"Projects" at georgesbasement.com

Oufitting a Sebastian treadle lathe

Sebastian treadle lathe
Progress to January 2005:

   The lathe as shown at left has no makers marks.  However, one like it is shown in Kenneth L. Cope's book, American Lathe Builders: 1810-1910, on page 157, under the heading of Sebastian-May Co., Cincinnati, Ohio, Fig. 3. My lathe came from a private party in Philadelphia around 1976 for $75; when I took the picture at left I had not yet re-installed the lead screw. 

   No change gears came with it, but I made a new banjo in 1977 and I've collected a few loose gears with what seem like a suitable pitch - i.e., considerably coarser than my nine inch South Bend lathe's DP18 change gears.
More about these gears later.
   There is something amiss with the main pulley - the belt was only tight when it was on the middle step.  I suspect that someone at the factory got it mixed up with an earlier or later run of parts ... or the base was made by Sebastian-May and the lathe by the Sebastian Lathe Company.  The patinas are identical; it was not a recent marriage.

Current Progress:

   First I had to deal with those mismatched pulleys.  I found a wide, flat-belt pulley and mounted it with oilite bearings in a piece of three-inch channel that is attached to the underside of the lathe's wooden shelf with a bolt and a wooden guide.
Belt-tensioning pulley
   The bolt's head is recessed into the wooden guide, so the only holes needed are for screws into the wooden shelf.

   The nut holds OK when just finger tight; the guide lets me adjust the belt tension by sliding the tensioner towards or away from the lathe bed. For the fastest speed, I have to unmount the tensioner.
To make a long story short, I made a set of change gears to replace the ones lost long ago (excepting the bottom one, found in my junk drawer):
Change gears for the Sebastian treadle lathe

   I had to make most of the blanks for the gears from scrap metal; five of them came from a chunk of a link of anchor chin over three inches in diameter that had been cut originally to make Charpy impact test specimens:

Hacksawing the anchor-chain link

   In order to save the last two of the five blanks, I had to exactly bisect the last remnant of the chunk of anchor chain:

Hacksawing the last two pieces apart

At last, after several slow days of hacksawing, I got the five blanks with nothing at all left over:

Five gear blanks
Other noteworthy details:
   Some of the newly purchased gear cutters for the DP20, 14-1/2 degree pressure angle gears came from China with a metric bore that had to be opened up with my fifty-year-old Dremel hand grinder:
Reboring the Chinese gear cutter
   Other blanks had to be rounded out from pieces of rectangular plate,
some by drilling a series of nearly overlapping holes:

Rounding out a rectangle by drilling a circle of holes

  ... others, by putting the blank on an arbor and tolerating a tedious series of interrupted cuts:

Lathe-turning a square gear blank
   Here is the Sebastian lathe's chart for threading with the original change gears:
Sebastian lathe threading chart
I also use a 40-tooth gear on the spindle, but add a 30/60 cluster gear and an idler to get the necessary even number of gears to produce right-handed screw threads and transfer the motion from the spindle gear to the lead-screw gear. The lead screw has left-handed threads.

My gears cover 5 to 80 threads per inch.

Examples of some of the turning and threading gear trains:
Fine feed of 0.0042 inch per revolution of the spindle away from the spindle:
Gear train for fine feed towards the tailstock
Fine feed of 0.0056 inch per revolution of the spindle towards the spindle:
Gear train for fine feed towards the headstock
Making an 8 tpi right-handed screw:
Gear train for threading 8 tpi right-handed
In order to fit these gears to the Sebastian lathe without modifying anything on the lathe, I had to make a couple of important adapters.
First, there had to be means to hold the stud gear onto the main spindle:

Making the stud-gear bushing

   The stud gear had to be driven by the left-hand end of the main spindle, so the operation at left is the cutting of the keyway that keeps the stud gear from rotating on the spindle; there's another key that keeps the bushing from rotating.
Finished stud-gear bushing in place on the spindle

   In the right-hand image the large nut is actually just a spacer, and the small cap screw does the affixing of the stud gear.  The spacer between the stud gear and the bushing is used when the gear train requires that the stud gear be on the outboard side as it is in the image at left.
Second, another adapter was needed to avoid modifying the lead screw:
Milling the integral-key bushing

   There was scant annular space between the inside diameter of the change gears and the outside diameter of the lead screw's means of attaching the screw gear.  There was just a short key in the lead screw at its shoulder, and the gears all have longitudinal keyways like standard change gears.

   The first step was to rough out the integral key that fits the change gear's keyway.
Shaping the integral-key bushing in the lathe
   The second operation involved removing the ridges left by the milling cutter, which I performed, somewhat tediously, by using the handwheel feed of my lathe and a square-ended tool as a shaper.

   After parting off the bushing, I bored it to fit the lead screw of the Sebastian lathe and milled a short radial key to drive the bushing, folowed by a great deal of hand filing and fitting to accommodate all the change gears.

Next: Making the threading dial that is essential to permit moving the carriage back to take another threading cut without losing the registry between the gears and the lead screw, without having to reverse the lathe while never disengaging the half nuts.