- I just found a series of 3 videos where he makes his gear and stepper
motor mount, ending up putting the gear in place and making it all
turn. He appears to use the Sherline threading set to sync the Z axis
to the spindle. I think you can get Mach3 to do that (I'm using
Mach3), so you don't need to have those gears there.
These appear to be the set, in order - about 1/2 hour of video here.
Sherline makes a part called a 6500, which is very similar in concept,
if not execution. http://www.sherline.com/6500pg.htm If I recall
correctly, they only make them on special order, but they are not that
expensive. It might be easy to just adapt their design, since it
seems to use parts on the current DC motor mount.
--- In SherlineCNC@yahoogroups.com, Martin Dobbins <trainnutz@...> wrote:
> I think the solution of using a timing belt drive and stepper has
some promise because it removes the requirement to measure and
maintain spindle speed and then feed it back into the control software
in order to cut a thread.
> Light cuts would prevent the spindle stepper from bogging down and
from there it's just a matter of a G code program to sync the spindle
speed with the feed to produce any number of different threads. In
his latest video he cuts an internal 3/4"-16 thread to mate with
the Sherline spindle nose as he makes an end mill holder from
scratch. His third video shows machining an internal thread on what I
believe is destined to be a dental implant.
> One of the things I like about these videos from Luiz is he
updates frequently; he has promised the third and final instalment of
his endmill holder soon and you can bet it will be posted within the
next few days.
> I'm more interested in the CNC lathe hardware than the machine
> controller. My attempts at CNC threading have not come out anywhere
> near that well. The belt drive and stepper on the spindle are obvious
> improvements I don't have, but I sure could use details on how to
> thread well with the CNC Sherline.
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> > A 1/4-20 is not a coarse thread for some people.started
> Until last year, I didn't consider it coarse, but when I first
> trying to thread with CNC, someone here told me it was easier to domentally
> finer threads. I understand a bit better why, now, but have
> filed 1/4-20 away as a "coarse" thread.We tend to think more like a 1/2-13 or 5/8-11 for a limiting size/TPI
combination on a Sherline, in steel.
>You still have to cut with the left side of the tool. The backlash
> How about if we run slower and take shallower passes? That would
> reduce the amount of load deceleration going on. The trade off is
> obviously that it takes longer. As I said, though, I'm a hobbyist.
> If it takes a few extra minutes to cut a thread that I need to cut
> once, it doesn't bother me in the slightest.
is too much to alternate directions and hold a tolerance. In order
to get enough tool pressure to take a minimum cut, you have to turn
at a minimum rpm. Each tiny pass will not cut, but only build tool
pressure until finally a massive chip is removed, drastically slowing
the spindle, affecting the cut pitch, and probably dropping steps
left and right.
Brass and aluminum are more forgiving then steel, but they want to be
cut at a much higher cutting speed to avoid galling and chip buildup
on the tool tip.
> Divide by zero doesn't work for much ;-) I found my spindle wasspeed
> slowing down by around 1% last time. Mach3 syncs to the slower
> and adjusts the Z axis feed rate very easily with that sort ofYou weren't loading the spindle, so yes Mach3 could keep up.
>The Sherline DC spindle, like most DC motors, has excellentYes DC motors have a near linear torque curve. Put an encoder on one
> low speed torque.
and you have a servo motor.
I would summarize that if you have very tiny threads to cut, you can
probably get Mach3 to work. That is OK for scale model engine
fastener creation, but probably not for general purpose kind of
We are still not going to offer or suport Mach3 threading on a lathe
because the area where it will work and where it will not is too
grey, compared with the clear delineation with a high res quadrature
encoder on the spindle. Maybe once the smooth stepper is out of
development, it will support a high enough resolution encoder. At
the present time Mach3 plus a smooth stepper costs more than DeskCNC
with controller, so it would also be a suboptimal solution.
Fred Smith - IMService