[R-390] Autopsy of a bad PTO.

[Jim Miller]

What Barry said about presetting the screws woke up another brain cell in my
fading mmory.  I recall reading in one of the other articles (Harvie's
maybe) that the first thing you want to do before starting the linearity
alignment is to preset the 48 screws equally aboot half way in or maybe a
little less.  There is a reason for this...  If the screws are already
pretty well cranked in before you start aligning, then at some point you may
run out of adjustment range on the "upper" screws, which will bottom them
out and start them grinding into the "bridge"..  The hard part to me is
presetting them all the same, you have to turn them fully in and than back
off about half the turns (or is it fully out?).  I don't recall the exact
number of turns.  While you have that bad PTO open with access to the disc
you might use it as a learning aid to see how many turns can be expected on
each screw to get a feel for the range od adjustment possible and how far to
back them out to preset them.  This is a real hard introduction for a new
390a owner, but once you have accomplsihed the PTO initiation, you will be a
true member of the fraternity.  Good luck!
----- Original Message -----
From: "Barry Hauser" <barry@hausernet.com>
To: "Jim Miller" <jamesmiller20@worldnet.att.net>; "Phil Atchley"
<k06bb@elite.net>; <r-390@mailman.qth.net>
Sent: Saturday, June 28, 2003 10:19 AM
Subject: Re: [R-390] Autopsy of a bad PTO.


> You're probably right about Plan B, and a replacement is on the way.
Since
> the present one would be a goner anyway, it might be worth experimenting
> with epoxy as I first suggested.  The entire space under the bridge would
> have to be filled to increase the surface area of the bond.  The surfaces
> getting the epoxy - top of ring under the bridge and underside of bridge
> would have to be roughened up to provide grab.  Most epoxies are fairly
heat
> resistant.  Wouldn't take much to try it.
>
> If you are going to try to fix that one, Phil, I would suggest pre-setting
> any of the 48 linearity screws to remove any "cliffs".  A key question has
> to do with how well you were able to reshape that bridge.  The flex would
be
> fixed with the epoxy.  I suppose you could dress up the surface of the
> bridge if there are some bumps and ruts in it.
>
> You could try re-spot welding it -- maybe with a high current battery and
a
> couple of makeshift electrodes.  Or maybe not. ;-)
>
> There's always Plan B.
>
> Barry
>
>
>
> ----- Original Message -----
> From: "Jim Miller" <jamesmiller20@worldnet.att.net>
> To: "Barry Hauser" <barry@hausernet.com>; "Phil Atchley"
<k06bb@elite.net>;
> <r-390@mailman.qth.net>
> Sent: Saturday, June 28, 2003 9:56 AM
> Subject: Re: [R-390] Autopsy of a bad PTO.
>
>
> > I don't want to sound too negative, but if that bridge is broken, I'm
> afraid
> > it's time for plan B (new PTO).  That is spring steel which won't solder
> > well at all.  Even if repaired, it may never be as smooth and repeatable
> as
> > an undamaged one.
> >
> > Jim
> >
> >
> > ----- Original Message -----
> > From: "Barry Hauser" <barry@hausernet.com>
> > To: "Jim Miller" <jamesmiller20@worldnet.att.net>; "Phil Atchley"
> > <k06bb@elite.net>; <r-390@mailman.qth.net>
> > Sent: Saturday, June 28, 2003 9:28 AM
> > Subject: Re: [R-390] Autopsy of a bad PTO.
> >
> >
> > > Hi Jim:
> > >
> > > Sorry ... I didn't notice your earlier post(s) in reply to Phil.
Thanks
> > for
> > > the new URL.  Those missing photos help make it clearer about the
action
> > > with the "footbridge" riding and straddling adjacent screws.  The
> > > overlap/staggering of the linearity screws is intended to avoid
jumping
> > > which could otherwise cause up-down variations in frequency as the
unit
> > > rotates.  (and how an abrupt jump from one screw to the next could
cause
> > > problems.)  The photos on your site seem to be clearer and larger as
> well.
> > > Even clearer to me that the little ramp or bridge should be rigid, not
> > > flexible.  If the metal will take to soldering, Phil could solder the
> > broken
> > > weld and perhaps fill the void under the bridge (no boat traffic) with
> > more
> > > solder. Of course, it would have to be reshaped as well as possible
> first
> > > and the final result deburred and lubricated with a small amount of
> > > non-running grease.
> > >
> > > Barry
> > >
> > >
> > >
> > > ----- Original Message -----
> > > From: "Jim Miller" <jamesmiller20@worldnet.att.net>
> > > To: "Barry Hauser" <barry@hausernet.com>; "Phil Atchley"
> > <k06bb@elite.net>;
> > > <r-390@mailman.qth.net>
> > > Sent: Saturday, June 28, 2003 8:38 AM
> > > Subject: Re: [R-390] Autopsy of a bad PTO.
> > >
> > >
> > > > I just noticed some of the photos in my Cosmos PTO article on Dave's
> > page
> > > > have become corrupted.  If anyone's interested, the original article
> is
> > at
> > > > the following url.  Copy anything you want.
> > > >
> > > > http://home.att.net/~jamesmiller20/cosmos.htm
> > > >
> > > > I tried emailing Dave but his email bounces.  I guess I like the
> Cosmos
> > > over
> > > > the Colling PTO because it appears to be relatively easier to
> linearize
> > > > despite Phil's nightmare.  I spent over a week (couple of hours a
day)
> > > going
> > > > through the stack (trial and error) in a Collins PTO, taking the
cover
> > > off,
> > > > tweaking, putting the cover back on, over and over.  I can see why
the
> > > > inventor of the Cosmos approach thought he had a better idea.
Sounds
> > like
> > > > someone in a past life got heavy handed with a screwdriver and
jammed
> > some
> > > > of the little screws.
> > > >
> > > > ----- Original Message -----
> > > > From: "Barry Hauser" <barry@hausernet.com>
> > > > To: "Phil Atchley" <k06bb@elite.net>; <r-390@mailman.qth.net>
> > > > Sent: Saturday, June 28, 2003 7:28 AM
> > > > Subject: Re: [R-390] Autopsy of a bad PTO.
> > > >
> > > >
> > > > > Hi Phil & gang:
> > > > >
> > > > > I dunno, there was a time there would have been several posts with
> > > > detailed
> > > > > "been-there-done-that" posts to assist you.  I've held back on
> > replying
> > > > > simply because I've never been that deep into a Cosmos.  Soooo..
.in
> > the
> > > > > absence of any experienced replies .... (maybe some were
off-list?)
> > > > >
> > > > > Somehow, I'd also assumed that with all the downloading you
> mentioned
> > > you
> > > > > had certainly come across Dave Medley's pages or another site with
> Jim
> > > > > Miller's "A JOURNEY THROUGH THE COSMOS (PTO)".
> > > > >
> > > > > The direct URL on Dave M's site is
> http://www.davemed.com/cosmos.html
> > > > This
> > > > > includes detailed photos, though there's something wrong with one
or
> > two
> > > > of
> > > > > the photos.
> > > > >
> > > > > Gonna try to shed some light on this, but again, bear in mind that
I
> > > have
> > > > no
> > > > > hands-on, so take it for what it's worth.
> > > > >
> > > > > >Since there is another PTO coming I went ahead and took this one
> > apart
> > > > all
> > > > > >the way down to the corrector disk to see if I could determine
the
> > > > failure
> > > > > >mode (not sure I can get it back together correctly 8^)
> > > > >
> > > > > Somehow, I'm not surprised.  I always take your "quit" and "throw
in
> > the
> > > > > towel" declarations with a grain of salt. (about the size of a
> > football
> > > > ;-)
> > > > > While you were tearing into that PTO, I was probably searching for
> > that
> > > > web
> > > > > article (or copping some Z's).
> > > > >
> > > > > >Anyway, I was
> > > > > >right.  The 48 tuning screws are rotated one by one past a round
> > spring
> > > > > >loaded thingy made of spring steel that has a small piece of
steel
> > that
> > > > > >looks kind of like a "footbridge" spot welded to it.  As the
screw
> > for
> > > a
> > > > > >particular segment of the frequency range (25 KHz steps) walks
over
> > the
> > > > > >"footbridge" it presses down on it and pushes the slug under it
> > further
> > > > > into
> > > > > >the coil.
> > > > >
> > > > > The web site photo shows this.  The spot welded piece looks more
> like
> > a
> > > > > triangle, so I'm not sure what you mean by a footbridge.  (Maybe
> like
> > > the
> > > > > ones in Japanese gardens and Central Park?) Check out the photo
for
> > what
> > > > the
> > > > > shape of it should be.
> > > > >
> > > > > >The "footbridge" was damaged in two ways.  First it had a BIG
dent
> in
> > > it
> > > > on
> > > > > >one side that would make screws riding on that side of the bridge
> > > > (they're
> > > > > >staggered) not press down as hard on the bridge. Secondly, the
spot
> > > weld
> > > > > >that holds one end of the bridge is broken loose so that it has
> lost
> > > some
> > > > > of
> > > > > >its "stiffness" and positive action.
> > > > >
> > > > > >In trying to fix the "dent" in the bridge I'm afraid that I also
> > > weakened
> > > > > it
> > > > > >some more as spring steel doesn't take kindly to dents and trying
> to
> > > > > >straighten them out.
> > > > >
> > > > > From the photo, it would seem that bridge is supposed to be rigid,
> not
> > > > > flexible, even if it's made of the same spring steel as the ring.
> > (Just
> > > a
> > > > > manufacturing convenience, vs. a solid piece of something, also
> > > avoidance
> > > > of
> > > > > dissimilar metals. Also, spring steel is fairly hard and less
prone
> to
> > > > > wear.)  Wouldn't it be solid if that other weld weren't broken?
> > > > >
> > > > > >The third problem I found was that some of the screws had
> apparently
> > > been
> > > > > >turned "counterclockwise" too hard, spreading the slot and screw
> too
> > > wide
> > > > > to
> > > > > >thread down into the disk far enough to reach the damaged bridge.
> > > These
> > > > > are
> > > > > >the culprits that probably had no adjustment affect as they
> wouldn't
> > > > reach
> > > > > >the "footbridge".  These are very tiny screws that are really
only
> a
> > > > screw
> > > > > >shaft with a "slot" in the end and a flat head on the backside to
> > "walk
> > > > > >across the bridge".
> > > > >
> > > > > Can't you turn them back down again while it's apart, to make sure
> > > they'll
> > > > > make it through?  Sounds like what you are describing is a false
> > > bottoming
> > > > > out of the adjustment screws.  The "no adjustment" effect might
also
> > be
> > > > due
> > > > > to the "bridge" being out of shape, partly flattened and flexing
> > flatter
> > > > due
> > > > > to the broken weld on one end and/or the dent.  Actually, if that
> > bridge
> > > > or
> > > > > arch was flexing, that would have messed up your linearity
> adjustments
> > > and
> > > > > may have contributed to the other problem.
> > > > >
> > > > > >NOTE:  A couple articles that I read said that there was a
flexible
> > > > Teflon
> > > > > >ring that these screws rode on forming kind of a cam.  This one
had
> > no
> > > > such
> > > > > >ring, only the spring steel thingy that the screw heads walked
> > across.
> > > > >
> > > > > Was that a Cosmos PTO in the articles?  May have been a different
> mfr.
> > > > >
> > > > > Again, keeping in mind the nature of the source, (not
> > > > > been-there-done-that) -- here's some partially lame advice:
> > > > >
> > > > > From the photo, it looks like the bridge should be solid, not
> > flexible.
> > > I
> > > > > imagine the screws should just catch the bridge on the rise, not
at
> > the
> > > > base
> > > > > near the spot welds.  If so, then you should be able to repair the
> > thing
> > > > > with epoxy, or perhaps a solder repair, if the spring steel will
> take
> > > > > soldering.  One way would be to fill the void in the bridge --
> > basically
> > > > an
> > > > > "arch support".  Reshape the arch as best as possible, using the
> photo
> > > or
> > > > > another unit as a guide.  Cut the corner off a piece of sheet
> metal --
> > > > > aluminum -- to make a small triangle support with a slightly
rounded
> > > apex
> > > > to
> > > > > fit the underside of the bridge and secure the whole business with
> > > epoxy,
> > > > > using a small clamp to hold in place until it sets.  Basically --
an
> > > > > orthothic shoe insert.
> > > > >
> > > > > Then fix the screws somehow, if they actually need fixing.  The
> photo
> > on
> > > > the
> > > > > website shows that quite a few screws are either not present or in
> the
> > > > fully
> > > > > backed out positioin.
> > > > >
> > > > > There's another thing.  I was a bit confused as to how this setup
> > could
> > > > work
> > > > > if the screws are riding up and down the arch, with gaps in
between,
> > > > causing
> > > > > reciprocating action.  That would mean that it would be nearly
> > > impossible
> > > > to
> > > > > have smooth action in terms of degrees rotation to frequency.  The
> key
> > > is
> > > > > that the adjacent screws are straddled so that the tip of the
> > > bridge/arch
> > > > is
> > > > > always riding on a screw or none at all.
> > > > >
> > > > > But -- what that means is that the screw setting should end up
with
> > > > > reasonably smooth transition from one to the next.  If there were
> too
> > > much
> > > > > of a differential from one (or a pair) to the next, it could jam
or
> > > cause
> > > > > roughness.  I would think that extreme differences between
adjacent
> > > screws
> > > > > might be indicative of a problem elsewhere -- worn lead screw or
> > > > something.
> > > > >
> > > > > Also -- does it seem possible to run a screw down far enough to
> > actually
> > > > > crush the bridge piece (or snap a weld)?
> > > > >
> > > > > The photos on that site are of fairly high resolution.  I blew up
> the
> > > side
> > > > > view of the "bridge" and it certainly appears to me that it should
> be
> > > > fairly
> > > > > or completely rigid, not flexible, if both welds are intact.  It's
> > > > basically
> > > > > triangular in shape, but with a smooth bend at the apex. With one
> weld
> > > > > broken, it will flatten under pressure and you won't get a
reliable
> > > > > adjustment.  That's my theory anyhow.
> > > > >
> > > > > Of course, as I'm typing the last of this speculative tract, Phil
is
> > > > waiting
> > > > > for the epoxy to cure or soldered the thing, or maybe hand carved
a
> > new
> > > > ring
> > > > > and "footbridge" out of some spring steel in his junk drawer.
> > > > >
> > > > > "Throw in the towel"  -- yeah, right.  We know you better than
that.
> > ;-)
> > > > >
> > > > > Barry
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > _______________________________________________
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> > > >
> > > >
> > >
> > >
> >
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