Hi. I'm trying to convert a process I have from an art-form to a
science.
I simply hand-polishing the face of a large lot of cylinders, each for
about a minute with 2000-grit sandpaper, but would like to keep the
pressure consistent. What device can I install to the lathe that will
report how much axial forces are being transmitted ? The lathe I am
using is a small Sherline benchtop.

Thanks.
Marcel

If you simply want to maintain a constant "axial force" and don't need
to know the exact value in inch pounds or whatever, just use an AC
clamp-on ammeter on the input to the drive motor.

Pete Stanaitis
--------------

wrote:
Hi. I'm trying to convert a process I have from an art-form to a
science.
I simply hand-polishing the face of a large lot of cylinders, each for
about a minute with 2000-grit sandpaper, but would like to keep the
pressure consistent. What device can I install to the lathe that will
report how much axial forces are being transmitted ? The lathe I am
using is a small Sherline benchtop.

Thanks.
Marcel

On Sep 19, 8:38*am, spaco wrote:
If you simply want to maintain a constant "axial force" and don't need
to know the exact value in inch pounds or whatever, just use an AC
clamp-on ammeter on the input to the drive motor.

Pete Stanaitis
--------------



thanks for the reply. I'll look into an ammeter that can be affixed
around a cable.

wrote:
Hi. I'm trying to convert a process I have from an art-form to a
science.
I simply hand-polishing the face of a large lot of cylinders, each for
about a minute with 2000-grit sandpaper, but would like to keep the
pressure consistent. What device can I install to the lathe that will
report how much axial forces are being transmitted ? The lathe I am
using is a small Sherline benchtop.
What you are asking for is called a dynamometer, but basically it is a
beam with strain gauges on it, and a readout box. A commercial setup
will cost at least 10x what the Sherline cost. You could make it, though.

Jon

On Sep 19, 10:48*am, Jon Elson wrote:
wrote:
Hi. I'm trying to convert a process I have from an art-form to a
science.
I simply hand-polishing the face of a large lot of cylinders, each for
about a minute with 2000-grit sandpaper, but would like to keep the
pressure consistent. What device can I install to the lathe that will
report how much axial forces are being transmitted ? The lathe I am
using is a small Sherline benchtop.

What you are asking for is called a dynamometer, but basically it is a
beam with strain gauges on it, and a readout box. *A commercial setup
will cost at least 10x what the Sherline cost. *You could make it, though.

Jon

Hi Jon, can you enlighten me on how one can make such a device ?
Marcel

On Sep 19, 4:53*am, "
wrote:
Hi. I'm trying to convert a process I have from an art-form to a
science.
I simply hand-polishing the face of a large lot of cylinders, each for
about a minute with 2000-grit sandpaper, but would like to keep the
pressure consistent. What device can I install to the lathe that will
report how much axial forces are being transmitted ? The lathe I am
using is a small Sherline benchtop.

Thanks.
Marcel

Marcel,
I assume, by axial force, you mean the force toward the headstock form
the tail stock end. The pressure on the sandpaper.

If so, then a postal scale can do the job. The little mechanical ones
for up to 16 ounces. Under $10 I think.
If you need more force, then an electronic postal scale would work.
(Some can be disassembled to remove the load cell. It's usually an
aluminum or steel gadget, about 2" square and 1/2" thick.)
You could also use a fish scale, perhaps 8" off center provide a
pivot, half way to the spindle a hole for fish scale, with your
sanding pad on center. The fish scale will read double the actual
pressure.
The easiest, but most work, would be to build a compression type fish
scale. It could mount in the tail stock. Bore a tube, insert a
spring, then a plug, lines and numbers on the plug, might need a way
to keep it from rotating.

Dave J.

wrote:
Hi Jon, can you enlighten me on how one can make such a device ?
You can probably buy strain gauges on eBay, or get new ones from some
outfit like Omega.
They are thin, stick-on pieces that have a resistance element that
changes under force.
If you put two on the top and two on the bottom of a beam, and wire them
up in a criss-cross manner, they make a 4-arm bridge. You want this so
that an electrical drawing would look like a tilted square with the top
left and bottom right element are on the same side of the beam.
This maximizes the unbalance of the bridge under force. You excite the
bridge with a constant current (or voltage) from the top to bottom, and
read the difference with an instrumentation amplifier such as the Analog
Devices AD620 taking its signal from the left and right junctions on the
diagram.
You could read out the result with a DVM, and create a calibration table
with weights or a fish scale.
Some reading on Google or WikiPedia might help.

Jon

--For more on this way of doing it google "prony brake".

--
"Steamboat Ed" Haas : "Hold on! we're passing
Hacking the Trailing Edge! : through the moronosphere!"
www.nmpproducts.com
---Decks a-wash in a sea of words---

On Sun, 21 Sep 2008 15:36:09 +0000, steamer wrote:

--For more on this way of doing it google "prony brake".

While "prony brake" is the historically correct term,
"pony brake" gets 32 times as many google hits on the
same subject (ie, dynamometers).

--
jiw

Umm... Some confusion on exactly what you are doing but if I'm reading
between the lines correctly,

When you say "polishing the face of a large lot of cylinders" I'll assume
you mean the "round part" and since you didn't specify inside or out I'll
assume out...

With all those *assumptions*.. uh why not make a real "prony brake".

Build some type of hinge on your tool post.

Measure distance from hinge point to centerline of work.

Make bar 6 time longer than distance to centerline (or 3 times or what ever
you like) and hook to hinge so one end is just under cylinder and other end
hangs over tool post.

Put 2000 grit on short end of bar under cylinder facing upwards.

Place weight of choice at other end of bar and polish...

Adjust weights till you like the finish...

Exact force can be calculated by multiplying weight by bar length... e.g. 3
foot bar hinged at 1 foot point, with weight out at 2 foot end from hinge
is multiply weight by 2. 6 foot bar would have weight 5 feet out, multiply
by 5....


--.- Dave (who could design a computer controlled servo with several force
gauges to do this with a snazzy readout and keypad for data entry and
ethernet link so you could control it from around the world, but... why?)




wrote in message
...
Hi. I'm trying to convert a process I have from an art-form to a
science.
I simply hand-polishing the face of a large lot of cylinders, each for
about a minute with 2000-grit sandpaper, but would like to keep the
pressure consistent. What device can I install to the lathe that will
report how much axial forces are being transmitted ? The lathe I am
using is a small Sherline benchtop.

Thanks.
Marcel

On 2008-09-21, Dave August wrote:
Umm... Some confusion on exactly what you are doing but if I'm reading
between the lines correctly,

When you say "polishing the face of a large lot of cylinders" I'll assume
you mean the "round part" and since you didn't specify inside or out I'll
assume out...

A cylinder need not be hollow -- unless you are talking about
part of an engine (steam or IC). Consider a bar which has been parted
off, and plan to polish the surface where the parting off occurred.

(Of course, I am not the OP, so I could be wrong.)

[ ... ]

--.- Dave (who could design a computer controlled servo with several force
gauges to do this with a snazzy readout and keypad for data entry and
ethernet link so you could control it from around the world, but... why?)

:-)

Enjoy,
DoN.

--
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