one word HACKSA
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I use the hach saw on smaller parts ,I cut it off .25-.60" from where
I want to be and face it off with a tool bit ,no chatter,no hastle.You
have to let the weight of the saw feed the blade to take light cut and
also have a slower rpm just to be safe
Q-Cut insert parting tool (Greenwood).
Hold in a back toolpost if possible.
Run fast and feed fast and firm.
Don't, repeat, don't run the lathe backwards with tool held upside down.
You will unscrew the chuck and disaster will surely follow!!!!
As an idea of speeds and feeds I would part off 1" dia brass bar on my
Myford Super7 running at top speed (2200RPM) with a Q-Cut tool in the
rear toolpost and feed in as fast as I can. Same with free cutting MS. I
might drop the speed a bit if i was parting off silver steel or
Practice on aluminium, about 2" diameter. HSS blade; about 30 deg rake, very
little clearance; side rake; very sharp; tool just below centre; right way
up and lathe running forward. When you can do that, nothing else is a
i know what you are saying about chucks coming un-screwed, and must admit i
have never thought of this as a problem, because normaly i use a chuck with
D style clamping (pin and cam). I should have realised a lot of smaller
lathes have a screw on chuck.
as a side note, if you have a secure chuck that will not unscrew, my method
is very good at eliminating chatter while parting off, and is my prefered
way of turning brass, save lots of little burns lol.
From the Keyboard of Tim Bird
Visit my updated website @ www.timbird.net
Thanks for all the tips. It is nice to know that I am not alone in
finding parting-off a problem, although obviously you have all found
your own various solutions. A Q-cut tool was mentioned several times. I
have not heard of this. Many of the commercial parting-off tools are
too big for a small lathe. Mine is a 3" from Axminster - probably
Chinese. I did manage to get it to work after posting my query, but it
still was not ideal and many of you suggested driving the tool hard
against the work, which I haven't been doing. I think my main problem
was that the ground angle at the end of the bit was not correct and the
tool was simply rubbing against the work piece. I was also positioning
the tool below the centre as recommended by one of my books. I have now
placed it on the centre line. The regrinding and repositioning seems to
work. I obviously need more practice to make sure that I have got it
right. Thanks a lot, Eddie Price
On 4 Jan 2005 05:49:21 -0800, email@example.com
I think, sooner or later, everyone has a problem,
with parting off. Brass is not normally too much of a
problem but something like 3" diameter work hardening
stainless steel can be a daunting task.
The the normal front mounted parting off setups need
the setup of both the lathe and the workpiece to be
exceptionally rigid. This is because any flexure increases
the cut depth and this can be a recipe for chatter or even
worse - catastrophic dig in!
A parting tool mounted upside down in a rear
toolpost is much more forgiving because flexure decreases
cut depth and this is an inherently stable configuration.
I regularly use a backmounted HSS cut off tool and
the comparative freedom from tool jams and chatter is well
worth the bother of providing the backmount facility.
An extra feature which works well on both front and
back mounted parting tools is a longitudinal groove along
the flat top face of the tool. Because the plunge cut chip
of a parting tool is in an extreme state of compression its
natural width is WIDER than the width of the cut and it will
try real hard to jam against the sides of the cut. If the
top of the tool is flat, the flat chip will try to form a
close coiled swiss roll which is probably the worst possible
shape for generating excessive side pressure.
The effect of the groove is to produce a chip which
is curved across its width instead of flat and this
curvature is more easily compressed by the sides of the cut.
The shape of the groove doesn't seem to be very critical - I
aim for a centred roughly semi circular groove a bit less
than half the width of the top face. A tool and cutter
grinder would make short work of this but I content myself
with a cutoff disc in a dremel grinder and a fairly steady
hand. I run the groove back for about 1/4" so that it
survives several resharpenings.
Resharpen on the front face only - about 10 deg
front clearance. Unless you're limiting cutting to small
diameters with relatively wide blades keep the front face
grind dead square on to the tool axis. Any angle here to
move the final pip to waste or the workpiece generates
undesirable sideways deflection
Because the side clearance on parting tool blanks
is so small and there is no side rake it's important to be
careful that the cutter is mounted truly vertical and
accurately square on to the spindle axis. Even with the
curved chip face there's still pretty severe pressure on the
sides of the cut so continuous brush or drip oil feed
lubrication is essential on difficult work material.
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