Sorry for the long answer to the above question.
As most of us are aware, Up to the late 60's most circulars were made of a mild steel, as they were sharpened by using a file and the teeth "set" by twisting alternately, and checked using a dial gauge, a bit like a large zippo lighter.
These saws were easy to burn and overheat and would wobble badly. and were hard work for the saw doc to restore to temper.
When the saw was changed the new saw was packed straight by using a felt wadding against the blade and just behind the gullet, and, sometimes a cut up a woodbine *** packet to get the tension just right.
The small amount of working temperature produced was quite important to get right for a good days cutting.
If you see an old saw today you should notice the gap for the felt and the various wooden "mouthpiece" used.
I believe The earliest circular saw TCT blades were inserted tooth, held in place by a spring clip affair, dangerous if they came out.
They were expensive but economic, long term, in a wood yard running, say a 48" saw blade as they stayed the same size.
These were sent away as we did not have the sharpening capabilities or tooth removal kit, this was before my time.
In the Late 60's "Novelty" saw blades came next, a set pattern of teeth and a gap for sawdust to be carried and ejected out of the cut.
Leading to man made particle blades.
The Laser welding today gives a fast lower temperature weld and today's grinding technology allows for a really high carbon blade that is more rigid and cheap to produce.
I have just paid £4.50 for a 200mm "nailsaw" that apparently will cut ferrous concrete nails and the like, Unbelievable!
The short answer is the mid 70's. Regards Rodders
