Microscopes

Out of the goodness of my heart rather than for any other cogent reason I occasionally glance at the microscopes of the local high school. For the most part microscope maintenance only comprises vacuuming bits of fluff off the eyepiece lens where they lie on the focal plane. Sometimes it includes cleaning the high power objective where the children plunge it into some aquatic biological specimen they are unable to see with the naked eye and are definitely unable to see when they use the microscope as Scuba equipment.

About ten years ago - actually it was nine according to my notebook - the school presented me with two identical wrecked instruments, and being
a) aware of the cost of school microscopes and
b) vicariously frugal
I cobbled the two together to make one intact and working one. Last week it was returned to me in a state where neither coarse nor fine focus would work. I pulled it apart and was interested to see what had happened to it in the interim.

Given that the lab technician doesn't dare touch the innards of the instruments and the schoolchildren don't have time I believe I may be able to surmise who might have effected - ahem - certain alterations to it. I offer the following hints to biology teachers around the globe as a consequence.

1. If you really do not know what you're doing, it can sometimes be wise not to do it.
2. If in spite of  1 (above)  you do inadvertently pull a microscope apart, it's quite a good plan to make detailed notes of every stage of disassembly so you know how to put it back together again afterwards.
3. Cheap school microscopes are still expensive.
4. Some instruments have the coarse focus pinion mounted inside an eccentric which is arranged to twist. If it twists one way, the rack becomes tight and immoveable. If it twists the other way, the stage falls out of focus and nothing but improvised props of petri dishes and other laboratory detritus will hold it in focus.
5. If, in an endeavour to correct the problem without recourse to knowledge or understanding you tighten up some suitable-looking screws VERY HARD, it is possible that the die-cast dovetail block will crumble.
6. If on reassembly you find several random parts left over, it's not necessarily best to put them in an icecream carton in a drawer somewhere else, and hope that tightening the screws VERY HARD will obviate their use.
7. And if you have removed any apparently surplus parts, it's as well to hand them over when asking someone to look at the instrument for you. Often the designer had some purpose in mind when he included a fine adjustment focus return spring and cap. Often he didn't simply pop them in there on a whim, or as a fashion statement.

I do hope these hints prove useful. There are a good many websites (warning: pdf) devoted to cleaning optical instruments, but there is one hint that I would add. When a lens is dirty, the dirt itself comprises some things (grit, fluff) and some stuff (oil, moisture) acting as a mordant. If you rub a tissue on the lens, the things (grit) are not miraculously removed from the stuff (oil), but rather are miraculously turned into a grinding paste. The lens designer would not thank you any more than Smetana would thank me for trying to play the Moldau on the mouth organ.

Corrosion. Nice.
 
Oh, and it's quite a good plan to keep your microscopes in a dry cupboard rather than the groundsman's potting shed.

Rob English Crash

Inattentive as I am to the doings of the ladies and gentlemen who inhabit the outpost of the Diaspora which lies a bit south of Vancouver, I was wholly unaware until this morning that Mr. English has had a mishap. 

Mr. English is not, as we all know, averse to mishaps but this one appears to be slightly less wise than his previous mishaps.

In the first instance he arranged for it to take place in our Colony of West America, and everyone knows that when an ambulance carts you into an American hospital the doctors all gather round gleefully rubbing their hands and feeling up your wallet. Well the doctors don't but the administrators do, and they'll only let their doctors take a peek if the wallet is sufficiently full.

In the second instance, carried away by the exuberance of Racing, he rode into a part of America that was already occupied. By a tree.

The speed was so great that the tree caught fire, of course, and all the other trees nearby did too, and you can see what that looks like here.

First reports omit the int'resting gory stuff, but some googling reveals that the ambulance gathered up shards of arm and shoulderblade, together with ribs to create Eve in sufficient numbers that if he was a Mormon he could have his very own Tabernacle Choir. - Unf. he isn't a Mormon. - Unf. Mrs. English would probably raise objections to a dozen extra wives. -

Current reports  suggest he's out of intensive care, and Mrs. English tells me he might be home tomorrow.

Anyone who wants to contribute to the pitifully inadequate income of Oregon's doctors can do so here and then they can write to this man  and encourage him to ignore all the sillies who oppose him and create an NHS, same as all other countries who like to consider themselves civilized, so that people who have negative tree interactions don't have the added complication of dying of financial worry.

Long Wheelbase resumed

Okay, where'd we get to? Somewhere or other I got distracted. - Actually this isn't true - what really happens - always - is that I find the smallest, tiddliest job and spend weeks staring at it wondering if there's an easier way. There never is. I just have to Get On With It.

In this particular instance it was how to mount the seat. So I did. First I had to calculate (guess) where the chain run goes, and then dodge it with the seat support. That meant welding it on the back of the base, not beneath the base.

Note favourite welding clamps: inner-tube strip. Jigged with bits of wood screwed together to ensure parallel sides ten inches apart. Overall seat width = 12"

Next, something to stop the seat support flopping over sideways.

 Cut...

... precision cold-set  (okay, whacked with a hammer)...

 and welded to the frame.

About now it occurred to me that I might, just might, not get the angle of the seat exactly right at the first weld. Actually, not might at all. I never have; never will. Ten miles into the first ride I'll know it's wrong. Slightly wrong, but wrong. Twenty miles and my back will be killing me. Dead.

All of which I didn't want to think about but now had to. So another week of staring dumbly at it before it occurred to me that the 1 1/8" seat support is the right diameter to sit neatly inside a retired head tube, and those I have in abundance.

 Sacrificed Raleigh head tube, plus one of two U-bolts

 Notches filed to weld titchy tubes for the U-bolts...

 ...and U-bolt tubes welded...

...and the whole welded to the frame. Now the seat can tilt.

So the next bit of complete engineering paralysis - if I can dignify anything I ever do with the epithet engineering - concerned how to use the former seat stays of the mixte frame, as seat stays. - Gah? - so I'm repurposing a thing to be what it already is. God I'm stupid. - Anyway the complication was that the Frenchmen who make Peugeot frames use 13mm OD tube, which is 0.3mm bigger than the half-inch ID tube I had. But luckily Messrs Huffy turned out to be generous in their half-inch tube,

and the already chopped-up bike yielded two bits that would slide over the seat stays. By cunningly keeping the ends of the bridge between them (above) I had some sticky-outy-bits to file neatly to accept a couple more bits of tube -

- which made the welding altogether easier. And here they are, one of them already drilled and hacksawn ready for the clamping bolts -

Then all that was required - another week's dithering - was to figure out how to weld the back seat support...

and close the ends off...

and get it in the right place. Which I dismally failed to do. Because I'm useless. It was a quarter of an inch too high.

So I made the extra little bits to screw the slidy-clampy-bits* out of the Huffy dropouts and welded other clampy-on-y-bits to the slidy-clampy-bits in a sticky-outy-sort-of-way so they'd all fit. Approximately. There isn't a pivot at the bottom of the seat stays. Some bending must perforce take place, but it won't be much.

And I screwed them together with 5mm bolts which, I believe, conversation with my brother who actually is an engineer having suggested, have a shear strength of about a third of a ton**. Which I don't weigh.

And conversation with Matt*** at the bike shop yielded a 42mm back tyre, which I rather hope, may make up for No Suspension. - We shall see. -

Anyway, here it is, roughly ready to start turning into a bicycle.

From behind...

and from the side.

*slidy-on-y-bits and clampy-slidy-bits are Highly Technical Terms, strictly used by recumberent (sic.) builders. (Shut up, Mrs. Hague.)

**actually he said a 6mm bolt has a shear strength of half a ton. But six sixes are thirty-six, whereas five fives are twenty-five, and twenty-five over thirty-six is about a third of a ton.

***who rides up Marahau Hill in ten minutes. Hmmph.