"Projects" at georgesbasement.com

10. Making crank screws for No.2 drills.
Many of the Millers Falls No.2 drills that have LRRCW's apparently came in knock-down mode, with a knurled thumbscrew holding the crank in place on the main gear wheel instead of the usual oval-head countersunk screw, which is often lost. These thumbscrews make it relatively easy to tighten the screw when it inevitably loosens during use. Making replacements is made more complex because the screw size is extinct, smaller than No.12-28 and larger in diameter than No.10-32; not only that, there are two sizes, small (0.178-28) and large (0.187-28) and a third size (0.187-24) for the two-pinion No.2 drills.
First crank screw
First one ...
Here's my first one, warts & all.
The original thumbscrews all have diamond-pattern knurling, so I made mine with straight knurls. The screw slot is extra wide, because that was dictated by the available slotting cutter.  All the rest were too thin ...

The wasp waist makes it an easy matter to capture the screw with a wire or string to tether it to the nearest spoke of the main gear, a feature never seen in the wild.

All my screws were made by chasing with a single point tool, as attested by the "stop" position of the thread at the bottom of the countersink bevel.  Only thread milling could approximate such a complete thread.  The tapped threads in the main gear's spoke has no countersink, so it is essential that the threads reach at least this far, lest they interfere with the threads in the main gear wheel.
Set length with a plung cut-off tool.
Although I changed the order of my machining steps during the course of the project, here's the earliest stage of the first screw, with a pass to establish the head diameter and then a second cut to establish the overall length of the screw and guide the cutoff (done last with a hacksaw).

Later on I settled on the following sequence: Turn an inch of the bar down to the diameter of the screw head (0.512 inch); turn 0.38 inch of the bar to the screw-body diameter (0.205 inch); bevel the end of the screw body; plunge cut the waist to 0.235 inch minimum diameter; finish the countersink head diameter to 0.38 inch; thread the screw body to 28 threads per inch, 0.187 inch pitch diameter (+0, -0.002 inch); plunge cut the head to a thickness 0f 0.15 inch, about 0.12 deep; knurl the head; part off with hacksaw; reverse the screw in the headstock and finish face off the top of the head, leaving a small pip in the center; plunge cut the 0.05 inch slot in the Atlas mill; and wire brush in the drill press to remove burs.
Finishing the screw body diameter
The cutting tool has a small tip radius to blend the bevel into the body, and it is set at 45 degrees to the screw axis to produce a 90 degree countersink.  After this cut, be sure to bevel the tip of the screw to blend the start of the thread into the body, which makes starting the screw into the tapped hole much easier.

I'm using sulfonated cutting oil which is meant for threading pipes. Smelly but effective.

The chuck is a Jacobs Rubber-Flex, bought new in 1960. Holds from 0.1 inch to 1.1 inch, but the South Bend lathe only passes 0.75 inch through the spindle bore.
Plunge cutting the waist with a form tool
The form tool used here is sized to shape the entire waist of the screw without any need for lengthwise feed.  It is important that there be relief around the entire 180+ degree tip so there's no binding on the sides of the cut.  The tool chatters unless the spindle speed is fairly slow, i.e., in back gear.  Note that I remembered to bevel the end of the screw body.
Threading setup
Here's my threading setup. I learned hand scraping and tool alignment by installing the taper attachment seen here.  The micrometer stop seen at lower left wasn't used for threading, but did come in handy for machining the head diameter and the screw body diameter to length.  Not seen at bottom right is the threading dial, which is essential for efficient thread cutting, as it eliminates having to reverse the lathe to reposition the cutting tool.  Be sure to set the compound rest at 29 degrees off the perpendicular to get a smooth finish on the screw threads; the main chip comes from the front side of the cutter, while the back side just shaves the flank that bears on the female threads when the screw is tightened.
First threading pass
Here's my first threading pass. Even with the relatively slim waist, the screw did not visibly deflect during threading, as each successive cut removes rather little metal.

It takes about six to ten passes to finish the screw to fit the tapped hole in the main gear.  Later on, I found my screw-thread micrometer and finished all the next ten screws to a pitch diameter within about +0, -0.002 inch. Below: threading done.
Knurling setup
The knurling tool came to me from tailgating at CRAFTS of NJ and puzzled me until I noticed the notch on the bottom, about an inch-and-a-quarter from the axis of the serrated cutter.  That notch is to be positioned on top of a firmly fixed fulcrum (a reversed tool holder set parallel to the lathe axis) and the handle (not seen at upper left in the picture at left) must be pulled down so the cutter comes up from below the workpiece axis with the workpiece rotating normally. This causes the leverage to increase as the cutter axis approaches a line drawn between the workpiece axis and the fulcrum position.  If you try this backwards, coming down through center, the setup becomes unstable and the cutter roll will snap through that imaginary line, damaging something; I didn't do that !

Detail of knurling setup
Slotting setup
I modified the workholder that I had used to finish the LRRCW mod's discussed above by drilling a hole slightly larger than the screw body down into the pair of bars and then wrapping a strip of paper around the screw. When I didn't tighten the vise sufficiently, the milling cutter simply slid the workholder out of the vise to the right. I left a pip in the center of each semi-finished screw so I could sight on it to center the screw underneath the cutter. I fed the knee of the Atlas mill upwards to make the slot deeper in the center.

The slot really isn't needed, as it's easy to make the screw plenty tight with bare fingers.

Screw holder

   Here's the screw holder taken apart.
A group of Millers Fals No.2's with LRRCW's.
Here's a group of Millers Falls No.2 drills with modified LRRCW's and their new straight-knurled take-down screws.

Below: all in a day's work (these are the large, 0.187-28 screws):

Ten screws: a day's work.

Some of the screws ended up with with fine reeding and some with coarse. I'm new at this knurling process, but I figured it out anyway ... Make the diameter a fixed quantity (I used 0.512 inch) and apply heavy pressure with the spindle in back gear; that forces deep enough marks that they catch the teeth of the knurling roller on subsequent rotations.
Tapered dowels
However, on further investigation, I discovered that I had picked the only three drills (above) that have large diameter tapped holes; others used smaller screws, with a pitch diameter of 0.178 inch instead of 0.187 inch; and a third group, usually the two-pinion drills, have coarser threads, 0.188 inch and 24 threads per inch.  Therefore, some means for remotely sizing the tapped holes in other No.2 drills became necessary. I chose the method shown at left: 5/16 inch hardwood dowels tapered down to about 0.1 inch at the small end over a distance of about four or five inches.

The dowels are: 0.178 - 28 at the top, 0.187-24 in the middle, 0.187-28 at the bottom.

Tapered dowels
Small 0.178-28 fine
Large 0.187-24 coarse
Small 0.178-28 fine
Large 0.187-24 coarse
Above: 0.178-28 dowel.
Above: 0.187-24 dowel.
It would be next to impossible for every user to make a perfect silicone rubber replica of the inside of the tapped threads in his No.2 drill.  The toolmaker's microscope and its specialized eyepiece provide the solution: The adjustable crosshairs in the eyepiece can be aligned so that the microscope measures the pitch diameter of the imperfect threads embossed into the wooden dowel.

In the upper pictures at left the crosshairs outline a perfect 60 degree thread form and are positioned over what little of the imperfect wooden replica thread exists; in the lower pictures, the same crosshairs outline the 60 degree groove between adjacent threads.

The distance between the upper and lower positions of the dowel on the microscope stage is the pitch diameter of the thread; and the left-to-right distance between adjacent threads (male or female) is the thread pitch, i.e., the reciprocal of the number of threads per inch, which are not counted like saw teeth, by the way.

The left-to-right position of the stage need not be adjusted during the process of measuring the pitch diameter, because each thread is diametrically opposite each groove.

Large 0.187-24 coarse on toolmaker's microscope

Here's what the setup looks like in the toolmaker's microscope:
Measurement 1, inches
Measurement 2, inches 0.4623
Measurement 3, inches 0.4619
Measurement 4, inches 0.4612
Average Pitch Diameter
Here are my actual measurements of the three tapered dowels after screwing them each just once into the appropriate specimen drills' main gears. 

The difference in pitch diameter between the large-28 and small-28 dowels explains how I could end up with two classes of knurled screws - the large-28 screw holes represent an extreme in the variability of the diameters of the tapped holes, and the small-28 screw holes are just enough smaller that they cannot accept my first batch of knurled screws, which are 0.002 inch smaller to 0.001 inch larger than the holes they would have had to fit inside.

The measurements of the two 28 threads-per-inch dowels also give me some confidence about the sizes of the batch of 24 thread-per-inch knurled screws which I intend to make next and about how I can fit new screws to threaded holes which are thousands of miles away and out of reach of any kind of commercial go/no-go thread gauge.

The Large-24 screw thread turns out to be a No.12-24 and the large-28 might be close to the No.12-28 size; compare to these standards.
Small 0.177-28 fine
The screws at left are the small, 0.178-28 size.  Below: 0.187-24 threads.

These are now for sale at $12 each with free shipping to the lower 48
; please include your 5/16 inch dowel that you have made as described above so that I can pick the correct size screw to send.

I made my dowels with a block plane, which took about five minutes per dowel; there's no need to make yours perfectly round.
Brown & Sharpe 22-30 tpi thread micrometer
Brown & Sharpe thread-measuring micrometer for 22 to 30 threads per inch.  The patent (1,629,406) is for a method of adjusting the thimble.  Nevertheless, when the point is brought into contact with the vee, the thimble reads zero, meaning that this micrometer measures the pitch diameter of the threads. It would not have been practical for me to try to make these screws with the alternative, three-wire method, which is far more tedious.
No.12-24 knurled-head crank screws