Re: small spindle ?

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, Larry Guthrie <yrralguthrie@...> wrote:
>
> I agree with most  but, 
>
>
> You took my statement out of context.  I said if....then..."the run out would depend on on the quality of the bearings." 
>
>
> 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.  
>
> 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. 
>
>
> ljg
>
>
>  
> Larry Guthrie
> yrralguthrie@...
> larry.guthrie@...
>
>
> ________________________________
> From: David G. LeVine <dlevine@...>
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Sent: Tuesday, June 12, 2012 7:41 AM
> Subject: Re: [CAD_CAM_EDM_DRO] Re: small spindle ?
>
>
>  
> 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)
>