Hints and Tips

SALT AND VINEGAR RUST REMOVAL
Buy the cheapest white vinegar you can find (this isn't a gourmet recipe) and some common table salt.  Dissolve as much salt in the vinegar as will dissolve (iow, make a saturated solution).  Make enough of this solution to completely immerse the part you wish to derust.
In a non-reactive container (plastic/glass is good, just don't use copper or galvanized, etc.), COMPLETELY immerse the part in the solution.  If the part is not completely immersed, you'll get a corrosion line at the air-liquid interface.  Do this outside or in some location removed from the good tools in your shop.  Hydrochloric acid fumes can play hell with metal surfaces.  A warm location may help speed the reaction but it's not mandatory.  Some undissolved salt in the solution is ok (in fact guarantees saturation), but use a plastic screen to keep the part from directly contacting the salt - at least, that's what I do.
Check the progress every hour or two.  The chemistry is complex and dependent on your particulars.  Time is not overly critical.  The solution will react only with the rust (ferric oxide) and, in the absence of air, will not react with the base metal.  Remove the piece from the solution, wipe (a little steel wool perhaps), and inspect the progress.
When the part is sufficiently derusted, wash IMMEDIATELY in warm soapy water, dry thoroughly, and oil with a good rust preventing oil - something like gun oil, don't use WD40!  If this isn't done the part will begin to rust again - and quickly.
I'm not a chemist but salt in vinegar will produce a mixture of mild hydrochloric acid and sodium acetate.  I believe the HCl breaks up the rust and the acetate binds with it to form a chelate (?) that binds the iron oxide. A real chemist could probably provide a better and more accurate description. Swimming pool acid (muriatic acid - dilute HCl) will also break up rust but it's aggressive and can easily cause adjacent rusting.  (If you have a pool, keep the acid away from your shop.)  I've had more success with the vinegar/salt. YMMV.
-Marv Klotz

COPPER SULFATE AS MARKING OUT DYE
As long as we're talking chemistry, here's another hint.  Dykem is not very
satisfactory for marking lines on a lathe tool bit while grinding to shape.
The rough and tumble action of grinding and cooling easily removes the marking
fluid and the lines.  If you can get your hands on a solution of copper
sulfate, dip the tool in that.  A light coat of copper will deposit on the
tool and it shows scribed lines well.  The electrochemical bond is stronger
than that of marking out dye and your marks will survive longer.
-Marv Klotz

GOT MILK ?
Copper is some of the meanest stuff on earth to machine or tap.  While you're
in the supermarket getting your salt and vinegar, pick up some whole milk - not
the watered down stuff the health-nazis want you to drink.  It's the preferred
cutting lube for copper.  Old timers swear by condensed milk but I've never
tried that.  Certainly easier to keep on hand in the shop.
-Marv Klotz

THE USEFUL CAT?
Most people regard cats as pretty useless creatures.  Well, after making your
nice copper part with moo juice, as outlined above, you may just want to put a
nice patina on it.  Bury it in the cat's litter box for a few days.  Instant
patina. 
-Marv Klotz

WHY YOU BOUGHT THOSE ELECTRONIC CALIPERS
If you own a pair of electronic calipers that have the feature of being able
to be zeroed at any point, here's a clever use of that feature.  Let's say you
want to measure the center-to-center distance between two equal diameter
holes. Use the inside measurement capability to measure the ID of one of the
holes. Zero the calipers at this setting.  In effect, you've now stored the
negative of the diameter of the hole(s) in the caliper's measurement memory.
Now use the inside measurement capability to measure across the outer edges of the two holes. Whatever is displayed on the calipers is the center-to-center
distance between the two holes - the diameter of the hole(s) has been
subtracted out for you automatically.  The same trick works if the two holes
are replaced by two equal diameter pins and you use the od measurement
capability of the calipers.

If you need the center-to-center distance between two *unequal* diameter pins,
measure the distance across them and the distance between them.  The average of the two readings is the center-to-center distance.  Works for holes too.
-Marv Klotz

CHECKING MICROMETER ANVILS FOR PARALLELISM
Use a ball-bearing ball.  They have tightly controlled sphericity (millionths)
and, with the point contact, can be "walked around" the anvil(s) to check them
for the same reading at various places.
- Norm Wells

SOLDER PASTE
One of the best tricks for soldering small parts neatly is to use the 'solder
paste' available at DIY stores.

Lacking that, you can obtain good results by doing what the jewelers do.
Pound a bit of solder flat on a steel plate and cut tiny 'pillions' (pillows)
from the strip with scissors.  Pillion size is dictated by the job but
something around 0.050" square works well.

After cleaning and fluxing the surfaces, flux the pillions (solder needs flux
too) and stick them to the joinline.  The flux will help them adhere.

When possible, heat from the side opposite the pillion locations.  This both
ensures that they won't be blown away by the draft from the torch and
guarantees that they'll be melted by the heat of the parts - which is the
proper way to solder - rather than being melted by the heat of the torch flame.
-Marv Klotz

SLITTING SAWS
Two 1/32" slitting saws can be stacked on the same arbor to make a very
serviceable 1/16" slitting saw.  This is a handy thing to discover (or
remember) late in the afternoon when you've just broken your last 1/16"
endmill (which you shouldn't have been using for this job in the first place).
(Guess how I discovered this?)

I knew there was a reason I bought pairs of slitting saws in small aliquot
sizes.

The application was milling a slot in the end of a (3/16" diameter)
cylindrical valve for a miniature steam engine.  With the rod mounted
horizontally in the vise, I inserted an adjustable parallel between the mill
table and the bottom of the rod.  After measuring the parallel height, I
increased it by half of 3/16" (the rod diameter) minus half of 1/16" (the
slitting saw thickness) = 3/32 - 1/32 = 1/16". Now the arbor is lowered to
bring the bottom of the slitting saw to rest on the parallel, ensuring that
the slot will be cut on the diameter of the part.
-Marv Klotz

MODELING CLAY
It seems one must be descended from the genus Octopus to hold everything when
making three wire measurements of the pitch diameter of a thread.  Like most
amateurs, I use children's modeling clay to manage the wires.  I've tried a
blob of it stuck on the mike frame and a blob on the surface gage sitting on
the cross-slide and adjusted to the height of the thread.  Both sort of work
but not very well.

My latest bodge has been more successful.  Get a bolt of the same size as the
thread you're cutting.  Secure the wires to this bolt using the modeling clay
to hold them in position.  Now the wires will be in exactly the configuration
you need for measuring the thread you're cutting.

If, like me, you made a tool setting height gage to sit on the top of the
cross-slide, clamping the bolt to said gage makes the job even easier.

Of course, if you're cutting a thread for which no matching bolt exists (e.g.,
cutting a fine thread on a camera lens filter holder), this won't work and
you'll have to work out your own bodge.
-Marv Klotz

PAINT
Another trick I've heard but haven't gotten around to doing...Degrease one end
of the wires and paint it fluorescent yellow so that, when you drop it in the
swarf in the chip tray (and you will), you'll be able to find it, maybe.

Art stores sell Sharpie-like paint markers - felt chisel tip but filled with
paint rather than ink.  Many colors are available but the high-visibility
fluorescent yellow seems to be the most eye-catching.

Some other uses for these paint markers.

Mark the rotation-restraint pin orientation on the front of the collet
chuck to make orienting the collet slot easy.

Mark the 'master pinion' hole on the 3jaw chuck.
-Marv Klotz

WORLD’S CHEAPEST TACHOMETER
It's seldom that one needs to know the rotational speed of the lathe accurately but, if you do and you don't have a tachometer about, here's one way to do it.

Get a length of all-thread and a nut to match it.  Grip the all-thread in the chuck and make two marks on it a convenient distance apart.  Thread the nut on up to one of the marks.  Now, with the lathe running, grasp the nut and time how long it takes to move to the next mark.

Given:

d = distance between marks (in)
p = pitch of all-thread (tpi)
t = time for nut to move between marks (sec)

then:

speed (rpm) = 60 * p * d / t

 

I found another use for them too.  The compound on my lathe is secured with two SHCS.  Swarf fills the socket head and has to be dug out every time I want to swivel the compound.  Cut a square of fridge magnet and stick it over the top of the screw.  When you go to pull it off, it will have lots of ferrous swarf stuck to it.  No worry.  Discard and snip off a new one.
-Marv Klotz