re:cleaning, lovejoy, black box tach, linear scales, making pulleys

Jack,

(Snips,inserts below)

>1) I was concerned that water might be too corrosive--but obviously
>it's worked for lots of people.

I've known and used the "dishwasher" trick for years. As to the
water... Be careful of "older" circuits. The sealants and "goops"
weren't as good back then. Stan Griffiths wrote a book on restoring
old Tektronix O-scopes and advised ionized water ONLY; and JUST PLAN
to REPLACE the caps. May not be pertinent to your current case, but
it's good to know. Some of these CNC things ARE getting up in years...

>2) I just picked up some new / surplus helical connectors. These
>things do wind-up<s>

Yes, the helical style "do" wind up. The "3/4 thru sawn" and the "u-
joint"(described in earlier posts) don't. URETHANE in
lovejoys "could" be a good thing. The rubber isn't...

3) In answers to a previous post I learned that both tachs and
encoders are used in servo systems because at one time processor
speed was too slow to calculate motor speed from the encoder output.
But why do tachs persist?

As explained in a previous thread: At slow speeds, the tach is more
accurate and reads direct. The pulse average-ing (to derive speed)
suffers from data starvation. (not enough pulses per unit of time to
ACCURATELY reflect the "real world" happenings at the axes)

>4) If fast responding, high resolution linear scales existed, isn't
>it the case that (at least for closed loop systems) backlash, ball
>screws, helical connectors, etc would all be irrelevant? Trying to
>measure position indirectly from a rotary encoder seems like the
>root of all evil. Maybe really high-grade scales wouldn't seem so
>pricey if you didn't have to retrofit ball screws. I understand
>there's a problem with table movement within the backlash zone, but
>why can't the motion controller mimic a human machinist's habits of
>taking up backlash when reversing direction?

Simple answer is: It CAN, when such simple "human machinist" motions
are being carried out... But when was the last time you saw a human
machinist spinning the wheels this way and that, to cut a compound
surface "on the fly" in some mold steel???

CNC allows things... AND REQUIRES things...

Second part of simple answer is: the "real world" physics (and
economics) of machine tools make the rotary encoder a good choice (a
nice compromise). The entire SYSTEM must be in balance, and choices
will be made, based on experience. And experience tells us
that "great feedback" (expensive, fast-acting, Hi-res scales) do not
REPLACE "tight, stiff" machine "iron"! But the same experience tells
us that at the hi-end , such scales ARE available AND useful!

>5) Somewhere (maybe in this group) I read a suggestion about making
>HTD pulleys by drilling holes around the desired OD and then taking
>a clean-up cut on the lathe. Flanges could be screwed on ex post?
>Has anyone done this? Unless I'm reading the price lists altogether
>wrong, an afternoon spent this way could be quite rewarding. Of
>course you'd go mad without a rotary table or index setup.
>Jack

That was one of our "across the pond" members, Ian, or Peter,I
believe...

The flanges are usually added later anyway and "staked" on. Most
pulley mfr's sell "pulley stock" which makes a lot of sense if you
are makin' a few. Typically about 8 inches long with a "stub" for
chucking, turn the steps for the flanges bore, part-off... Next!...

Hope this helps.

Ballendo