[R-390] Oldham Coupler Idea

[Jim M.]

In case it hasn't been said, the surfaces of the coupler should NOT be snug
tight.  There should be about 1/32 spacing between the surfaces according to
the technical manual I have.  If they touch or are too tight, the pressure
on the PTO shaft can cause instability and warble (in CW signals) when
tuning.  The coupler disc should be able to move freely.  I think the whole
purpose of the coupler is to accommodate slight misalignments between the
PTO shaft and the main tuning shaft, which are inevitable.
Jim N4BE

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Flowertime01 at wmconnect.com
Sent: Sunday, November 18, 2007 1:04 PM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Oldham Coupler Idea

Jon,

On most receivers the shaft alignment is very good.

The shafts and coupler have more than enough mechanical stiffness.

With the original specified spring, the spring provided enough tension to 
keep the coupler parts "lashed" together to remove slop but not so much
tension 
as to deform the shafts.

In mechanical assemblies, the order in which retainers are tightened often 
have a big effect on the final alignment. You may want to consider
"resetting" 
your VFO if you feel yours is too far out of alignment. If that work still 
leaves your VFO with more offset in the coupler than you would like, you can
start 
to file mounting holes to get more freedom and range of adjustment.

You should be able to reset the VFO to remove all angle off set so the 
coupler faces set flat to each other. 

Most couplers are die cast and the face of each side is not real square to 
the bore. This is an effect of cooling casting or not an exact drill press
to 
jig alignment during manufacturing. It is close enough for government work.
Live 
with this. Some times flopping one coupler side around 180 degree will get a

better fit. You get the error in each side to complement for a best fit.

There is some shaft to shaft off set.
You can adjust out the side to side off set.
If the off set is from the VFO setting to close to the chassis it can be 
shimmed to remove the off set.

If the VFO sets to high, you will likely have to live with that off set of
do 
a major over haul of the front box assembly to can front plate on the VFO to

adjust the off set.

Mostly life is good enough and we just live with it as is. That coupler with

one spring will compensate for the range of offset.

I hope this provides enough depth to help you get your receiver into a 
mechanical condition you can live with without modifying your coupler.

Once you get the alignment correct, more springs just are not needed.
The coupler becomes a method to effect module disassembly and repair, as 
opposed to a device to compensate for poor part fabrication.

Roger AI4NI   </HTML>
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