The Saga of

The Poorman's Gear

and The Old Barnes Lathe


by Stan Moore -- March 31, 2003



Lathe2 In 1948 a fellow machinist of my grandfather had a metal lathe with a full assortment of tools and attachments which he wanted to sell. Grandpa told my dad that it was an excellent bargain -- the tools alone were worth the price, and that he should buy it for me.
The lathe was made by W. F. & John Barnes Co., in Rockford, Illinois, U.S.A, sometime after 1880.

Dad offered to buy it on condition that the machinist give me lessons on how to properly use it. It's agreed, and after I spending several evenings in the man's garage learning the principles of operating the lathe, it was disassembled and moved to my shop behind our garage.

It was driven by an array of flat leather belts and wooden pulleys which would have been powered originally by a constantly turning shaft running the length of the factory's ceiling (powered in turn by a steam engine or water wheel).

It still uses the flat belts,
but the power shaft is now
turned by an electric motor.

Lathe3

In 1957 I was called to active duty with the Navy. The lathe was dismantled, and stored away.

Upon returning from the Navy, I retrieved the dismantled lathe, removed the old black paint, refinished it in orange, and installed it in my new house.

gearset

It was at this point that I discovered a critical piece was missing -- the 104 tooth change gear. Not only could I not machine threads without this gear, I could not even drive the lead screw to do ordinary turning -- no combination of the other gears would span the gap between the spindle and the lead screw.

Because of its age, a replacement gear could not be found (the 14 diametrial pitch of these gears is no longer in common use). I would somehow have to make a replacement, and gears are not easy to make !

To have such a gear custom made would have been prohibitively expensive. So after struggling for years with various ways I might be able to make such a gear, I hit on the idea of molding the gear teeth using RTV (Room Temperature Vulcanizing Rubber). Of course the teeth would not be as precise as machined teeth, but in this application should work OK.

I first cast a cylindrical block of plaster, and machined a depression in it to hold the 52-toothed change gear from the set. A center post held the gear in position. The outside diameter of the depression was made slightly larger than that of the gear. smmold
smworm

Next RTV was poured around the gear teeth, and allowed to cure. The rubber ring of teeth was removed from the mold, and a second ring made.

Each ring was then carefully cut in two.

A second larger block of plaster was cast, and a depression machined calculated to be exactly the size of a 104 tooth gear plus an allowance for the RTV rings.

The two RTV rings were opened and inserted end to end in the large mold.

lgworm
coreface

A core of polycarbonate plastic was now machined to fit inside the RTV teeth.

Grooves were cut in the outside edge to help key the gear's teeth.

The core was placed in the mold, and Quik-Cast (a polyurethane material from Tap Plastics) was then poured into the space between the RTV teeth and the core piece.

quikcast
teeth

The Quik-Cast was allowed to thoroughly cure ...

then the RTV pieces were
removed, and the gear
lifted out of the mold.

wormout
teeth3

After a light machining
to remove the flash, the gear
was nearly ready to use.

Finally the center hole was sized,
and a keyway broached.

The gear was ready for service.

biggear
inuse3

The new gear
performed perfectly.

So now, after some
40 years of frustration,
I have a fully functional
lathe ready for the
next project.