Re: [CAD_CAM_EDM_DRO] Re: small spindle ?

I worked for SKF bearing company in research and development a good many
years ago. They make bearings as accurately as they can but most of them
do not meat the very high accuracy they would like. These are the
cheaper bearings for less demanding applications. Inspection determines
the most accurate and all grades in between. By chance and chance
alone (within certain perameters) a small percentage are very accurate
and the larger quantites are of lesser quality. They do everything they
can to insure that the high quality bearings really are high quality and
meet that standard. If you buy high precision bearings it is very
unlikely there will be less quality than advertised.
To stay within even .001 run out on a cutting tool all parts of the
spindle, tool holder, tool must be very accurate likely measured in
Microns or tenths of microns. The good news is it gets easier all the
time to hold these close tolerances with modern machines.
SKF bought a new Landis grinder that was guarenteed to grind
roundness within two tenths of a micron with a micron being 50
millionths or 1/2 of one tenth of a thousandth this was in 1963. I think
these figures are correct but it's been a while? It took Landis about 6
months of tweeking to get the machine to grind to that accuracy. That
lasted only a few months because as the machine wore that accuracy was
lost. I bet those kinds of accuracy are routine today? Doug

On 06/16/2012 08:00 AM, turbulatordude wrote:
>
> Bearings are only 1 part for control of run-out.
> if the bore is not concentric with the balls in the race, that will
> cause run-out.
>
> if the bore is not a perfect fit for the tool shaft, the tool will
> have run-out that has no effect by the bearings.
>
> if the bearings or the housing, get warm and change, that will cause
> run-out.
>
> if the clamping mechanism for the tool takes the tool off center, that
> will cause run-out.
>
> There are some fundamental parts that effect run-out and with some
> care you can make a spindle with run-out of less than 0.001.
>
> the real question is the person selling the parts and their point of
> view. if they make 100 parts and the absolute worst has a run-out of
> 0.0015 and 99 have run-out of 0.0002, do they claim 0.0015"
>
> if they make 99 that are 0.0015 and one that is 0.0002, do they claim
> 0.0002 ?
>
> modern sales would say they have shop-grade and sell at one price and
> then QC grade and sell for more.
>
> Dave
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com
> <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>, Larry Guthrie
> <yrralguthrie@...> wrote:
> >
> > I agree with most but,Â
> >
> >
> > You took my statement out of context. I said if....then..."the run
> out would depend on on the quality of the bearings."Â
> >
> >
> > I've forgotten exactly what I said, but I think I was talking about
> adjusting the play out of the spindle similar to how it is done on a
> high dollar adjustable lathe chuck. Â
> >
> > A lot of your comment was a bit esoteric, considering we are mostly
> talking about a hobby machine with an over all tolerance of maybe .001
> in.Â
> >
> >
> > ljg
> >
> >
> > Â
> > Larry Guthrie
> > yrralguthrie@...
> > larry.guthrie@...
> >
> >
> > ________________________________
> > From: David G. LeVine <dlevine@...>
> > To: CAD_CAM_EDM_DRO@yahoogroups.com
> <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
> > Sent: Tuesday, June 12, 2012 7:41 AM
> > Subject: Re: [CAD_CAM_EDM_DRO] Re: small spindle ?
> >
> >
> > Â
> > On 06/09/2012 05:30 PM, Larry Guthrie wrote:
> > > The runout would depend only on the quality of the bearings.
> >
> > Not true. The shaft also affects runout. Let's start with a simple
> > shaft with a hole and setscrew for 1/8" bits (like a Weldon shank
> > <http://www.tools-n-gizmos.com/specs/Tapers.html>.) If the hole is
> > oversized, the tool will shift during operation and will run out more
> > than the bearings, even if initially the spindle is initially adjusted
> > to zero. If the shaft deflects (bends) due to cutting loads, that shows
> > up as runout, especially if the deflection is permanent. If the shaft
> > wears loose in the bearings, or the bearings wear loose in the bore,
> > that is another static form of runout.
> >
> > Then we get to dynamic runout. If the bearing has zero runout when not
> > moving, the hydrodynamic effects on the lubricant film can change the
> > center. This can be a few millionths to many thousandths. Add in out
> > of round balls or rollers and runout can get pretty bad.
> >
> > > By the way, why aren't spindles made with the outside rectangular?
> They would be much easier to mount.
> >
> > Actually, some spindles are made in rectangular form factors, but they
> > are more expensive. DOM tubing is generally round (or is supposed to be
> > round =-O ) and is cheap for what it is. Making round holes in mounts
> > is easier than making arbitrary shapes. Machining costs money, take a
> > round spindle blank, chuck it in a CNC machine and round bores are
> > easy. Features which are not symmetrical to the main bore are always
> > harder (hence more expensive) to machine.
> >
> > Let's start with two spindles, one hexagonal, one round. Either the hex
> > spindle must be cut from a round blank or the hex blank must be bored
> > out. The round blank can be a simple hollow piece of pipe (or tubing.)
> > Machine the bearing mounts, both need similar amounts of work until
> > internal stresses in the metal do their work. The stresses in the hex
> > are different from those in the round, aging to allow those stresses to
> > be relieved (this can be time or thermal processing or both), costs
> > money. Once the internal stresses are relieved, the spindle must be
> > machined again to final dimensions. Machine any feature and the process
> > may need to be repeated. Metrology is not really a science, it is a
> > black art! And grinding bores is not a trivial task. The issue gets
> > bad quickly if the metal has internal stresses. Check out the bore
> > requirements for precision bearings.
> >
> > Dave 8{)
> >
> > --
> > /"Political Correctness is a doctrine, fostered by a delusional,
> > illogical minority and rabidly promoted by an unscrupulous mainstream
> > media, which holds forth the proposition that it is entirely possible to
> > pick up a turd by the clean end."/
> > (quoted from http://www.wattflyer.com/forums/showthread.php?t=30060)
> >
>
>



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