Re: Electronic Lead Screw & Power Cross Feed | Poor Man's CNC ?

I think the CNC setup is actually considerably more complex than
what is contemplated in the strictest sense of an electronic
leadscrew and I'll tell you why. It all sounds like a case of "Gee,
if I have to hook up a stepping motor anyway, why not just go CNC?"
However, let's look at a couple of different reasons why that is not
really the case.

First, we have to make sure we are doing an apples to apples
comparison. It is certainly true that there are no electronic
leadscrews to be bought off the shelf today unless you want to count
the short-lived Frog CNC. I will therefore readily admit that the
development of an e-leadscrew from scratch will certainly be more
complex than to piece together a CNC system from off-the-shelf
components. So let's assume the e-leadscrew exists. Not so far
fetched, BTW. As was pointed out, there is the Frog CNC and also
this conversation keeps coming up on all sorts of boards. Clearly
there is demand or interest, and someone is going to get around to
building one. Heck I heard Cletus Berkeley say he was going to look
into it over on another board, and there is a fellow on the Home
Shop Machinist board that has built an electronic gearbox for a gear
hobbing machine, so someone WILL do it!

So what would this new animal be like? Well, it's going to be very
simple because it doesn't have to do much. Again, if you have ever
seen a Frog CNC, there is nothing to it. It's a tiny little circuit
card with a membrane keyboard and LED readout that's built around a
PIC controller. It's got a stepper driver on board and takes a
spindle encoder signal in.

Let's imagine something very similar to the Frog CNC will work. In
fact, I think it will be very similar to the Shumatech DRO in terms
of the complexities involved (hence a thread about this on that
board too). Lots of folks manage to get one of those DRO's up and
running for around $150 plus the cost of the scales. Picture
something similar here. You order the blank PC card from a
Shumatech-like entity, buy your parts to populate it, solder it
together, and $150 plus a little time later, you are ready to plug
it into your spindle encoder and leadscrew stepper motor you got on
eBay.

Which brings me to my second point. If that solution existed today,
it's a lot simpler than full CNC. If I can really build the thing
for $150, buy a surplus stepper from eBay, and hook together a few
parts for a spindle encoder, it is hard for me to regard that as
even approaching the complexity of CNC.

Let's just break it down. I have to have a PC for CNC. What if I
don't have a spare sitting around? Even a cheap obsolete PC costs
as much as the DRO. I have to configure it properly for my
software. TurboCNC doesn't want to run on Windows XP, so I gotta go
deal with that. Mach will run on XP, but the software costs as much
as my PIC controller for the leadscrew and its just one piece of the
solution. I need a Gecko drive, which is another $100. It's very
possible my PIC-based project can deal with driving one stepper
right on the card for its $150 cost as we already saw with the Frog
CNC device. What about backlash? The CNC crowd certainly spends a
lot of time talking about it and going on about ballscrews to avoid
it or various other solutions. Ballscrews are big bucks. The e-
leadscrew doesn't care about backlash because the operator deals
with it as a matter of course. How about a breakout card so my PC
can talk to my Gecko drive? Campbell designs makes a great one, and
oh by the way it too costs as much as a Shumatech DRO. Maybe I'd
like a nice pendant, because I really don't care to type on the
keyboard and click the mouse, I want to work on my lathe for crying
out loud! www.lowcostcncretrofits.com has one that plugs into my
USB port (hope I didn't buy an old 486 machine to save money!).
Guess what, it too costs about what that darned Shumatech DRO would!

Now just about every component in the CNC system has cost as much as
the e-leadscrew electronics, each and every one of them has a
learning curve before I can get it to work at all, and we haven't
even gotten on to the real learning curve associated with the fact
that your machinist may know full well how to make parts with his
lathe but not know the first thing about CNC, or care to learn.
He's just tired of digging around in the swarf to find the right set
of gears to cut a thread he needs or change the feed speed to get
rid of some chatter.

It's all fine and well to argue CNC is better, but its really better
at solving a completely different problem and it is far from being
simpler or "you might as well go for CNC if you are going to go to
all this trouble anyway."

BTW, the clever thing about the Frog CNC is you can use it as an
electronic leadscrew AND as a breakout box + stepper driver. This
way you get both CNC if you hook up all the extra components and a
vastly improved manual lathe if you want to focus on one-off parts.
That too would be a nice attribute for the e-leadscrew when it is
available.

Best,

BW


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Paul Kelly" <tech@c...>
wrote:

>
> This thread crops up with some regularity.
> Yep, you could make a setup, as described, work.
>
> Or you could add one more motor. And use simpler, off the shelf

electronics

> (or simpler, 'you build em', electronics) and have a CNC setup.

Typically

> the proponents of the electronic gearing systems feel that,

because you can

> do so much more with it, a CNC setup must be more complex. In

fact, this is

> not the case. Vaso alludes to the reality of the situation. The

issue is

> mostly about stepping out of your comfort zone and learning a new

thing...

>
> PK
>
> -----Original Message-----
> From: CAD_CAM_EDM_DRO@yahoogroups.com
> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Vaso
> Sent: Sunday, 4 December 2005 5:54 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: [CAD_CAM_EDM_DRO] Re: Electronic Lead Screw & Power Cross

Feed |

> Poor Man's CNC ?
>
> I've done machining for several years, but I'm new to CNC. I'm an
> electronics engineer, so an electronic approach to gearing - rather
> than mechanical gears - appeals. This PLL (Phase Lock Loop)

method is

> well-known in electronics.
>
> Maybe electronic gearing could be called the "Poor Man's CNC". I'm
> less interested in full programmable CNC right now than I am in
> correcting some deficiencies in the SIEG C6B lathe I just bought.

The

> C6B has variable spindle speed, but fixed saddle traverse - so feed
> rate is either 0.1mm/rev or 0.2mm/rev and switching between the

two is

> awkward. There is no Quick Change Gear Box, so threading requires
> manual gear substitutions. There is no Power Cross Feed, and there

is

> no taper attachment. Seems to me PLL control of the lead screw, as
> described in this article, with the enhancement of microprocessor
> control of speed ratios, could give practically unlimited threading
> and traverse speeds. Power cross feed could also be arranged by

this

> method. If Power Cross feed linked to lead screw speed, then this

is

> effectively an electronic taper attachment. Several tricks short of
> full CNC could be microprocessor-controlled.
>
> Am I missing something ?
>
> I'm new at this. Could someone give me a head start on the kind of
> stepper (?) motors I should be looking at, encoding wheels, and
> microprocessor/computer control ? Someone who owns a SIEG C6 or
> Grizzly G0516 might also be interested or could supply conversion
> information.
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, juan gelt <juangelt@y...>

wrote:

> >
> > i will say that the circuit is primo basis for a
> > tach/speed controller. he has 40 holes on his spindle
> > sensor disk that he was gonna up to 120.
> > we know (i'm still amazed!) that you can do threading
> > with turboCNC and a single index point on spindle.
> > his circuit didn't have indexing, nor require it to
> > make 2 motors run in synch. the circuit deserves a
> > star for precisely comprehending and solving a
> > problem- but i'd say, once you have tachometry, speed
> > control and indexing, you've got all there is to get.
> > then it's just a matter of resolution and how fast you
> > can do whatever you want with it.
> >
> >
> > --- turbulatordude <dave_mucha@y...> wrote:
> > > juan gelt <juangelt@y...> wrote:
> > > >i believe the system will work with some limits of
> > > > accuracy. however, i also have a question on the
> > > > actual utility of it. if you are already CNC and
> > > > have a spindle encoder, you have a much more elegant
> > > > route to all the control, no?
> > > >
> > > Congratulations on being the first to accress this for it's
> > > technical merits ! (I was geting to cut this thread.)
> > >
> > >
> > > I have an old SB lathe with manual change gears.
> > > I was thinking something like this would be a way to
> > > just add variable speed to the spindle and also add electronic
> > > thread cutting.
> > > I didn't read thru the article with any accuracy,
> > > just briefly and I did not see if the unit has a single

alignment

> > > point per revolution.
> > > What actual value would this be to a home shop ?
> > > And, is it more effort than adding CNC ?
> > > Dave
>
>
>
>
>
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