On 2008-05-02, Joseph Gwinn wrote:
In article ,
"DoN. Nichols" wrote:
On 2008-05-02, Joseph Gwinn wrote:
In article ,
"DoN. Nichols" wrote:
[ ... ]
As am I. I've got the 5418 (similar bed profile, but manual
change belts), and have very little chatter.
[ ... ]
You know -- there is one other possibility which occurs to me.
I presume that your lathe, like mine, has the hollow level adjusting
screws in the feet of the bed through which pass the bolts to lock it
down to the stand. If you have something like the near side bolt loose
and the level adjusting screw a little clear of the stand, the bed would
wind up under torque, which could give you similar behavior.
Do you mean the bolts between cabinet and the floor, or that hold the
headstock to the bed? I assume you mean between headstock and bed.
I see that you figured out what I was talking about from
examining the manual for the 5418. Since I don't have the manual for
yours, I had not realized how different they were.
Ahh. Yes. It will take a while, but I may scan my manual, which does
not appear to be copyrighted.
Hmm ... beware that you can't e-mail it to me. There is a limit
of 30K total size on incoming e-mail, to keep virus infections out of a
couple of small mailing lists which I host. No problem with my systems,
of course -- but I first turned on the limit when I got over 300 copies
of a new spam on the first day, and 200 more on the next day. I forget
what it was, but it was spreading like wildfire, and it took a long time
to clean out my mailbox enough so that I could read valid e-mail.
Did you get a proper sensitive level and adjust the bed to
proper level at both headstock and tailstock end? (I did.)
I do have such a level (Starrett model 98-6), and did level the bed by
adjustment of the leveling feet between cabinet and floor.
Hmm ... not nearly as sensitive. The 98-6 (and the rest of the
98 series) have a sensitivity of 0.005"/foot, while the No. 199 "Master
Precision Level" has a sensitivity 0f 0.0005"/foot -- ten times the
sensitivity. But, of course, the 98-6 gets you close enough if you then
do the "turn two rings on a single bar and measure them" operation
afterwards.
I have not yet done the bar turning test, but intend to, once the more
immediate problems are at least understood if not resolved.
O.K.
I probably should repeat the leveling exercise, as based on the other
kinds of ignorance-induced problems I've already found, it's likely that
the lathe was left unleveled and thus twisted for years, and may have
taken a set that needs to relax out.
Good idea.
[ ... bed twist ... ]
O.K. As long as you are that close, it would not really matter.
Where it would matter is turning some distance from the headstock, or
running something like a 1" drill bit in the tailstock -- especially
with a long workpiece extension from the chuck.
While using the 1" drill, the bed will most certainly wind up a bit. I
guess that what would resist permanent twist would be the leveling, with
the lathe resting on a concrete floor, as it now does.
Better with the near foot on the tailstock end and the back foot
on the headstock end bolted down, even if the other two are not. That
should resist the twist introduced by the drilling.
[ ... ]
O.K. Quite different. The 5418 is supposed to have the cabinet
bolted firmly to the floor (I don't), and the bed leveled relative to
the stand and chip tray.
The 5914 manual also speaks of bolting to the floor, but few people
actually do this I suspect.
Indeed -- unless forced by OSHA inspectors. :-) Now, if I were
doing lots of faceplate work, I would bolt it down just to be sure that
the lathe does not start walking around the shop with a bit of imbalance
on the faceplate. :-)
I looked the the 5418 manual. Now I understand. The designs of 5914
and 5418 are very different in this area. But there is no harm in
making sure that all those bolts are nice and tight, especially those
holding headstock to bed.
Agreed. Check the tailstock end too -- because that is what
would flex when the torque is transmitted from the spindle to the
carriage. It would wind up the bed (a little, at least).
The tailstock now clamps pretty firmly to the bed. This is one of the
first things I cleaned and adjusted, mainly because it was easy and
could be done without the manual.
It was not the tailstock to the bed that I was thinking of. I
was assuming that it would be well clamped, and for turning it would not
make a difference anyway. But bed feet to stand and/or stand to floor
are where the wind-up could be controlled.
BTW For parting there used to be a gooseneck parting tool. It went
in a lantern style toolpost, came out, turned up, formed an
Omega shaped arch, back down to where the parting tool is
actually clamped. The result is that excessive cutting forces
tends to move the tool away from the workpiece, thus eliminating
chatter. But your machine *should* be rigid enough to not need
this, especially with an Aloris style quick-change toolpost, and
the T-profile parting blades.
I vaguely knew (from reading old books) that there was such a tool, and
that it involved a gooseneck, but I had the "picture" upsidedown in my
mind, and couldn't see how it would work. I just googled it, and found
a book from 1910 that explained the principle as applied to use in a
planer. They did understand the self-feeding effect, saying that the
gooseneck would eliminate gouging the work, but a sufficiently rigid
machine didn't need gooseneck tools.
Yep.
http://books.google.com/books?id=Skd...lpg=RA8-PA36&d
q=gooseneck+tool+lathe&source=web&ots=edrQWKc6hu&s ig=QsKeq0Vn7zebOdjC5ydY
KtuqnkA&hl=en#PRA8-PA35,M1
Hmm ... I don't think that I'm going to bother cut-and-pasting
all three chunks of that URL. I know the tool anyway, and see them
occasionally on eBay auctions.
It occurs to me that a negative rake cutting tool could be set up to
develop enough outward force to at least partially counteract the
tendency to self-feed.
Right.
Perhaps this is why one commonly stated cause of
chattering is too-sharp tools. When one carefully blunts such a tool,
one puts a little bit of very negative rake right at the cutting edge.
How much backlash is there in your cross-feed leadscrew? The
self-feed can take the slack out of a worn leadscrew/nut pair. And you
want the cross-slide gibs to have a bit of drag, too.
[ ... ]
Hmm ... another thing to check. While you have chatter, see
whether there is any relative motion between the headstock and the bed.
If it is not clamped down firmly enough, or if there are chips trapped
between the headstock and the bed, that could introduce enough give to
create problems.
Hmm. Offhand, I don't see any safe way to do this, as my hand would
need to be very close to the spinning chuck, or to various gears and the
like.
There is space where the outer ways stick out from under the
headstock (which is clamped to the inner ways) and you should be able to
check back along the near side far enough to be clear of the chuck.
I think I'll just torque all the clamp bolts, to see if any are loose.
O.K. That will deal with loose bolts, though not with chips.
I doubt that the headstock was ever unbolted, at least not by the people
who caused all the ignorance-induced problems. Taking the headstock off
would have frightened them, at least one fondly hopes that it would. In
any event, chips can only get in there is the headstock is unbolted.
Well ... you have the lathe in your basement I believe? Some
people disassemble the lathe to several heavy components and take each
down separately. If you didn't, perhaps someone else did previously.
The headstock is located on the bed ways by careful fitting of headstock
bottom to ways, plus a pair of steel dowel pins to prevent sliding.
O.K. Mine has one taper pin, not two dowel pins.
Unlike the 5418 manual, in the 5914 manual, there is no
procedure for adjusting how the cast iron stuff rests upon the sheet
metal stuff.
O.K. This assumes that the sheet metal stuff is rigidly bolted
to the floor, I guess.
That would make sense. In the 5914, these adjustments have moved to the
cabinet-floor feet.
O.K. This produces fewer paths for swarf to get down into the
drawers and the motor/pulley assembly in the pedestals.
Enjoy,
DoN.
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