Hello..
I wanted to ask anyone if they have attempted to do this on their
lathe. I only have a metal lathe and want to cut a flat archimedes
spiral onto a 1/8" thick piece of lucite. The spiral, fairly coarse,
would be something on the order of 6 turns/inch. The diameter of the
plastic would be about 3.5".

In any case, I could use some pointers as to how and efficently
accomplish this. Thanks for any advice you may offer.

-jim

Jim Flanagan wrote:

Hello..
I wanted to ask anyone if they have attempted to do this on their
lathe. I only have a metal lathe and want to cut a flat archimedes
spiral onto a 1/8" thick piece of lucite. The spiral, fairly coarse,
would be something on the order of 6 turns/inch. The diameter of the
plastic would be about 3.5".

I've done this. I needed 3 TPI for a heating element in a water boiler.
The ratio was so
low I was afraid of damaging the gear train, so I decided to run the
lathe "backwards".
What I mean is that I did not use the drive motor, but I turned the
cross slide handle
manually, while the threading gear train was engaged. The gear train
turned the
headstock. I carved the major part of the thread with a Dremel-type
tool in the
toolpost in two passes. I then ground a form tool to clean up the
groove and
get to the desired profile. I took about 10 passes with the form tool,
feeding in a
bit with then compound each pass.

You can probably do your 6 TPI spiral with the conventional drive
arrangement
on the slowest backgear setting. A Dremel-type tool with a carbide
rotary file
would be good if the spiral groove needs to be deep, otherwise you'd
need a lot
of passes.

(I assume you have power crossfeed on your lathe, otherwise you will need to
rig something to drive the crossfeed.)

Jon

On Thu, 27 Oct 2005 20:23:48 GMT, Jim Flanagan
wrote:

Hello..
I wanted to ask anyone if they have attempted to do this on their
lathe. I only have a metal lathe and want to cut a flat archimedes
spiral onto a 1/8" thick piece of lucite. The spiral, fairly coarse,
would be something on the order of 6 turns/inch. The diameter of the
plastic would be about 3.5".

In any case, I could use some pointers as to how and efficently
accomplish this. Thanks for any advice you may offer.

-jim



is this the spiral made up of semi circles with increasing radii? If
so you can't do it on a lathe. You should be able to cut a "true"
spiral taking a facing cut at a "heavy" feedrate like .170" per
revolution *if* your lathe will do it. Of course there are details to
work out.
Randy

On Thu, 27 Oct 2005 20:23:48 GMT, Jim Flanagan
wrote:

Hello..
I wanted to ask anyone if they have attempted to do this on their
lathe. I only have a metal lathe and want to cut a flat archimedes
spiral onto a 1/8" thick piece of lucite. The spiral, fairly coarse,
would be something on the order of 6 turns/inch. The diameter of the
plastic would be about 3.5".

In any case, I could use some pointers as to how and efficently
accomplish this. Thanks for any advice you may offer.

-jim
It sounds like you want to cut a spiral on the face of a disc. Others
have responded with methods for cutting the OD of the part which would
give you a helix. If you are needing to cut a spiral then a manual
lathe isn't the best way for this because they are set up for
threading parallel with the Z axis, not the X axis. I have cut scrolls
on CNC lathes, but the CNC doesn't care which axis is being geared to
the spindle because it's all done electronically. If your lathe X axis
advances .200 for each revolution of the handle then you would need to
figure out some way to turn the handle 1.666666 revs for each rev of
the spindle. I can think of lots of ways to directly gear the
crosslide (X axis) to the spindle but they all would take a long time
to do. But if you can cut the groove in one pass I have an idea.
Remove the handle from the X axis and tighten the chuck on a drill
motor onto the shaft that the handle mounts on. With the drill motor
spinning at top speed see how long it takes the X axis to traverse the
required distance. Set the spindle speed on your lathe to the rpm that
will give you the pitch you want. Set the tool for the desired depth
of cut but have the tool pretty far in the X plus direction to give
the drill motor time to come up to speed. Start the lathe and then
pull the trigger on the drill motor. Crude, but it may work.
ERS

Eric R Snow wrote:
On Thu, 27 Oct 2005 20:23:48 GMT, Jim Flanagan
wrote:


Hello..
I wanted to ask anyone if they have attempted to do this on their
lathe. I only have a metal lathe and want to cut a flat archimedes
spiral onto a 1/8" thick piece of lucite. The spiral, fairly coarse,
would be something on the order of 6 turns/inch. The diameter of the
plastic would be about 3.5".

In any case, I could use some pointers as to how and efficently
accomplish this. Thanks for any advice you may offer.

-jim

It sounds like you want to cut a spiral on the face of a disc. Others
have responded with methods for cutting the OD of the part which would
give you a helix. If you are needing to cut a spiral then a manual
lathe isn't the best way for this because they are set up for
threading parallel with the Z axis, not the X axis. I have cut scrolls
Most newer lathes have "power crossfeed". As well as the half nuts
on the leadscrew for threading (Z axis), they have a keyway in the
leadscrew that drives a power take-off arrangement that turns the
crossfeed (X axis). Some lathes have different feed ratios on
the crossfeed, so you have to compensate in the gearing. The Atlas,
for instance, has an 8 TPI threading screw and a 10 TPI crossfeed screw.
So, they ingeniously put a 20:16 tooth gear set in the apron so the
feeds come out the same for both axes of motion. But other models
may need a different setting when using the crossfeed.

One complication is there won't be a threading dial for the crossfeed,
so you might want to just leave the crossfeed engaged throughout the
entire operation, and back the spindle up to wind the crossfeed back to
the start of the thread. If you disengage the power crossfeed,
it likely won't start at the right alignment between the feed and the
spindle when you re-engage it.

Jon

On Thu, 27 Oct 2005 22:21:11 -0500, Jon Elson
wrote:

Eric R Snow wrote:
On Thu, 27 Oct 2005 20:23:48 GMT, Jim Flanagan
wrote:


Hello..
I wanted to ask anyone if they have attempted to do this on their
lathe. I only have a metal lathe and want to cut a flat archimedes
spiral onto a 1/8" thick piece of lucite. The spiral, fairly coarse,
would be something on the order of 6 turns/inch. The diameter of the
plastic would be about 3.5".

In any case, I could use some pointers as to how and efficently
accomplish this. Thanks for any advice you may offer.

-jim

It sounds like you want to cut a spiral on the face of a disc. Others
have responded with methods for cutting the OD of the part which would
give you a helix. If you are needing to cut a spiral then a manual
lathe isn't the best way for this because they are set up for
threading parallel with the Z axis, not the X axis. I have cut scrolls
Most newer lathes have "power crossfeed". As well as the half nuts
on the leadscrew for threading (Z axis), they have a keyway in the
leadscrew that drives a power take-off arrangement that turns the
crossfeed (X axis). Some lathes have different feed ratios on
the crossfeed, so you have to compensate in the gearing. The Atlas,
for instance, has an 8 TPI threading screw and a 10 TPI crossfeed screw.
So, they ingeniously put a 20:16 tooth gear set in the apron so the
feeds come out the same for both axes of motion. But other models
may need a different setting when using the crossfeed.

One complication is there won't be a threading dial for the crossfeed,
so you might want to just leave the crossfeed engaged throughout the
entire operation, and back the spindle up to wind the crossfeed back to
the start of the thread. If you disengage the power crossfeed,
it likely won't start at the right alignment between the feed and the
spindle when you re-engage it.

Jon
Jon,
I know that most lathes have a powered X axis. But the gear ratio is
really high. On one lathe in my shop the X axis advances about .014"
on the diameter for each revolution of the grooved rod that supplies
power to both axes. This guy needs about .320" on the diameter. So if
I was to use the power feed the grooved rod would need to spin 23
times as fast as the spindle. With the gears in my lathe I can't do
this.
ERS

In article ,
says...
Eric R Snow wrote:
On Thu, 27 Oct 2005 20:23:48 GMT, Jim Flanagan
wrote:


Hello..
I wanted to ask anyone if they have attempted to do this on their
lathe. I only have a metal lathe and want to cut a flat archimedes
spiral onto a 1/8" thick piece of lucite. The spiral, fairly coarse,
would be something on the order of 6 turns/inch. The diameter of the
plastic would be about 3.5".

In any case, I could use some pointers as to how and efficently
accomplish this. Thanks for any advice you may offer.

-jim

It sounds like you want to cut a spiral on the face of a disc. Others
have responded with methods for cutting the OD of the part which would
give you a helix. If you are needing to cut a spiral then a manual
lathe isn't the best way for this because they are set up for
threading parallel with the Z axis, not the X axis. I have cut scrolls
Most newer lathes have "power crossfeed". As well as the half nuts
on the leadscrew for threading (Z axis), they have a keyway in the
leadscrew that drives a power take-off arrangement that turns the
crossfeed (X axis).

But in order to cut the approx 6 TPI spiral the feed would
have to much coarser than what's available on small lathes.

Ned Simmons

Eric R Snow wrote:
I know that most lathes have a powered X axis. But the gear ratio is
really high. On one lathe in my shop the X axis advances about .014"
on the diameter for each revolution of the grooved rod that supplies
power to both axes. This guy needs about .320" on the diameter. So if
I was to use the power feed the grooved rod would need to spin 23
times as fast as the spindle. With the gears in my lathe I can't do
this.
On the 10 and 12" Atlas lathes, the crossfeed was exactly equal to the
logitudinal feed. On my Sheldon R15 lathe, the crossfeed is 1/2 the
longitudinal feed. I've never seen a lathe where there was so much
reduction from the leadscrew to the crossfeed screw. That doesn't
make much sense, as it would require the leadscrew to turn pretty fast
when roughing a facing cut at higher spindle speeds. I can't recall
a lathe where the ratio was far outside the range I quote above of 1:1
to 2:1. Just curious, what lathe is that that has this high reduction?

Jon

On Fri, 28 Oct 2005 19:52:49 -0500, Jon Elson
wrote:

Eric R Snow wrote:
I know that most lathes have a powered X axis. But the gear ratio is
really high. On one lathe in my shop the X axis advances about .014"
on the diameter for each revolution of the grooved rod that supplies
power to both axes. This guy needs about .320" on the diameter. So if
I was to use the power feed the grooved rod would need to spin 23
times as fast as the spindle. With the gears in my lathe I can't do
this.
On the 10 and 12" Atlas lathes, the crossfeed was exactly equal to the
logitudinal feed. On my Sheldon R15 lathe, the crossfeed is 1/2 the
longitudinal feed. I've never seen a lathe where there was so much
reduction from the leadscrew to the crossfeed screw. That doesn't
make much sense, as it would require the leadscrew to turn pretty fast
when roughing a facing cut at higher spindle speeds. I can't recall
a lathe where the ratio was far outside the range I quote above of 1:1
to 2:1. Just curious, what lathe is that that has this high reduction?

Jon
This particular lathe is a Jet 1440. 14 inch swing, 40 inches between
centers. This lathe is a copy of a Clausing, I think. Like all the
larger lathes I've run, Sheldons, Clausings, Howas, etc. this one has
a lead screw for threading and a separate grooved shaft for power
feeds. One revolution of this shaft equals about .014 for the
crossfeed and about .019 for the longitudinal feed. This is normal.
And it does make sense. It lowers the torque on the gear train in the
headstock and the shaft that turns the gears in the carriage.
ERS