Newsgroups: rec.crafts.metalworking
Subject: Re: Cast Iron Warpage ?
From: Robert Bastow <teenut@home.com>
Date: Thu, 30 Sep 1999 06:40:25 GMT

That is a good question Mike.

There is a tendency to imagine that our machine tools are as solid and immovable
as the Rock of Gibraltar.  But it just isn't so!

It wouldn't take a great deal of instrumentation to demonstrate that the weight
of a medium sized dividing head or a large machine vice will cause a measurable
deflection on the structure of even a quite heavily built milling machine.

Yes, those deflections can become permanent! I have seen Bridgeport tables with
.020" plus of permanent bow in them due to the practice of mounting a dividing
head at one end and a large vice at the other.

I almost bought a large jointer once (12" industrial, heavyweight dude) until,
upon arriving to inspect the machine at the used M/c tool dealer's, I noticed
that a large disc grinder was sitting on the out feed table, both covered with
equal amounts of dust.  

Upon removal and close (eyeball) inspection, it was obvious that the outfeed
table was permanently bowed a good 1/4" (Bowed as in curved..not sagging on the
dovetail slides..the infeed table was as flat as the day it was made!!)

Cast Iron is deceptive stuff..it has the appearance and reputation of the Rock
of Ages!!  Wonderful, irreplaceable, stuff as it is for machine tools...rigid it
ain't!!

Bottom line..We need to put heavy weights on our machines..and work around the
deflections..but don't leave them there for extended periods.

teenut

mike II wrote:
> 
> Once finances allow, I'd like to get a dividing head to keep the small
> rotary table company. Is it normal practice to keep these rather heavy
> dividing heads on the milling machine or would that cause the table to
> eventually warp? The more I read about seemingly rock-stable materials
> like metals, the more un-rock-stable they appear.
> 
> Semi-Mandatory RCM ENGINE content:
> 
> I've heard of cast car cranks having to be stored upright on their
> ends so that warpage does not occur, but for all I know that MAY be
> just an 'urban myth'...
> 
> mike

Newsgroups: rec.crafts.metalworking
Subject: Re: Cast Iron Warpage ?
From: Robert Bastow <teenut@home.com>
Date: Thu, 30 Sep 1999 12:53:12 GMT

I don't think you need worry about a large vice in the middle of your table
Eddy.  Especially on a Mill/Drill type machine which has solid support at that
point.

The references I made were to cantilevered loads..say a large vice at one end
and a large dividing head at the other end of a long table..say on a Bridgeport
type machine.

I have a large (6" Kurt)vice for my Deckel..for use when required..but it
doesn't stay there any longer than required.  Fortunately, most of my work can
be handled by the smaller 4" vice that came with the machine.

I think it may help people to understand that cast iron falls *roughly* half way
between aluminum and steel in terms of "rigidity".**

**Based on Modulus of Elasticity..(Youngs Modulus) of 30x10 to 6th for steel and
its alloys, 10 to 11 x 10-6 for aluminum and cast iron which ranges from 12 to
19 x 10-6 depending on class.

No machine tool is totally rigid...I have to remember not to lean on the
tailstock of my lathe when doing a finishing cut..otherwise the taper is
measurable!!

My Apprentice superintendent used to clip me round the ear for leaning on the
lathe...I thought it was for "Idling" until he explained the above to me
(graphically I might add!!)  So I leaned on my tool locker..he clipped me
again..this time it WAS for "idling"!!

teenut

As an aside..How DOES one write 30x 10 to the power of 6 on a keyboard that
won't put the 6 "upstairs"   Is there a convention?

Eddy Wells wrote:
> 
> Robert,
> 
> That's a new one, to me....
> 
> I have a 6" BP vice I leave on my import
> mill/drill.(in the middle of the table)
> 
> You say that's a bad idea ?? NOW what am I
> going to do ??
> 
> Eddy Wells