On 2008-05-06, Joseph Gwinn wrote:
In article ,
"DoN. Nichols" wrote:
On 2008-05-05, Joseph Gwinn wrote:
[ ... ]
Yep. I wanted a lathe with integral cabinet stand, on the theory that
it would all fit together better.
And you got that. (And got rid of the chatter problem with the
new gib. Congratulations.
Thanks. I've been reflecting on how I came to the conclusion that the
5914 needed new gibs.
The key was the gross tilting of the toolpost, which moved something
like a tenth or even an eighth of an inch, and yet nothing broke (except
for a tool bit now and then).
There is a reason people don't make springs out of cast iron, so the
castings could not be bending enough to explain such large deflections.
So it had to be the joints and/or slideways. The only joints were
firmly bolted (toolpost to slide) or wedged (tool holder to toolpost),
and no relative motion could be felt. And the headstock was firmly
bolted to the bed.
This left the slideways, of which there are three.
The first is between the bed ways and the carriage. This originally had
~0.003" wear-induced clearance, reduced to ~0.001" by removal of one
0.002" brass shim from each of the two rear hold-down plates. The
carriage is about 12" wide along the bed, so this 0.001" could account
for only about 0.001" of the tilt (measured at the end of the 5"
overhang). Only ~0.099" to go.
The second is the cross-slide dovetail (~2" wide), and the third is the
compound dovetail (~1.625" wide). The observed wear (~0.004" in both)
would easily explain the observed deflection, given the leverage from
the overhang plus the 2:1 amplification in each of the 60-degree
dovetails.
And -- your compound has less adjustment range for the gib
because the dovetail itself is shorter, so the compound would show the
problems sooner, given equal wear.
And it didn't feel right when I tightened the gibs. The effect on
slideway drag was very gradual as I tightened the gibs; one would expect
the effect on drag to be far more abrupt. This pointed to misshapen
gibs springing under pressure, versus being in pure compression.
Yep! Good diagnostics.
BTW -- the squeal might be because the trepanning tool is not
ground to give proper clearance on the curve of the slot.
That also happened, when the groove got deeper, until I ground a little
more off the bit.
O.K.
[ ... ]
If you are not on Windows, why would this be a problem?
Because I don't depend on them *always* focusing on Windows
systems, just because they are the easiest target. There have been
experimental attacks which used javascript, or java, and I see lots of
information about security holes in the flash plugins (information from
the CERT mailing list). Anything attacking something other than the
basic native machine language can be made to work on other systems.
It's true that everything has vulnerabilities, but as a matter of actual
(versus theoretical) risk, once you leave Windows things get pretty
quiet, and the expense (dollar cost and time cost and lost opportunity
cost) of security soon outweighs the cost of cleaning up the occasional
problem.
I read in one of the Mac magazines that only 10% or 15% of Mac owners
use any kind of add-on anti-virus product, and the unprotected Mac
owners are none the worse for it, and have been for years.
Unix/Linux users have even less to worry about.
Yes -- though there is a tradeoff to being a user of the most
numerous unix version -- which I think is now Solaris 10. That makes it
the next likeliest target.
By contrast, an unprotected Windows machine on the web will last a few
days at most, and a dialup machine might manage months before getting
caught.
An unpatched Windows box, from first connection to the net in a
college dorm, has an expected mean-time-to-infection significantly less
than the time needed to download the patches via the net -- even with a
fast pipe. This is why at least some colleges (those who care about
security) will not connect a new box to the net until one of their staff
have come around with a DVD or CD containing all the patches and applied
them. This at least slows down the infection rate somewhat. :-)
[ ... ]
I have the gibs adjusted so there is much drag, but the cross-slide
backlash is about 0.020", and the compound slide backlash is about
0.006".
O.K.
I figured out how better to adjust things, and got this down to ~0.003".
Good!
I should say how I did this. It turned out to be simple. There is a
black steel collar upon which the dial rotates, the collar being fixed
to the screw shaft with a setscrew. Loosen setscrew. Tighten the cone
nut (or nylock nut) until the screw shaft binds, then back off just
enough that the screw shaft turns freely. Tighten setscrew.
Oh -- the thrust bearing was loose. On the cross-slide of mine,
the handcrank screws onto the leadscrew and then is locked by a cone
nut which goes into a countersink in the crank (IIRC). It is easy to
get this too tight. But it is also easy to tell that this is the source
of the play by feel. You feel a bit of a "thud" as the bearing play is
taken up, while the backlash in the actual leadscrew/net interface is
less sudden. :-)
Before doing this, it helps to disassemble, clean, and lubricate the
entire dial assembly, so things can turn freely.
Of course.
[ ... ]
Did you ever figure out how much of the 0.070" was the screw versus the
nut? I think I recall you saying that the Acme threads were worn down
to sharp points, which would imply that screw wear was the larger
contributor.
It was about half. Cranking the cross-slide out to near falling
out of the nut reduced the backlash to 0.036".
I just tried this same crank-it-out test on the 5914: the backlash is
0.020" throughout the range, which implies that the bronze nut is the
culprit. And implies that the screw is far newer than the bronze T-nut
it now mates with.
That narrows things down significantly.
Hmm. The nut is far cheaper than the screw, and very easy to install.
Replacing just the nut might be worthwhile.
I think so.
[ ... ]
In the shoes is the worst. And chattering tools generate particularly
annoying swarf - millions of sharp little steel needles. Coolant helps
by wetting the whole mess down, keeping it from blowing around in the
shop.
O.K. I don't have problems with the shoes. I wear
oil-resistant steel toed boots, and the legs of my pants come down below
the top of the boots, so it would have to bounce off the floor and come
up to get in. :-) Given some of the things I have dropped, I am glad to
have those steel-toed boots. :-)
And if you want nasty needles, try a horizontal mill with a
conventional milling cutter on steel. :-) I'll take what comes from my
lathe any day. :-)
Someday I'll have the room for a horizontal mill. I keep running into
jobs for which it would be perfect. But it sounds like a perfect
application for copious flood cooling, if only to control the swarf.
The Nichols horizontal mill takes a lot less space than many,
and (usually) offers a choice between leadscrew or lever feed through a
rack-and-pinion drive for the X-axis feed. And -- there are a pair of
micrometer stops which can be set up to restrict the X-axis travel
rather precisely. Nice for certain forms of production work.
Enjoy,
DoN.
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