Re:Re:Lathe threading

I wrote: [andrews answers] below
<snip>[But it does make it possible, which is something,

>considering the price. ]
>Maybe an air cylinder to move the tool slide in and out quickly,
>could be an add-on?
>[Except the air cylinder has a fixed stroke length, right? Would you
>count on the air pressure to hold the cutter into the material so it
>didn't jam up? I suppose this could be adjusted for, but it might
>take a few tries.]

Agreed, the possibility is intrigueing, hence my response(s).

A nice thing about air cylinders is the compressability of air. As
you point out, it COULD rely on air pressure to hold the cutter in
position, if the cylinder were appropriately sized. Surplus, they ARE
CHEAP!!! The compressibility comes into play so that you can use an
adjustable stop and only use as much of the cylinder travel as
necessary for the current cutOr use the air to move a DE-STA-CO type
over center lock. The point is an easy way to move the slide in and
out (dont touch that shoulder!!!)

[For this sort of thing, do you really need to keep track of
fractional spindle revolutions?]

In the 1st part of my response I "theorized" how it might be done,
using only your description. Lets see, if we are cutting 10TPI, AND
we have a way to instantly move the cutter into and out of
position,then the scenario appears to be:

Wait for the magnet to come flying by. When it does we need to get
into cutting positon (cutting the material) and move the carriage
.100 BEFORE the next magnet fly-by! Then repeat this for the length
of the thread. Finally, get the tool out of the cut before we cut
somewhere(or something) we shouldn't.

UNLESS we have already determined(with some pretty good accuracy and
repeatability) the spindle speed, it would appear IMPOSSIBLE to know
how fast to move the carriage to cut the threads. "Fractional spindle
revolutions let us split the possible error into smaller parts.

I am curious how he does it, but more interested in the possibility
that someone ON our list could do it better,and maybe make some money
in the process. So I "theorized some more", shown below.

>Just doing threading on a lathe does not require a PC for control,
>and he's taken an interesting approach. I might suggest using a real
>encoder and some simple divider circuitry or s/w (this IS a PIC type
>project). One encoder for the spindle, one stepper for the carriage,
>and a hand calculator size "black box" to set TPI.

[I think that mounting the encoder would present some problems in
this sort of machine. The magnet solution sounded a lot simpler. ]

It may be, but not by much,IMO. And the power of having the encoder
to use .... Really, there are LOTS of ways to mount encoders and it
shouldn't really take much more than the magnet(easy) and the magnet
sensor(probably very similar problem to mounting the encoder!)

[I haven't seen a Sherline threading attachment anything like this- is
there any info about it on the web? I thought the way they did
threading was by using change gears.]
Andrew

Sometimes you can "read between the lines" of what a manufacturer
has released, and infer where else they may be going.

1.Sherline has engineered and implemented stepper mounts for nearly
all their products.
2.Sherline has the "Black box" I spoke of already; it drives steppers
and can be CASCADED. The commands available clearly point to the
POSSIBILITY of using a couple of these for lathe threading.
3.Joe Martin, in his book "tabletop machining, said a lot about where
he saw his company going over a year ago.( When Joes' longtime
partner Carl died, Joe had to do some things by himself that he had
help with before) In the book, while he was givin' some good ole
general buz'ness advice, He said, I SURE WOULDN'T build my business
DEPENDING on someone ELSES PRODUCT OR DESIGN. THAT MANUFACTURER MAY
GO INTO THE SAME THING I AM TRYING TO DO AND WILL CERTAINLY HAVE THE
ADVANTAGE.

The above is paraphrased, but I remember when I read it almost TWO
years ago, that the sherline retro-fitters had some interesting days
ahead! (the book was out before the release of the sherline CNC
mods;The stepper rotary table was in beta.)

Ballendo