Re: [CAD_CAM_EDM_DRO] Sherline CNC retrofit

Yo Jan;

The next time you make one of these, you might try something a friend advised me
to do on the ways. It might just be the berries for your z axis. He said to
spread a very fine abrasive suspended in oil on the ways, and run them from end
to end numerous times, adjusting the gibs, and adding more abrasive/oil, until
the travel became glass smooth from end to end. Clean it all off, and replace
with just way oil. A bit time consuming, but worth while, for ways/gibs, and
possibly, your z axis.

Just a thought.....

Bill

On Tue Dec 10 21:26:58 2002, JanRwl@..., <JanRwl@...> wrote:

>OK, Gang! Bill says go ahead, so...
>
>Backlash and lead-screws: First, gawk at Photos in Album #17 (first Album on
>p.2 of PHOTOS). I grant you these snapshots were NOT made with the intent of
>showing details of the lead-screws, per-se, but these two items WERE 100%
>home-brew. Now the lathe, as you can see, is controlled by a Tandy 1500HD
>(1991!) laptop running MSDOS GWBASIC. NO mouse nor Windows nn! (See further
>comments on electronics below!)
>
>As I had built an earlier similar lathe in '84 using a long-discontinued CBM
>PET (which also is still going, in use!), I already had a "feel" for BSA's
>ACME lead-screws and their Turcite nuts. This is a fiber-glass-impregnated
>PTFE plastic, so it has "controlled" friction and is sturdy. However! The
>fiberglass in it has a peculiar property! For my use of this machine, most
>of the "Z-travel" (that'd be "X-travel" in Cartesian-speak!) is within the
>same 4", so that portion of the lead-screw where the Turcite preloaded nut
>bears over that part of the screw is highly-polished, and the friction there
>is NOTICEABLY less (when the screws' handwheels are turned by hand,
>stepper-windings OFF). That is, the glass fibers impregnated in the Turcite
>act as "potted abrasive", and have actually POLISHED the screws in that
>portion!
>
>These screws are 4 mm/turn ACME, 20 mm dia., stainless steel. Those Turcite
>nuts (bright red plastic) are made in TWO halves, each of which have two "90°
>wide" fingers which, when properly meshed as they are sequentially screwed
>onto the screw-stock, "lock" one-another so that if either turns, the other
>must follow; no angular "play" between them. Then, a rather heavy
>coil-spring fits between these two halves, pressing them apart, so one half
>presses on the "right side of the threads" and the other half presses against
>the "left side of the threads". ONE half is also externally threaded so that
>it screws into a black-anodized aluminum flange-ring which makes bolting the
>whole assembly to the mechanism (in this case, the "saddle" of the lathe).
>
>Now these screws and nuts are BSA products, and are fine stuff, if pricey.
>But all considered, having these lead-screw parts made by a good job-shop
>charging, say, $75-$150 per hour would cost at least twice as much, assuming
>it would even be POSSIBLE to get the same quality/consistency.
>
>The "friction load" of these nicely-hefty nuts on the 20 mm. dia. screw-stock
>is much more than one would like to have on any kind of manually-operated
>lathe's lead-screws, but the hefty BIPOLAR Size-34 steppers clearly don't
>care at all! So, with no "play" (aka "backlash"), and steppers which manage
>fine, this is a "slop-free" arrangement.
>
>I built this lathe simultaneousely with a "twin" which got shipped to a
>customer in Ohio (he supplied is own laptop) in the latter quarter of '99. I
>had not yet heard of Gecko, and though everything is working perfectly on
>both machines, I perhaps wish I had, as I would have saved considerable
>$heckles using the G210 drives (were they available in '99?)! I used "black
>boxes" by the stepper-manufacturer, Superior Electric. These "black boxes"
>contain TWO bipolar-chopper drives AND a 120/220-240 VAC-to-DC power-supply
>which have opto-isolator inputs, "All Windings OFF" inputs (to remove DC from
>the motors for set-up, etc.), and a sturdy "important-looking" box. The only
>"electronics" left for me to do was to build a simple "buffer-interface"
>between the laptop's "printer port" and the opto-isolator inputs on the
>stepper-drive box. I used a 74HCT541 Octal non-inverting buffer, a pair of
>74HC4538 monostables to "set the pulse-width", and a ULN2003 Darlington
>driver to "light up" said opto-isolators. OH, I had to make a tiny 5VDC
>supply for that, as this laptop did not have a USB nor "game-port" to supply
>the +5VDC.
>
>The first two bits of the parallel-port are for "Z", the next two for "X" (on
>a lathe, "left-right" is the Z axis, and "north/south" is the X axis. There
>are more than one "Now, lessee..." stories as to how that came to be, and I
>must admit I use standard Cartesian "X" for East-West, and "Y" for
>North-South, but DON'T TELL ANYONE!. Then the next two bits are XOR'ed to
>operate the electropneumatic (100 psi "shop-air") tail-stock valve, and the
>final two bits are XOR'ed to operate the spindle-motor SSR's. Three-phase,
>so three SSR's!
>
>These Superior Electric "black boxes" are their series "SS2000---" They cost
>me over $700 each. I am sure I could have built power-supplies for $20, and
>a pair of G210's would have been less than $300. So, I could have saved over
>$350 per lathe, had I only known of Mariss' fine product! But the SS2000
>things work fine, so... One thing it took me a day or so to "get over": I
>had built several stepper-motor things using old UNIpolar systems with big,
>hot "L-R ballast resistors", so I had a subconscious "need" to think the DC
>supplies had to be able to supply the "rated current" to the motors. That
>is, if each of two windings wanted 4 amps, two motors, the DC-supply would
>have to supply 16 amps. But with Bipolar Chopper Drive, if your supplies are
>going to be six times the "motor voltage", they need supply only a fraction
>of the CURRENT, as no power (that's Watts!) is wasted as HEAT in those
>ballast resistors! So, for two Bipolar motors rated at 3.5 amp per winding,
>you would need NOT 14 amps, total, but only about 3 amps, total! Really!
>Blew me away when Mariss explained this to me in an e-mail about a season
>ago!
>
>Jan Rowland
>
>
>[Non-text portions of this message have been removed]
>
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