On 2008-05-02, Joseph Gwinn wrote:
In article ,
"DoN. Nichols" wrote:
On 2008-05-01, Jon Elson wrote:
Joseph Gwinn wrote:
I think I've figured out a big piece of the mystery of what I
generically called chatter in the "Clausing 5914 Chatter ..." threads.
[ ... ]
I had some real problems doing these types of operations on
Atlas/Craftsman lathes. The 5914 is a MUCH sturdier lathe with
a much heavier bed casting, so I'm surprised you were having
this sort of trouble.
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.
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.
After that,
did you make sure that the hold-down bolts were tight (and didn't
disturb the leveling)? *This* may be where your flex is -- especially
since you have a longer bed than I do (I believe), and thus more total
flex possibility.
Hmm. This I did not think of, or check. But I will.
I don't see why bed length would matter, given that while trepanning all
the action happens within a foot of the chuck face.
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.
Get it chattering and feel each foot with the adjacent finger on
the stand so you can detect relative motion between them. If you find
any, you'll need to tighten the hold-down bolts, and probably re-level
the bed.
What I'm not quite sure of is which bolts you mean. On the 5914, the
headstock is bolted to the bed with four solid 3/8-16 hex socket cap
screws and two clamp bars, and the bed is bolted to the head pedestal
foot, which is in turn bolted to the cabinet, all with solid
non-adjustable bolts. The only hollow bolts I know of are in the
leveling feet between cabinet and floor, which doesn't seem relevant to
chatter (versus inability to turn a cylinder due to bed twist).
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.
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).
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 suspect that on the 5914 they just machined the mating surfaces of
cast iron components close enough that adjustment wasn't needed, and
that the two pedestal feet isolated the bed and headstock sufficiently
from the sheet metal cabinet and chip pan that adjusters were not
needed.
Perhaps the bed feet were machined flat on the bottom, then
bolted to a thick flat plate (say 4" thick or so), machined flat on the
top, the bed mounted on this, and the ways finish-ground this way, so it
could get all the twist out of the bed by adjusting the cabinet feet.
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.
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.
Good Luck,
DoN.
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