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the geometry tests would be checking the saddle to bed alignment, then the
is checked using the saddle as a base. I've heard that somewhere before
then the tailstock is aligned to center with spindle. The saddle can wear
quite a bit more than the
ways, very common. The temperature in the shop can effect the twist of the
I would run an indicator on the saddle with the compound removed checking
the outside ways in the
area you mentioned Mark and map the drop on the side of the lower V so you
can see if it is indeed
low from wear. You can compensate some of this by twisting. Using a larger
bar for test cuts is for
reduced movement from tool pressure as is a lighter cut. headstock bearing
wear can also effect movement
of the test bar.
With an indicator on the good test bar in a four jaw with the piece dialed
in, run the indicator down the
bar with the saddle with the headstock bolts just barely snug. tighten
each clamp evenly watching the test indicator
and adjust the bolts for the best indicator reading as you tighten. do
this before twisting the bed. Twist the bed by
test cuts. remember the bed may still move more after twisting depending on
temperature, the next day you might have to back it off a bit.
----- Original Message -----
Sent: Tuesday, March 11, 2014 3:46
Subject: Re: [SOUTHBENDLATHE] Head stock
"PS He more or less managed to twist the bed in a way that would
practically eliminate the taper. Therefore, the lathe could have passed
inspection that way."
NO WAY !
The first thing the tester did was level the bed, then perform the
geometry tests. The cutting tests were next(chatter test and 2 collar
It is more likely that, instead of cutting a nice taper you'd end up more
or less with a two diameters piece, with an abrupt change in diameter when
the carbide tool starts to bite into the piece (cutting from tailstock to
headstock) or starts gliding over the surface (cutting the opposite
I don't think Mark has mentioned anywhere that he has used a
Anyhow, hopefully we haven't been very successful in
scaring Mark away and I hope that he will intervene in the discussion by
filling in with missing details.
PS He more or less
managed to twist the bed in a way that would practically eliminate the
taper. Therefore, the lathe could have passed inspection that
On 03/11/2014 02:48 PM, Jim B. wrote:
I do know that, (from my sad
experience) trying to cut an unsupported 6”, or even a 4” length, with a
carbide tool, using a light cut will result in a taper.
Carbide, unless you take the time to
hone/polish it, should not be used for light cuts. It just skims over the
A nice sharp, polished HSS tool, with
a rounded point might be OK.
I agree that we miss a few details (e.g.
material of the bar, etc.), but by the overall description that Mark gave
in his original post, I have the impression that he knows at least the
basics (light cuts, not a really skinny test piece, etc.).
least for me it would be quite challenging to be able to remove such a
strong taper and cutting true the whole 5-6" if the taper were mostly
caused by a lousy cutting setup.