Subject: :home-made lathes, Petro-Bond

From: [email-masked] (Bob Streimikes)
Date: 15 Jan 1995 20:08:34 -0600

What is the recomended parting compound when working with petro-bond?

Tails of homemade lathes of any sort would be of great interest.

Also, In Gingery's book on the metal lathe (page 70) he states that
Back gearing is the only way to operate at low speed and high torque
and states that book six will tell how to do it.But book six doesn't
include back gears.  It seems to me that there are at least two
alternatives to back gears, chain drive and toothed belt drive.
has anybody out there solved this problem either with back gears
or other means? Comments?
Regards,
bob (Kingston Wa)

---

From: [email-masked] (BrnzCaster)
Date: 16 Jan 1995 02:01:07 -0500

Bob,
I'll let others help with the lathe q's, but with regards parting for
oil-based sands, you can use the same materials as for water-based
systems.
Personally, I've used plain CORN STARCH for years ... it doesn't spread
all over the ram-up area like the finer commercial partings and it works
just fine.
Winston

---

From: [email-masked] (Stuart Friedberg)
Date: Mon, 23 Jan 95 19:51:32 GMT

In article <[email-masked]>,
>or other means? Comments?

I built the Ramah Machines (Ben Fleming) lathe, but used Gingery's
4-speed transmission to drive it.  I ran through a number of different
setups trying to get a low speed of about 70 RPM.  What I have right
now is good for about 1/2HP, and the remaining problem is not in
the final reduction drive.  I've marked tips/lessons with a (*).

My motor is a standard 1750 RPM TEFC.  Obviously, to get down to
the neighborhood of 70 RPM, I need about a 25:1 speed reduction.
I do this in three stages.  The motor-to-1st-cone stage is about
a 4:1, based on a pulley on the motor shaft somewhat smaller than
the recommended minimum size (1.5 or 1.75" pitch diameter) and a
9 or 10" pully on the 1st cone pulley jackshaft.  (*) I use 4L belts
rather than A belts because they bend around the small pulley better,
and yield less slippage.

The two opposing cone pulleys are standard 2-3-4-5" die cast cone
pulleys, giving 4 speeds with speed "reductions" of about 0.4:1
through 2.5:1 .  I think I junked one or two that weren't well balanced,
but later discovered that it was more a matter of unopposed setscrew
pressure pressing the pulleys cockeyed.  (*) For some pulleys,
especially smaller/non-cone ones,  you can add additional opposing
setscrews to reduce or eliminate this problem.  I was originally
using just setscrews on flats filed on the 5/8" jackshafts, but
had some slippage problems.  I ended up milling keyseats in the
jackshafts to match the ones the pulleys came with and ended that
hassle.  (Note: I used the lathe to do the milling.)

Early on, I experimented with a variety of non-standard belts designed
for A pulleys.  I tried some segmented molded plastic belts from Berg.
These proved to be unsatisfactory.  They consistently broke at the
cable splice joining them into belts.  Shock loads from interrupted
cuts might have accelerated this process.  I tried some link-type
belts.  These were noisy, hideously expensive, and didn't seem to
produce much of an improvement for this application.  (Note: I said
"for this application," so no flames, OK?)  I ended up using 4L belts
between the cone pulleys.  Cheap, effective.  Good quality ones are
quiet.

I decided I was getting too much slippage in the final reduction
drive which was originally a 1.5 or 1.75" pitch diameter A pulley
on the 2nd code jackshaft and a 4.25" A pully on the spindle, which
is the largest that will fit inside the Ramah headstock (a used
Cummins diesel piston).  Probably the solution is a bit of overkill,
but (*) I went with a 1" wide, 0.5" pitch (100H) standard timing
belt, and pulleys of 12 and 28 teeth (from memory, maybe it was 14
and 30).  This certainly isn't torque limited, but I did encounter
a tooth hopping problem which was quite disconcerting the first
time it happened.  Wham!  Wham!  I fixed this by (*) hacking up a
turnbuckle to fix the distance between the 2nd jackshaft and the
spindle by pressing the floating transmission arm away from the lathe
bed.

The end result is a 4-speed (70 to 500 RPM, approx) transmission
that does an honest 1/2HP of applied power with no trouble in the
middle two speeds (I can bog the motor cutting metal), and some
slippage under load in the extreme speeds, due to the small ends
of the cone pulleys.  I would have to fix this if I planned to
upgrade the motor to something larger.

Stu Friedberg ([email-masked])