Don Foreman wrote:

I have a T-shaped parting tool in an Aloris BXA7 holder that won't cut
straight. It drifts to one side or the other as the cut progresses.
The bit is .063" at the bottom, .094 at the top, .686 high. As far
as I can tell the cutting edge is ground square (parallel to the
lathe axis), the bit is vertical in the holder to within a thou or
two, and the bit was square with the workpiece at center height.

I have a thinner tapered parting bit that does cut straight. It's
.0625 at the top, .043 at the bottom, .687 high.

The lathe is a 15x50 gearhead, no problem with stiffness or rigidity.

I'm not exactly a newbie with a lathe, but this one has me puzzled.


Well, the most common cause is the front end of the tool is not parallel
to the spindle axis. But, if the side of the tool is not at an exact right
angle to the lathe axis, then the side will rub on the cut face as the tool
goes in, and it will force the tool to one side or the other. You don't
get this with a tool that is tapered behind the cutting edge, but the
long parting-off tools have no side relief whatsoever, and will rub
and be deflected. I generally accept that this will happen, and accomodate
it.

Jon

I have a T-shaped parting tool in an Aloris BXA7 holder that won't cut
straight. It drifts to one side or the other as the cut progresses.
The bit is .063" at the bottom, .094 at the top, .686 high. As far
as I can tell the cutting edge is ground square (parallel to the
lathe axis), the bit is vertical in the holder to within a thou or
two, and the bit was square with the workpiece at center height.

I have a thinner tapered parting bit that does cut straight. It's
..0625 at the top, .043 at the bottom, .687 high.

The lathe is a 15x50 gearhead, no problem with stiffness or rigidity.

I'm not exactly a newbie with a lathe, but this one has me puzzled.

Any suggestions about what's going on here, please?

Thanks!

Don Foreman

Hey Don:

The only part you didn't mention was overhang - or how far the parting tool
is sticking out.
This happens occasionally to me and I will pull back on the depth of the
tool to get it started.

On Tue, 27 Jul 2004 14:11:07 -0500, Don Foreman
wrote:

I have a T-shaped parting tool in an Aloris BXA7 holder that won't cut
straight. It drifts to one side or the other as the cut progresses.
The bit is .063" at the bottom, .094 at the top, .686 high. As far
as I can tell the cutting edge is ground square (parallel to the
lathe axis), the bit is vertical in the holder to within a thou or
two, and the bit was square with the workpiece at center height.

I have a thinner tapered parting bit that does cut straight. It's
.0625 at the top, .043 at the bottom, .687 high.

The lathe is a 15x50 gearhead, no problem with stiffness or rigidity.

I'm not exactly a newbie with a lathe, but this one has me puzzled.

Any suggestions about what's going on here, please?

Thanks!

Don Foreman
Don,
Sometimes, when this happens to me, the parting blade will be dull on
the side(s) just back from the cutting edge. So, instead of having two
sharp corners there will be a slight radius along one edge. This is
the edge where the top meets the side. Then, grinding the tool back
fixes the problem.
ERS

Hi, John! Yeah, there was quite a bit of overhang.

Did you move? I enjoyed your zinc-casting site, saw mention of a
barn. I don't remember seeing a barn in SLP!


On Tue, 27 Jul 2004 14:24:51 -0500, "John Hofstad-Parkhill"
wrote:

Hey Don:

The only part you didn't mention was overhang - or how far the parting tool
is sticking out.
This happens occasionally to me and I will pull back on the depth of the
tool to get it started.

I never would have thought of that, Eric. Thanks! I'll try grinding
the top a little.

On Tue, 27 Jul 2004 12:44:29 -0700, Eric R Snow
wrote:

Don,
Sometimes, when this happens to me, the parting blade will be dull on
the side(s) just back from the cutting edge. So, instead of having two
sharp corners there will be a slight radius along one edge. This is
the edge where the top meets the side. Then, grinding the tool back
fixes the problem.
ERS

In article ,
Don Foreman wrote:
I have a T-shaped parting tool in an Aloris BXA7 holder that won't cut
straight. It drifts to one side or the other as the cut progresses.
The bit is .063" at the bottom, .094 at the top, .686 high. As far
as I can tell the cutting edge is ground square (parallel to the
lathe axis), the bit is vertical in the holder to within a thou or
two, and the bit was square with the workpiece at center height.

I have a thinner tapered parting bit that does cut straight. It's
.0625 at the top, .043 at the bottom, .687 high.

[ ... ]

Any suggestions about what's going on here, please?

Hmm ... one possibility is that either the compound or the
toolpost are slipping under the greater cutting forces with the wider
parting tool. This will change the angle of the tool, and will cause it
to drift. (Obviously, if it is higher than center, you have extra force
on the end of the tool, but I presum that you have eliminated that as a
cause.)

One trick which may prevent the toolpost from rotating under
pressure is to take some thin cardboard or thick paper, cut it to match
the footprint of the toolpost, with a hole to pass the clamp-down bolt.
This will deform into any small imperfections in the finish of the top
of the compound and the bottom of the toolpost, and make it harder for
it to turn in place. If it is the compound turning, instead, I will
leave it to you to figure out how to prevent it from turning.

You *do* have the carriage locked to the bed while you're doing
this, don't you?

Now I will sit back and see what others say.

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Don Foreman wrote in
:

I have a T-shaped parting tool in an Aloris BXA7 holder that won't cut
straight. It drifts to one side or the other as the cut progresses.
The bit is .063" at the bottom, .094 at the top, .686 high. As far
as I can tell the cutting edge is ground square (parallel to the
lathe axis), the bit is vertical in the holder to within a thou or
two, and the bit was square with the workpiece at center height.

I have a thinner tapered parting bit that does cut straight. It's
.0625 at the top, .043 at the bottom, .687 high.

The lathe is a 15x50 gearhead, no problem with stiffness or rigidity.

I'm not exactly a newbie with a lathe, but this one has me puzzled.

Any suggestions about what's going on here, please?

Thanks!

Don Foreman


Don,
If there is any perceptable difference in the edge radii on the tool, it
will pull. You may not *think* you can flex the tool holder...but you
can.
Cutting tools, especially grooving type tools, will follow physics and
take the least resistive path. If one corner is machining more freely
than the other, the tool will drift to that side.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

On Tue, 27 Jul 2004 22:32:51 GMT, Anthony
wrote:

Don,
If there is any perceptable difference in the edge radii on the tool, it
will pull. You may not *think* you can flex the tool holder...but you
can.
Cutting tools, especially grooving type tools, will follow physics and
take the least resistive path. If one corner is machining more freely
than the other, the tool will drift to that side.

Toolholder is not flexing or turning, nor is the compound. The
parting tool flexes in the cut, is still square after the cut is
made.

The edge radii explanation makes sense. It's new, but that doesn't
mean it's well-ground. Import, from India. The thinner bits I have
no problem with (other than breaking if push them too hard) are from
Mo-Max in Cleveland.

Don.

Between Anthony and Eric, your problem is explained.

Cutoff and deep grooving is one area where carbide inserts really shine
compared to HSS bits. I went with Manchester Separator style. (there's also
a Kenametal copy) This is sooo much better, you'll never use HSS again.

Karl

Don Foreman wrote:

I never would have thought of that, Eric. Thanks! I'll try grinding
the top a little.

You usually don't want to grind the top especially if this is the long
blade type. Grind the front face back. Also, a machinest aquaintance
told me to experiment with the angle of the front face (i.e. front
clearance). There is an optimum for best cutting versus chatter. I
found this to be true.

Ted

I never have ground the top of a parting tool -- but then I've never
had problems with them either. I'll try a little grinding before I
pitch it and pick up a new one.

Karl sure likes his carbide tool. Maybe I'll try one of those.

On Wed, 28 Jul 2004 17:42:51 GMT, Ted Edwards
wrote:

Don Foreman wrote:

I never would have thought of that, Eric. Thanks! I'll try grinding
the top a little.

You usually don't want to grind the top especially if this is the long
blade type. Grind the front face back. Also, a machinest aquaintance
told me to experiment with the angle of the front face (i.e. front
clearance). There is an optimum for best cutting versus chatter. I
found this to be true.

Ted

Thanks, Eric and Anthony! I ground the top of the bit a little and
ground a bit of relief on the top of the T as well. It runs much
better now. I think I got bit by bad import quality on this one.
The Mo-Max Cleveland bits cost twice as much, but they sure work well!



On Tue, 27 Jul 2004 14:11:07 -0500, Don Foreman
wrote:

I have a T-shaped parting tool in an Aloris BXA7 holder that won't cut
straight. It drifts to one side or the other as the cut progresses.
The bit is .063" at the bottom, .094 at the top, .686 high. As far
as I can tell the cutting edge is ground square (parallel to the
lathe axis), the bit is vertical in the holder to within a thou or
two, and the bit was square with the workpiece at center height.

I have a thinner tapered parting bit that does cut straight. It's
.0625 at the top, .043 at the bottom, .687 high.

The lathe is a 15x50 gearhead, no problem with stiffness or rigidity.

I'm not exactly a newbie with a lathe, but this one has me puzzled.

Any suggestions about what's going on here, please?

Thanks!

Don Foreman

On Thu, 29 Jul 2004 00:19:16 -0500, Don Foreman
wrote:
Glad I could help Don. About those Cleveland bits. Worth more than
twice what you paid. They really work so much better than the imported
ones. Especially ones from India. I bought, by mistake, some of the
Indian ones. Ended up throwing them out. Good for absolutely nothing.
And will make you think you have a problem with your setup or
technique. In the future, you will probably find it works best to just
grind the face of the parting tool. Grind back far enough to restore
the original tool profile. Then, if you need to part off a large
diameter, you won't need to grind more on the top or sides.
Eric

Thanks, Eric and Anthony! I ground the top of the bit a little and
ground a bit of relief on the top of the T as well. It runs much
better now. I think I got bit by bad import quality on this one.
The Mo-Max Cleveland bits cost twice as much, but they sure work well!



On Tue, 27 Jul 2004 14:11:07 -0500, Don Foreman
wrote:

I have a T-shaped parting tool in an Aloris BXA7 holder that won't cut
straight. It drifts to one side or the other as the cut progresses.
The bit is .063" at the bottom, .094 at the top, .686 high. As far
as I can tell the cutting edge is ground square (parallel to the
lathe axis), the bit is vertical in the holder to within a thou or
two, and the bit was square with the workpiece at center height.

I have a thinner tapered parting bit that does cut straight. It's
.0625 at the top, .043 at the bottom, .687 high.

The lathe is a 15x50 gearhead, no problem with stiffness or rigidity.

I'm not exactly a newbie with a lathe, but this one has me puzzled.

Any suggestions about what's going on here, please?

Thanks!

Don Foreman

Eric R Snow wrote:

On Thu, 29 Jul 2004 00:19:16 -0500, Don Foreman
wrote:
Glad I could help Don. About those Cleveland bits. Worth more than
twice what you paid. They really work so much better than the imported
ones. Especially ones from India. I bought, by mistake, some of the
Indian ones. Ended up throwing them out. Good for absolutely nothing.
And will make you think you have a problem with your setup or
technique. In the future, you will probably find it works best to just
grind the face of the parting tool. Grind back far enough to restore
the original tool profile. Then, if you need to part off a large
diameter, you won't need to grind more on the top or sides.
Eric

Thanks, Eric and Anthony! I ground the top of the bit a little and
ground a bit of relief on the top of the T as well. It runs much
better now. I think I got bit by bad import quality on this one.
The Mo-Max Cleveland bits cost twice as much, but they sure work well!



It seems the Cleveland tools were actually less expensive.

michael