Re: Random...

Oz wrote:
Woodburning stove starts pumping smoke into room.

This is considered to be a Bad Thing.
Room pongs, occupants may get CO poisoning etc.
No more fires.

Chimney cowl is a "lobster pot" type - so called because its made of
stainless steel plates and looks a bit like the armour of a lobster
tail. It rotates so that it faces away from the wind.

Unfortunately it doesn't any more, rotate that is, there is a tight spot
where it jams, so although it will rotate 300deg, there is 60 deg where
it won't.

Do some investigation and find a replacement costs circa 400 quid (its a
10" one), so decide a repair will be in order.

Eventually get man to take it down (notes change hands).

Discover that the shell is indeed stainless, but the key thing, the
bearing, is made from 3/4" galv water pipe, a couple of brass bushes and
a cut down 10mm bolt (200mm long) with a dome nut to seal and a ball
bearing probably once in the end of the bolt, but now jamming system.
Everything that can rust, has rusted.

Naturally the dome nut, the fixing plate and the fixing nut have all
been welded together, but delicate use of small angle grinder separates
everything out.

OK so decide to do a more permanent job. Get SS bar from Ebay, thread
the end. Luckily a 10mm bolt is 10mm clearance and typically about
9.7mm, so can ream out (worn) brass bushes. Pop bearing housing into
lathe and run a 10mm long pattern drill right through.

Bother. 10mm bar won't go reliably through the two bearings (not quite
perfectly aligned). Can't easily get a 10.2mm long pattern drill.
Luckily the drill for a 12mm tapped thread is 10.2mm and I have one
(standard length), but it won't go right through and the (welded) nut on
the end prevents me from reversing it (lathe, small, 22mm through bore).
Manage to do it from the other end using battery drill set on low clutch
(brass snatches easily and with 0.2mm to remove can be nasty). Wipes
nervous sweat from brow...

OK, now, how about a new bearing. Get set of stainless 1/4" ball
bearings (racing bikes for the use of) couple of quid from ebay, and
push one into rebate cut in end, having checked BB are stainless by
immersion in 26% nitric acid (dairy cleaning for the use of). Job is a
goodun.

Now, how about the bottom bearing. Hmm, ss ball bearings are likely to
be HARD, check it out, find somewhere about 300 brinell (3 mohs). So
perhaps use a soft material to get a good bearing, say PTFE. A bit
worried that PTFE might get too hot (its a chimney, right) and also
might wear quickly if the bearing gets contaminated (rust, soot etc).
Only other alternative would be something seriously hard like agate,
although that's barely hard enough. Hunt about for thin agate slices,
none to be found although some very pretty 6mm thick decorative slices
(rather big) are available. Decide that cutting them, even with a
diamond angle grinder, might be somewhat of a mission, too thick,
anyway.

Hmmm....

Maybe I can get some fused silica glass. Silica is pretty damn hard (7
mohs), against the stainless at about 3 mohs. Borosilicate glass is only
about 4 mohs so quartz is the only way.

Yippee! Have lots of big old crystal resonators, they are quartz and
will be admirable. Hunt furiously for an hour before admitting to self
that I must have binned them in one of the many post-retirement disposal
operations. Find a few other things that should have been elsewhere
though, so not entirely wasted.

Check out ebay, doesn't appear to be any. Most of the modern ones are
really tiny though. Not the nice big ones we had in my youth. Check out
a whole bunch of possibilities and basically end up with UV optical
windows, a tad pricey at around a tenner, but hey. Ring up best supplier
on price for his comments (hoping he would throw in a few broken bits
FOC) and he says 'oh no, you use sapphire'.

Oz faints.

"Sapphire

The advantages of sapphire as a design material are numerous. Extremely
high use temperature (2000C), hardness (9mohs), optical clarity,
flexural strength, and chemical resistance make this an increasingly
popular choice. Applications include grocery store scanner windows,
watch glasses, and countless semiconductor and aerospace/military
applications."

Ok so sapphire is really hard, its has a hardness of 9 mohs (diamond is
10), so admittedly its not likely to do much wearing out. However
sapphire is a gemstone, like ruby and stuff so how much is a 10mm diam x
1mm thick polished optically clear sapphire window ferchristsake?

We aren't talking watch bearings the size of a sand grain now are we?

Ye gods...

Er,

How about £7.95.... + P&P & vat?

Oz faints (again)

OK...

Apparently its used for covering quite a few optical things, like
cameras on speedway bikes and the like, where stones and abrasive sand
abound. One wipe and its clean and unscratched. I wonder if you can get
glasses made from it?

I think I'll araldite it to a hard 1mm SS plate and put 1mm of rubber
underneath because it would be a bugger if it shattered.

You don't think I've gone a tad overboard on this do you?

Depends if it has fixed the original smoke problem. :-)

--
Old Codger
e-mail use reply to field

What matters in politics is not what happens, but what you can make people believe has happened. [Janet Daley 27/8/2003]
.

Relevant Pages

  • Random...
    ... Discover that the shell is indeed stainless, but the key thing, the ... bearing probably once in the end of the bolt, ... be HARD, check it out, find somewhere about 300 brinell (3 mohs). ... FOC) and he says 'oh no, you use sapphire'. ...
    (uk.business.agriculture)
  • Re: Seasoning a Stainless Blast Deflector
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