • place the spout and the top piece over the brass argon purging tube. it helps if you can contain the argon in some kind of make shift container. it will help hold the argon around your weld site. turn on the argon. wait a moment for the argon to push out the air.
    • start by placing a small tack on one end of the cap and spout. let cool(no picture sorry)
    • adjust the pieces if necessary. add another tack to the opposite side. let cool
    • adjust if necessary. add a tack perpendicular to the other two. let cool.
    • if everything is square you can start welding. aim the torch slightly more onto the spout. you are going to do this to put most of the heat onto the thicker of the two pieces.
    • it is best to do a few small weld beads opposite to each other and let it cool between tacks to avoid warping the thin sheet metal too much.
    • once you are done welding you can straighten out the sheet metal with hammer and then grind down some of the weld so the last of the liquid can escape out of the flask when you pour it out.
    • Next step is to add the top of the flask to the four sides. try to center the piece so it leaves open corner weld joints on all four sides. hold it on with some tape.
    • stick argon purg hose inside bottom, put tape on bottom to help hold hose and help contain argon inside.
    • add a tack to the top and sides. be sure its away from the previous tacks otherwise it will spring open when heated.
    • adjust if needed use the hammer to bonk everything back into alignment and add tack welds near each corner
    • tape the bottom piece paying attention to centered it like the top piece. take your time to align all the pieces to be open corner joints.
    • stick the argon hose into the spout and give it a moment to purge out the air. tack the bottom on one side then adjust it as you tack weld all the way around.
    • now that all sides are on and everything is lined up good place tacks welds every inch or so all the way around the flask.

    Step 4: Turning the Spout and Making the Cap

    for this flask I used a lathe to turn a stainless spout from a piece of 5/8x16 threaded 304 stainless rod. if you cant find threaded rod you can use a 5/8" bolt and hack off the top with the saw. A week ago I decided to try and use coconut oil as a food safe alternative lubricant rather than tap magic or metal cutting fluid. it seemed to work great, it definitely smelled way better than the traditional cutting fluid, as it burnt up I got a wicked hankering to cook some stove top popcorn. while using the coconut oil my tools stayed plenty cool and sharp throughout the entire process. This time today I used the cutting oil because it was in a more convenient oil can.

    Spout

    • start by squaring or facing off the piece
    • next cut about a 3/16 inch of the treads off of the outboard end with the carbide insert. doing this removes some of the treads so it takes less time to unscrew the cap. It also makes for a smother surface on your drinking lips.
    • you will want to round the leading edge of the threads with a file so the cap has a nice smooth starting point. this thread is thinned out here from most of it being machined off. it will jam up in the responding threads in the cap. you will want to test it with the 5/8 nut to assure a good start.
    • at this point its a good idea to slightly break the square edges on the spout so they are not sharp on your lips. you will still want to keep it flat and square in the center so it can make good contact with the lid and seal tight.
    • decide how long you want to make the spout stick out above the flask. I have made some where the cap almost sits flat on the top of the flask. I like to see the threads sticking out under the cap. I really like how it looks like a bolt.
    • use the cutter to cut off the treads at what ever distance you prefer. leave about a quarter inch of smooth space
    • drill a 3/8th inch hole thru the spout past the desired over all length
    • its time to cut the spout off of the rest of the threaded rod. my parting tool was missing so I used a the cutter to mark a square scribe across the rod while the lathe was spinning.
    • once the line is marked you can turn off the lathe and finish cutting the part off by hand while it is steady in the chuck.
    • put the new part in the chuck and face off the back side where it was cut off.
    • machine a lip so the hole on the top piece of the flask body has a ledge to sit on. this will help a lot when you are trying to weld the spout on.


    Cap


    • take a piece of 16ga 304 stainless and scribe a small 3/4 inch diameter circle on it using the dividers.
    • you can cut it out many ways. I happened to use a jewelers saw. the nickle in the stainless steel makes it very tough and durable. Use lots of lube and take your time cutting it out because it is very unforgiving.
    • once you have it cut its a good idea to take the sharp bur off the disc with sand paper or a file
    • I used a piece of scrap metal and i wanted the cap to be flat on the inside so i flattened it using some sandpaper over a flat piece of polycarbonate plastic.
    • wash off the lubrication.
    • place the cap over the argon purging set up and turn on the gas
    • hold down the cap with a clamp or something heavy and tack the cap onto the nut on one side.
    • make sure that the tack weld did not lift up the cap-- adjust it back if it did and tack the other side of the cap. let it cool
    • make two more tacks perpendicular to the original two tacks. let it cool
    • make two more tacks on the remaining two corners of the nut. let it cool
    • weld the cap onto the nut make sure you alternate your placement of welds and let them cool off between every inch of welds to avoid warping of the stainless steel.

    Step 5: Welding of the Body

    when you are welding you are subjecting the metal to extreme differences in temperature. you are heating it up so much that it is changing phases from solid to liquid.... you being such a smart person soon realizes that the metal is growing in size! when you advance the torch along its path and let the metal cool off enough it freezes back to a solid again and it shrinks. when it cools down to room temperature it shrinks even more. when welding all of this expanding and contracting happens very fast in the metal. the heating and cooling translates to warping caused by different tensions in the sheet. you can very quickly build up a lot of heat in any welded structure especially a small item like a flask very quickly and cause very bad warping. stainless has extra elements in its alloy that have different heat coefficients than iron so it even more susceptible to warping from heat input when compared to plain low carbon steel. stainless steel also retains much more heat than regular steel so it takes longer to cool. I happen to have a copper chainmail scarf that I made for a costume a long time ago. I now keep it with my welder because it is an excellent heat sink. As an added bonus it is also a great ground to ensure a very solid electrical connection.

    There are ways to combat warping. I use some of these examples on this project.

    • one way is to deposit a series of small one inch weld beads in opposite places on the structure to even out the pulling forces.
    • another way is to manage the heat input - avoid heat build up by welding in short bursts and let the piece cool between.
    • you can cool off the metal quicker by using a heat sink such as copper.
    • you can purposely have the weldment out of alignment so that when the weld cools it pulls the part into the correct alignment.
    • as the purging argon passes over the metal it helps to slightly cool the metal

    I wrap the piece in the copper scarf and start to weld small one inch beads all around the flask letting it cool off a bit before I put the next one on in a different location far away from the last weld. because the flask is so lightweight it tends to move around when you are trying to weld on it. to combat this I use the solid block of steel on top of the flask to help hold it in place.

    Step 6: Testing the Flask for Leaks

    because alcohol is a pretty intense solvent you want to make sure that there are no tiny pin hole leaks in the flask. the ethanol can make a tiny hole slightly bigger. it is also pretty thin and can creep out of tiny holes. its a good idea to test your vessel for any leaks. i submerged it under water then put an air hose with a rubber tip on the spout with about 40 psi. there was some holes that needed to be filled. don't forget to purge out the air with the argon before you fix the holes.

    Step 7: Finishing

    • if you wanna easily be able to slide the flask into your pocket take off some of the high spots with a hand file. make sure you put pressure on the push stroke and lift up when you pull the file back to you. I put the flask in a vise to hold it securely. Its a good idea to sandwich the flask in between a couple pieces of softer metal such as aluminum copper or even cloth to help reduce the chance of scratches in the stainless steel.
    • to knock off some of the shine you can sand it with some sandpaper. I used a mostly burnt up piece of 80 grit so it was more like 120 or 160 grit.
    • hit it with a non woven abrasive pad (scotch brite) if you want it to be even more matte. this also helps even out the lines from the sandpaper and gives it a nice brushed finish giving it a warm worn look. Its hard to capture the different steps of the finishes on the camera because the stainless steel it so shiny in the different lights and white balance conditions. it does make a notable difference when you look at it with your eyes.
    • rinse out the flask with some water and you will be ready to fill it up and enjoy a tasty sip of your favorite spirit on the go, wherever and whenever you desire... as long as you are wearing pants or have a purse to store it in that is.

    Congratulations

    After reading and following along with me you are now a master flask welder with your very own hand made stainless steel flask. If you however forgot to do any or all of these steps and you have ended up with a melted pile of crusty burnt stainless or more likely just simply lack the access to the tools required to build your own you are in luck. As I stated in the first paragraph of this instructable I have made a few of these flasks. On my instructable profile I have a link to my etsy page (capitancobre) where you can put in an order for your very own hand made flask. I have a few different flasks options to choose from and you could even do a totally custom size if you wanted something extra special.

    I am entering this instructable into the metal working contest so if you enjoyed it please feel free to vote for me.

    Thanks for reading!!!!

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      5 Discussions

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      Tuomas Soikkeli

      Tip 2 months ago on Step 3

      Thin plates needs to be tack weld more frequent than thicker ones. When plate heats when welding, plates expand and gap between plates comes wider. Also its good to make welds to same direction in this kind of project, otherwise result is twisted square.

      Also, if you smoothen tack welds by sanding them down, before welding.
      Final weld comes also smoother.

      FFC8UL4JE4KNGGG.LARGE.jpg
      1 reply
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      GregS278

      2 months ago on Introduction

      I'm not gonna start by telling you that you should have used this in your welding!

      But you have got to tell me what you keep in your favorite flask? I like peach moonshine!

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      AndrewA167

      2 months ago

      First, thank you for this instructable; it was very enjoyable to read and look at the clear pictures, which were very helpful to learning. You included lots of great tips which could be applied to much more than just "making a flask", which I liked.

      Also, your last bit about selling the flasks on etsy was a nice and humorous addition; I don't have a need for a flask (as I don't find myself hanging around black-tie weddings often!), but if I did - I don't have a TIG welder nor the experience (nor a lathe) - so you providing that option is a nice touch...and for a handmade product your pricing is decent too!

      Regarding etsy (for others - you have to go to his instagram first, where there's a link to etsy - I was not able to find his direct link off his instructable profile), one thing you might also offer is that copper chain mail scarf; as a hobbyist welder, that looks very useful (alright, I know you can't really do this, as handmaid chain mail is anything but inexpensive, and that single scarf probably took forever to make, even with the simplest link style - but I really liked it as a welding tool - the use possibilities are great to think about).

      Finally, the only other thing I have to offer is another possibility for "food grade" cutting oil (and coconut oil is an interesting alternative to try); it's actually something old-timers have recommended for over a century: bacon grease. The downside is that it will rapidly go rancid, but even rancid it is said (I've never tried it - as I said, I don't own a lathe) to impart a very pleasant smell to the shop (well - if you enjoy bacon of course - if you're a vegan or vegetarian, you probably won't have any bacon grease lying around anyhow).

      Anyhow - thanks again for the great instructable; I hope to be able to catch more of your future tutorials (I'm thinking about checking out your steam boat one)...

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      DennisO22

      2 months ago

      The stainless steel alloy containing 8% Nickel and 18% Chromium is an Austenitic Stainless steel. That means it retains an austenitic structure at room temperature when normally it is only present above the upper critical point (the temperature at which all changes in the structure of the steel have taken place. This makes it suitable for a wide range of manufacturing process. This temperature will depend upon the alloy content of each metal. Austenitic stainless has a low coefficient of thermal conductivity and a high coefficient of expansion - this is why it can suffer 'Severe Distortion' when being welded unless precautions are carried out. The blackening of stainless steel is caused by Oxygen. Which is why welding filler wires for welding stainless steel contain the deoxidizers Aluminium, Titanium and Niobium. Often referred to as either 'Double Deoxidized' (two of the three) or Triple Deoxidized (all three). These are incorporated in the electrode/filler wire coating. You should also use 'Thoriated' (contains Thorium) tungsten electrode for D.C welding and a 'Zirconiated' (contains Zirconium) for A.C welding.