I have an old taiwan made 14 x 40 lathe (late 70's vintage, TWS brand)
which was already pretty beat when I aquired it (free!)

For the most part, things work well and it can maintain tolerable
accuracy for what I do so I would like to replace the one part that
brings it down: The cross feed screw. This screw is fairly typical in
style, several steps, each with different threads journals and keys for
the handles, bearings and such with a bronze nut on the under side of
the cross slide. Bronze nut is split with a wedge that adjusts via a set
screw to take up backlash. The wear in the middle is such that taking
up backlash there makes it tight at the ends of movement. Also, the
arrangement is constantly loosening.

So..here's the question. I know that I can't find an exact replacement
and need to scab together a new system. I can go high end and use a
ball screw, or lower end using something similar to what exists or
somewhere in between. My guess is that the designs haven't changed much
so I might be able to find a similar screw that could be modified from
the Grizzly or Jet parts depts.

Any suggestions on the best bet in the long run (other than buying some
better iron)? I hate to open a can of worms and turn this into a
nightmare project but it really needs to get done soon.

Thanks,

Koz

From what I've seen, ball screws are far more aggressive TPI, and
unsuitable for manual work - in that I wouldn't use it, but you're not me.

There was an article in HSM or PIM covering the use of moglice - a kind
of an epoxy with embedded material for repair of a lathe lead screw.
This approach would allow you to use your existing lead screw.

Some of your friction would be expected to be also from the worn ways of
the cross slide, so merely replacing the lead screw does not guarantee
elimination of binding.

Koz said the following on 7/28/2005 11:13 AM:
I have an old taiwan made 14 x 40 lathe (late 70's vintage, TWS brand)
which was already pretty beat when I aquired it (free!)

For the most part, things work well and it can maintain tolerable
accuracy for what I do so I would like to replace the one part that
brings it down: The cross feed screw. This screw is fairly typical in
style, several steps, each with different threads journals and keys for
the handles, bearings and such with a bronze nut on the under side of
the cross slide. Bronze nut is split with a wedge that adjusts via a set
screw to take up backlash. The wear in the middle is such that taking
up backlash there makes it tight at the ends of movement. Also, the
arrangement is constantly loosening.

So..here's the question. I know that I can't find an exact replacement
and need to scab together a new system. I can go high end and use a
ball screw, or lower end using something similar to what exists or
somewhere in between. My guess is that the designs haven't changed much
so I might be able to find a similar screw that could be modified from
the Grizzly or Jet parts depts.

Any suggestions on the best bet in the long run (other than buying some
better iron)? I hate to open a can of worms and turn this into a
nightmare project but it really needs to get done soon.

Thanks,

Koz

I had a worn out cross-feed lead screw on a 1962 Colchester Triumph.
There's no problem getting lead screws material, just matching the end
with the bushing and pinion.

I bought a new length of lead screw and and a new bronze nut. The nut
had to be machined to fit, but they're supplied oversize for this.

I cut off the old section of thread and kept the section throught the
bushing and the pinion. Throught this I bored and reamed a hole on
center. I machined the end of the new lead screw section with a
matching diameter. The fit was reasonably tight, but I put a split pin
in just to make sure.

Bruce

On Thu, 28 Jul 2005 09:13:06 -0700, Koz
wrote:

I have an old taiwan made 14 x 40 lathe (late 70's vintage, TWS brand)
which was already pretty beat when I aquired it (free!)

For the most part, things work well and it can maintain tolerable
accuracy for what I do so I would like to replace the one part that
brings it down: The cross feed screw. This screw is fairly typical in
style, several steps, each with different threads journals and keys for
the handles, bearings and such with a bronze nut on the under side of
the cross slide. Bronze nut is split with a wedge that adjusts via a set
screw to take up backlash. The wear in the middle is such that taking
up backlash there makes it tight at the ends of movement. Also, the
arrangement is constantly loosening.

So..here's the question. I know that I can't find an exact replacement
and need to scab together a new system. I can go high end and use a
ball screw, or lower end using something similar to what exists or
somewhere in between. My guess is that the designs haven't changed much
so I might be able to find a similar screw that could be modified from
the Grizzly or Jet parts depts.

Any suggestions on the best bet in the long run (other than buying some
better iron)? I hate to open a can of worms and turn this into a
nightmare project but it really needs to get done soon.

Thanks,

Koz
Ballscrews will turn if pushed on the end. So this means that if the
tool wants to dig in it can cause the ballscrew to turn which lets the
tool dig in even more. You may also have a hard time finding a
ballscrew with a pitch as fine as you current leadscrew. Acme thread
is best in this application.
ERS

On Thu, 28 Jul 2005 09:13:06 -0700, Koz wrote:

I have an old taiwan made 14 x 40 lathe (late 70's vintage, TWS brand)
which was already pretty beat when I aquired it (free!)

For the most part, things work well and it can maintain tolerable
accuracy for what I do so I would like to replace the one part that
brings it down: The cross feed screw. This screw is fairly typical in
style, several steps, each with different threads journals and keys for
the handles, bearings and such with a bronze nut on the under side of
the cross slide. Bronze nut is split with a wedge that adjusts via a set
screw to take up backlash. The wear in the middle is such that taking
up backlash there makes it tight at the ends of movement. Also, the
arrangement is constantly loosening.

So..here's the question. I know that I can't find an exact replacement
and need to scab together a new system. I can go high end and use a
ball screw, or lower end using something similar to what exists or
somewhere in between. My guess is that the designs haven't changed much
so I might be able to find a similar screw that could be modified from
the Grizzly or Jet parts depts.

Any suggestions on the best bet in the long run (other than buying some
better iron)? I hate to open a can of worms and turn this into a
nightmare project but it really needs to get done soon.

Thanks,

Koz


My fathe rin law has a Taiwanese late, of similar size and age. The lead
screws appear to be made from free machining steel, so wore out quickly. A
few years ago, I got a length of 4140 ground leadscrew from MSC in th
eright pitch (and left hand). He cut off the worn one and welded or pinned
on a piece of the new one. They also had the nuts, which would have had to
be made to fit under the cross slide, but in his case, the bew screw and a
bit of adjustment made it ok. I expect it to last for a long, long time
It was around $US100 for a 3' length
Geoff