On 2016-11-29, Bob La Londe wrote:
"DoN. Nichols" wrote in message
...
On 2016-11-28, Bob La Londe wrote:
Well, I just had my first failure with my PM 1440. The cam-lock on the
tailstock broke. This lathe has been just so amazing compared to my
other
Chinese lathes that I got my feelings hurt. LOL.
[ ... ]
This brings us to failure number two. After I put it back together I
threw
a piece of stock in the chuck and turned a point to align the tailstock
to.
Then I threw a dead center in the tail stock and started lining up the
points. When I got out my loupe I found the center was blunt. Looked
like
[ ... ]
so maybe that's the norm. I don't know. Both centers came with the lathe
so
perhaps they are just lower grade Chinese parts. Do all dead centers
have a
domed tip when looked at under a glass?
Well ... there are hardened centers, designed to go in the
tailstock, and mild centers, designed to go in the headstock and be
trued up before use. The hardened centers are more likely to have good
sharp tips.
I don't think eaither dead center I have is hardened. I may just have to go
out and spend a 3 dollars on one. There are times when I really need a dead
decenter rather than a live center for turning.
BTW -- at one time, a "live center" was simply the rotating
center in the headstock spindle, and the dead was one in the tailstock.
They were otherwise identical -- if the same Morse taper. Once we
started getting centers mounted in bearings so they could rotate in the
tailstock, the name drifted.
And the "live" one in the spindle was typically soft so it could
be trued *just* before mounting the workpiece. The "dead" one in the
tailstock was more likely to be hardened.
And have you ever seen a "half center"? A hardened center for
the tailstock with almost half of the diameter ground off so a facing
tool could get to the center hole to finish the end of a shaft. I've
got one of those -- but too small for my main lathe. Nice for doing
things that the ball bearing center won't allow.
But remember -- the center drills are designed to drill a small
hole followed by a 60 degree countersink so the point normally floats in
air -- or in whatever lubricant you may have put in the center hole. :-)
But... But... But... I might forget.
In which case, let it remind you. :-)
Old lathes tended to have a cavity in the casting near the front
where the ram comes out, and a plug/dipper in there. It used to be
filled with white lead to use as a high-pressure lubricant for the dead
center -- before the world got scared to death of lead and mercury. :-)
As an alternative way to center the tailstock -- do you have a
Blake Coax or one of the import clones thereof?
Crap clone. And a couple Last Words and an inspection mirror as an
alternative.
O.K. So you have those as an option.
If so, put the shank of
the coax in a collet or in the chuck (collet is better, if you have
them), and set the finger to either trace the ID of the Morse taper
socket in the tailstock ram -- or put the center in and trace on the OD
of it. Set the spindle to a slow speed (back gear) and adjust the
tailstock to minimize the wiggle of the needle. Note that some lathes
when new come with the tailstock just a little above center, so as the
tailstock wears, it first gets closer to center before it starts getting
worse, so you proably won't be able to find a truly wiggle free position.
I may try the pinched plate method just to see how it compares for results.
I didn't mention the pinched plate because of the questionable
state of your centers. I first learned about that in the manual for a
Unimat SL-1000 (where the headstock rotated instead of the tailstock
offset for turning long tapers). And they showed a double-edge razor
blade as the pinched plate. I often use a 6" scale for quick-and-dirty
center checking.
Enjoy,
DoN.
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