Hi Steve:
The socket head set screw with hex lock nut support the rear end of the
main tuning shaft screw. There is a cup on the end of the screw shaft
and a cup in the end of the set screw. A small steel ball rides between
the two and it sets the preload and endplay applied to the cone and ball
bearing at the front end of the screw shaft.
To locate it, look at the screwshaft rear end. THe setscrew is adjusted
thru a hole in the rear cover. Use care to make sure the allen key goes
in straight and isn't tangled up in anything else.
The cone and ball bearing at the frame front is a bearing that can take
a small amount of pre-load, so I actually adjust the end screw for zero
end-play but err on the side of a hair tight rather than a hair loose.
As the everyhing heats up, the endload will go up as well but should all
result in a very smooth and loose dial feel with absolutely no end play
or lateral movement.
If you ever adjusted loose ball and cone bearings on a bicycle front
wheel, this is the same bearing but the setscrew is at one end to create
the pre-load.
It takes an extra long allen key or a ball-hex driver to adjust this, a
standard length key is not long enough.
Let me know if you find this ok, else, I will see if I can take a
picture or two that show all this.
Curt
KU8L
Steve Wedge wrote:
Curt -
Thanks for the advice. Where is this "hex" for the endplay that you're talking
about? I'm about ready to buy a junker to steal its PTO...
73,
Steve
Message: 3
Date: Wed, 13 Jul 2011 19:02:12 -0400
From: Curt Nixon <[email protected]>
To: Steve Wedge <[email protected]>
Cc: Drake List <[email protected]>
Subject: Re: [Drakelist] R-4A PTO, Part Deux
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi Steve:
THe PTO that I have worked on have a diamond shaped hole in the coil end
coverfor the back end of the brass shaft and are not tight at all.
Shaft just kind of rides there. However, ANY slight movement of that
end will cause a frequency abberation. If there is any type of build up
of debris or gunk there, or inside the coil between the form and the
metal slugs stacked on the shaft, it will make the shaft bump and create
a jump.
I generally pull the whole shaft assembly and clean it thoroughly with
lacquer thinner or similar--even some fine wet or dry 400 grit could be
used. Also clean the square hole well with some thinner or 99% iso
alcohol. What you want is a low friction dry sliding condition at the
back end.
Be sure the brass rod is not coming in contact with the housing and
there can be no relative motion between elements or shield back there.
I use a dry spray lube that is like graphite powder on the shaft but dry
works just as well. NEVER any type of oil or grease or non-drying
cleaner/lube.
Of course, any free play in the FRONT bearings or slider will do the
same. I assume you have cleaned and lubed and re-set the shaft end-play
bearing? THat adjustment is a hex thru the back end of the coil base.
It should be baled off and then adjusted in (tighter) JUST until there
is no endplay. The difference between good and poor on this adjustment
is a praction of a hex flat. Perhaps a couple of degrees on the set
screw. But it makes all the difference.
Hope this helps some.
I have completely field stripped several Drake PTO assemblies in the
last year and haven't lost a single patient yet! Just take your time.
Curt
KU8L
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