Some more background information from Brett, the petitioner:
By now, I guess you are aware of my goal - to get
proper saw files made once more. This is being done in collaboration with people who really know what they are talking about (I'm a novice).
There are two distinct, and fairly evenly split camps on the vitues of a taper amongst these 15 experts. Those who want it back (as it used to be) and those who struggle to see the benefit. It comes down to personal preference, as Nicholson reflected in their 1942 Catalogue, and I quote:
"Handsaw Blunt Files are frequently preferred to Handsaw Taper Files by carpenters and other EXPERT saw filers for sharpening handsaws with 60° teeth. They are parallel in width and thickness but their tooth construction is identical with Handsaw Taper Files. Edges set and cut to file the gullets between the saw teeth."
So, there has always been two camps. We should not forget a couple of very important points that are supremely relevant:
- 1. The were no power saws in those days, so saw filing was critically important, and was done by every professional woodworker on an almost daily basis (particularly here in Oz where they were using ultra hard timbers for housing construction during the MASSIVE housing boom after ww2)
2. The situation is now reversed so that most pros use power saws with TC tipped teeth, and it is primarily amateur woodworkers who are doing the saw filing. Only a few of this group can class themselves as "experts".
What we can glean from that is that a parallel file is ONLY for experts, and so by default, a taper file must make things easier, or more reliable, in some way for the non-expert.
One of the collaborators is Mark Aylward (aka "Claw Hama" over here). He has been classically trained in the art of filing TWICE in two apprenticeships, and these days he is a professional woodworker. Mark is also an excellent lateral thinker (as Tradesmen tend to be). He just wants to get the job done.
His thoughts on the taper are as follows:
The taper serves several purposes as I have been told and taught over the years from my Grandfather, school teachers and reading material etc.
1. By placing the small tapered end in the gullet you can see the teeth, angles etc clearly before starting your stroke.
2. A constant even taper allows you to push through the full length of the stroke and keep even cutting pressure on the file and consequently the teeth. You don't want a shoulder at some point along the way to change or alter your nice steady flow of your cut.
3. Even if filed badly there is still a good chance you will get a (leading) cutting edge on your tooth with the small built in fleam from the angle on the file. Even a Rip saw can commonly have 4° fleam, so 5° ish with the angle of the file. This small amount of fleam on a Rip saw is to help keep your saw cut clean and not too furry. Also once you have sharpened and set your saw you should do a light run down the edges with an oil or diamond stone to get rid of any little burrs or edges that may catch in your kerf.
All this is still on the side of the tooth on a rip saw when most/all of the cutting is done on the pitch/tip of the tooth with a Rip saw (as you all know) The angle of attack on this is adjusted with your rake angle. The tip of the tooth with a 4° fleam will have a slight angle across it but if you look at a lot of the high tech circular saw blades these days they have exactly that also. Shouldn't make much difference one way or the other to your hand saw. (only my humble opinion).
In other words, as you start from the toe, by keeping constant force in the push, the file gradually begins removing metal on the way through, so the taper compensates for this ever increasing gullet width (microscopically) and so there is always constant contact and the same pressure being applied.
Of course I accept, as does Mark, that different people will have different positions on some of these finer points (e.g. fleam).
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.Dick 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.Dick, 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.
