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April 24, 2006 4:48 AM   Subscribe

I need to remove a fairly thin but durable chrome plating from a threaded area in a brass boiler tank.

I have an espresso machine with a brass boiler tank which you seal by screwing in a cap into a chrome-plated threaded hole on the top. The chrome plating is flaking off, getting into the water, and I want to remove the plate fully from between the threads without getting it professionally de-plated, I assume by scrapping it off after weakening it, but I know not of what I speak. Any tips?

Please help me. I can't use the machine until I do this, and I don't know how you non-caffeinated people deal with you call reality, but I want off this ride protno.
posted by dong_resin to Food & Drink (12 answers total)
If it's already coming off, you should be able to do pretty well with just a steel brush.
posted by Steven C. Den Beste at 5:10 AM on April 24, 2006

I guess my real question is has anyone done this, and is there a chemical or mix which speeds things? The chrome is sporadically weak, scrubbing it off and out of the grooves could be a lifelong proposition.
posted by dong_resin at 6:05 AM on April 24, 2006

You could plate some copper or more chrome over the top of it, that may prevent the flaking.

Simplest option is to go buy a tap for cutting threads, making sure it's for the correct thread. Run the tap through and it should cut every little bit of chrome off. You may need a tap-wrench if you don't already have one; depending on the thread size this could be a cheap or very expensive proposition.

Another option is to buy a matching thread, coat it with fine grinding/lapping paste and lap the chrome out.
posted by polyglot at 6:50 AM on April 24, 2006

not the answer, but if you get stuck and need a good interim machine, look at capresso. i kind of love mine.
posted by patricking at 7:08 AM on April 24, 2006

How hot does this portion of the machine get? You could wrap the threads in teflon plumbers tape to prevent flaking, or at least hold the flakes in place. Cost: about 69 cents a roll. for that price, you could just rewrap every time it disintegrates. I'm not sure of the thermal properties of that tape, but it works well enough on my hot water facuets, which are pretty damn hot.
posted by cosmicbandito at 7:21 AM on April 24, 2006

If the chrome continues down into the water vessel, there may be no end to the flaking, since you'll probably loosen new areas while scraping off old ones.

If the threads are large-diameter and fine- pitched, I would be hesitant to run a tap in there. That kind of situation is made for cross-threading, and if you do that with a tap, you won't have any threads left.

You might get by with scraping the threads using a thread file. (Sorry about the crappy picture; finding a file that has those internal-thread chasers on the ends wasn't easy.) Or you could use a tap that's much smaller in diameter than the hole, but has the right thread pitch, to scrape the threads.

Bear in mind that the plating adds some thickness to the metal, reducing the diameter of the hole. Removing it all may make the threads too loose.
posted by Kirth Gerson at 7:32 AM on April 24, 2006

Tapping is probably the obvious solution but that still depends on what is under the chrome and the remaining thickness you have left. Also you will need a new plug. Sort of tricky for a home job. If that plug isn't fit to water and pressure tightness you are out of the coffee business.
You don't want to replate but how about securing the remaining chrome? Instead of removing the chrome, seal it to the threads. I would suggest heating and rapid cooling but if it is on brass forget that. The only other option I can think of is by chemical electrolysis. Maybe you can find a plater that will do only that.
posted by goodman at 8:31 AM on April 24, 2006

I'm going to suggest the power-tool upgrade to "steel brush": use a dremel with the wire brush attachment.
posted by IvyMike at 9:14 AM on April 24, 2006

The tank is plated for several reasons, not the least being that originally, the plating is found to be less reactive with steam and water than the tank's base "brass" vessel material. Steam is quite corrosive on its own, and if your efforts produce even small scratches into the base tank material, the mechanical abrasions you create will provide sites for steam to induce additional cracking and weakening of the tank, which are really hard to see with the naked eye. Also, what you call "chrome" plating is probably a number of thin layers of nickel, zinc and chrome, which have, in various places, become dislodged from the tank substrate by a combination of mechanical forces and steam pressure corrosion. Without the plated coating intact, the tank may already be, or may soon become a dangerous pressure vessel.

And a steam explosion, even in a fairly small and low pressure vessel such as a small espresso machine, is nothing to take lightly, particularly if you are standing within a few feet when it happens. The plating failure is your warning, as a consumer, that your machine has either reached the end of it's useful life, or needs major service, including a tank replacement, and maybe heater block service. If your machine is an inexpensive one, such as this, you definitely just to want to replace it, as it is not worth fixing. More expensive machines may be worth repairing, but replacing a major part like a reservoir, and inspecting and cleaning heaters, pumps and metering blocks should only be done by competent commercial shops, with the tools and materials to do the job right, and check the pressures and temperatures are correct when finished. If your machine is a pump type, where the internal pressures can be above 4 or 5 bar, this is definitely not a do it yourself project.
posted by paulsc at 10:01 AM on April 24, 2006

I've used teflon tape on my espresso machines a few times and it seems to hold up just fine under the temperature. So if you think you're OK w.r.t. what paulsc said above, teflon tape may do the job on the cheap.
posted by turbodog at 12:20 PM on April 24, 2006

After analyzing your spelling and grammar in your initial post and your reply, I would suggest that, whatever means you use to remove the chrome, you caffeinate yourself first.

You have my sympathy.
posted by ikkyu2 at 1:42 AM on April 25, 2006

The phrase "bite me, ikkyu2" does come to mind, but that could also be the caffeine withdrawal.

Thanks for the help everyone-- the idea of the tank's structural integrity being held together by a think layer of chrome hadn't occurred to me, and as it is still under warranty, I'll just send it back.
posted by dong_resin at 3:29 AM on April 25, 2006

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