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I'm considering making a 26 quart boiler using two 13 quart mixing bowls from Sam's Club and was wondering if anyone has every soldered or welded two of them together... I am planning on soldering them as I've had pretty good luck soldering stainless in the past... If I knew a tig welder I'd probably go that route... Not sure how many ports the unit will have other than electric element and column ports...

I was originally going to solder two 13 liter stock pots together but they are actually more expensive and taller than I want unless I was to make a horizontal boiler with them... The spun bowls are more durable so that was also a major consideration...
Edited to include image...

If you had a TIG welder, i could see it working better, but to just solder the bowls together could prove to be pretty tricky. I dont know what kind of lip the bowl has on it, but it could be difficult if it is just a rolled bead trying to solder them together. You just wouldn't have much metal to metal contact for the solder to grip. It would probably be too much of a hassle to try and cut the bowls so they had overlapping fingers that you could solder. For my first still build, i got a 30 qt stainless stock pot at a kitchen store at a local outlet mall for only 40 dollars. It had 18 gauge wall thickness, and a stainless lid to go with it. I snatched it up immediately. All of the other large stock pots were around $100.00 each, or had the newer tempered glass lids so you can see inside, and that just wouldn't work. If you have any kind of outlet mall near by, or a big box store such as Bed Bath & Beyond, or Linens and Things (they went out of business around here), they usually have some cheap stuff. I got excited at Wal-Mart the other day because i saw 34 qt stock pots for $30.00, but I was quickly disappointed. Aluminum.

The mixing bowls are $9.87 each, which makes them my cheapest option, plus they make for a shorter boiler which means my column can be taller... My plan is to tin the flat edge of both bowls prior to joining them... They have a rolled rounded bead on the outside of the flat lip which should allow for a small V which should fill in flush as the two bowls bond together... Binder clips will be used for alignment and bonding tension...

I've done similar seams before and was just wondering if anyone has actually used similar SS soldered joints before... My previous joints have never been at what will be the half full level, which is actually my greatest concern... I do have several other options but would like to try soldering first...

If you can get it to work, that is definitely the most economical choice, and if it allows for a taller column, even better. I was worried the bowls would be something like this bowl. If you can get a good flat to flat connection like the drawing on the right, the capillary action between the bowls should suck the solder in and let them bind fairly well. That is especially true if you tin both rims first. Do the bowls have a large enough flat section on the bottoms that allow them to sit stably? Wouldn't want the still to topple over with the high center of gravity the column will give it. Definitely dangerous in several ways.

CountryHam, I do know what I'm doing, just in case you were in doubt... Yes, the bowls have a wide flat rim which is why I have chosen them, but that wasn't even a concern... I, quite honestly, was only curious whether anyone had ever used a sweat solder joint with stainless steel where the solder joint was a major structural element - nothing more... Perhaps I wasn't explicitly clear in that regard... If someone was to respond that they have experienced a joint failure then that may have confirmed my only safety concern... I'm left to assume that you don't have that experience and therefore can't comment on actual first hand durability...

Your diagrams and input might help others who may potentially entertain the same construction, however... You're definitely better at rendering quick diagrams than I am...

Rad, i was never in doubt that you didn't know what you were doing. Lets see....4000 posts, and a regular contributor to most every thread i've read on here....yep, i think that makes you just a tiny bit experienced. I was simply responding to a post with a comment. Wasn't trying to step on any toes. To answer your assumption, no, I've never soft soldered two stainless steel bowls together. I do however have a degree in mechanical engineering with a focus on metals and machine design. Working in a manufacturing environment, and designing machines that can very easily seriously hurt a person, a safety first mentality eventually flows through your veins. I was simply trying to say that if prepped correctly, and with a large enough base for stability, it would be fine. Standard plumbing solder has a shear and tensile strength that, even including a safety factor of 2, will exceed any moment you could put on the joint. The US standard plumbing solder has a melting point of around 450 degrees Fahrenheit, so you definitely shouldn't be reaching any point where thermal fatigue might set in. Apparently commenting on something that i don't have first hand experience on offended you in some way, so my apologies.

Rad
With all due respect I am looking at an apparent heat loss from your source given the radius of the bottom bowl.
Perhaps a "collar" a few inches below the lip of the bottom bowl might retain the heat loss that will travel up the sides of that radius.
I hope my few posts to this forum won't dismiss my input.
As a retire EE I'm now caught up in this hobby that I enjoyed as a kid back with Fred and Barney in the suburbs of Bedrock.

Doc

Thanks, stock doc... I'll be using an internal electric element but have still been considering insulating the boiler - not that I'm thrilled with the prospect of covering shiny stainless...

CountryHam, it was my oversight in not being more specific... I just didn't want you wasting more time with details that wouldn't be directly helpful to me, but, as I stated, your points may prove helpful to others so your efforts were by no means wasteful and appreciated in that aspect...

I've been eying those bowls for about a year now, every time I walk past them in the store and say "Hmm"... Time to pull the trigger...

Rad,
How will you install the element (level)?

Rad I have soft soldered stainless valves on 30gal kettles at work they are 1 1/2" and have about an inch or so slip over. They last a little while but even with just screwing and unscrewing a rubber plug into the valve breaks the solder loose. They are 11ga pots and the valves are 3/16" thick. I have used a half hard brazing solder that lasted better but its expensive and can be hard to find sometimes. Let me know if you want some info on it and I'll see if I can find the pack I have. Another think I thought about is will the bowls warp when you get them hot enough to solder or weld together? Just some thoughts I work with stainless alot at work.

LWTCS wrote:Rad,
How will you install the element (level)?

The thumper on my Frankenstill, albeit copper was a soldered seam down the side and the top and bottom are just butt seams with plenty of solder, I havn't had any problems yet, I even dropped the stillhead when I was hosing it out, and still held firm.

rad,
A thin walled sphere will radiate that electric heat as a loss big time.
You'll probably need to cover up that polished SS.

It's my rookie opinion the SS half and quarter kegs are an ideal choice from a cost and efficiency perspective.
I have a 1/2 lined up from my local pub. He pays a $30 deposit on each so when one comes up missing he pockets my $30
and I'm good to go. He thinks I'm cutting off the top and it's going to become a 15 gallon stock pot.

Doc

Hey rad, for additional structural support to the joint, would it be possible to hammer the lip flat on both bowls in 4 (or more) spots equidistant from each other and drill a hole and bolt the bowls together in addition to solder?

Chasin' Tales wrote:Hey rad, for additional structural support to the joint, would it be possible to hammer the lip flat on both bowls in 4 (or more) spots equidistant from each other and drill a hole and bolt the bowls together in addition to solder?

I'm not planning on any mechanical fasteners to hold the two bowls together it's gonna be an all or nothing effort by the solder... Given the wide mating surface my only real concern would be distortion and given that I'll only be using 1500W it's unlikely that distortion would be a concern...

I'm also considering flanging the coupler by cutting slits and folding tabs on the outer and inner surfaces of the bowl before soldering in place from both sides... This joint is actually the one I would be most concerned with considering the proximity to the element...

Thermal efficiency is going to be way better than my stock pot on top of an electric stove element, insulated or not...

I keep thinking about your element position in relation to the configuration of the boiler vessel.

My local restaurant supplier had some pretty good looking bain marie pots.
I was going to use a bain marie for the Humper Thumper, but concluded that I needed a bit more stout and needed to put some real heat to adaquately weld my fittings. Bain maries would not offer the structural integrity I needed for my crazy ass build.

Those Bain maries were about $14 a peice.

Just thinking about two bain maries joined.

A mini drum (horizontal). You could land the element precisely closer to the bottom.
Put some pegs or some kid of afixed rack to elevate high enough to install a cute lil dump valve on the under side.
Put some loops (or the like) for carry handles.

Just a thought.

Soldering aside, It appears to me that you would also have to have a support arm (or some form of support) for your column as the round bottoms of the bowls appear to be a point of instability. there is not much 'flat' bottom on those bowls. Maybe you could match a bowl to a large pot, and solder those together, , , -hey-

I'm going with the bowls, just need to go next door to Sam's Club and buy them... I've been looking at any stainless steel container for a couple years now... Anything I use has to be locally sourced because I have to be able to hold an item in my hands before spending my money...

The bottoms of the bowls have a flat area in the range of 8 - 9 inches in diameter which is part of why I have chosen this particular bowl... I can also get 13 quart stainless dog bowls with flat bottom almost 12" in diameter at the local Tractor Supply Center but they are more expensive... Storage space is my major concern and I still don't know where I'll find space for this boiler once constructed...

I'll post some pictures once I get the bowls and start assembly... Even though having the element horizontal isn't a critical issue I do intent to have it mounted horizontal rather than angled unless doing so proves to be more bother than it's worth... I just need to be able to run a range of boiler charge sizes from 2 gallons (8 liters) to 5 gallons (20 liters)... The element mount point will be situated with the lowest amount in mind...

Heat input is going to be critical, as with welding or brazing any thing that is thin, distortion becomes a problem. Those two mixing bowls will be a challenge. One why to help with that problem is to use a "heat block". It is a chunk of aluminum of copper and put it behind the area you are brazing or welding. This helps keep the heat in one area. But in you're case that is near impossible due to no access to the back side of the joint with out cutting a hole. So another option is to run down to your local welding shop a get some "heat dam". It is an insulator puddy that welders and brazers use to isolate heat to one area. I would start by tacking the two bowls in the four quadrants with about a 1" long tack. From there it's going to be a feel for how much you can get brazed before the joint starts to separate due to heat. I would also alternate opposite sides around the joint as you braze, (using the heat dam around the area you are torching) let cool (naturally) and do another small section. Keep this up until the full joint is sealed. I would also recommenced using the smallest torch tip that will get the job done. like a N0 1 or 2 oxy/ace tip, that will also help keep the heat localized.

Good advice for straight up brazing, ozone39... However, when soldering stainless by first tinning each surface beforehand requires a different method... The tinned halves will be clamped together using binder clips and the joint gradually heated until the solder just starts to flow... By tinning with sulfuric acid, and then only using flux paste sparingly, if at all, very little heat will be required... The entire process will be done with a propane torch using very low heat so distortion won't be an issue... Soldering problems tend to stem from too much heat far more often than not enough...

Are you using a silver solder then?? A BCup or Cup type filler???

rad14701 wrote:The tinned halves will be clamped together using binder clips and the joint gradually heated until the solder just starts to flow... By tinning with sulfuric acid, and then only using flux paste sparingly, if at all, very little heat will be required... The entire process will be done with a propane torch using very low heat so distortion won't be an issue... Soldering problems tend to stem from too much heat far more often than not enough...

Yep, thats the way to go (imo). Cept I might be inclinded to use the iron. Maybe not. Good luck on that.

Definitely is going to be a one of a kind (till someone replicates it).

LWTCS wrote:Yep, thats the way to go (imo). Cept I might be inclinded to use the iron. Maybe not. Good luck on that.

Definitely is going to be a one of a kind (till someone replicates it).

Something like THIS...???

Ooh.

So I recon it won't really be a one of a kind? But it will be handsome.

Rad,

I've had good success at soldering together a SS stockpot and a SS bucket.

Pretinned as you suggest, but using a 550 watt iron.
The tip is plenty hot to flow the solder, but keeps the heat localised.
Never encountered a distortion issue.

FWIW
squidd