Re: Quil Bearings.

"Harrison, Doug" wrote:

> From: "Harrison, Doug" <dharrison@...>
>
> > -----Original Message-----
> > From: Paul Corner [SMTP:Paul.Corner@...]
> > Sent: Monday, January 10, 2000 5:55 PM
> > To: CAD_CAM_EDM_DRO@onelist.com
> > Subject: [CAD_CAM_EDM_DRO] Quil Bearings.
> >
> > From: Paul Corner <Paul.Corner@...>
> >
> >
> > A quick Question for the machine tool experts.
> >
> > How much radial play if any is acceptable in the quil bearings ?
> >
> > I had a DTI on the side of the collet chuck, and got a reading of one thou
> > or
> > 0.025 mm. Could it be my bearings are on the way out, if so, the EMC
> > upgrade
> > will have to wait until I've recovered from the fee Bridgeport will charge
> > - I
> > doubt it will be cheap.
> >
> > Regards, Paul.
> >
> Did you have the indicator clamped to the quill or to the head? The
> quil in a bridgeport can deflect in its bore by that much. You might have
> been measuring quill-to-head play and not bearing play. Just a guess.

I took great care to do these measurements when I put a J head on my
antique round-ram Bridgeport. Even though the quill looks like somebody
used an air chisel on it, it still is an extremely close fit, and I was unable to
detect any deflection at all, even at 50 Lbs side force. (I get about .001"
deflection of the entire head at 50 Lbs.) At the spindle, I get about .0005"
or so deflection, measured directly on the spindle nose. This is mostly
squeezing out the lube film on one side of the bearings. You can tell, because
the deflection cause by side force will not return until you apply some force
in the opposite direction. That is characteristic of fluids, not metal deflection.

Now, these measurements won't tell you about your machine. So, first, as
Doug suggests, try to isolate the spindle deflection from the quill+head
deflection, and measure as close to the quill nosecap as possible. Spindle
bending is pretty small on the J head, but the more moment arm you use,
the larger it looks, by the lever effect. How much side force are you
applying? 50 Lbs is a good number (and a lot less than moderate cutting
forces).

Finally, before ordering bearings, make sure the quill nose cap is tight.
They can come loose. There is a setscrew on the backside of the quill
that is supposed to sit in a dimple in the threads of the nose cap, to
keep it from unscrewing. The machine will definitely get loose if the cap
starts to loosen, as that is what provides the bearing preload. The setscrew
should not be very tight, as that distorts the quill, and causes jamming.

Does oil drip out of the spindle, and do you have to wipe the spindle nose
off before starting the machine? If not, then oil is not making it down to
the bearings. There is a big oil cup on the side of the head, and it has a
material like a pipe cleaner to wick oil out along a tube, and drip it into
the open top end of the quill. (The small oil cup is for the backgear.)
If the pipecleaner is mangled, the oil may be dripping in the wrong place.
If the bearings are dry, you will get more clearance (and, of course,
it will get worse).

Jon