Saw sharpening - broke tooth while setting

[baldpate]

Hi,

a while ago I acquired a big-ish old backsaw (14" blade, 13tpi, crosscut), and the time came today to give it a sharpen and set. I've not had a problem previously setting a saw (no expert, but I've done it half-a-dozen times now), but this time for the first time I managed to break a couple of teeth - not by trying to set them in the wrong direction, I hasten to add!

Before resharpening, I tried to guestimate the existing set by gently applying the set to the tooth at the extreme end of the blade. I was using a Somax (the one for fine teeth, 12-20tpi) and tried it on the No 8 setting, and the tooth broke; I assumed, the setting was too coarse, and so used a No10 setting for the real thing after sharpening. All fine until about 1/3 along on the first pass a tooth broke, and further on another (even though by then I was going very softly).

Now all the other saws I've sharpened have been relatively modern (max 20/25 years old, I'd guess). This one is stamped Taylor Brothers, which would make it about 100 years old, if I understand correctly. So my question is : could age be the reason? Does the steel get more brittle with age? Or did they perhaps use a more brittle steel in the first place to make saws in those days?

Thanks for any enlightenment

 

[James C]

I'm not sure if it helps but I bought a Taylor Brothers Rip Saw with a course 4 1/2 tpi.

I used the coarse somax 4-15tpi and found it quite difficult to get the teeth to shift but not brittle just resistant.

Also I found most vintage saws are made with proper spring steel and should be able to withstand a decent set.

I don't seem to get your saw set settings, with my somax you set by the tpi, so I don't understand why you have a 8 and 10 setting on a 12-20tpi set.

 

[Jacob]

I had the same prob with a very similar saw (very old 14" Spear&Jackson 13 tpi) . I broke enough teeth to make topping necessary and then re-sharpened. This time I set them finer and there was no prob. I also followed Paul Seller's advice - which is to file all saws with 9 or more tpi as rip cut. Makes sharpening simpler and seems to work!

I don't seem to get your saw set settings, with my somax you set by the tpi, so I don't understand why you have a 8 and 10 setting on a 12-20tpi set.

Apparently the anvil on Somax is marked 4 to 12 which is not TPI but is just an arbitrary scale. This makes sense as tpi/set aren't in a fixed relationship - it's all relative.

 

[baldpate]

I had the same prob with a very similar saw (very old 14" Spear&Jackson 13 tpi) . I broke enough teeth to make topping necessary and then re-sharpened. This time I set them finer and there was no prob.

Thanks Jacob - good to know I'm not alone. So maybe age is the reason, one way or another.

I also followed Paul Seller's advice - which is to file all saws with 9 or more tpi as rip cut. Makes sharpening simpler and seems to work!

Interesting advice - I might try that on the next one in the line-up.

I don't seem to get your saw set settings, with my somax you set by the tpi, so I don't understand why you have a 8 and 10 setting on a 12-20tpi set.

Apparently the anvil on Somax is marked 4 to 12 which is not TPI but is just an arbitrary scale. This makes sense as tpi/set aren't in a fixed relationship - it's all relative.

Yes that's right. Somax do two sets, one for saws up to 12tpi (or is that 15??), and one for saws with finer teeth. Both anvils have the same markings (though presumably on the coarser set they at least bear some sort of crude relationship with tpi).

 

[Cheshirechappie]

On reasonably clean steel, there's no reason for age embrittlement, but if there's any corrosion present, it might have gone deep enough to affect the material. That said, the older grades of steel may not have been quality controlled to the same degree as modern ones (the monitoring equipment not being available to older steelmakers, especially the smaller concerns), so there may be some variation between batches in exact chemical composition and heat treatment; it's quite possible that some older saws are a bit more brittle than others of similar age.

I have an oldish Drabble and Sanderson 14" 11tpi that I refiled to rip. When I set it, I aimed for the absolute minimum of set - about a quarter of blade thickness, which gives me a kerf of 1 1/2 times blade thickness. I've used this on some cuts deep enough to almost foul the back spine, and had no problems with binding. I notice some of the American sites suggest setting using figures such as 5 thousands of an inch each side, but I don't think accuracy of this order is necessary (actually, 5 thou is about 1/4 of blade thickness in the case of the D&S), just try minimal set and then give it a test drive. If it binds, up the set a tiny smidgen, and try again.

 

[James C]

Looks like I'll be getting the callipers out when I'm sharpening next then. I assumed that teeth would move (within a certain range of course) on a sliding scale due to 8tpi giving teeth of roughly 1/8" in size and so on and so forth.

 

[bugbear]

I recall speaking to a retired saw doctor (we were both attending a specialised tool sale), who now restores and sells pre 1900 saws as a hobby.

Old saws tend to be much harder (*)

He used the style of set shown by Pedder

post716750.html?hilit=%20heat%20gun#p716750

which he said was much gentler and more controllable than the #77 type.

BugBear

(*)

The saw that is easily filed and set is easily made dull. We have frequent complaints about hard saws, but they are not as hard as we would make them if we dared; but we shall never be able to introduce a harder saw until the mechanic is educated to a more correct method of setting it.

 

[baldpate]

@ Cheshirechappie: Thanks for the advice. I've measured the new kerf, and it looks as if I have slightly increased it - now 1.05 mm, whereas previously 0.9 mm. This is on a plate which is 0.75mm, so well within your rule of thumb. Next time, I'll try 'sneaking up on it' though.

@bugbear: thanks for the information - I might have a look at one of those 'continental' type sets - they come up every now & then on ebay. What your saw doctor acquaintance had to say sounds like the voice of experience.

 

[pedder]

@ Cheshirechappie: Thanks for the advice. I've measured the new kerf, and it looks as if I have slightly increased it - now 1.05 mm, whereas previously 0.9 mm. This is on a plate which is 0.75mm, so well within your rule of thumb. Next time, I'll try 'sneaking up on it' though.

@bugbear: thanks for the information - I might have a look at one of those 'continental' type sets - they come up every now & then on ebay. What your saw doctor acquaintance had to say sounds like the voice of experience.

Old steel can be brittle, but I think you overset the saw.

0.4mm set is too much for a tenon saw for dry wood. 0.2mm is ok.

I've never seen a continental saw set wich could set blades as thin as a tenon saw (0.8mm). The ones I've see where for much thicker blades.

Cheers
Pedder