| Once I started making
gears for my South Bend lathe, Sebastian treadle lathe, Goodell-Pratt
No.29-1/2 lathe, and Cincinnatti indexing head and installed a
threading attachment to my Derbyshire instrument lathe, it became time
to outfit another Derbyshire 10mm Elect lathe bed ...
The image at left shows three cross slides (clockwise,
starting from the upper left): a German Wolf-Jahn, an American
Derbyshire 10mm Elect, and an unknown make. The third cross slide is
much smaller than the other two, and was probably made for a Geneva
pattern jewelers lathe like the brand new (?) one that I bought from a
machinery dealer in Bogota, Columbia in 1967.
The Wolf-Jahn cross slide has lost the gib for the bottom
slide, probably while a previous owner was preparing it for sale; it
was never operated without that gib, because there are no gouges in the
adjoining dovetail surface. It awaits some quality machining time on my
part, as the gib was only about a sixteenth of an inch thick,
five-sixteenths wide, and three-and-a-half inches long. The
sixty-degree bevels along each edge are what make it such a project.
Furthermore, simply milling down a thicker piece of mild steel is bound
to cause severe distortion (from previous experience), so I'll have to
shape both wider surfaces to the sixty degree angle (and drill the
center hole) before parting the gib from a donor slab.
The last slide needs no repairs at all. The Derbyshire
cross slide is relatively unworn, but it came to me with several
issues, including a bent gib in the middle slide, an unmatched top
slide missing its gib, and a longitudinal feed nut that fits the feed
screw but whose mounting holes didn't match the holes in that unmatched
| Here's that bent gib.
Someone had wanted to immobilize the middle slide, so he tightened all
the gib screws; but the screw closest to the handle was not over the
slide's dovetail, so it deflected the gib. Then that user moved the top slide over the bent gib, causing a permanent bend. Subsequent operation bent the gib even more and raised the chip seen here. First, I sawed off most of the chip flush to the gib surface with a jewelers saw,
then flattened the gib against an anvil using a soft intermediate piece
of aluminum as a cushion and then whacked it with a three-pound hammer (several times !) and draw filed it to eliminate the residual bend. Full travel of the top slide is now restored.
The finished gib will go on the left, where its centering pin can be
seen. Note also that the mounting holes for the feed screw nut are
staggered ... whereas the nut supplied with the feed screw has holes
that are in line. I draw-filed the gib to an appropriate thickness
after drilling its center hole.
The 2nd tap that I tried fit the holes !
It's the #3-48 size, but a loose fit; a #4-48 tap won't fit at all.
I single-point-threaded a plug from a 3/16ths inch mild
steel rod to fit the threads in the mounting holes, cut it flush in the
first hole, and put the rest in the other hole before cutting it off.
The plugs were necessary because the holes in the feed nut overlap the holes in the unmatched top slide.
I centered the alignment hole in the gib by selecting how much to remove from the beveled edges.
More to come: The "unmatched" top slide is
actually quite a close fit to the middle slide, so it probably was also
made by Derbyshire, and probably to the same gauges, but I will be hand
scraping all the sliding surfaces to correct for the uneven wear. The
cross slide also needs an extended tee nut to make a strong attachment
of the cross slide to the Derbyshire Elect lathe bed; I'll make that
with my South Bend shaper. The Wolf-Jahn cross slide also needs a wear
plate for fastening to its lathe bed.
| I thought long and hard
how to align the holes in the top slide to the holes in the feed nut,
which fits in a narrow passage underneath the upper surface of the
middle slide and has a wing protruding through a slot in the middle
slide's dovetail as can be visualized in the image at left. The
overlaps cover half of each hole, so the plugs had to be each drilled
half away. I dared not try to cut threads in such holes, lest the tap
spin a plug. What I used is called a roll pin or spring pin, whose
patent may or may not predate the design of this cross slide.
I started the alignment process by finding a number-size
drill bit that closely matched the holes in the tab of the feed nut and
using that drill bit to make starting dimples in the cross slide
mounting surface. Each of those dimples straddled the nearby plug. Then
I used another number-size drill bit to make a pair of relatively
tight-fitting holes for the nominally 3/16ths-inch size roll pin that I
selected, followed by enlarging each hole at half the depth with a
larger drill bit that was a lesser force fit. The pin was driven all
the way into the first hole, cut off with an abrasive disk, the
remainder driven into the second hole and finally cut off as seen at
The fit of each roll pin in the bottom half of the drilled
holes was not so tight as to lead to distortion of the struck end of
the roll pin ... but that was to be cut off anyway.
The feed nut was then driven onto the pins with some light
taps from a small (6 ounce) hammer. Its fit is "OK" but is slightly
askew, making the feed handle turn rather too stiffly, so the pins
& holes will have to be addjusted with files ... the backlash is
due to several factors, and a little lost motion in the fastening of
the feed nut will not be material to operation if that operation is
thereby made satisfactorily less stiff. What happened is that the plugs
and cast iron aren't quite the same hardness, so the drills didn't
exactly follow the beginning spot drill dimples.