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Posted by Joseph Gwinn on April 7, 2008, 10:10 pm
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> I have a 5914 that shakes hard with a cut off blade.
> I am tense, and when the shaking causes something to fall over in the
> pan of the lathe, I just about jump out of my skin.
I burned those nerves out long ago.
The cutoff has made sharp bang noises, to the point I thought something
must have broken, but no damage ever found. I think it was passing a
lump of chips, apparently because the tool was cutting on the side
because the toolpost had rotated.
I also had it stall the workpiece in the 3-jaw chuck, which did not
stop. Very dramatic. I backed off, then resumed cutting off. The
workpiece now wobbled a bit, but the cutoff succeeded without further
drama. I must have pushed too hard, but I'm getting the feel.
I buy used tool bits cheap, precisely so I don't need to cry when I
break something. My objective is to not break the lathe, but all else
is open season.
> I now hack saw off pieces and then face it with the lathe.
But I'm stubborn, and am using cutoffs as a way to uncover accumulated
problems, so they can be fixed. If the lathe can part off, everything
else will work.
This is an industrial lathe, and would have been laughed off the planet
if it were unable to part off. So if it cannot now do cutoffs,
something is wrong and ought to be fixed.
Joe Gwinn
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Posted by Joseph Gwinn on April 8, 2008, 9:21 am
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> On Mon, 07 Apr 2008 22:10:04 -0400, Joseph Gwinn
>
> >
> >> I have a 5914 that shakes hard with a cut off blade.
> >> I am tense, and when the shaking causes something to fall over in the
> >> pan of the lathe, I just about jump out of my skin.
> >
> >I burned those nerves out long ago.
> >
> >The cutoff has made sharp bang noises, to the point I thought something
> >must have broken, but no damage ever found. I think it was passing a
> >lump of chips, apparently because the tool was cutting on the side
> >because the toolpost had rotated.
>
> The banging noises come from the workpiece loading up, jamming in the
> work, then coming free again. Push harder, or a smidge less.
That was my guess. The sidewalls of the groove are ragged and galled,
which is a clue.
Need to find the optimum degree of push.
> Proper
> tool nose geometry is essential. Grind it in a pickle fork
> configuration, with a chip breaker in the middle.
> Going in with a flat bladed "chisel" on a smallish lathe is
> problematic.
The top of the T is scooped, but gently. The blade is 1/8" wide by
11/16" deep. I'll have to try putting a narrow groove in the center,
using a Dremel tool. Need to make sure the center can still cut,
though, as there would otherwise be no place for the resulting disk to
go.
Some of the carbide inserts used for cutting off also have this
geometry. I recall that the Manchester ones do, from the photos in the
J&L catalog.
> >I also had it stall the workpiece in the 3-jaw chuck, which did not
> >stop. Very dramatic. I backed off, then resumed cutting off. The
> >workpiece now wobbled a bit, but the cutoff succeeded without further
> >drama. I must have pushed too hard, but I'm getting the feel.
>
> Check center height. You must be DEAD NUTs and on center.
It was right on. Think it still is. Will check, though this has not
tended to drift.
> >I buy used tool bits cheap, precisely so I don't need to cry when I
> >break something. My objective is to not break the lathe, but all else
> >is open season.
> >
> >
> >> I now hack saw off pieces and then face it with the lathe.
> >
> >But I'm stubborn, and am using cutoffs as a way to uncover accumulated
> >problems, so they can be fixed. If the lathe can part off, everything
> >else will work.
> >
> >This is an industrial lathe, and would have been laughed off the planet
> >if it were unable to part off. So if it cannot now do cutoffs,
> >something is wrong and ought to be fixed.
> >
> >Joe Gwinn
>
> http://yarchive.net/metal/parting_off.html
>
> From Robert Bastow.
I'll read it.
Joe Gwinn
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Posted by Joseph Gwinn on April 8, 2008, 11:21 pm
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> On Tue, 08 Apr 2008 09:21:20 -0400, Joseph Gwinn
>
> >
> >> On Mon, 07 Apr 2008 22:10:04 -0400, Joseph Gwinn
> >>
> >> >
> >> >> I have a 5914 that shakes hard with a cut off blade.
> >> >> I am tense, and when the shaking causes something to fall over in the
> >> >> pan of the lathe, I just about jump out of my skin.
> >> >
> >> >I burned those nerves out long ago.
> >> >
> >> >The cutoff has made sharp bang noises, to the point I thought something
> >> >must have broken, but no damage ever found. I think it was passing a
> >> >lump of chips, apparently because the tool was cutting on the side
> >> >because the toolpost had rotated.
> >>
> >> The banging noises come from the workpiece loading up, jamming in the
> >> work, then coming free again. Push harder, or a smidge less.
> >
> >That was my guess. The sidewalls of the groove are ragged and galled,
> >which is a clue.
>
> How much side relief are you grinding in? Should be just a couple
> degrees, but you DO need side relief
It was none, but it appears that a few degrees helps a lot. Teenut also
discussed this at length. I'll try it.
> >Need to find the optimum degree of push.
> Sometimes spinning faster helps. I part off at about 600- 800 rpm on
> stuff under 1"
I have not been successful at that speed. I don't think that the back
gear reaches that high.
Joe Gwinn
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Posted by Joseph Gwinn on April 9, 2008, 11:12 am
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> On Tue, 08 Apr 2008 23:21:34 -0400, Joseph Gwinn
>
> >
> >> On Tue, 08 Apr 2008 09:21:20 -0400, Joseph Gwinn
> >>
> >> >
> >> >> On Mon, 07 Apr 2008 22:10:04 -0400, Joseph Gwinn
> >> >>
> >> >> >
> >> >> >> I have a 5914 that shakes hard with a cut off blade.
> >> >> >> I am tense, and when the shaking causes something to fall over in
> >> >> >> the
> >> >> >> pan of the lathe, I just about jump out of my skin.
> >> >> >
> >> >> >I burned those nerves out long ago.
> >> >> >
> >> >> >The cutoff has made sharp bang noises, to the point I thought
> >> >> >something
> >> >> >must have broken, but no damage ever found. I think it was passing a
> >> >> >lump of chips, apparently because the tool was cutting on the side
> >> >> >because the toolpost had rotated.
> >> >>
> >> >> The banging noises come from the workpiece loading up, jamming in the
> >> >> work, then coming free again. Push harder, or a smidge less.
> >> >
> >> >That was my guess. The sidewalls of the groove are ragged and galled,
> >> >which is a clue.
> >>
> >> How much side relief are you grinding in? Should be just a couple
> >> degrees, but you DO need side relief
> >
> >It was none, but it appears that a few degrees helps a lot. Teenut also
> >discussed this at length. I'll try it.
> >
> >
> >> >Need to find the optimum degree of push.
> >> Sometimes spinning faster helps. I part off at about 600- 800 rpm on
> >> stuff under 1"
> >
> >I have not been successful at that speed. I don't think that the back
> >gear reaches that high.
> >
> >
> >Joe Gwinn
>
> Why use back gear?
Because it seems to be required to avoid chatter on this lathe.
The highest marked backgear speed is 280 rpm on the 5914.
One difference seems to be that the usual roughing cuts are cutting on
one side or the other, so the main force pushing tool into work is
parallel to the spindle axis, while in parting or grooving the main
force is perpendicular to the spindle axis.
The down force (from work spinning into the top of the tool bit) is the
same in both cases.
Having chatter while parting off but not while roughing would thus point
to the spindle bearings, as has been discussed.
Joe Gwinn
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> I am tense, and when the shaking causes something to fall over in the
> pan of the lathe, I just about jump out of my skin.