[GreenKeys] Model 15 Mainshaft

[George B. Hutchison]

Hello - - -

It would be prudent to check out the center of the mainshaft.

The mainshaft is hollow.

Properly assembled there is a long felt wick which runs from one end 
of the mainshaft to the other.

Wherever there is a component on the mainshaft which is not affixed 
to the shaft, there is a cross wick about 1/16" diameter and long 
enough to extend through the shaft. This is to provide a reasonably 
constant supply of oil to the rotating components.

The drive gear end of the mainshaft has a split plug with a leather 
washer for a gasket.

The selector end of the mainshaft consists of the cam sleeve with an 
inner and outer "Sandwich" of two clutch disks with a graphite 
impregnated felt disk between them.

The outside end of the selector is a polished clutch disk with a 
threaded "stem" which is part of the clutch "sandwich".  The stem 
thread is a left hand thread. Were it not left handed, the selector 
cam assembly would not stay together, due to the direction of 
rotation of the main shaft. Careful scrutiny will show that the 
outer disk is marked "Left Hand Thread".

The center of the sandwich is a felt washer which has been 
impregnated with graphite.

The inside clutch disc is also polished, and has some grooves 
machined in it so that it will engage some lugs on the inner end of 
the selector cam sleeve. (The lead looking thing with all of the 
spikes sticking out, and the stop arm attached to the outer end of 
the cam sleeve).

The inner end of the selector cam sleeve also has some lugs on it 
which engage a polished disk which just happens to be indentical to 
the one on the other end of the cam sleeve. There is another felt 
inside of it which constitutes the meat of the sandwich. The 
innermost clutch disk has a loading spring which is compressed by a 
threaded capstan nut (looks like a copper washer with notches around 
the rim).

The more the spring is compressed the more pressure on the inner and 
outer felt clutches. Too much tension will cause the clutches to 
heat up from friction, shortening their life, and the increased 
tension will also add to the amount of force that the end of the 
selector cam stop arm will exert agains the selector trip latch, 
causing the stop arm and the trip latch lever to wear faster, which 
is not good.

Getting back to the main point of this epistle, take a handy-dandy 
pump oiler, and using a shop rag as a gasket between it and the main 
shaft' frive gear end, pump oil into the main shaft until it starts 
to flow out of the small hole in the selector cam retaining screw 
(the one marked "Left Hand Thread". )

If oil flows out freely, HOORAH - Your mainshaft is clear.

If there is no oil flow, this is indicative of the fact that the 
mainshaft has most likely overheated at some point, causing the oil 
to congeal in the felt, causing a blockage similar to the one I 
recently had removed from my heart.

The only cure is to disassmble the main shaft, and bore it out with 
a long drill, 1/8" in diameter, and long enough to go through the 
entire length of the mainshaft. Such drills were called "Main Shaft 
Drills".  Nowadays similar drills are available at Lowe's and Home 
Despot in the Klein Tools Display. modern usage is for the 
installation of burglar alarm wiring, but they work very well on 
Model 15 mainshafts.

The mainshafts wicks are not unobtanium, but are hard to find. A 
good substitute would probably be to take a couple of strands of 
wool yarn and twist them together, and snake them through the 
mainshaft. If you studiously oil your mainshaft every month or two, 
you can probably get by without the cross wicks, but the cross wicks 
do add a means of slowing down the comsumption of oil by metering it 
out.

As a side note, you can check the condition of the selector cam stop 
arm and the trip latch lever by rapping the pivot screw of the 
indicator arm of the range finder with a plastric screwdriver 
handle. If the machine goes "Ka-Chunk" every time you rap that 
screw, either or both the stop arm or the trip latch are worn, and 
you'll get poor selector performance.

Should they be worn, the best cure is replacing both. It is possible 
to resurface the latching edges with a fine India stone, but the 
duration of the cure is indeterminate, depending on how far the 
hard-facing of the two engaging surfaces has been damaged or worn 
away.

It is almost a certainty that if a mainshaft has been over-heated, 
it will NOT come apart easily. Should this be the case judicious use 
of wooden blocks,  rawhide mallets, pieces of oak doweling, etc., 
should do the job.

Once apart clean all of the components well, and clean the bearings 
and re-grease them as well.

A model 15 mainshaft will only go together one way. Save some time 
and aggravation by placing the parts in the sequence they are 
removed, and pointing in the direction they were pointing when you 
took it apart.

Proficiency in Model 15 "Mainshaftry" will amaze your family and 
friends, and is easy to attain. Just take one apart and reassemble 
it perhaps ten or fifteen times - piece of cake!!

W7TTY