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

Sir John, there is no paradox in what you say, I quite agree with
it. To whit:

- If I have to design and engineer the electronic leadscrew
from scratch, I'll deal with CNC.

- If it already existed in a form similar in cost and
complexity to the Shumatech DRO, I would buy the e-leadscrew and
consider CNC at some other point.

Apples to apples. It isn't, BTW, $70 of CNC versus $150 of the
other. It was $70 for the old PC (which may not run the software I
wanted to run, BTW) and then something more for the Gecko drives and
breakout box. Else we're building some as yet unnamed box to go
between old computer, stepper, and encoder. And then how much
trouble is it for all of that to peacefully co-exist and find space
on my workbench versus the little box that has it all under one roof?

The same arguments go on all the time with computers. There are
many so-called "appliances" available. Routers and other network
gizmos are the most common, but we also have file server appliances,
firewalls, and all sorts of others. They're all just computers
inside. Heck my silly Home Theater surround processor is a theater
inside. Tivo's are Linux computers inside.

My iPod is a little computer masquerading as a music playing
appliance. Why don't I just mount the $70 PC to my bicycle
handlebars and listen to that instead of buying the iPod for much
more money than this silly e-leadscrew? Fact is I like my iPod
because it is purpose built for what I wanted and it does its job
very well.

For all of these appliances, before they got built and marketed,
there were many someone's out there saying, "Wait, I can do this
with software on my PC, and I can do it better than your appliance,
why would I want that?" Sometimes they were right. But there are
many examples where the appliance is great and even peacefully
coexists with software solutions.

If you want to do CNC things, then by all means, CNC. If you want
to do manual lathe things, what a nice appliance this would be to
have. In terms of debugging it, I offer again the example of the
Shumatech DRO. I can find no reason why the e-leadscrew should be
any harder than that very successful and desireable product.

BTW, why would I need a DRO? I already have my PC, my encoders, and
Mach. What a stupid idea DRO's are. Heck a CNC rig can't even use
one for anything, so it's a total write off compared to the e-
leadscrew. We must take the DRO off this Yahoo Group name because
it is just too stupid to talk about one. Stupid electronic
leadscrew too. Stupid, stupid, stupid! Now I've got to go and lie
down in a dark room and plan my CNC lathe conversion. LOL!

Best,

BW

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "John Stevenson" <john@s...>
wrote:

>
> Go and get a coffee, this could be long,.....................

we'll wait.

>
> Ready ?
>
> I got involved with this about three years ago as I could see a

product at the end of it.

> The Frog is able to do this but I didn't like it as being too

crude, no screen and relying on croaks to tell you where you were.

> My idea was to split the drive train of a manual lathe. Top part

of the existing train drove a shaft encoder, bottom part drove the
existing leadscrew via a stepper motor.

> By using the halfnuts as normal you could spin between a manaul

lathe and a power feed / screw lathe.

>
> Stumbling blocks I came across, One I knew sod all about

electronics that little in fact that when I had a brain wave the
light didn't come on <g>,

> no problem, adopt the method called chequebook engineering and pay

someone to do this bit.

>
> Next problem was operation.
> In 'my' method you had the lathe running, half nuts engaged, small

amount of feed applied to cross slide [ X ] and you pressed start.

> The preprogrammed move then waited for the encoder signal and

drove the stepper motor vis a buch of magic spiky things

> in a set relationship, a set distance and stopped the screw at

this point which should be in a run off groove.

> You now wind out the X, manually, press a button, being return or

start again if the program is clever enough and it goes back to the
start point.

> Next step is to put the next feed on and press start again etc.

etc. until full depth is reached.

> Now the program running this can be anything from simple two way

movement where all

> control like depths of cut is via the operator or more technical

where the program works the lot out and just requires a start signal
at various points thru the program until it stop at the finish.

>
> The actual programming shouldn't be too hard as it's a division

program just like my gear hobber. An example:-

> Leadscrew of 8 tpi, 200 step motor driving screw at 1:1 and a 500

count encoder.

> To cut 8tpi the leadscrew has to move 1" for every 8 revs of the

spindle, 8 revs equals 4,000 pulses of the spindle. The leadscrew
also has to do 8 revs so the motor will be expecting 1600 pulses

> So to gear 1:1 for 8 tpi we need a divide by chip that can output

4000 / 1600 = 5/2 so for every 5 pulses it receives it sends out 2.

>
> 16 tpi will be 5/1
> 32 tpi will be 10/1 etc
>
> These are not very good figures and a bit of time spent working

out encoder counts will be able to get a better set of ratios, this
just lays out the idea.

>
> Now taking this one stage further it's a single axis CNC program,

Aaagghhhh shouts of dismay, we don't need no steenking CNC's I hear

> But it is.
>
> Now the opposition comes into play, too expensive, we want a

little box about $150 and no CNC.

> So lets look at a cost breakdown
>
> We will gladly pay $150 for this but what is 'this'
> First we need the $150 black box, then a stepper motor and a

driver and a shaft encoder and a few mechanical bits. OK with me so
far?

>
> Now we look at a single axis CNC route.
> No black box but an old PC and a software licence, then a stepper

motor and a driver and a shaft encoder and a few mechanical bits. OK
with me so far?

>
> Hang on, what's changed? we now have an old PC and these are

usually free or very cheap, OK for arguments sake we say $30 and a
license at $40 - $70?? and we were happy with $150??

>
> So we now have what we were looking for , no development, no

waiting and we save money ?

>
> No, just re read all I've typed and I can't see where I have gone

wrong, why have I talked myself out of reinventing the wheel.

> It's not full CNC, it only drives the leadscrew, when the 1/2 nuts

are disengaged it's a manual machine.

>
> I need to lie down in a dark room with a damp copy of Exchange and

Mart over my eyes...........bye.

>
> John S.
>
>
>
>
> This e-mail was scanned for viruses using BitDefender
>