Newsgroups: rec.crafts.metalworking
Subject: Re: Set up and levelling
From: Robert Bastow <Teenut@hotmail.com>
Date: Fri, 05 Feb 1999 20:16:08 GMT

In the FINAL analysis you can't.  But you can go along way to having a good
understanding.

The turning test is the final "proof of the pudding"  In my time I have
installed scores of lathes and other machine tools.  Yes, we would go throught
all the static tests with sensitive levels and test bars etc.  But I never once
yet met a machine shop owner or plant manager sign off on a machine and accept
the invoice, without seing it "Cut Metal"

The tendence is, as home shop machinists, especially people new to the business,
to think that a lathe, because it is "heavy" and made out of "Metal" is a rigid
chunk. That  the only difference between "Static" and "Dynamic" is "Movement". 
Nothing could be further from the truth.

First of all, there is nothing that is perfectly flat,level, round, rigid,
square or straight.  It is all degrees of the above.  In real terms, the bed of
a typical HSM lathe is aboud as rigid as a wet noodle.

I have learned not to stick my neck out here, even to play "devils advocate" 
But am as sure as I can be that if you were to set up a brand new example of
such a lathe,to be perfectly level and statically aligned, you would be left
wondering where the problem was when you did a machining test!

Why?  A ton of reasons.  Differential expansion of the headstock and PART of the
bed as things warm up.  Twisting of the bed as you tighten the tailstock down. 
Even more twisting as the carriage with its lop-sided weight and offset thrust
vectors starts traversing down the bed.

Can you stop this?   No!

Can you work around it?  Definitely!  Just a tweak of the cross level may bring
the "Cut Metal" result WITHIN ACCEPTABLE PARAMETERS!!!

What are those parameters?   You tell me, it's your lathe and you are paying the
tab.

Press hard..You're making three copies!  ;^)

Robert Bastow

J. Reid wrote:
 
> Yes lots of things interact.  So how to tell if problems are caused by way
> twist or wear,headstock cant or tailstock centering?
> Can these effects offset each other in the test operation but cause
> trouble later?
> 
> On Wed, 3 Feb 1999, Robert Bastow wrote:
> 
> > I have to second Jims thoughts on this..level is nice, but it is
> > TURNING results that count in the end.
> > 
> > You can set up to levels and test bars all day long..  but until you
> > cut metal and measure THOSE results you truly have nothing but a guess
> > and by golly as to how all the different bits interact DYNAMICALLY!
> >
> > Robert Bastow
> >
> >
> > > I just use a 6 inch carpenter's level when I start to set machines
> > > up.  Just because I don't like the tools rolling around in the chip
> > > pan.  After that, I use the collars on the test bar.
> > >
> > > Have fun with your new toy!
> > >
> > > Jim

Newsgroups: rec.crafts.metalworking
Subject: Re: Why are my bored holes tapered?
From: Robert Bastow <Teenut@hotmail.com>
Date: Sat, 06 Feb 1999 16:21:24 GMT

This is what I refered to in my recent post on setting up.

Because of inevitable clearances and thrust vectors working in differnt
ways...if you think about it..it is virtually impossible for a lathe to both
turn an o/d AND bore a hole that are both dead nuts.  The age condition setup
etc., only determine the DEGREE to which this becomes a problem.

As I said before, it is a compromise, and a compromise that only you can
determine.

My lathe is pretty "tight" and I have chosen to set it up so that it will bore
"dead nuts" at the expense of having it cut an external taper of 0.0001 to
0.0003" on an unsupported external diameter of about 3"in length.

This is the maximum length that I am likely to cut without tailstock support. 
Anything longer gets it, as does anything shorter, if it is thin and/or I need 
more accuracy.

My philosophy on this, is simply that it is more difficult to correct a tapered
bore, and a few rubs with emery paper will easily take off  a few tenths of
external taper.  Likewise you CANNOT use T/S support to correct internal taper.

Yer pays yer money, yer takes yer choice!!


Robert Bastow

Larry Meile wrote:
 
> I have an old Atlas 6" engine lathe with flat ways and plain bearings.
> When I turn an outside diameter, I can get a six-inch or so cylinder
> that is within a thousandth.  If I mount a boring bar on the toolpost
> and turn an inside diameter, it ends up tapered with the mouth about
> three thousandths larger than the bottom of the hole.
> 
> I have checked:
>    Play in the bearings.  A dial indicator shows no visible slop on a
> bar clamped in the chuck.
>    Play in the apron.  A thousandth or two might show up here under
> moderate (cutting) load.  However, both cuts are taken in the same
> direction.
>    Boring bar interference.  I thought perhaps the boring bar had i
> nsufficient clearance so that it was being deflected by the hole as
> it entered the cut.  This does not seem to be the case.
> 
> What have I overlooked?

Newsgroups: rec.crafts.metalworking
Subject: Re: Test Bars Sag
From: Robert Bastow <Teenut@hotmail.com>
Date: Mon, 08 Feb 1999 16:59:47 GMT

For this reason "Real" test bars are not solid.  They are drilled out with a
series of decreasing diameter drills, right up to the start of the taper shank. 
Thus they retain maximum stiffness with minimum weight.

A plug is then shrunk in the open end, before machining, heat treatment and
finish grinding.

Robert Bastow


Eric Taylor wrote:
 
> Connelly, in Machine Tool Reconditioning, says that a 1" x 12" steel
> test bar, clamped at one end, will sag .00038" at the other end. I
> need to figure the sag for other lengths and diameters. Specifically
> right now,  it's for my HF7x10, whose max chuck swallowing capacity is
> 5/8". Would anyone know the general equation for sag, or simply (I can
> use Connelly's figure a starting point) how the sag changes  as a
> function of length and diameter (exponential, square, cube, or ?)
> 
> Thanks very much for any help.
> 
> Eric

From: Robert Bastow <"teenut"@ hotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Floor mounting
Date: Thu, 02 Mar 2000 05:02:00 GMT

No. Certain larger machine tools..lathes, floor borers etc rely on very accurate
leveling and a special concrete floor/foundation, as part of their "Structure"
They are levelled, bolted and grouted in.

A lot of older machines were lightly built by today's standards and had to be
bolted down to give the needed rigidity.

OTOH modern tools tend towards much more massive and rigid steel box weldments
or castings and can happily function at an angle of 45 deg to level!!

The Fadal VMC I am expecting shortly is simply plonked on resiliant pads.

teenut

RobHarMill wrote:

> >Subject: Re: Floor mounting
> >From: Robert Bastow "teenut"@hotmail.com
> >Date: 2/29/00 11:01 PM Eastern
>
> >The only machine lagged to the floor in my 8000 sq ft Tool and Die
> >shop, is an ancient wide belt sander, that tends to fall over if you
> >bear down too hard on it!
>
> question--- is this the only reason (instability) that you bolt any machine
> down?

From: Robert Bastow <"teenut"@ hotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Floor mounting
Date: Thu, 02 Mar 2000 05:07:59 GMT

Not unless I am installing a 30 foot floor borer..then I rent an aouto
collimator..haven't done that in years (Hope never to do it again!!)

I have a Moore & Wright "Precision" Level..good for about .0005" per foot, and
that does for me.

As I have previously stated: So long as it doesn't look crooked from across the
room, and so long as the oil and coolant levels are draining the right way, I
don't pay in-ordinate attention to "Dead Level"

It is simply a means to get things reasonably close..befor doing test bar and
turning tests.

teenut

George Glines wrote:

> teenut,
>
> Do you use those fancy and expensive machine levelers or ???
>
> Thanks,
>
> George