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Thread: Taper Ground Dovetail Saw
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31st August 2016, 11:24 AM #1
Taper Ground Dovetail Saw
Pursuant to discussion we were having over here (Help with a Dodo (Disston 77)) concerning another members excellent find of a Disston 77 I thought to have a try at making a taper ground dovetail saw blade.
Taper grinding involves removal of 0.005" to 0.010" of thickness of the steel saw blade above the toothline. Mike Wenzloff does his taper grinding using a flap disk driven but an angle grinder followed by much polishing. I currently taper grind using a 6"X48" belt grinder though I have ideas of making a dedicated grinding machine for blades.
This is the business end of my grinder. I usually use ceramic or Norzon grinding belts.
6x48 belt grinder.jpg
In practice I hold the handle end of the blade with my left hand at the top of the belt housing. I then use my gloved right hand to press the blade gently and progressively against the belt. This is an extremely dangerous process - If you do it and hurt yourself YOU'VE BEEN WARNED!!
I lay out a series of paint marker lines on both sides of the blade like so. The saw plate here is 0.020" 1095. Note the toothline at the top.
taper ground DT blade marking before grinding.jpg
After three passes over the grinder on each side you can see that the marks are removed from the back-side of the blade.
taper ground DT blade marking after first grinding.jpg
And after 10 passes on each side the marks are nearly gone.
taper ground DT blade marking after third grinding.jpg
It typically takes me something like 25 to 30 passes on each side to knock off 0.005" or so, less if the grinding belt is new.
While grinding I stop periodically and take measurements. Here's the profile of the completed blade.
taper ground DT blade profile gradient 2.jpg
The markings are the delta's, i.e. at about 1 cm above the toothline the blade is 0.018" (- 0.002"), at 2 cm it's 0.016" and at 3 cm it's 0.014". All of the way at the top it's 0.012". Should be good to run without set.
And with a medium brass back in place.
taper ground DT blade with back.jpgInnovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.
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31st August 2016, 12:28 PM #2
On looking about the Forum I see that Derek had a go at this too. Taper grinding a dovetail saw – a grand failure at the first attempt
Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.
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31st August 2016, 12:32 PM #3
The first post here links to a video that shows how Disston ground blades. A look at how Disston did It
Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.
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