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Hi, ignorant newbie here; just bought a new 7x12 lathe but as yet tooling
and metal not arrived -but my dial test indicator has...

I decided to place the Centre from the tailstock into the headstock chuck
and test. It's a long way out and is visible by the naked eye alone -
perhaps by 0.5 -10.8mm. Yes I've taken the centre out and repositioned it
-but still the same.
What's the best advice? (All I could think was to take out the (numbered)
chuck jaws/teeth and to gently file down as appropriate)

Many thanks,

Richard

Hi Richard,

Welcome to the club.

Don't start filing anything just yet! It's too hard to put all the
little filings back. Gotta be pretty sure that's what you need to do
before getting drastic.

Firstly, I assume you're talking the regular (Sieg style) Chinese
7x12 here? If so, the tailstock has an MT2 taper. So how did you
chuck the centre? It won't sit well in any parallel jawed chuck.
What's the wobble look like if you stick something known to be
cylindrical in there? Say a short water pipe offcut - or a bit of
round bar when your metal arrives.

Even a Philips head screw driver for now. At least they are usually
pretty parallel down to the tip - not like the straight screwdrivers
that have a forged bulge.

Also, remove the chuck (3 awkward nuts at the back of the chuck) and
check all is clean in the recess where the chuck sits on the flange.
I'll bet the flange runs true. Does the chuck face?

John



--- In 7x12minilathe@..., Richard Stevens
<rtjstevens@...> wrote:

Hi, ignorant newbie here; just bought a new 7x12 lathe but as yet

tooling

and metal not arrived -but my dial test indicator has...

I decided to place the Centre from the tailstock into the

headstock chuck

and test. It's a long way out and is visible by the naked eye

alone -

perhaps by 0.5 -10.8mm. Yes I've taken the centre out and

repositioned it

-but still the same.
What's the best advice? (All I could think was to take out the

(numbered)

chuck jaws/teeth and to gently file down as appropriate)

Many thanks,

Richard

Hi Richard,

I'm no expert on the subject, but I would get more info from some
people either at these groups or some websites (i.e. mini-lathe.com
etc.) before you start filing on the jaws individually. If I
understand it correctly, most 3-jaw chucks will show some runout.
Not sure what is considered "acceptable" though. I've seen some
sites where a Dremel type rotary tool is mounted to the tool post to
lightly grind the jaws concentric. Lots of really knowledgable
people in this group and others that will help you out I'm sure.
Just some friendly advice. Good luck.

Frank


--- In 7x12minilathe@..., Richard Stevens
<rtjstevens@...> wrote:

Hi, ignorant newbie here; just bought a new 7x12 lathe but as yet

tooling

and metal not arrived -but my dial test indicator has...

I decided to place the Centre from the tailstock into the

headstock chuck

and test. It's a long way out and is visible by the naked eye

alone -

perhaps by 0.5 -10.8mm. Yes I've taken the centre out and

repositioned it

-but still the same.
What's the best advice? (All I could think was to take out the

(numbered)

chuck jaws/teeth and to gently file down as appropriate)

Many thanks,

Richard

Hi Richard you cant use the tailstock centre as it has an MT2 taper and will not centre properly in the chuck. In the absence of any decent proper round stock (drill rod or similar)a decent 1/2" or so drill bit using the shank would be enough to indicate off.

My lathe out of the box gave <0.01mm (<0.4thou") so theres something seriously wrong if you get 50-100x that!

If you still get those sort of readings It is just possible that the chuck is mismounted so remove it (protect the ways!) any try checking for any swarf or other debris and then remount and try again. Failing that remove the chuck and indicate off the spindle, it is just possible that the bearings are loose.

If it genuinely is that then don't mess with it send the chuck back.

Trying to file the jaws to suit is a no-no, the jaws are hardened so you would ruin your file ant you could not do it with any level of accuracy.

Gerry
Leeds UK

From: Richard Stevens <rtjstevens@...>
Reply-To: 7x12minilathe@...
To: "7x12minilathe@..." <7x12minilathe@...>
Subject: [7x12minilathe] 3-jaw chick out-of-true?
Date: Sat, 03 Mar 2007 08:55:55 +0000

Hi, ignorant newbie here; just bought a new 7x12 lathe but as yet tooling
and metal not arrived -but my dial test indicator has...

I decided to place the Centre from the tailstock into the headstock chuck
and test. It's a long way out and is visible by the naked eye alone -
perhaps by 0.5 -10.8mm. Yes I've taken the centre out and repositioned it
-but still the same.
What's the best advice? (All I could think was to take out the (numbered)
chuck jaws/teeth and to gently file down as appropriate)

Many thanks,

Richard

_________________________________________________________________
Match.com - Click Here To Find Singles In Your Area Today!

Thanks -will try...!

BW
RTJ

There's no way a chuck with parallel jaws will accurately grip a
tapered piece; since the TS center has a tapered shank...

A better test bar is one of the nicely finished, straight rods from a
discarded printer. The stock chucks usually have a few thou of
runout. Some of that can be removed by disassembling the chuck &
deburring the internals. In particular, the jaw "teeth" usually have
significant burrs keeping them from accurately seating against the
scroll. Also, if the jaws don't slide easily in the chuck body,
you'll get significant runout. The body is fileable, the jaws are
hardened & have to be done with an abrasive.

Roy

--- In 7x12minilathe@..., Richard Stevens
<rtjstevens@...> wrote:

Hi, ignorant newbie here; just bought a new 7x12 lathe but as yet

tooling

and metal not arrived -but my dial test indicator has...

I decided to place the Centre from the tailstock into the

headstock chuck

and test. It's a long way out and is visible by the naked eye

alone -

perhaps by 0.5 -10.8mm. Yes I've taken the centre out and

repositioned it

-but still the same.
What's the best advice? (All I could think was to take out the

(numbered)

chuck jaws/teeth and to gently file down as appropriate)

Many thanks,

Richard

--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@...> wrote:

The body is fileable, the jaws are
hardened & have to be done with an abrasive.

Roy

Hi Roy,

Oh no - not another use for the valve grinding paste! Dare I suggest
removing any serious burs with a file and then seating the jaws to the
scroll with a little lapping? I've only just finished lapping my gibs
& dovetails (with stellar results). Now you're hinting at lapping the
3-jaw. And the 4-jaw could run smoother. When will it all end?

John

A chick with three jaws?...now THAT'S scary!!! Best run for the
hills...FAST!...

==============

Now why didn't I spot that? Out of true too. And Roy reckons he can
knock the rough edges off with a file!



--- In 7x12minilathe@..., "markzemanek"
<markzemanek@...> wrote:

A chick with three jaws?...now THAT'S scary!!! Best run for the
hills...FAST!...

==============


--- In 7x12minilathe@..., "born4something" <ajs@>

wrote:

--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@> wrote:

The body is fileable, the jaws are
hardened & have to be done with an abrasive.

Roy

Hi Roy,

Oh no - not another use for the valve grinding paste! Dare I

suggest

removing any serious burs with a file and then seating the jaws

to the

scroll with a little lapping? I've only just finished lapping my

gibs

& dovetails (with stellar results). Now you're hinting at

lapping the

3-jaw. And the 4-jaw could run smoother. When will it all end?

John

i trued my 3 jaw with a dremel tool . took my dremel and jb welded a aluminum block to one side so i couuld mount it on my lathe . then ran my lathe at about 200 or more rpm with the jaws opened and ground the inside legs to true . i found the artical at one of the minilathe sites work great , my jaws were really out of true when i got my lathe

born4something <ajs@...> wrote: --- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@...> wrote:

The body is fileable, the jaws are
hardened & have to be done with an abrasive.

Roy

Hi Roy,

Oh no - not another use for the valve grinding paste! Dare I suggest
removing any serious burs with a file and then seating the jaws to the
scroll with a little lapping? I've only just finished lapping my gibs
& dovetails (with stellar results). Now you're hinting at lapping the
3-jaw. And the 4-jaw could run smoother. When will it all end?

John






---------------------------------
Everyone is raving about the all-new Yahoo! Mail beta.

You don't want to lap the jaws to the scroll. The scroll is actually
a helical shape, so you'd find the contact patch with the jaws moves
as the jaws travel in & out. All you need to do is remove the burrs
from the ends of the jaw teeth & chamfer all the corners. Some
flavor of abrasive tool in a Dremel/Foredom gets it done in short
order. Since the body is "sort of" cast iron, a little work with
rifflers gets the jaw slots trimmed up to allow free sliding.

Roy

--- In 7x12minilathe@..., "born4something" <ajs@...>
wrote:

--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@> wrote:

The body is fileable, the jaws are
hardened & have to be done with an abrasive.

Roy

Hi Roy,

Oh no - not another use for the valve grinding paste! Dare I

suggest

removing any serious burs with a file and then seating the jaws to

the

scroll with a little lapping? I've only just finished lapping my

gibs

& dovetails (with stellar results). Now you're hinting at lapping

the

3-jaw. And the 4-jaw could run smoother. When will it all end?

John

Yup! One of the 14" ones, wielded as a club.

Roy

--- In 7x12minilathe@..., "born4something" <ajs@...>
wrote:

Now why didn't I spot that? Out of true too. And Roy reckons he can
knock the rough edges off with a file!



--- In 7x12minilathe@..., "markzemanek"
<markzemanek@> wrote:

A chick with three jaws?...now THAT'S scary!!! Best run for the
hills...FAST!...

==============


--- In 7x12minilathe@..., "born4something" <ajs@>

wrote:

--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@> wrote:

The body is fileable, the jaws are
hardened & have to be done with an abrasive.

Roy

Hi Roy,

Oh no - not another use for the valve grinding paste! Dare I

suggest

removing any serious burs with a file and then seating the jaws

to the

scroll with a little lapping? I've only just finished lapping

my

gibs

& dovetails (with stellar results). Now you're hinting at

lapping the

3-jaw. And the 4-jaw could run smoother. When will it all end?

John

Hi Roy,

That's a rather valid (and perceptive) point. I'd never realised the
compromises necessary in the spiral scroll design concept. The
spiral radius changes between the inner and outer extremes. On
inspection, the jaws are machined with the tightest radius on the
outer of each tooth and enough slop between teeth that they don't
jam at the outer extremity. From a theoretical standpoint it's ugly
as hell with all the load carried on minimal area for largeer
workpieces. From a pragmatic standpoint, how else do you get the
self tracking convenience?

Good news, NO MORE LAPPING needed, just lube!

John



--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@...> wrote:

You don't want to lap the jaws to the scroll. The scroll is

actually

a helical shape, so you'd find the contact patch with the jaws

moves

as the jaws travel in & out. All you need to do is remove the

burrs

from the ends of the jaw teeth & chamfer all the corners. Some
flavor of abrasive tool in a Dremel/Foredom gets it done in short
order. Since the body is "sort of" cast iron, a little work with
rifflers gets the jaw slots trimmed up to allow free sliding.

Roy

--- In 7x12minilathe@..., "born4something" <ajs@>
wrote:

--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@> wrote:

The body is fileable, the jaws are
hardened & have to be done with an abrasive.

Roy

Hi Roy,

Oh no - not another use for the valve grinding paste! Dare I

suggest

removing any serious burs with a file and then seating the jaws

to

the

scroll with a little lapping? I've only just finished lapping my

gibs

& dovetails (with stellar results). Now you're hinting at

lapping

the

3-jaw. And the 4-jaw could run smoother. When will it all end?

John

G'day John et al.
We now know the blood(y) line of this Three Jaw Chick; she of sired
by Imprecise, out of True.
My wife is a loverly lady (chick) but occasionally she has one jaw
too many, a three jaw chick must be a fearsome beast.

Seriously, Roy's advice is good, there may be the opportunity for a
bit of gentle lapping but certainly no room for the village
blacksmith. We gets what we pay for. Three jaw chucks were only ever
seen as quick and easy for general work; precision requires either
collets or a four jaw chuck with setting up. The most repeatable
means of centering is to work between centres

One good turn deserves another.
Regards,
Ian

--- In 7x12minilathe@..., "born4something" <ajs@...>
wrote:

Hi Roy,

That's a rather valid (and perceptive) point. I'd never realised

the

compromises necessary in the spiral scroll design concept.