Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Ian Stirling
 
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Default turning a narrow slot

Walter Harley wrote:
I have a Sherline! Finally broke down and got myself a lathe. Now I am
trying to learn to use it.

I want to turn a rectangular-profile slot approximately 1/32" wide, into an
acetal (moderately hard plastic) shaft with an OD of 1/2". The slot wants
to be maybe 3/32" deep; that is, OD of the inside of the slot is 5/16". (In
case this description is unclear, imagine making a grommet.)

What kind of tool should I use to do this? Should I use a parting tool?
Should I try to grind something more or less like a parting tool?

My concern with doing it with a parting tool is that, although it might work
for this particular problem, I think I'm limited to cutting a slot exactly
the width of the parting tool. It would be nice to learn how to make slots
of various widths, including fairly skinny ones.


You can take the parting tool out, and make another cut to the correct
depth - if it's rigid enough, to add.
For skim cuts this probably won't work, but if you've got over 50% of the
tool in the work, it may work well enough.
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Harold & Susan Vordos
 
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Default turning a narrow slot


"Walter Harley" wrote in message
...
I have a Sherline! Finally broke down and got myself a lathe. Now I am
trying to learn to use it.

I want to turn a rectangular-profile slot approximately 1/32" wide, into

an
acetal (moderately hard plastic) shaft with an OD of 1/2". The slot wants
to be maybe 3/32" deep; that is, OD of the inside of the slot is 5/16".

(In
case this description is unclear, imagine making a grommet.)

What kind of tool should I use to do this? Should I use a parting tool?
Should I try to grind something more or less like a parting tool?

My concern with doing it with a parting tool is that, although it might

work
for this particular problem, I think I'm limited to cutting a slot exactly
the width of the parting tool. It would be nice to learn how to make

slots
of various widths, including fairly skinny ones.

Thanks in advance!

Piece of cake, Walter. Acetal machines beautifully so there should be no
problem with the cut. Grind yourself a parting tool that has relief top to
bottom on the sides and front of the tool, and a slight taper front to
back, then put the radius of the wheel on top, making sure it starts at the
cutting edge and goes positive towards the rear. Finish the tool by honing,
keeping the corners sharp and the front square. The top grind of which I
spoke means the grind will be deeper at the shank than at the tip, where it
cuts, and will give you a small amount of positive rake. That makes the tool
cut quite well and promotes chip flow. I've been grinding parting and
grooving tools that way for years with outstanding results. Make sure the
cutting end is square, not ground to the side, and not grooved like Tim
suggested. He'll come to understand that's not a good idea as soon as he
starts grinding parting tools.

The width of your parting (or grooving) tool should be no wider than the
desired width (duh!), and if it's a little narrower all you have to do is
mike the tool so you know the width, then cut your groove on location and
move over the prescribed amount, using a dial indicator (long travel) the
amount necessary to achieve the desired width. That's how one cuts snap
ring or O ring grooves and other undercuts when you don't have the exact
size tool on hand. With a square ground end you can move from one side to
the other when you're to depth and end up with a very nice bottom cut.
This will all make complete sense to you the first time you try it.

Speed doesn't matter with acetal. The faster the better. You won't hurt
the tool and you damned sure won't have any trouble with the plastic
melting. The faster you run it, the better it machines.

One word of caution. Grinding a parting tool that thin requires a wheel that
has no bounce in it, so make sure your grinding wheel is running very
smoothly. The thin section of tool likes to break off at the shank when it
bounces. You'd also not want to make it very long so it has rigidity in
keeping with machining steel.

If you're lost on my description, I'd be pleased to send you a scan of a
tool so ground. Contact me on the side if you're interested.

Harold


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Don Foreman
 
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Default turning a narrow slot

Grind a 1/4" HSS bit to 1/32" width for about 1/4" of length to
form a parting/grooving tool. A bit of relief front-to-back and
top-to-bottom doesn't hurt, but very little is required. Once
it's made well, stay away from the grinder thereafter. You can dress
it up when it needs it with a few strokes of a diamond hone. I have a
couple of such bits I've been using for a decade, will admit that I've
also broken a few, It only takes about 10 minutes to grind a new
one.

You'll find a lot of other uses for that bit as well. With the
skinny part that short, it's no problem to skin a slot to wider width
if the cutting corner is sharp. This is one place where you don't
want a radiused edge. Such a tool won't deflect in acetyl or even
reasonably free-machining metal. I've recently used such a tool on
303 stainless. Just a couple of days ago I was making cylindrical
bushings of steel, OD of .205", ID of .165 or so. I drilled
barstock for ID, machined to OD for half an inch, parted off bushing
of various lengths in the region of .015 to .030 with such a tool.
The experiment was a flop but the machining went OK....

I've made many narrow slots in acetyl, most a lot deeper than 3/32"
when making high-voltage high-frequency pi-wound coil bobbins. For
deeper cuts (some .750 deep, .032 wide) I used a cutter made by
silver-brazing material from a broken HSS slitting saw to a 1/4"
square of mild steel and grinding to shape. No relief on the sides of
that tool but it runs straight and true.




On 1 Aug 2004 00:23:31 GMT, "Walter Harley"
wrote:

I have a Sherline! Finally broke down and got myself a lathe. Now I am
trying to learn to use it.

I want to turn a rectangular-profile slot approximately 1/32" wide, into an
acetal (moderately hard plastic) shaft with an OD of 1/2". The slot wants
to be maybe 3/32" deep; that is, OD of the inside of the slot is 5/16". (In
case this description is unclear, imagine making a grommet.)

What kind of tool should I use to do this? Should I use a parting tool?
Should I try to grind something more or less like a parting tool?

My concern with doing it with a parting tool is that, although it might work
for this particular problem, I think I'm limited to cutting a slot exactly
the width of the parting tool. It would be nice to learn how to make slots
of various widths, including fairly skinny ones.

Thanks in advance!


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jim rozen
 
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Default turning a narrow slot

In article ,

My concern with doing it with a parting tool is that, although it might work
for this particular problem, I think I'm limited to cutting a slot exactly
the width of the parting tool.


Basically you just use a parting (well, in this case it would be
called 'grooving') tool that is *narrower* than the groove
you want to cut.

If you want a 0.100 wide groove, you can use a .093 wide tool
and plunge at one side, and then shift over seven thou to make
it the correct width.

Just be aware that parting tools are not terribly rigid in
the side-to-side direction. So you either need to plunge
into solid material, like the first cut, or take a fairly
small cut on the side. Minimize the tool overhang and of
course use the widest tool you can.

Jim

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