In article , mongke wrote:
Hi all

I'm looking for an reliable online source for slide rules in the US. Note
that I don't need antiques nor collectables, but a slide I can learn with
and use daily in the shop.

You don't *want* collectibles, but I don't think that anybody
still makes the things, so any you find *will* be a collectible, and
you'll have to look in such a place.

These days, you would do best to go to yard sales, antique
dealers, and eBay to find them. I got my first ones from Sears (rather
poor ones, but enough to learn on, and I was a kid then.

Later, I got a pocket sized (5") all metal one from Pickett --
bought from a local office supplies store.

My first *good* 10" one was from Lafayette Radio (now long out of
business). That was around 1960 -- and the quality of the slide rule
was excellent, though most Japanese tools and equipment was rather poor
quality at that time.

After that, I picked up several used K&E ones (including one
barely used from a summer hire who changed to business after a summer of
actually *working*. :-)

My best two are a 20" K&E, and a Russian circular slide rule in
a pocket-watch case. (The K&E is the more accurate, of course -- but
the Russian one is fun.)

Now -- if you are planning to use this in the shop, I should
perhaps point out some limitations:

1) A slide rule can't add. It multiplies, divides, squares and
square roots, logs, trig functions, and exponentials, but not
any good for adding.

2) A slide rule is of limited accuracy. For the most part, you
should not expect to get more than three significant figures
out of it -- though this varies somewhat with where on the scale
you wind up, as things are spread way out at the low end of the
scale, and scrunched up at the high end. If you are working in
inches, say 1.25", you won't be able to calculate anything to
0.001" (where you are machining).

If you want more significant figures, you need a longer scale.
20" is not enough for machine shop work. Big circular slide
rules squeeze a bit more scale length in a given maximum
dimension, but still is not adequate. A big cylindrical slide
rule might work -- but it would be awkward to use.

3) *You* have to keep track of where the decimal point goes. Now
this is very good practice for a sanity check on the results of
an electronic calculator, but can really trip you up until you
are used to it.

Frankly, for shop use, I would consider an abacus or a soroban
(the Japanese version, with significant differences) to be more useful,
as you can put the decimal where you want it, and keep several
significant figures of accuracy. (Think of the slide rule as an analog
calculator, and the abacus or soroban as a digital one.

The slide rule was *great* in circuit design, as the components
were usually not made to a precision as great as the slipstick could
deliver. I would never consider it to be the best choice for machining.

And these days -- *I*, at least, need my glasses and good light
to read one. :-)

Also -- in today's world, I would suggest a good scientific
pocket calculator -- kept in a Ziploc baggie to keep swarf and coolant
out of the thing, but to allow you to see and use the buttons and the
display through the clear back of the baggie.

Also wanting to buy large surplus diodes (for future DC welder
construction). Someone posted an url (a dependable supplier?) but I cant
remember it.

I'm afraid that I don't remember it either.

Good luck,
DoN.

P.S. I also almost got arrested because of one. I was wearing it on
my belt, and a policeman thought that it was a knife. :-)
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