I picked up a used medium size hobby type lathe but the tooling is the
wrong size. The bit is about .045" above the center line of the chuck.
I searched the web and couldn't find any info on the placement of the
tooling. Should the cutting edge be level with the horizonital center
of the chuck, slightly below? Right now it doesn't cut steel well at
You should buy a copy of "How To Run a Lathe" originally published by South
Bend in the '40s. It's a good primer on turning metal and being a newbie
myself, I find myself referring to it often. E-bay is filled with folks
selling various iterations of this book.
Unless you are either facing to the center, or cutting a taper or
profile, you should give the tool greater relief by setting it .005 to
.010 from center. For turning and facing set the tool below center. For
boring set the tool above center. The rule is - Turn below, bore above.
I belive the answer you're looking for is how to get the tool up to it's
proper cutting level... I can be shimmed, or better yet, buy yourself a
QCTP that allows use of several sizes of tool bits, all of which are
infinitely adjustable as to height. You won't regret the purchase.
Cutting edge must be exactly on the centreline of the work.
Easiest way to check: (with lathe turned OFF!) gently pinch a 6" ruler
beteeen the cutting tool and the work by feeding the tool forwards slowly.
If tool is on centre height the ruler will be upright. If too high the top
will tilt away from you. If too low the top will tilt towards you. Amazingly
easy and quick method.
It may be that you have an adjustable tool holder - if not you need a
smaller tool bit or grind the top to lower the cutting edge the 45 thou that
Not if it starts out above center, as he has stated is the
For a HSS bit, the option would be to grind the top down to
bring it close or below, and use shims to fix that. Or perhaps to use
smaller tools -- though a properly made toolpost should have the top of
the tool mounting slots at or slightly below the center height. In
other words, it should not be *possible* to put in a tool which would
have its cutting height much above center.
The problem *may* be coming form a QCTP (Quick Change ToolPost)
which is too large for the machine -- or even a turret toolpost.
It would help to have a bit more detail about the machine (in
particular, its size) and the style of toolpost. Maker might help. (Is
it an import or a US-made one?)
Let's start with the size of the lathe -- swing (maximum
diameter which can be turned above the ways) and maximum distance
between centers (distance between the point of a center in the headstock
spindle and the point of one in the tailstock with the tailstock at the
very end of the bed, and with the tailstock ram cranked as far in as it
can go without ejecting the center).
As to the toolpost, if you are asking such questions, perhaps
the best bet is to photograph it and put the image in the dropbox (visit
and read on how to submit things to the dropbox. Then, once you have
your image there, post the name of the file, and the URL given above.
Whatever you do, *don't* post the image directly to the
newsgroup. That is a no-no, and it won't even reach some, because many
news servers automatically drop images posted to discussion newsgroups.
Once we have the image, we'll probably need to have some more
information. For example, if it is a quick-change toolpost, you will
need to look for markings which give the size. If a turret toolpost,
there need to be two measurements:
1) Height of center above the compound.
2) Heights of bottom and top of the tool slots above the compound.
For the quick-change toolpost, the height of center above the
compound will be needed. The other figures can be looked up for the
common sizes. (My 12" lathe has a quick-change toolpost whose size is
called "BXA" by some makers and "Series 200" by others.
I presume that if it is a QCTP you have already found the height
adjustments on the tool holders.
He says it is already 45 thou *above* center, Bill. His problem is to
get the cutter *down* to center. He hasn't yet told us what toolpost
style he has, what tool bits he's trying to use, what toolholders he
has, etc. So we can't yet give him any real help.
The tool height isn't itself so important as you might think - it
depends on the tool's top angle. The _combination_ of the two is
crucial, but you can play one off against the other.
You do need to have quick and easy control of the centre height.
Either an adjustable toolpost (screw up and down), a rocker toolpost
(tilting) or something like a four-way toolpost that's adjusted by
shimming. Thick shims are fine (hacksaw blade is traditional) - we're
not talking tappet-setting accuracy here.
Ideally the tool height is 5° above the centre height - i.e. about 20
thou high for 1/2" bar. If you set if too high you'll get rubbing
under the tool's edge, an overheated tool and very poor cutting. If
you set it too low you'll get chatter.
The tool is generally a horizontal bar. Naturally it will deflect
slightly under load, so for small deformations of a horizontal bar,
this will be vertically downwards. If the tool contacts on or below
the centre height, then this deflection downwards will tend to reduce
the cut depth, reduce th eforce and reduce the deflection - the tool
now bounces upwards, repeats the cycle and you see chatter.
If the tool is at its optimum height (slightly above centre), then it
will still deflect downwards but this is always tending to _increase_
Yes, the optimum height varies with diameter. You generally leave
this set for a particular tool, but you might well set it lower with a
fine tool for small work. For facing work it's OK to run on center. A
quick facing cut is also another way to measure tool height - a centre
pip means you're off centre, a cylinder left is low, a cone is high.
With your tool height chosen, you can check the most crucial of all
settings - the tool top angles. There's a top slope back along the
length of the tool and a side slope across it. These vary hugely for
the shape of the tool, the type of work you're using it for, and the
material you're turning. For rough steel try a top slope of 8° and a
side slope of 15° - go "blunt" for harder materials, "sharper" for
heavy work in free-cutting materials. Some materials (like titanium)
are awkward - you have to use an extra-sharp tool. At this point
you'll be checking the references, like Machinery's Handbook.
The clearance angle is the angle at the front or side face of the
tool. It doesn't affect the cut much, it just needs to get out of the
way and not rub. So try twice the centre height - about 10°.
If you're turning brass, then that's a different material altogether.
It's more of a scraping cut, so use a tool that has minimal top slope
and is set on the centre line (but watch out for that chatter).
I disagree. If the tool is set high, any deflection pulls it
deeper into the cut and makes it worse. If the tool is set on center,
any deflection pulls it out of the cut and reduces the load.
I always set mine right on center.
-- Another way to center the tool bit on centerline of lathe is to use a
surface gage. Assuming the headstock and tailstock are in alignment, place
the surface gage along the ways of the lathe and place the tip on a live
center in the tailstock. then simply move the surface gage along the ways so
that its tip is near the tool bit tip. This works quite well with a qctp.