Tried to estimate the bed wear today.

I did the following: placed a digital indicator (0.001mm resolution)
with the magnetic base on the carriage. Its point was resting on the
non-worn part of the bed where the tailstock rides.

I moved it all the way away from the headstock and reset the dial to
zero.

I was hoping that as I moved the carriage along, the indicator would
show a positive number, as the bed would go lower due to its wear
closer to the tailstock.

It indeed happened. The number on the indicator started rising from
zero and rose to 0.05 millimeter (or 0.002 inch).

I repeated the procedure several times, every time the reading would
return to zero as I returned the carriage back away from the
tailstock, and the max reading was consistently 0.05 or 0.06mm, or
0.002 inch.

So, my obvious question is how to read this number, do you think that
the wear is bad or not bad?
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rOn 2008-07-18, Ignoramus20788 wrote:
Tried to estimate the bed wear today.

I did the following: placed a digital indicator (0.001mm resolution)
with the magnetic base on the carriage. Its point was resting on the
non-worn part of the bed where the tailstock rides.

I moved it all the way away from the headstock and reset the dial to
zero.

I was hoping that as I moved the carriage along, the indicator would
show a positive number, as the bed would go lower due to its wear
closer to the tailstock.
^^^^^^ headstock, sorry

It indeed happened. The number on the indicator started rising from
zero and rose to 0.05 millimeter (or 0.002 inch).

I repeated the procedure several times, every time the reading would
return to zero as I returned the carriage back away from the
tailstock, and the max reading was consistently 0.05 or 0.06mm, or
0.002 inch.

So, my obvious question is how to read this number, do you think that
the wear is bad or not bad?

--
Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
posting on Usenet.
http://improve-usenet.org/

In order to tune the lathe, three tools are needed. The first is a precision
level and the second is a spindle test bar and the third is a dial
indicator. With these tools, all measurements and adjustments can be made.
First, the level of the bed must be established. Not so much for the
operation of the lathe in this instance, but to establish a measurement
baseline. To do this correctly, be prepared to twist the bed. This sounds
impossible, but the bed is actually quite plastic and it is easy to achieve.
The bigger the lathe, the easier it is Remove everything from the bed. You
can cheat and remove everything but the saddle if you want, but it is better
to remove everything. if the lathe has an underlying bench or cabinet, you
may want to unbolt the bed, jack it up and drill and tap two holes in the
bed legs at the tail stock ends. Install two jacking bolts in these holes
and remove any shims that may exist under these legs and rebolt leaving
these new screws loose. Now level the bed horizontally at the headstock with
the cabinet feet, then level the bed longitudinally with the cabinet feet,
alternating back and forth to the best possible position. Don't worry about
the horizontal plane at the tailstock, that's why we have the jacking
screws. With the bed firmly bolted down measure the horizontal level
incrementally from the headstock end to the tailstock end and record your
readings. Now you have established the bed twist. Recheck the headstock side
and be certain it is still level. Place the level across the tailstock end
and with the jacking screws twist the bed to level, often checking that the
headstock side isn't changing. If it does, adjust with the cabinet feet (the
cabinet is twisting) Repeat this until the horizontal plane is the same at
both ends. Then with feeler gages measure the gap between the feet and the
cabinet, make a shim pack to the measured dimensions and rebolt the bed.
Check for level again and repeat 'till square. Now by measuring the
difference in level across the bed, you can establish the wear. (The level
is calibrated) Once that is accomplished, reply with your readings and we
will talk about that and perhaps the next episode, the headstock.
Steve

"Ignoramus20788" wrote in message
...
Tried to estimate the bed wear today.

I did the following: placed a digital indicator (0.001mm resolution)
with the magnetic base on the carriage. Its point was resting on the
non-worn part of the bed where the tailstock rides.

I moved it all the way away from the headstock and reset the dial to
zero.

I was hoping that as I moved the carriage along, the indicator would
show a positive number, as the bed would go lower due to its wear
closer to the tailstock.

It indeed happened. The number on the indicator started rising from
zero and rose to 0.05 millimeter (or 0.002 inch).

I repeated the procedure several times, every time the reading would
return to zero as I returned the carriage back away from the
tailstock, and the max reading was consistently 0.05 or 0.06mm, or
0.002 inch.

So, my obvious question is how to read this number, do you think that
the wear is bad or not bad?
--
Due to extreme spam originating from Google Groups, and their
inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
posting on Usenet.
http://improve-usenet.org/

On Jul 18, 12:00*am, Ignoramus20788 ignoramus20...@NOSPAM.
20788.invalid wrote:

I repeated the procedure several times, every time the reading would
return to zero as I returned the carriage back away from the
tailstock, and the max reading was consistently 0.05 or 0.06mm, or
0.002 inch.

So, my obvious question is how to read this number, do you think that
the wear is bad or not bad?

My first lathe had ~0.025" of bed wear and still could turn straight,
which is the real test. Use it, make some parts and measure them, then
decide if the lathe is good enough for the sort of work you do. I
adapted to that worn lathe by doing critical work at the tailstock end
where the bed and leadscrew were in good condition.

On Thu, 17 Jul 2008 22:58:11 -0500, Ignoramus20788
wrote:

I was hoping that as I moved the carriage along, the indicator would
show a positive number, as the bed would go lower due to its wear
closer to the tailstock.

Since the carriage tracks the worn surfaces, the wear is probably
worse than you measured. As you go toward the headstock with the
indicator mounted on the carriage, the indicator is dropping in height
as you head towards the headstock, nulling some of the reading.

Ignoramus20788 wrote:
Tried to estimate the bed wear today.

I did the following: placed a digital indicator (0.001mm resolution)
with the magnetic base on the carriage. Its point was resting on the
non-worn part of the bed where the tailstock rides.

I moved it all the way away from the headstock and reset the dial to
zero.

I was hoping that as I moved the carriage along, the indicator would
show a positive number, as the bed would go lower due to its wear
closer to the tailstock.

It indeed happened. The number on the indicator started rising from
zero and rose to 0.05 millimeter (or 0.002 inch).

I repeated the procedure several times, every time the reading would
return to zero as I returned the carriage back away from the
tailstock, and the max reading was consistently 0.05 or 0.06mm, or
0.002 inch.

So, my obvious question is how to read this number, do you think that
the wear is bad or not bad?

That is quite good for a well-used lathe. I had about .013" on
my Sheldon 15" lathe, and decided that was much worse than I
could live with. Making estimates of the overhang and lever
arm, I calculated that it would put a .016" taper or barrel
shape in a 1" diameter part. That was totally unacceptable to me.

What you have to do is repeat the test with the indicator at the
REAR way, riding on the reference surface of the tailstock way
(assuming a classic American-pattern lathe). If the wear shows
a roughly similar change, you are in great shape, as the wear is
roughly symmetrical front and back. Also, gravity and the
distortion caused by flame hardening the bed may have put a sag
in the bed, and your measurement technique may be picking that
up, too. (My Sheldon's 6-foot long bed had a .003" sag in the
middle, probably caused by the stresses induced from the flame
hardening.) The inverted-vee changes the force vectors causing
more wear on the front way than the back, and the dribbling of
chips increases wear on the front way, too. But, the critical
thing is the relationship between the front and rear way. If
the wear is relatively similar, the taper on parts will not be
large. Assuming the front way has all the wear and the back is
unworn, then you might get as much as .005" of taper on the
diameter of a part. Measure the distance between the two ways,
and measure the distance between a line front-to-back between
the ways and the spindle centerline. On most lathes, the height
of the spindle above the ways is very roughly similar to the
spacing between the ways.
You can work out the trig for your particular machine.

If the wear is similar front and back, then the tool will just
move up and down, not in and out, and the taper will be vastly
smaller.

Jon

Grunty Grogan wrote:
On Thu, 17 Jul 2008 22:58:11 -0500, Ignoramus20788
wrote:


I was hoping that as I moved the carriage along, the indicator would
show a positive number, as the bed would go lower due to its wear
closer to the tailstock.


Since the carriage tracks the worn surfaces, the wear is probably
worse than you measured. As you go toward the headstock with the
indicator mounted on the carriage, the indicator is dropping in height
as you head towards the headstock, nulling some of the reading.


On most "American pattern" lathes, there is a "reference
surface" ground right at the top of the inverted vee, and
another at the top of the tailstock vee in the rear. Nothing is
supposed to ride on these surfaces, and they are ground at the
same time as the rest of the bed's critical surfaces. You level
and align the bed using these surfaces, for instance. I think
Iggy was riding his indicator along these reference surfaces
(actually only the front one). This should measure bed wear
pretty well. it will miss sag in the middle of the bed due to
gravity and stresses from flame hardening, but those are less
important.

Jon

On Fri, 18 Jul 2008 07:50:00 -0400, Grunty Grogan
wrote:

On Thu, 17 Jul 2008 22:58:11 -0500, Ignoramus20788
wrote:

I was hoping that as I moved the carriage along, the indicator would
show a positive number, as the bed would go lower due to its wear
closer to the tailstock.

Since the carriage tracks the worn surfaces, the wear is probably
worse than you measured. As you go toward the headstock with the
indicator mounted on the carriage, the indicator is dropping in height
as you head towards the headstock, nulling some of the reading.

Mount the indicator on the tailstock, as the tailstock ways see the
least amount of use on MOST lathes

Gunner