Thread chaser for immersion heater

The local brewery uses immersion heaters in the hot liquor tank. This runs at about 78 C so develops a fair amount of limescale. Any idea where we might find a 2 1/4 bsp thread chaser to clean up the threads when replacing elements? (£300 for a "proper" tap is a bit of an investment).
I'd wondered about fabricating something from three or four 5/8 BSW or UNC taps (which also have 11 tpi) on an adjustable or "soft" mandrel.
Tank and bosses are stainless, so hydrochloric acid not a good idea.
(Chief beer taster. I get to check a pint out of every barrel they produce. £50 a week; not much, I know, but it's all I can afford)

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Citric acid works quite well on scale and its used in brewing for a lot of things.

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tony

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Snap:-)
regards

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Go for it.
The other way is to hand-file teeth into a strip of O1 steel, then harden it (which is easy with O1)

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Alternatively make your own tap from a bit of, eg, EN8. For that job you might not even need to harden it.
Have you tried plumbers' merchants in case there's a standard item for less money than a proper tap?
Tim

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Angle grinder?
Seriously. Take a scrap element and cut a few slots in the thread such that the *forward* face cuts when you reinsert it.
regards

writes
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Thanks, I had wondered about doing that, so I'm pleased to have several endorsements. Most of the old elements have brass nuts, but I think there might have been a steel one there as well. Part of the problem is that there is a bit of pickup and distortion, so it needs to be done a bit carefully. Might make the thing up with slit right through the ring so it can be collapsed if it jams.
Havn't been able to find a purpose made tool anywhere, but I thought if they do exist someone here would know. The Travers link posted elsewhere is the nearest.

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As has been suggested the standard trick to make a "poor man's tap" is to grind flutes into any bolt or fitting of the same thread size such that A) the flutes are completely below the root diameter of the thread and B) the leading edge of the flute is vertical in the clockwise direction so it acts as a cutting edge just like a proper reamer.
I make these routinely for non standard thread sizes for cleaning out bolt threads in engines using old bolts and the edge of the wheel of my bench grinder. You only need to flute the first few threads for it to work nicely. They'll clean out crap and corrosion and even correct light damage in soft materials although of course they won't cut a new thread like a proper hardened tap.
Alternatively as the tanks are stainless steel not soft brass you could use a small rotary wire brush in an electric drill such as these.
http://www.tool-wise.com/products/spindle_mounted_crimped_wheel_light_duty/index.html
One of those would whiz through limescale without hurting the thread itself. I use those in my high speed rotary grinding equipment for cleaning out cylinder heads and engine blocks. You can get smaller ones for use in Dremels and similar and in fact the high speed of the Dremel would maybe make it worth getting one of those too. A cordless one like this
http://www.argos.co.uk/webapp/wcs/stores/servlet/ProductDisplay?storeId 001&catalogId00002201&productId00642739&langId=-1&engine=froogle&keyword=Dremel+Lithium-Ion+Cordless+Rotary+Tool&_$ja=tsid:11527|cc:|prd:0072492|cat:Power+Tools
would make it easier to use without having to rig up extension cables to each tank. Dremel do their own brushes in carbon steel, stainless steel and brass. Brass would be very gentle on the steel of the thread while still removing the limescale although I doubt they'd last very long. Ideally for a steel brush you'd want wire of 0.3mm diameter or less. The 0.35mm wire is more aggressive and less able to reach into the roots of the threads. With 0.3mm wire brushes I can even clean up aluminium cylinder heads without marking the alloy if I don't run the brushes at too high a speed. With 0.35mm wire it tends to scratch a bit at high speed although on stainless steel it would be fine.
Be aware though you do tend to lose strands of wire from time to time so you'd need it to not be a problem if one of those fell into the tank. I'm sure everything is filtered at some later stage though.
http://www.dremeleurope.com/gb/en/start/index.html

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http://www.tool-wise.com/products/spindle_mounted_crimped_wheel_light_duty/index.html
http://www.argos.co.uk/webapp/wcs/stores/servlet/ProductDisplay?storeId 001&catalogId00002201&productId00642739&langId=-1&engine=froogle&keyword=Dremel+Lithium-Ion+Cordless+Rotary+Tool&_$ja=tsid:11527|cc:|prd:0072492|cat:Power+Tools
Good idea, not sure why I didn't think of that; I have mains and battery dremels although the batteries are getting tired, and I have a birthday coming up so might just drop hints around the family.
But I'll also try to knock up something from an old element.
I've only used the cheap wire brushes that tend to come in the kits and as you say they don't last long. I'll order myself some better ones.
The beer isn't really filtered, but it gets strained to remove the malt and hops which would probably catch any lost wires. Also, it's "real", i.e. cask conditioned, so anything which reached the barrel will end up in the yeast layer at the bottom, and anyone who drinks that probably wouldn't notice....
(I'm not being totally flippant, there will certainly be carry over of shed limescale from the hot liquor tank, but you don't find that in the beer).

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How about the type of thread repair tool such as at www.travers.com, part: #51-050-000. Like a pair of opposed arm plyers with a chaser on each arm. HTH.
Good luck with your brew.
PaulS

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I'd wondered if there was such a tool, but I had never come across one before. The thread files also look useful: have downloaded the catalogue for a later browse!

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Tracy Tools only list BSP taps up to 2" at £20 and http://www.tracytools.com/tapsanddiesbsp.htm says they do up to 6" poa. Give them a ring; I'm sure it'll be far less than £300.