How to Make An Affordable and Effective Heated Tank For Acid Etching - Part 1

I like to acid etch blades that I build using apple cider and/or ferric chloride. I also manganese park firearms and tools. Assuming the part is prepped properly, there are two common needs in all of the above – the part must be submerged and the solution heated. So you have two options, buy a stainless tank and heat source or build one using PVC pipe. These next couple of posts are going to dive into how you can build an affordable and very effective heated tank to finish you parts plus have some fun doing it.

PVC or CPVC?

We can use rigid PVC pipe as the container to hold the etching solution. It’s cheap, easy to find and easy to work with. I need to explain a few things first about what we can and can’t do with it.

In plumbing, rigid PVC pipe has an operating temperature of 140F degrees. The reason for this is that PVC is a thermoplastic and begins to soften with heat and will burst due to the pressurized water. We don’t have much pressure to worry about other than atmospheric pressure but you don’t want to push plain PVC towards 200F – it really isn’t designed for it.

If you want to do parkerizing at 190F, then you need to use CPVC pipe. CPVC rigid pipe has extra chlorination that allows it to withstand 200F while delivering water under normal household pressures. Fun trivia, CPVC was invented by Genova Products in Michigan.

If you are trying to figure out what you are looking at, if the pipe is white, it is probably PVC. If it is cream colored, it is probably CPVC. It ought to be labeled/printed on the side of the pipe also but be on guard for people putting stuff in the wrong bins at a store or clerks not knowing what is what.

In this post, I am working with regular PVC purchased from my local Ace Hardware because the tank is for acid etching knives and will the liquid will be 90-110F on average. If I ever build one for parkerizing, it would be in CPVC. The reason it’s an “if” is that I already have a big stainless steel parkerizing tank but it’s a headache to drag out and set up whenI need it.

The Parts List

Basically, we are going to build a tube with a cemented permanent cap on the bottom and a threaded cap at the top. You can go with any size you want. For most blades I work with, 3″ is plenty and I wanted it to be portable.

Let me give you a piece of advice – it’s aways better to be a little bigger than you think you need than to find that out later. When in doubt, make it wider and taller — within reason of course. Note, I knew a 3″ diameter and about 16″ tall would meet most of my needs but not all and I was fine with that. I’ll pull out my four foot stainless tank when I need to do something huge like a cleaver.

In terms of parts, you need the following:

A length of pipe of the diameter that is needed
A coupling for that size
A threaded adapter for that size – you cement it onto the end of the pipe and it gives you a national pipe thread on the other end
A threaded plug that fits into the adapter
An end cap of one type or another. If you use 3″ or 4″ pipe, you can use a toilet flange adapter to actually both plug the end and allow you to connect it to the wood if you aren’t making it very tall. I would be worried about torque on a tank with an overall length of 24″ or more. In those cases I would cement on a normal end cap and build up a crade around the pipe to support it.
You may want a drain for a big tank – I didn’t need one for this little unit because I can easily lift it even when it is full of the acid etching solution.
PVC cleaner and cement (note, PVC and CPVC use different cement)
Wood to form a base to keep the pipe from tipping over so it needs to be both wide and heavy enough. Really it’s up to you as to how you secure it to be vertical. I like a mobile base but you could tie it to something, etc.
A heating source and controller – we’ll get into more detail in the next post.

Weight Considerations and a Drain

Bear in mind that this tank can get pretty heavy if you plan on using really big piple (6″ or bigger). Water weighs 8.34 pounds per gallon. You will find that other liquids can weigh more. Apple cider vinegar may be around 8.6 pounds and ferric chloride might weigh 10-12 pounds per gallon depending on the concentration.

I bring the weight up because if you are thinking of building a big tank, the weight is going to add up and you may want to install a drain near the base. There are two big reasons you need to think about this – you may want to move the unit around plus you will need to change the solution as it ages and breaks down from use.

This is my 3″ tank I just built. The toilet flange us availab;e for 3″ and 4″ pipe and is handy for smaller tanks. I’d build a cradle/surrounding frame to support a bigger tank.

The pictured tank is about 16″ tall with 3″ pipe and has about a gallon of 70% ferric chloride and 30% apple cider vinegar in it. I can move it around very easily and portability was one of my design goals.

Assembling The Pipe

PVC is really easy to work with. You cut the pipe to the length you want or have the store do it for you. I use a big miter saw for stuff like this to get nice square ends and use an airline to blow all the loose plastic out (wear safety glasses).

To “glue” the pipe together, you first prime the surfaces and then apply the cement. Note, PVC and CPVC use the same primer but different cement. In this case,I use Oatey’s purple primer and clear cement. Read the directions on their box just to make sure. Bear in mind the solvent is really thin and is going to run everywhere – especially in cold weather.

I’m a creature of habit. I’ve had very good luck with Oatey products so I stick with them. There are other brands out there such as Ace’s own private labled stuff, but I stick with Oatey to avoid surprises. When following their directions and using their products, I’ve not had a joint fail/leak yet,

The Base

To make the tank stable, you need a big enough base both in terms of area and weight. I had some old 1×12 stock that I chopped into squares and stacked if four deep for weight. You can do whatever you want and your goal is stability, however you get it.

I centered the flange on the first board and screwed it in. I’m not sure I would trust the flange to handle the potential torque of a long pipe. For me, once I get around 24″ overall, I am going to build a cradle and not subject that flange to a ton of stress.

I then applied epoxy and clamped the layers together. I was kind of experimenting as I went. Just one piece of wood wasn’t heavy enough so I then added the additional layers after. I could have glued the base and then used longer screws to secure the flange had I known more up front. I wound up with four layers of wood in the end.

I have another tank that is full of a boiled linseed oil an turpentine mix that I use for hydrating wood handles in khukuris and cleavers that I restore. It has a rounded end bap on the bottom and the base is more like a heavy cradle made up fo 2×4 lumber that gives it weight and then goes up the sides to provide support.

This is a 4″ pipe with a wood scaffold base. It’s very stable. This is a tankI use for moisturizing and treating long wood hanndles.

Summary

That’s it for now. In the next post we are going to talk about heating the tank. This is where I did the most experimenting and can share some ideas with you.

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