On Thu, 19 May 2005 21:37:22 -0700, "Harold and Susan Vordos"
wrote:
"Tom" wrote in message
...
Harold and Susan Vordos wrote:
"Tom" wrote in message
...
Harold and Susan Vordos wrote:
"Tom" wrote in message
...
snip----
Harold, what's this I hear you're reluctant to put Colchester
bearings
in your Graziano? :-) Graziano thought they were good enough..
Tom
Chuckle! Not really reluctant. Just too poor. Mind you, I have
no
quarrel with Gamet bearings (which is what Colchester used).
This
old
retired dude is looking for something more affordable, but I
wouldn't
hesitate to buy the Gamet variety if all else fails. The
original
bearings served me well----and owe me nothing. They're still very
serviceable, but I'd like to eliminate the .0002" runout that I
didn't
used
to have. Many think it's no big deal, and I can't argue with them,
but
when you know it can be better, it's hard to ignore.
The number of jobs I ran with only a couple tenths tolerance are
hard to
forget. I've always considered myself a good lathe hand, but not
good
enough to work without a tolerance! :-)
Larry Jaques suggested I'd have a hard time putting anything on Mars
with
that much runout. If I can't trust Larry, who can I trust? g
Harold
It's like owning a Ferrari, generic parts don't exist,
so one has to suck up the damage to one's wallet. :-(
BTW, Colchester use Gamet bearings because they own them.
They don't come cheap for Colchesters either.
Tom
Yeah, I was surprised to find they weren't French owned. The name is a
real sleeper.
I learned it's a good idea to shop----the latest contact was
considerably
lower in price than I had been quoted before. Gunner really came
through.
The supplier is checking to see if there are any substitutes, but I'm
not
holding my breath. The thought was to get away from the high speed
bearings.
My machine runs at only 29% of the speed ratings of the Gamet bearings.
Could be I could use an angular contact bearing in place of the
originals.
Could be I'd be asking for trouble, too. Any thoughts on that idea?
Harold
I'd be very surprised if you'd get angular contact bearings that
would fit the Gamet bearing dimensions and still compare load rating
wise. How are yours preloaded?
Tom
I've never had the headstock apart, but from indications, there's a threaded
collar that establishes preload. Problem is, the manual doesn't address
assembly, just shows the exploded view, and so far I've found nothing that
indicates preload values of any kind. The main bearing is a double row
opposed roller type, with split inner races. I can't help but think that
going to a ball type would sacrifice load capacity. One of the things
I've given some thought to is adjusting the bearing ever so slightly, with
the idea that it might have worn enough to be slack. Question is, how much?
If that worked, I'd have no need to change out the bearings. I'd like
that!
Maybe I should touch base with someone that has been there, done that. I
hate to run blind on something of this nature. Ignorance can get real
expensive.
Harold
You can adjust preload? Then by all means do so. Put a dial
indicator on the side of the spindle and with a 2' bar in the spindle
bore, apply a bit of side to side pressure and tighten up the preload
collor a tinsey bit until the indicator shows minimal movement In BOTH
directions. And I mean tiny wheenit itsybitsy tightening each time.
Run the spindle at 2000 rpm for 30 minutes and see if there is any
unusual heating of the headstock over the bearing location (check
temps now before doing this as a reference.
But personally..I think you are guilding the lilly at .0002 backlash.
Btw..is that TIR? .0001 each way, or .0002 each way?
Also..did you measure the backlash cold, or warm? Makes a huge
difference.
Gunner
"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.
Think of it as having your older brother knock the **** out of you
for torturing the cat." Gunner
|