Re: [CAD_CAM_EDM_DRO] Re: Tooth belts & gear suppliers

Let me insert what my stepper machine does for me, ......with belts.

What: Cnc Router

Control: FlashCut Why ? It's windows. I used DOS, lotsa different DOS, Now I
want windows, So, I got windows.
(went thru a couple actually)

Drivers: MicroKinetics DM 4050's Not my first choice, but lets see, Feed and
clothe Kids? or Big Money Drives ?
(back then, they were indeed "big money" drives. Gecko did not exist!)

Power Supply: MicroKinetics 36V Similar to above, Keep wife ? Or high voltage
drive? I NEED wife !

Motors: MicroKinetics 450oz (2) and (1) 160oz ok, so I was weak at the
time..........

X-Y Method: Pulley and Belt X-Y 30 tooth on the motors - 20 on the leadscrews.
(used to be 30:30 but these motors run out of oooph at high rpm. Enter in a 36
volt system....)
These drive a Rolled 1/2" diameter 4 start Kerk with Antibacklash nut (VHD8050)
.500 Lead (2 turns per inch) Why Not?

Z Method: Belt and Pulley 1:1 ratio Driving a 1/2" diameter Kerk with
Antibacklash nut .200 pitch Leadscrew (5 turns per inch) (should really be a .25
lead but shhhh, don't tell anyone)

Linear: Typical Round Thomson Style Rail (NB) with low profile supports and Open
Bearings Works for me !

Limit switches: Typical Cherry Snap type lever switches. Ah, the beloved Cherry !

Results: With 8th stepping, under way, the above delivers a resolution of
.000467115097" . This would be .0037369 for one full motor step.

Does it cut to that ? Heck No. So what. But, I will say that anything I have
ever thrown my digital caliper on is within .001. (Mit Caliper - Not Micrometer)
Not too stinkin' bad for a Flatbed "Moving Gantry" Router using belts.

I heard all the arguments that moving table is better. Even worked with them, on
them, modified them. I KNOW it has a bigger footprint for sure. Look at it this
way, I could build a screwed up inaccurate moving table machine as well as a
screwed up moving gantry..... See ? there is NO difference !

I did have .200 lead on all axis but who needs that resolution on this type
machine ? You can't get any speed out of that !

Once I put a 2" Dial on each side of the Gantry. I ran a loop back and forth a
gazillion times with a healthy delay between direction changes so I could read
and log each dial reading. Of course my dials only show .001, and it was always
right on.
Did the same with all the axis'.

What can she push ? I never had a good way to figure this other than my wifes
bathroom scale (see I told you I need her !).
I ran a straight line in X and did the same in Y pinning the scale tight to an
object that was not going to move. At 25ipm when the motors stalled the scale hit
180lbs. At 60ipm, the scale hit 140lbs. Due to the "New Shape" of the scale, I
was not able to carry out any more of these scientific tests ! I did fit in one
more more gentle crash, er test, on the Z axis which pushed a healthy 110lbs at
25ipm. I can not imagine what a 70 volt supply would do to my scale.....

Maximum speed: Well, though I can get the wretched thing to run X-Y rapids at
600ipm.... it is not reliable. 400ipm is more realistic and dependable but I
really never run it at that level. I need to keep my machine on casters... and
well, I hate chasing it all over the room ! My preference is 200ipm so it does
not run anything or anyone over. Z axis can only do about 275ipm max.
repetatively.

Homing: Cherry Switches.... I do not care how many times I run the machine home
with a dial indicator in place to double check, a good Cherry snap switch will
repeat .0003. Yep, the area must be kept clear of refuse but if yo do it right
with the little roller, it will "scrub" off anything on the way in. Make sure you
use Cherrys with a healthy spring.

Ballendo has preached the first rule of machine building. "It only has to be
built to accomplish a given task." All I can add is "within your budget." (btw -
my plan set is within most peoples budget, just not the parts to build the darn
thing!)

My machine has done that and more. It's more than I expected. It has proven
itself dependable and trustworthy. I can do fine work, diamond drag, signs, even
some aluminum machining here and there. It is not a mill though. Never said it
was. But it does cut without overshooting, undershooting, ragged edge, etc.

If my Belts and Pulleys are LOSING 2 or 3 steps here and there..... It is keeping
it a highly protected secret from me !

Jan, This is NOT an attack.... I've worked on and built direct drives too. It
just takes a little more thought process, something my old brain is running out
of the ability to do. If one has the ability by all means go for it.

For those interested, The above leadscrew combinations work quite well for a
small flatbed router. Do the .25 lead though on the Z axis, and don't fear 300oz
motors on the X-Y..... I would use them next time instead. Especially with higher
voltage. Want to save a little on Linear slides...... Go ahead Use Frelon.

FlashCut ? Good things on the horizon for you FlashCut supporters.....

And if you have to mix and match junk for drive electronics, hey, you can always
change that. Just don't skimp on "Structure" and "Design".

How about you guys ? Anyone care to put their "results" in print ? Even your
follies ! This would help all of the newcomers to this great sport, er hobby!

I hope the above encourages,

Chris Luebke
DATA-CUT



JanRwl@... wrote:

> In a message dated 05-Nov-01 09:28:38 Central Standard Time,
> mikep_95133@... writes:
>
> > Belts and pulleys are a mistake?
> >
> > Why?
>
> In MY opinion, the added "slop" would introduce error in EITHER direction
> between the motor and the lead-screw position, equal to two or three steps.
> Of course, this would be "non-cumulative", I guess, but "sloppy" for
> machining!
>
> If the belt were made tight enough that there was no "take-up", causing the
> above, the added TENSION/friction would be rather severe, it seems to ME!
> AND, the stretch of a fiber-core,neoprene "timing belt" would introduce an
> "all-new" pitch between the teeth of the belt which might "fit" the
> cog-wheels OK, but it would surely cause an "accumulative" error, wouldn't
> it???
>
> If the stepper is connected directly to the screw via one of the high-tech
> "bellows couplings" or the "multi-helix" couplings (EDM aluminum stuff), with
> CLAMP-hubs (not "set-screws"), you have no "lost motion" the chosen coupling
> does not introduce.
>
> I may be no wizened PhD machinist, but I KNOW what I have observed over the
> years. I find it interesting that so many on this list talk about using
> "timing belt" connection between stepper and lead-screw!
>
> Oh, it may "work" for some — those who "just don't SEE that". Lotsa luck!
>
> Jan Rowland
>
> [Non-text portions of this message have been removed]
>
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