The drive center in my lathe always seems to tighten in too well. It
takes far too much force to pop it back out. On occasion, I've had to
resort to turning it with a pipe wrench before it would pop out. I
originally thought I did something wrong, cranked in too hard on the
tail stock, but it keeps happening. It has to friction fit or it won't
turn anything, though. Any ideas?
Heating the spindle is a bad idea. In any case, it would get to be a real
pain pulling out the torch every time you wanted to change centers. It
should be tight. Use a heavy bar through the spinle for a knockout and it
should pop right out. The knockout bar is far more effective than a wrench.
Is your lathe spindle hollow (mine is)? A long rod and a few
good swats have always worked for me.
(top posted for your convenience)
Keep the whole world singing . . . .
DanG (remove the sevens)
I hade the same problem with one of the lathes in my high school wood shop.
The problem was short drive center. The center was made shorter by students
hitting the center with a metal hammer, mushrooming and shortening the
center length. When the center was inserted into the tail stock it would be
to short to bottom out as the tail stock hand wheel was backed off. I
disassembled the tail stock, removed the stuck drive center. I then had the
metals teacher build up a weld on the drive center, ground to shape.
Problem solved. Student know better than to use a metal hammer but doesn't
I do have a knock out bar & yes, the shaft is hollow - it's a year old
14" Delta lathe & it comes with a light, steel bar with a plastic knob
at one end. It works, but only if I've turned for a short length of
time & haven't tightened the tailstock much at all. Otherwise, I have
to lock the head, start cranking with the wrench & hit at the same
time. It didn't start out this tight, but seems to have gotten
tighter. The amount of force needed just isn't right. When the center
pops out, it's like a bullet.
High Score, Thanks for the idea on the heat, but I'd rather not. Can't
imagine that would be good for it. Might peel the finish & let it
rust, not to mention all the sawdust around.
I've only been using a lathe for 2 years & my first one was a cheap HF
one that I hated. Still, it didn't have this problem. I'm thinking I'm
doing something dumb - I usually turn bowls, so this doesn't come up
often. What about a few drops of oil?
brid, The typing paper would wrap around the shaft? Could you expand
Again, thanks for the ideas. - Jim
I know I get a little lazy sometimes and drive in the center with a
ball-peen hammer instead of looking for a wodden mallet, and the end
of the spur gets a bit mushroomed. I just grind a little of the burr
off on the belt sander, and it works like a charm again. Obviously,
this isn't the best thing to be doing, but it sure beats buying a new
Aut inveniam viam aut faciam
You gall the center? That's the only thing I've ever had problems with. If
so, clean the surfaces up with some 400 wet/dry and lap the interior with
I imagine the paper would bridge the worst of any galling.
I think the best knock out rod is brass (it is more dense than steel by a
considerable margin). I have always just thrown the rod down the headstock
hole to release the drive center. A longer rod will help also. Of course
you will want one hand on the center to keep it from dropping and getting
Check the condition of it. Then maybe fix it, or even buy a better
one. A 2-prong is a useful upgrade over a 4 prong anyway.
Centres are driven out from the back, so a good one has a small
reduced diameter section here. If there's any burring, then it doesn't
cause a jam. Burred centres don't locate accurately or grip well
unless you drive them in hard, and that obviously makes them hard to
extract. Cheap ones don't always do this, or they just have a small
chamfer. Take an angle grinder and turn a small reduced teenon onto
the back of it.
There's also the question of hardness. A good centre has quite hard
surfaces to the Morse taper. If it's too soft, then it's too "grabby"
and also becomes hard to extract. A Morse taper relies on an accurate
fit and little deformation of the centre - once you've knocked it ever
so slightly loose of the taper's grip, it comes completely free.
It came stock with the machine, so it probably is a cheap one. I'll
see if there's galling, but I've checked for that a while back & don't
believe there is. I haven't tried grinding a taper on or cleaning it
with 400 grit sandpaper. I'll try those to see if it helps, but cheap
& soft is probably the problem, so I will buy a new one.
Thanks to all for all the ideas.
Jim, I have the same lathe. Never heat or twist the spur to remove it. If
you clean it up and remove all of the galling from both the headstock and
the spur, re-install it with only a light tap from a wood mallet or scrap.
If it fits properly it will hold very well. In addition, if you
over-tighten the tailstock center, it will force the spur to deep as well.
Bottom line, a Morse taper get its holding power from slightly different
tapers. A light touch in installing is all that is required.
Morse Tapers, a known as a slow release taper, have 8 different tapers,
mostly 5/8 inch per foot. A #2 Morse has a taper of .049950 minor size is
.5720 and the major is .700 As these self centering tapers meet, the two
gradual tapers join in slightly different points creating a wedge.
Simple answer is above.
I think his point was that the tapers aren't different; as you point
out, the tapers are the same. At any given station through a male and
a female MT, the diameters are identical if they are in contact, and
not identical if they're not, which is a paraphrasing of your point.
But the taper (the rate of change in diameter) is the same, which was
You're both right, just expressed it differently (and ambiguously).
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