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

>grr...that's the problem with analogies. i put my foot
>in with analogies, but i'm not gonna now immerse
>myself...lol

Don't feel bad.. I'm sure all the people driving cars *wish* they were
flying planes. Particularly during rush hour. :)

>i suppose you Can spend as much as you like to cnc a
>500$ lathe...but i question the assumption that $2000
>is the mean, average or normal figure - for a desktop,
>certainly.

My $2,000 figure was based on components for my 9x20 lathe..

2x Stepper/Servo motors @ $100 ea.; $200
2x Gecko G2x0/3x0 @ $120 ea.; $240
1x Power Supply @ $150
1x PC w/Monitor @ $250
1x Parallel Port Breakout @ $50 (could be twice that)
1x Ballscrews @ $300 (this item could be debatable and is probably more
expensive)
1x Replace single phase spindle motor w/3 Phase @ $75
1x VFD @ $175 (so I can control spindle speed)
2x Timing Belts, Pulleys..etc @ $30; $60
1x Limit switches, wiring, misc @ $100
1x Replace bearings and re-design motor mounts to control backlash @
$100 (probably more)

Total: $1,430

So, less than $2,000 but still quite a bit. And no, I don't want to
debate the exact dollars - depending on what and how you buy, you could
be quite a bit higher or lower. But I suspect that in general hardware
will run around $1,500. And even then you still have a relatively crappy
CNC lathe. (No power tailstock, no turret, no easy way to setup a
barfeeder..etc..etc. However, those items may not be important in this
class of machine.)

And yes, a Sherline or Taig would be much cheaper. Probably more like $5-700.

>i don't see how you can synchronise lead screw and
>spindle significantly cheaper or with less enjoyment
>than full cnc, at least on a desktop lathe like a taig
>or sherline. until the motors are in the hundreds
>dollar range, they arent the main cost of such a
>project.

Well, let's see.. Assuming you can get the control for $150, you still need:
1x Motor @ $100
1x Power Supply @ $125
1x Sensor of some sort to provide feedback on spindle speed @ $10
1x Timing belts, pulleys..etc @ $30.

You probably don't need to worry about backlash since you're probably
only going to be cutting in a single direction. You don't need to worry
about controlling spindle speed since you're only going to be cutting at
a single diameter (unless you have those really special DEEP threads),
you may or may not worry about limit switches, you probably don't need
ballscrews since you're only worried about accuracy over relatively
short distances.

Total $415 - despite what I said before.. At $415, I'd probably just go
on with my manual turning..... However, since you're probably not too
concerned with rapid speeds, you could use a smaller motor and gear it
down more, so $50 for the motor, which would let you use a much smaller
power supply, so $50.. At $290 it starts to look attractive to me again
although that's still a bit high just to do threading.

>i question the assumptions made regarding all the
>difficulties of CNC. if you want to design a circuit,
>you can go ahead and master orcad or altium...use your
>scope and soldering station to wire up a
>breadboard...or etch your own pcb...or create the
>files and send out $ for one...then you can test your
>board, but you still have to cnc an axis PLUS encoding

The capabilities of your axis don't have to be as good as for CNC.

>as well as the spindle encoder. well, those 2 things

You don't actually need a spindle encoder - you just need a tach.

>have to happen for full cnc anyway, so that's even.
>so you are trading off the shelf parts for a pcb
>design project to test (and will probably work without
>much tweaking) and to avoid the agony of attaching a
>stepper to the existing cross-slide screw and a 100$
>tablet pc to give you EvErYtHiNg you can gt by
>designing a 'less than' circuit...and lots more...of
>course, if you were to do an electronic spindle/lead
>synch, yu'd get a chance to do a lot of lovely math
>fun! but you can get that with cnc, too if you wanna
>do it the hard way..
>
>so that is not an effective trade (for me, with my
>skills, for my purposes) but then, i already know
>gcode consists mainly of the line and the arc and is
>sooooo not a hairy deal to put any effort into
>avoiding it...i already know all about designing a pcb
>so there is no great joy or novelty in that for me and
>i'll happily put my effort into what i see gets me a
>better return for marginally larger cost.
>
>i further question the assumption that $150 is the
>full and complete expense for developing the
>synchroniser. unless your wage is normally under 2
>digits and on the RIGHT side of the decimal point,
>your time is gonna have to count...

I don't think anyone is thinking they're going to make money making this
board. But then, I could be wrong about that!

>my cnc machines all have handwheels, btw. there's an
>assumption i outright reject. i use manual or cnc, as
>i please..

Don't let Ballendo hear you say that! (Although I happen to agree.)

--C.S.