Relative newbie chiming in here. I've had a bunch of experience with
this lately, turning some 1 inch Al down to 0.5 inch in the center of
a shaft. I'm finding that these 7x12s can hog out up to 0.020 inch
with either a HSS or a cemented carbide bit, but the finish is not
very good. I use this for a roughing cut to remove a lot of material
quickly. The speed is about at the 9:30+- position in the LOW range
using a slow and even hand feed on the carraige.
Then, back off the bit and skin off 0.001 or 0.002 on each pass with
the speed dial about 12:00-1:00 until I arrive at my final diameter.
I find I can get a good finish with the carbide bits, a better finish
with a sharpened HSS. Patience is the key. Dry or lubed with TapMagic
seems to make no difference on the Al. Finish it off with emory cloth
(s). Another Yahoo group recommended using polish while the piece is
still on the lathe, but I haven't gotten that far yet.
In general, I'm not too pleased with the commercial carbide bits, but
I think they are cheapy Enco bits. If I buy carbides in the future,
I'm going to buy some top quality ones and see how they do.
Larry
New Orleans
--- In 7x12minilathe@..., "Ed Paradis" <eparadis@a...>
wrote:
Rich, I wouldn't say that the speeds are totaly inappropriate for
the
7x's, but I would use them as a general guide. For most steels, I
generally run at a lower speed, typically between 9:00 and 11:00 on
the dial (in low range), and with aluminium, I run at higher
speeds,
typically 10:00 to 1:00 on the dial. The finish is more of a
function of how deep you're cutting and the type of toolbit you're
using. I use predominatly carbide (brazed/cemented & inserts) and
get a pretty decent finish. On the roughing cuts, I'll go anywhere
from about .015 to .020 on steel, as much as .050 on Al. I let the
machine tell me when I'm a little too aggressive, usually groans or
chatters if I'm taking too much (or stalls when it hogs in)... For
my finishing cuts, I generally only go .001 - .002 deep and speed
up
the machine (around 11:00 to 01:00 for steel, 01:00 to 05:00 for
Al)
and manually advance the carriage. I always use some form of lube,
usually "tapmagic", applied with a small brush to the rotating
piece
and I'm usually pretty happy with the result. I keep some strips
of
400 grit wet/dry close by to polish a little while rotating also
(be
careful it doesn't pull you in). The finish is generally better
also
if you use a more blunt or rounded radius on the toolbit with light
cuts rather than a sharp pointed one, in my experience.
Ed
--- In 7x12minilathe@..., Richard Kleinhenz
<woodnpen@o...> wrote:
I understand that cutting speeds published in the books are
generally used for large machines, and that they are totally
inappropriate for our 'toys'. (I have a 7x12). We should go by
what
feels right.
I am looking for a little guidance here. Say I machine 3/8" or
1/2" 1018 steel. Where should I be approximately? I have an
inexpensive indexable toolset from LMS. The surfaces I get are
nothing to write home about... Can anyone with some experience
steer
me in the right direction? Should I always apply cutting oil? How
much to remove in a pass? What speed? I am on the low range.
What
dial setting appr.? It seems easier to take a heftier cut than a
small cut... something seems wrong ;-) Is there something like a
lower limit for a lathe cut?
I get by, because I don't need a good finish on these simple
bushings I make, but I sure would like to do it better eventually.
Thanks for any pointers!
--
Regards,
Rich
========================================
Richard Kleinhenz
mailto:woodnpen@o...
========================================
