[R-390] Pinned down

[Chris Kepus]

Hi Miles, I'd prefer to leave it alone.  Unfortunately, the two PTO units
need work.  The designers came up with way to use a 1000 unit turns counter
by limiting the travel from 000 to 450 (plus or minus a dozen units or two)
by utilizing two " lever arms".one on the main PTO shaft and one on the
idler shaft.  They are oriented so they come into contact at approximately
985 (-15 units from 000) preventing further CCW rotation of the PTO shaft
and come into contact again after some  4 5/8 rotations of the PTO shaft in
the CW direction at approximately 485 on the turns counter dial. When these
two arms come together,  the PTO shaft rotation is stopped preventing
over-rotation of the PTO slug and possible damage to the PTO.  In service,
this clever gearing scheme to provide a 1 Khz readout with lower and upper
limits has been compromised by heavy handed users.  In one case,  a lever
arm on the PTO shaft was over-torqued to the point where the attaching pin
sheared.  In another case, the alignment of the turns counter, PTO shaft,
idler shaft and lever arms was somehow screwed up likely by an over-zealous
knob twister.   In both cases, I want to remove the arms from the shafts and
start over by setting up the PTO as intended to fully rotate through its 450
KHz tuning range.

 

Protecting the PTO is a priority so caution will be the watchword as work
proceeds.

 

Should drilling be necessary, your suggestions are very helpful.

 

From: k2cby [mailto:k2cby at optonline.net] 
Sent: Tuesday, June 19, 2012 1:57 PM
To: 'Chris Kepus'
Subject: Pinned down

 

My own strong recommendation is to leave well enough alone.
You ought to be able to clean the gears adequately without disassembly.

Moreover, the shock of removing the pins is likely to fracture the coil
slug, coil form (or something else) even if you use a jeweler's
(toolmaker's) bench block to work against.

 

That being said, if you must unpin the gears, try a small diameter (they go
up to size #80) twist drill. Cut it off with a Dremel tool if you need to.
They are much tougher than a brad or wire nail. Next step up: a carbide
printed circuit board drill - they are hard as a rock but brittle. Last
resort - cozy up to your local dentist and ask him for a worn out (or
broken) burr. They are really tough.

 

Good luck!

 

Miles B. Anderson, K2CBY
16 Round Pond Lane
Sag Harbor, NY 11963
Tel.: (631) 725-4400

Fax.: (631) 725-2223
e-mail: k2cby at optonline.net