Immediately after the first World War, Mr. James Hartness, President of Jones & Lamson Machine Company, designed an instrument primarily for checking screw threads, a simple optical device. Produced under the direction of Russell W. Porter, it provided an optical image of a thread, quickly and accurately checking its pitch, form and lead.
It proved that tools such as taps lacked the accuracy we had thought was built into them. It proved that elements of design accuracy were lacking.
Ralph & Ernest Flanders with the Longstreth Medal in 1942. Duplicate medals were given to each brother.
Briefly, of every factor that was needed for an accurate tool, only the OD grind of the threads and shank were accurate. The elements that really were needed to make an "accurate" tap were missing: an accurate thread form concentric to axis of tap rotation, accurate lead, and ground finishes on any part of the tool controlling the above.
Seeing the need, my brother Ralph E. Flanders, of Jones & Lamson, designed a tap grinder for correcting the thread form after the work was hardened, a machine not then available.
At the time, I was involved in experimental work at Jones & Lamson. One day my brother approached me and we discussed the problem. I was very much interested in his design. There was little money available at that time for experimental work, but he suggested that I might be able to find a couple of men to work with me in building and testing his new experimental machine. I could keep a record of time spent by all of us and eventually we would be compensated. We could use any equipment in the Jones & Lamson plant that we needed. (Fig 1).
I had no trouble finding two associates - Ellsworth Johnson and Ed Black - so we went to work. In about a year we had produced a machine and prepared it for test. It was called a tap grinder.
It was designed around a twelve-inch diameter grinding wheel, 3/8 of an inch thick. This was adequate for grind- hardened thread forms that were roughed out and heat treated. We set a standard of 20-pitch and coarser for pre-threading. Threads finer than 20-pitch we ground on hardened tap blanks from the solid. A truing device for dressing the grinding wheel to the 60 degree form required was mounted behind the grinding wheel and used auto- matically as needed.
The automatic grinding cycle was as follows: The wheel made a grinding pass
from the tailstock to the driving end of work at the headstock. Next the wheel
pulled back from the work being ground, returning rapidly to the tail- stock
position.
TAP GRINDER, the first thread-grinding machine built
by Jones and Lamson for finish-grinding taps.
The lead of the screw was
furnished by a cam
rather than by a lead screw.
It would repeat this sequence until the finish grind cut was made. If wheel dressing was required to perfect the thread form, a small infeed of the diamonds on the truing device was made, generally about .0015". The truing device diamonds made a pass across the wheel form, correcting any wear on flanks and OD. Often more than one tap might be correctly ground with one wheel form correction.
In developing a successful method of grinding threads we found ourselves devising methods that were entirely new and yet were very effective.
A great deal had to be learned about the new production grinding cycle required for fast automatic operation of the process. For instance, what type of grinding wheel would give the best service for a new grinding application? Naturally we started with standard vitrified wheels because of their rigidity and general use on high-speed steel at a peripheral speed of 6,000 ft.min. But we discovered by tests that the design of the resinoid-type wheel met our standards better, and the nature of that type lent itself better to high-speed stock removal when used with the right surface-grinding speed of 10,000 ft./ mm. and the right type of coolant.
This brings up another factor that was unexpected but proved to meet a production need. Ordinary water-soluble grinding fluids were a disappointment. They were not designed for the heavy cuts and work speeds we established. The form on the grinding wheel broke down rapidly and excess heat was indicated by discoloration of the work. This forced us to consider some other coolant. An oil coolant is used a great deal in stock removal in turning and milling steel in place of a water-soluble agent ordinarily used in grinding high-speed steel. This we tried.
The improvement in this application was immediate. The grinding wheel removed more stock, it held 600 thread form longer, and there was no evidence of burning. The resinoid type of wheel worked well with a cutting oil for a coolant. This use for thread grinding is now standard. It is good not only in grinding high-speed steel but works equally well in miscellaneous applications that came later in meeting automotive and aviation needs.
I have tried to show how the manufacture of the first tap grinder led us into a new metal-removing field which has found wide application in the machine tool industry. It was one of the high points in the years of my experience to have had the satisfaction of working out a new successful grinding process for a new need. I cannot remember at this time any tap manufacturer into the '30s who did not find use for this grinder.
The importance of our joint work was recognized by the Franklin Institute of Philadelphia. On April 15,1942, my brother Ralph and I were joint recipients of their Longstreth Medal for the year "in consideration of the development of a thread grinding machine, including a method for truing the grinding wheel, its mounting and control, insuring accuracy and invariability of the resulting screw threads."
