Is this possible? How difficult would it be to pick up the thread after
moving the stock? I want to turn a 2 start 10 TPI Acme thread on a 1/2
inch rod 3 foot long.

I have thought about sectioning the rod, threading the sections and
pinning them back together after aligning the thread starts. Would that
work and would it be smooth operating?

Just wondering!

Andy

TheAndroid wrote:

Is this possible? How difficult would it be to pick up the thread after
moving the stock? I want to turn a 2 start 10 TPI Acme thread on a 1/2
inch rod 3 foot long.

That sounds like a pain, and for reasons you haven't considered as well
as ones you have. Long thing shafts do not turn well - you would need
to set up a follower rest on the carriage to support the work, and it's
possibly going to hit burs from the partially turned thread, etc. Not
fun.

Unless there's extreme personal need to do the whole thing yourself
just to prove you can, getting the project working is best achieved by
buying the threaded rod you need, or modifying the specification
(change the nut) to one that you can buy. The accuracy and smoothness
will no doubt be much, much, much better. Note that you can partially
bore out the old nut and use a cast in place low friction epoxy
(moglice) to make one from the new screw.

I have access to a Clausing 17x80, but it does not have a follow rest.
As you say, turning a thin shaft without one is impossible.

Maybe I could get a description from someone on how one would mount on
the carriage? I can build one easily enough, I just don't see where it
mounts.

This is for a home built plasma cutting table. That's why I need the
length.

Andy

TheAndroid wrote:
I have access to a Clausing 17x80, but it does not have a follow rest.
As you say, turning a thin shaft without one is impossible.

Maybe I could get a description from someone on how one would mount on
the carriage? I can build one easily enough, I just don't see where it
mounts.

Probably bolts to the side of the saddle below the cross slide, I'd put
it on the headstock side though I suppose it could mount on the other
and reach around somehow. You might have to take the saddle off and
drill and tap mounting holes.

This is for a home built plasma cutting table. That's why I need the
length.

Do like everyone else who builds that project and buy rolled acme
screws and nuts, they are cheap. You can even get motion-transfer
grade ballscrews for fairly cheap.

You still get to play with the lathe as you machine the ends.

TheAndroid wrote:

This is for a home built plasma cutting table. That's why I need the
length.

Oh, they not only whip when being machined, they can whip in use when
rapiding around to reposition too. So I'd buy the largest diameters
screws my budget and avaialable space could support. 5/8" minimum,
3/4", 7/8" even 1" for the lower axis.

TheAndroid wrote:
I have access to a Clausing 17x80, but it does not have a follow rest.
As you say, turning a thin shaft without one is impossible.

Maybe I could get a description from someone on how one would mount on
the carriage? I can build one easily enough, I just don't see where it
mounts.

This is for a home built plasma cutting table. That's why I need the
length.

I'd have to agree with the other responder. Acme threaded rod is too
cheap to go through this agony.

Follwoing up on what others said:

Just buy the acme threaded rod. I was reading my www.use-enco.com
catalog this morning, 1/2" ACME by 3' was $4.59 on sale. You can't beat
that doing it yourself.

1/2" is probably too small. Eulers theorm says that if the length is 89
times the diameter it will buckle. Safe design would trim that down to
the 30 to 50 times range. On a threaded rod you use the minor diameter
(bottom of the threads), 1/2" acme has a .375" minor diameter so 36"
shaft will be at a ratio of 96:1 WAY to spindly.



TheAndroid wrote:

I have access to a Clausing 17x80, but it does not have a follow rest.
As you say, turning a thin shaft without one is impossible.

Maybe I could get a description from someone on how one would mount on
the carriage? I can build one easily enough, I just don't see where it
mounts.

This is for a home built plasma cutting table. That's why I need the
length.

Andy

On 5 Jan 2006 09:21:47 -0800, wrote:

TheAndroid wrote:
I have access to a Clausing 17x80, but it does not have a follow rest.
As you say, turning a thin shaft without one is impossible.

Maybe I could get a description from someone on how one would mount on
the carriage? I can build one easily enough, I just don't see where it
mounts.
snip
see http://www.mcduffee-associates.us/ma...g/TRAVEL~1.HTM

Uncle George

TheAndroid wrote:

I have access to a Clausing 17x80, but it does not have a follow rest.
As you say, turning a thin shaft without one is impossible.

Maybe I could get a description from someone on how one would mount on
the carriage? I can build one easily enough, I just don't see where it
mounts.

This is for a home built plasma cutting table. That's why I need the
length.

Andy



What you need is a Ball Screw . I think I have one that long in my junk
pile.

Bill K7NOM

It would be awesome if you had two!!!!! I would be very interested!!!!

BTW, thanks everyone for the input. I looked at threaded rod, but
multiple start rod from McMaster were 49+ dollars for 6 feet. I was
hoping to trade some time for cost on these screws.
Additionally, the steppers I have are rated at 240 oz/in in bipolar
mode. I wanted to minimize the torque required to turn the screw. I
think a 1"" screw at 3 feet would simply weigh too much for these
motors to turn and stop at reasonable speeds.

As far as follow rests go, the links provided have given me much to
think about. I will probably move ahead on building one as you never
know when the need will come up!!!!!

Andy

Do you have a reference for Eulers therom? This sounds like something I
may need to research a little more before I start building.

According to :
TheAndroid wrote:
I have access to a Clausing 17x80, but it does not have a follow rest.
As you say, turning a thin shaft without one is impossible.

Maybe I could get a description from someone on how one would mount on
the carriage? I can build one easily enough, I just don't see where it
mounts.

Probably bolts to the side of the saddle below the cross slide, I'd put
it on the headstock side though I suppose it could mount on the other
and reach around somehow. You might have to take the saddle off and
drill and tap mounting holes.

The one for my Clausing (12x24") mounts to the flat tops of the
extensions to the left of the carriage. There are threaded holes with
studs in them. The follower rest drops over those and is secured by
nuts run down onto the studs.

Good Luck,
DoN.

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wrote in message
oups.com...
TheAndroid wrote:

This is for a home built plasma cutting table. That's why I need the
length.

Oh, they not only whip when being machined, they can whip in use when
rapiding around to reposition too. So I'd buy the largest diameters
screws my budget and avaialable space could support. 5/8" minimum,
3/4", 7/8" even 1" for the lower axis.


Hmmm, I was debating if I should use a 2 inch dia ground ballscrew (8 feet
long with ballnut, brand new for $125...gotta love Boeing Surplus!) on *my*
gantry table design....it seemed rather large, but I guess it woudl cut down
on the whip...and I have it...kinda a shame to use it on a machine that will
probably only cut wood...

TheAndroid wrote:

BTW, thanks everyone for the input. I looked at threaded rod, but
multiple start rod from McMaster were 49+ dollars for 6 feet. I was
hoping to trade some time for cost on these screws.

Why do you want multiple start threads? I think the usual use is to
have a faster lead than the apparent groove pitch so that high powered
systems can rapid quickly.

Additionally, the steppers I have are rated at 240 oz/in in bipolar
mode. I wanted to minimize the torque required to turn the screw.

Which is probably not aided by a multiple start thread?

Though I do think there is something about with ordinary screw threads,
a finer pitch does not actually get you much mechanical advantage as
friction dominates. A cheap ballscrew on the other hand...

You may want to look at toothed timing belts for connecting the motors
to the screws. This can let you change the ratios experimentally, but
it also introduces a nice solution to the problems of misalignment and
vibration damping between the motor and screw. Without a belt in
there, you'd need a flex coupling.

According to Rick :

wrote in message
oups.com...
TheAndroid wrote:

This is for a home built plasma cutting table. That's why I need the
length.

Oh, they not only whip when being machined, they can whip in use when
rapiding around to reposition too. So I'd buy the largest diameters
screws my budget and avaialable space could support. 5/8" minimum,
3/4", 7/8" even 1" for the lower axis.


Hmmm, I was debating if I should use a 2 inch dia ground ballscrew (8 feet
long with ballnut, brand new for $125...gotta love Boeing Surplus!) on *my*
gantry table design....it seemed rather large, but I guess it woudl cut down
on the whip...and I have it...kinda a shame to use it on a machine that will
probably only cut wood...

One possible approach to minimizing whip is the one which
Bridgeport used for the X-axis on their CNC machines -- starting as
early as the BOSS-3.

They simply rigidly mounted the leadscrew to the table at one
end, and instead rotated the ball nut in paired bearings. Of course, it
made manual operation pretty much impractical without the computer
aiding in a sort of "fly-by-wire" technique, as the nut was down under
the table mounted to the saddle along with the motor.

But a skinny enough and long enough leadscrew will still develop
resonances at the right (or wrong) frequencies, so fatter is better.
You just may have less mass to accelerate rotating the nut instead of a
fat long leadscrew.

Enjoy,
DoN.
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According to :
TheAndroid wrote:

BTW, thanks everyone for the input. I looked at threaded rod, but
multiple start rod from McMaster were 49+ dollars for 6 feet. I was
hoping to trade some time for cost on these screws.

Why do you want multiple start threads? I think the usual use is to
have a faster lead than the apparent groove pitch so that high powered
systems can rapid quickly.

Note that *some* types of garage door openers have triple-start
Acme threads. And the ends have 'D' shapes (IIRC) to allow them to be
coupled together in sections to adapt to the needed travel of the
garage door.

They run in aluminum extrusions, and the "nut" is a plastic one
long enough to bridge over the coupling gaps.

The maker said that shorter sections were not available (I
needed one to clear the enclosed I-beam supporting the next floor), and
when I suggested that I would just have to modify the existing ones,
they said that it was not possible. :-)

Of course, it was possible, if you have a lathe with a big
enough spindle hole to accept the OD of the rod -- and even my Compact-5
was big enough for that. :-)

Good Luck,
DoN.
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--- Black Holes are where God is dividing by zero ---

Sorry, I didn't explain fully. I get going sometimes and miss
details......

Multiple start threads allow me to get the faster lead without
extensive thread depth. I wanted to cut the 2 start 10 TPI because the
10 TPI thread depth would leave me much more root diameter of the screw
(vs the 5 TPI depth) thus hopefully reducing flex. My real target is 5
TPI as my steppers are 200 steps per rev. That gives me a .001
resolution. I can drive my steppers at about 150 pulses a second
without missing steps. This gives me around 9" a minute top speed
movement. This is a bit fast for plasma cutting heavy material , but
keeps me well within the capabilities of the steppers without
introducing potential backlash other than from the leadscrews. I plan
on making anti-backlash nuts for those.

Even so, I want to reduce the rotational mass the steppers are turning.
The suggestion by Don is very interesting! I plan on having a laptop
control for the table anyway so I don't care if I can manually place
the cutting head. I need to see if I can find how they drove the nuts.

Andy

Thanks for the help everyone! I had posted a reply to the question
about why I needed multiple starts, but apparently it fell into the bit
bucket.

I'd like multiple starts because it allows me to have 5 TPI lead
without the thread depth of 5 TPI. This leaves me with more root
diameter of the screw which will presumably give me more strength. My
stepper motors use 200 steps per revolution. With a 5 lead, I get .001
per step resolution. That's really the aim.

Andy

My replies keep getting eaten!

Thanks for the help, everyone!

I want multiple starts in order to increase the root diameter remaining
of the rod after threading. 2 starts use half the thread depth.


Andy

My replies keep getting eaten!

Thanks for the help, everyone!

I want multiple starts in order to increase the root diameter remaining
of the rod after threading. 2 starts use half the thread depth.


Andy

According to TheAndroid :
My replies keep getting eaten!

No they don't. *We're* seeing them all. It is Google (which
you are using for posting) which is sometimes *very* slow at getting an
article from their posting into *their* view of usenet newsgroups.
Everyone else sees them before you do.

Good Luck,
DoN.

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--- Black Holes are where God is dividing by zero ---