So, what is meant by a proper taper?
Here is a picture of three files. The middle one is from Claw Hama (so we don't get our Marks confused). The two either side are a Grobet "Swiss" and an F.**** and they were both delivered to me in the last week or so.
The middle file is a Wiltshire Austalia made around 1940-1950, and is Mark's favourite file by far (although he can't use it forever).
I'll have a bit more to say about the Grobet & F.****, but for the moment let's concentrate on the taper. Ok, ok, they have no taper to concentrate on, so let's move on.
I think we can accept that Claw's 1940 Wiltshire is the benchmark for taper shape. With that in mind I have measured the taper more thoroughly, dividing it into eight 10mm sections down the 80mm toothed area, and this shows that that taper is a very gentle curve, not a straight line. I did separate measurements for all three sides, and will show the averages.
Going from the shoulder down to the toe, the average angle of taper every 10mm is as follows:
0.2°
0.2°
0.3°
0.5°
0.9°
1.2°
1.7°
2.1°
and the average of the whole taper is 0.9°.
This shows that in the first third the taper is almost non-existent, starts to get going a bit in the middle third, building up to the maximum taper in the toe third. So no real surprise there, as it can be seen visually.
IMPORTANT: When I first started on this analytical journey a month ago, I couldn't for the life of me see why the taper was so important to some people. However, when I saw what Claw was on about it came to me all at once: the taper compensates for metal loss as the stroke progresses and keeps everything even and constant throughout the stroke. Bleedin' obvious when you see the real deal innit?
So yes, I am prepared to change my position in the face of supporting evidence and good argument. This is science, not stalwart opinion. I had originally planned to design a range of non-tapered files to present to the manufacturer, and they would have had a longer toothed area for each relative size, so that a good stroke length can be achieved - thus more efiicient. Not having a taper would also hhave meant that the number of different files could be significantly reduced (and that's really complex and long winded to explain)
The situation now is that a proper taper range (with proper corner radii and toothing) will be the first priority, and blunt-end, untapered files will still be on the burner, but at a lower heat.
Cheers
Brett