I was setting a couple of saws today (first time doing this).
Both saws had been sharpened and were cutting okay but jamming in the kerf after going down about 1/2″ to 3/4″ and they had absolutely no set in them as far as I could see or feel.
I used a Record 77 saw set plier.
First saw was a Warranted Superior backsaw that I got for £5 on Ebay, It was formatted as 13 PPI and I set the pliers to the maximum setting which is 12 PPI.
This saw set okay and afterwards it cuts significantly better than before and goes right down until the back reaches the workpiece.
Next I tied to set my Dad’s old Grove dovetail saw (probably was his Dad’s as well so I reckon its at least 100 years old).
It was formatted at 11 PPI and I kept the pliers at the maximum 12 PPI.
Several of the teeth fractured straight across near the root with an audible crack and looks like brittle fracture. Maybe the steel has become stressed or work-hardened from too much setting over its lifespan? (I’m not a metallurgist so that’s a guess)
So it looks like I’ll need to file down the teeth and re-cut the saw but before I go to all that effort I would appreciate any thoughts on whether the same problem will recur after I’ve done that or would the brittleness only be confined to the existing teeth rather than extending into the saw plate?
If I remember correctly in one of Pauls saw sharpening or q&a videos he mentioned he would just keep using the saw if it cut straight and the missing tooth would reappear after a couple of sharpenings. If its only one or two tooth I would probably just try that sollution first, would save a lot of work and time if it works.
Only one thought. I remember from somewhere or other that you should not apply the setter to the base of the tooth but rather part way up. Supposedly applying the tooth setter at the base increases the chances of breaking the tooth. I have generally followed this advice and (knock wood) have never broken a tooth.
You now have me wondering whether steel can get brittle. I am pretty ignorant about this, but doubt that it can become brittle unless heated in a way that changes the structure of the steel.
There are several things that could contribute to brittle teeth in addition to where on the tooth line you set a tooth.
What can change the structure of steel is the amount of brown oxide ( rust ) or black oxide ( patina ) the saw plate has endured in its lifetime. Any iron that is converted to oxide increases the proportion of carbon in the remaining steel and also makes that steel more like a sponge or Swiss cheese, making it weaker and more brittle. Take a loupe to an old saw and you may see some of that.
And there is the possibility that older cast steel wasn’t always as uniform as modern steels to begin with. One of the processes a saw plate used to go through was hammering to tension the plate near , but not on, the tooth line. What this did was work harden ( paul calls it “consolidating” when he talks about card scraper sharpening ) parts of the plate that eventually became part of the tooth line with repeated sharpening. Generally, the better saws had more of this hammering done than cheaper plates because it was skilled labor intensive. A study of old Disston saws reported no difference in the steel between their saws but reported their “extra refined steel” likely only referred to the amount of tensioning in more expensive saws.
One saw company, Simonds, stopped making handsaws around 1923 over a labor dispute about the relative higher pay of these specialists compared to other workers who unionized.
I don’t think modern factory produced saw plates suffer from any work hardening-tensioning as part of the saw making process, and probably haven’t since at least WWII. At least I haven’t seen any pictures of gangs of workers hammering plates with hammer and anvil since the 20’s or 30’s. Later sawmakers either used more complex steels or ignored the issue altogether. Modern induction hardened saws have never seen a hammer. Only modern “boutique” sawmakers might do some tensioning, and if they do, they are sure to let you know it.
One other issue could be at play here especially if this is your first time setting a saw.
If you apply set in the wrong direction, a tooth is more likely to break. You may have tried to set a “left-leaning” tooth to the right (or vice-versa). The extra deflection created by bending a tooth the other direction can cause fracture.
Thanks for all of the replies.
Sanford: I didn’t apply the pressure to the base of the tooth. I did them all the same and most bent okay but some (4) just snapped right off.
Can steel get brittle? Well I don’t know the technical term but if you bend a piece of metal back and forth repeatedly it will eventually fail and crack along a straight line where it’s been bent.
Larry Geib: Thanks for a very detailed answer – rust is maybe the issue since the old Groves saw had been lying in a shed for probably 50 years since it was last used and I did clean a lot of surface rust off (with sandpaper, by hand).
Austin Connor: I didn’t reverse the tooth direction because there was zero set left in the saw when I started, however I’ve no idea how the teeth were aligned 100 years ago.
I used the saw yesterday and it cuts okay so I think I’ll just live with the defects for now.
Thanks to you all for helping.
- You must be logged in to reply to this topic.