The Conference on Screw Threads.
Page 13
If you've noticed an error in this article please click here to report it so we can fix it.
A Conference was convened by the Engineering Standards Committee on the 24th October, at the Institution of Civil Engineers, and to this representatives from the Royal Automobile Club, the Institution of Automobile Engineers, the Commercial Motor Users' Association, the Agricultural Engineers' Association, and the Society of Motor Manufacturers and Traders were invited. The Conference was held with a view of ascertaining how far the series of fine threads laid down by the Committee (full particulars of which have been issued in their Report No. 20) were adapted to the special conditions of design existing in motorcar construction. The chair was taken by Mr. H. F. Donaldson, Chief Superintendent of the Royal Ordnance Factories; and Chairman of the Sectional Committee on Screw Threads and Limit Gauges.
It might be of interest if we recalled the fact that three series of threads have been standardised by the Committee :
t, British Standard Whitworth ; 2, British Standard Fine Threads; 3, British Association.
Some very interesting evidence was given by, amongst others, Mr. Lanchester, Mr. O'Gorman, Mr. Orcutt, and Mr. Godfrey Brewer, and it transpired that, for most purposes, the existing standard, fine threads were deemed suitable for employment in car construction. Mr. Lanchester pointed out that, whereas the gradation in the series of fine threads, in sizes relating to the strength of the bolts, was satisfactory in sizes lin. and above, the jump from a 5-16in. to a kin. bolt was proportionately too great, and did not allow of sufficient latitude in design. He sug,gested, for the Committee's consideration, the insertion of an intermediate size. He stated that the screw threads adopted by his firm changed from English to metric pitches at a diameter of 5-16in., where a convenient relationship. existed between these two systems of pitches, which was based on the fact that 8mm. closely approximated to a diameter of 5-t6in., and he suggested a similar step in theCommittee's tables. It would appear, therefore, that, instead of carrying down the standards to kin. before adopting the BA. metric pitches, it would be desirable, at any rate for motorcar work, to make the change at 5-16in. and to consider the adaptability of this to general engineering work. Attention was called to the necessity of standardising thethread commonly used on sparking plugs and which has a 1.5mm. pitch, since several firms were manufacturing a thread which, though closely resembling this, did not interchange with it.
Mr. Orcutt spoke in favour of the limits laid down by the Committee, by the aid of which it was hoped to secure inter.. changeable work, and he referred to the present, unsatisfactory state of much of the work turned out by the majority. of the bolt and nut manufacturers. To his knowledge, so difficult had one prominent engineering firm found it to. secure anything like reasonable accuracy in the bolts and nuts supplied from manufacturers' stock, that it was about to institute a nut and bolt department of its own.
The difficulty of obtaining reasonably-accurate bolts and nuts was confirmed by others present, one member of the Committee stating that his firm had already been forced to. adopt a similar course to that referred to by Mr. Orcutt. The results of the Conference may be summarised as follows :—
I. An expression of approval on behalf of the automobile industry of the work already carried out by the Committee, and the suitability of the British Standard Fine Threads for
employment in car construction. • 2. The advantage of lightening the existing 'Whitworth. Standard nuts by reducing their width across the flats when employed in motorcar construction.
3. The desirability of adding certain special standardi threads to those already standardised by the Committee.