"Projects" at georgesbasement.com 

Overhauling and oufitting a Derbyshire instrument lathe
First assembly of Derbyshire Elect lathe
   This lathe's Elect headstock and bed were given to me by a former associate near his retirement. The three-axis tool slide came along later, as did the Derbyshire tailstocks.
First assembly - different tailstock
   Alas, all I had for collets was the one beat-up step chuck shown in these images.  I also acquired a ball bearing Derbyshire headstock, but that one has no key for a collet and no collet drawbar. 

Lots of work to be done !

  Lucky me got a complete threading attachment at a bargain, so I installed it, starting by tapping the center hole in the lathe bed No.10-32, using the base plate of the attachment as a template to spot the two 0.125 inch holes for the dowel pins, drilling and reaming them, and making a thick paper "gasket" to compensate for the spheroidal shape of the end of the bed and get a solid mounting of the base plate.   With fear and trepidation I lined up the gear supplied with the threading attachment in my South Bend lathe's four-jaw chuck, got it centered and free of wobble to less than 0.001 inch with a dial indicator, and bored it 0.001 inch oversize.  On the Derbyshire lathe's spindle, there is no perceptible runout or wobble, and the gears mesh smoothly with no variation in noise during running.  Note the split in the center bushing.
   The stud gear slides smoothly onto the rear end of the lathe spindle and clamps easily, once I replaced the No.6-32 slotted-head set screw with a socket head set screw. 

   Then I dragged out the countershaft and scraped off a multi-decade accumulation of lard (?) oil to reveal the beauty shown below:
Threading apparatus
Threading apparatus
Threading apparatus
   The lathe's two pedestals are meant to hold the lathe onto a bench with a pair of two-part cap screws, which will have to be made when mounting time comes about.  Right now, it's just a stud at one end.
   The Derbyshire lathe's longitudinal feed screw is left-handed, so the train of gears has to have an even number of axes.  My first attempt at 1.25 mm pitch thread-cutting gears is shown below.  Two idler gears are required, if only to get one gear that will reach the stud gear from the too-short banjo.
  After struggling with the three-dimensional puzzle for a couple of days, it hit upon me to use something other than the supplied T-bolts to attach that reluctantly reaching gear.  I used a 7/8 inch long No.5-40 socket head cap screw to hold the first compound 48/72 gears in the train.
   The second compound gear is the metric-converting 127/50 pair.  My South Bend lathe uses 127/100, as does gear gear set I made for my Goodell-Pratt lathe, whose gear trains are easier. Note that the 72/36 compound gear pair is separated to get the 2:1 upspeed needed to obtain 1.25 mm pitch.
   I work out the trains this way:

0.050 inch (20 tpi lead screw) times 60/48 times 72/36 times 50/127 gives 0.0492+ inch (1.25 mm).

  Note how I rearranged the pairs. No idlers !
Metric threading
Metric threading
Metric threading
Metric threading   The threading attachment comes with three banjoes, two right handed and one left handed.

   What's needed for this lathe is a different third banjo that's about 1/2 inch longer so that the first compound gear can always be meshed with the 60-tooth stud gear.

Making the longer banjo   The needed smaller banjo was a nice milling project.  The only lathe work was driling and boring the hole for the stud that the banjo has to fit.  I re-used the clamping screw after drilling and tapping the appropriate cross hole and then splitting the bottom end of the banjo.

   Both the new banjo and the original one are steel, but the original banjo was polished and then nickel plated.  I checked with a magnet, as it seemed to be brass at first ...

   Reducing the thickness of the slotted portion was an interesting problem, which I solved by gripping the big end of the banjo in the Atlas MM's vise and suporting the thin end of the banjo on an adjustable parallel while the banjo was cantilevered over the MM's table.

   I cut the slots with a 1/8 inch diameter end mill, plunge cutting at the ends of the slot and feeding back and forth between stops about 0.030 deep at a time.
Making longer banjo
The longer banjo reaches just past the edge of the 60-tooth spindle gear; I had to reduce the width of that gear by about 50 mils so it would fit between the two gears in the first compound gear. 

   Compare the image at left with the image in the row immediately above this row of images of the original banjo and ad hoc No.5-40 cap screw needed to get the first gear in the compound to reach the 60-tooth gear. 

  Next, I faced the problem of how to disengage the drive to the lathe's tool rest in a convenient manner. Remember, there are no half nuts on a jeweler's lathe !

   The first method I tried was to put an unused banjo to work as a stop to limit the back travel of the last banjo in the gear train.
   Here's how the last banjo rests against the banjo that has the stop in place - that's just a repurposed idler gear stud.
   Now it's easy to loosen the clamp screw on the last banjo and then swing the last two gears out of mesh; or back in mesh.
Gear shift stop
Gear shift stop
Gear shift stop
   It bothered me that there was no mechanism for disengaging the drive to the compound slide other than moving the gears as described in the row above.

   Below at the top is the original drive shaft; note that the two U-joints are not accurately aligned.

   Next is my extension drive shaft and the start on the engaging mechanism.  Below that is the 0.032 inch thick, 0.625 inch diameter HSS milling cutter that made the 0.042 inch wide slot on my Atlas MM.
  The cam that one turns to engage and disengage the drive is shown in process below, held in a 3/32 inch collet to have the center "throw" turned down to fit inside the slot in the extension drive shaft. 

   I made no alterations to the original drive shaft; that way I could start over if I made any mistakes.
   Here's how that cam works.  The slot in the closest cam enables me to rotate the key down into the slot in the extension driveshaft.  There's an over-center stage which keeps the cam engaged while driving the feed screw.

   In the lower image I have disengaged the key by rotating the cam 180 degrees counterclockwise.  Now the feed screw turns independently of the driveshaft. 

   A few "oops" cuts are evident but inconsequential.

   Eventually I extended the keyway in my
driveshaft extension and shortened it by an inch so that the compound cross slide could be set closer to the headstock. 

  The completed driveshaft assembly is shown below.  I also offset the slot in my driveshaft extension from its keyway to compensate for the error in alignment of the original U-joints.  I could have made the offset greater, but it's good enough for now.
   The lantern style toolpost that I fit to the top slide of the compound has no rocker, so I made a screw-type height adjuster.
   The internal thread was by far the more difficult; I left a rim on the male portion of the height adjuster so I could grip it while fitting the thread.
   The rim is gone now that the threads fit smoothly. The pins eliminate the need for that rim so I can rotate just the upper portion.
   At left and below are the height adjuster's extreme high and low positions, which are about an eighth of an inch apart.
Height adjuster
Height adjuster
Height adjuster
Heifght adjuster
   Threading is easier and produces better surface finishes on the flanks of the threads if one feeds the 60 degree tool at 29 degrees from the axis of the workpiece.  On a conventional lathe with a tool carriage, cross feed slide and adjustable angle top slide, this is an easy matter to arrange for either external or internal threads.  On this lathe, there is no carriage, and the top two slides are fixed permanently at ninety degrees to each other, so the 29 degree offset is achieved by setting the bottom slide at 29 degrees and the upper slides parallel to the work axes.
   I made a semi-permanent internal threading setup by making a new fence with the 29 degree offset built into its integral key that engages the slot in the bottom of the bottom slide.  The fence also has the side facing the lathe bed machined at 30 degrees from the vertical to engage one of the faces of the prismatic ways.

   External (i.e., male) threads are to be handled without changing the 29 degree fence by making another tool holder with a slide motion built in, like I the one I made for the Goodell-Pratt No.29-1/2 lathe.
   I tried to set the vise of the Atlas milling machine at 29 degrees when I milled the integral key, but it came out closer to 30 degrees, so I made an approximate adjustment when I machined the 30 degree beveled face of the fence in my South Bend shaper.  The result is shown below - just a little over 29 degrees on the protractor of the Derbyshire compound.
Internal threading setup
Internal threading setup
Internal threading setup   It is very difficult to read the degree markings on the Derbyshire slide because the marks are mostly underneath the top slide.  You'll have to view this image full size to even begin to see the zero line and its relationship to the calibrated angles.
External threading setup
External threading setup
External threading setup
External threading setup

   Here's the slide I made for external threading in the Derbyshire lathe. 

   There was less vertical room here than for the slide I made for the Goodell-Pratt lathe, so the arrangement is a little different.  Both the top and the bottom portions of this slide have slots to fit the 3/16 inch tool bit.  I also made a cup follower for the 1/4-28 screw that acts to feed the bit into the workpiece, because the brass ring tilted too much.

     Note in the third column above that there is plenty of "meat" above the tapped hole for the 1/4-28 screw on which to clamp the slide.  The intended angle, i.e., less than 30 degrees, causes the right-hand side of the 60-degree bit to cut a much thinner chip than the left-hand side. This keeps the two chips from interfering with each other and also keeps the right-hand chip from forcing the tool slide ahead of the proper longitudinal feed rate.
   I already had a T rest, but I had to make the saddle shown below.   I hand scraped it to fit the ways of the Derbyshire lathe and also made the T bolt and clamping nut.
   The saddle allows one repeatedly to adjust the lateral position of the T rest without causing localized wear to the bed of the lathe. 

  The T rest is also extremely snugly held with little turning effort needed on the clamping nut.
   I was in a quandary about driving the lathe (as motors are pretty dear on the Internet) but then I rediscovered an old pedestal fan motor made by Westinghouse a long time ago.  It needed a new cord and some brushing out of accumulated oily dust, but I got it back together and running smoothly on 2.0 amps of 110 volt current.  Luck was with me, as it turns in the right direction.
Tee rest shoe
Tee rest shoe
Motor mount   
There are no mounting lugs, so I strapped it onto a wooden cradle cushioned with jute weatherstripping; those are the remnants of the belts used to drive another project.

   The two metal strips serve as ersatz dovetails to hold down the motor, yet permit adjustment of the belt tension.

   The 3/8 by 17 inch long V-belt arrived after this image was made but functions OK, albeit a little stiff.  Perhaps that is good - it is very hard to stall the motor, once it's been started.