Backsaw making

[bugbear]

I suspect there is a good deal of long-standing myth about 'tension' in saw blades, probably going back to 19th century marketing hype.

I don't think Grimshaw was selling saws, but he goes into some detail on tensioning. He didn't think it was a myth.

BugBear

 

[Cheshirechappie]

I suspect there is a good deal of long-standing myth about 'tension' in saw blades, probably going back to 19th century marketing hype.

I don't think Grimshaw was selling saws, but he goes into some detail on tensioning. He didn't think it was a myth.

BugBear

I think Grimshaw uses the word 'tension' in connection with his description of correcting out-of-flatness of saw blades by hammering. He does not suggest that a flat saw blade can be improved by hammering.

(By the way, Grimshaws's is the best description I have yet found on how to flatten a buckled saw blade by hammering.)

 

[Isaac S]

I think Grimshaw uses the word 'tension' in connection with his description of correcting out-of-flatness of saw blades by hammering. He does not suggest that a flat saw blade can be improved by hammering.

(By the way, Grimshaws's is the best description I have yet found on how to flatten a buckled saw blade by hammering.)

That is also my take on what Grimshaw wrote. If anyone is interested in reading it for themselves, it is available for download as a pdf on wkfinetools. I'd post a direct link, but it appears that I am new enough that I am not yet allowed to do so. The pages of interest are 102-106.

I recall reading something in one of Grimshaw's books that led me to believe that he had extensive experience in sawsmithing, which may be why his explanations are relatively clear.

Disston, on the other hand, in their "Handbook on Saws" does talk about tensioning in this passage on page 21:

"Now follows tensioning. In this the blades are hammered so that they shall not be too fast or too loose; but shall possess the proper tension, spring or character. If the blade is what is termed "fast" the metal is too long on the edge and needs expanding through the centre, or, if too "loose" the metal must be stretched on the edge. A saw not properly tensioned will run out of its course, in other words it will not cut straight and true."

Again, this book can be found at wkfinetools

Exactly what this means, I don't know. Then, as now, writers could be frustratingly imprecise in their use of technical terms. To me, it almost sounds like tensioning was the process of removing internal stresses from the blade.

I would also add that I can find no reference in either Disston or Grimshaw to tensioning (whatever they meant by that) backsaws.

 

[Cheshirechappie]

I'd agree that the Disston paragraph is a difficult one to interpret accurately, but as it may well have been written by someone in the marketing department after discussion with the production foreman, and without the benefit of modern understanding of materials science, perhaps that's understandable.

If I were having a stab at interpreting it, I'd guess that it again refers to hammer flattening of buckled blades after heat treatment. The "fast" blade - metal too long on the edge and needing expanding through the centre - is one that is flat in the middle, but buckled on the edge, and to correct this, the centre is hammered to stretch the metal until it matches the edge in length, thus straightening things up. The "loose" blade is the opposite - flat at the edges but cockled in the centre, so it must be stretched at the edges by hammering, so that the edge is lengthened enough to pull the cockled centre flat.

In all, it's not as comprehensive a Grimshaw's description, as he covers the actions required to correct several other types of sawblade distortion. In addition, the unduly cynical might suggest that it's not in a manufacturer's interests to be too publicly specific about the tricks of his trade!

In a sense, hammer flattening is a way to even up internal stresses. In a thin sheet, the stresses set up by heating and fast quenching can (at least in part) relieve themselves by distorting the sheet, so hammering in effect redistributes the internal stresses to give the shape wanted to the sheet (i.e. flat).

 

[pedder]

Sorry, I'm late and after Issac entry I can't add much to this thread but I want this quote not to be uncommented:

all the other saws we tested from North America had milled brass backs glued on or the moulded Veritas. Much easier and cost effective methods but once glued they cannot be reworked or removed.

They can be removed. I do this in a very secret process with a heatgun. :lol:

Peter, why didn't you test a Bad Axe saw? They have folded spines.

Cheers Pedder

 

[Peter Sefton]

Hi Pedder
We would have loved to have tested the Bad Axe saw and your own but we can only test what we are given. I like the idea of the heat gun, but not too much heat I would guess.

Cheers Peter

 

[JohnPW]

Re folded back vs slotted back

I would think that's down to a big manufacturer making lots of saws compared with a small maker who makes just a few. The big manufacturer has the heavy machinery to fold the backs whilst it would be easier for a smaller maker to saw a slot. It's like drop forging vs machining from a solid block.