True enough. I use the 4-jaw when I need absolute
concentricity on an existing workpiece. Not to put
down Rick's idea - I think it's great and will
probably make one someday.
Frank Hoose
--- "roylowenthal <roylowenthal@...>"
<roylowenthal@...> wrote:
OTOH, when you're doing repairs/mods to existing
stuff, the lack
of concentricity is a problem. I'm using the 4 jaw
until I finish
the Rick Kruger style adjustable backplate (I'm too
cheap to go the
collet route.)
Roy
--- In 7x12minilathe@..., Frank Hoose
<fhoose@y...> wrote:
Something to keep in mind: a little runout of the
chuck, say .002 or .003 won't affect most projects
as
long as you don't remove the workpiece from the
chuck
until all operations are completed.
The reason is that as soon as you turn the
workpiece
down by more than .004, the resulting workpiece is
exactly concentric with the lathe axis within the
accuracy of the spindle bearings (typically .0002
-
.0005 on the minilathes).
This is why I was able to turn a piece of brass
down
to .034 dia. and then drill a .016 hole through
it.
lathe.com/Mini_lathe/Capabilities/Capabilities.htm#tiny
More recently, I needed some test pins for making
temporary connections to a tiny DIN connector on a
video camera. I turned the pins from brass to a
dia.
of .020. They were concentric even though the 4"
chuck
holding the 1/8 brass stock I started with
probably
has about .003 runout.
Frank Hoose
--- "Craig C. Hopewell
<chopewel@r...>"
<chopewel@r...> wrote:
John,
I have not heard of this problem before, but I
am
new
to the hobby, and if any lathes had this
problem I
would
have expected it on mine ( 8^) or 8^( - don't
know
which).
I would want this to be accurate, especially if
removing
and mounting the chuck regularly. If under
warranty I
would request a new spindle. If not under
warranty
a
new spindle is available from
www.littlemachineshop.com
for $29.95. Alternatively, an adapter plate
similar to
those necessary for a four inch chuck could be
made.
Craig
--- In 7x12minilathe@..., "John
<moran03@e...>"
<moran03@e...> wrote:
The raised land on my spindle plate measures
2.154
rather than 2.165
as given on the mini-lathe site. Sure enough,
the
recess in the
chuck
measures 2.165.
In order to mount my 3 jaw chuck I first snug
the
nuts slightly, put
a rod in the chuck, and use an indicator on
the
rod. I rotate the
chuck so the high point is up and tap the
chuck on
the top with a
block of wood; this is not a well controlled
process so it typically
takes several minutes to get TIR between 1 and
2
mils, when I
tighten
the nuts.
Is there a better way to center the chuck?
Is the mis-match between the land and the
recess
common? I expected
the chuck to center itself on the spindle land
but
this mis-match
apparently precludes that.
John
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