Thread: Disston D-8 replica

I got a chance to re-do this plate today. It is now 0.024" at the top of the toe and tapers smoothly back from there. This is going to be a worky addition, took me about an hour to do this.
Better taper grinding of D8 saw plate.jpg

Looks good.
What are you using to do the tapering?

Thanks, I use my 6" x 48" belt grinder and a ceramic belt. Rough shaping on 60 grit followed by 120 grit and buffing. Lot's of finesse too.

Thanks. Sounds tricky. Are you just holding the plate by hand or do you mount it on a backing board. Is there a risk of losing the temper?

Originally Posted by hiroller

Thanks. Sounds tricky. Are you just holding the plate by hand or do you mount it on a backing board. Is there a risk of losing the temper?

At this point I'm doing it by hand. I've gone through a lot of gloves, blood and fingernails learning how to do it without getting hurt. You have to take it easy with the cutting so as to not overheat the steel. Lot's of passes with cooling in between.

I got all three of these D8 blades taper ground and toothed today. Here they are after lapping.

These are both set up the same. 22 inches long toothed 12 ppi set with cross cut rake.

second 22 inch d 8 toothed 12 ppi.jpg22 inch taper ground d 8 toothed 12 ppi.jpg

This one is 24 inches long and is toothed 10 ppi.

24 inch d 8 toothed 10 ppi.jpg

These three are also my first blades that are hammer tensioned. Worked out really well. All three are dead straight and bear no marks of hammering after the surface preparation.

While I was at it I realized that I didn't have a saw set up for inletting the handles for the 0.035" thick blades so I made these up. These are both 13 ppi and have an extreme degree of taper grinding running from 0.035" at the tooth line to 0.025" a the back. Think Disston 77 but smaller.



taper ground back saw blades toothed 13 ppi.jpg

Originally Posted by rob streeper

At this point I'm doing it by hand. I've gone through a lot of gloves, blood and fingernails learning how to do it without getting hurt. You have to take it easy with the cutting so as to not overheat the steel. Lot's of passes with cooling in between.

Sounds like a fair bit of trial and error. Are you going with or across the grain or both?
Other than pictures of giant stone grinding wheels in the Disston factory, I have no real knowledge of how this was or is done.
I expect that taper formed a key part of the balance between saw hardness and teeth workability in the design and construction of saws.

Originally Posted by rob streeper

second 22 inch d 8 toothed 12 ppi.jpg22 inch taper ground d 8 toothed 12 ppi.jpg


These three are also my first blades that are hammer tensioned. Worked out really well. All three are dead straight and bear no marks of hammering after the surface preparation.

Those look good, Rob. Can you talk more about the tensioning. I've been trying to figure out exactly what people mean by that term and how it works, but haven't been able to wrap my mind around it yet.

Originally Posted by Isaac S

Those look good, Rob. Can you talk more about the tensioning. I've been trying to figure out exactly what people mean by that term and how it works, but haven't been able to wrap my mind around it yet.

Isaac,

I gather that the Disston works used mechanical hammers to work harden the blades followed by some hand work on an anvil to true them up.
In my experiments I have run two lines of hammer strikes, more or less continuously down the length of the blade. I'm using a 5 lb. cross-peen sawyers hammer. The first pattern of strikes I run down the centerline of the blade. The second along the back side of the blade. I have found it fairly easy to control the flexure of the blade. After the hammering I grind the blades to remove the marks. I intend to test the hardness of the hammered areas but just haven't gotten around to it. I will post the results on the hardening thread I'm currently doing battle on.

Cheers,
Rob

Originally Posted by hiroller

Sounds like a fair bit of trial and error. Are you going with or across the grain or both?
Other than pictures of giant stone grinding wheels in the Disston factory, I have no real knowledge of how this was or is done.
I expect that taper formed a key part of the balance between saw hardness and teeth workability in the design and construction of saws.

Well, if the grain of the steel is parallel with the long axis of the roll I'm working with the grain. The grind marks on the steel as it comes from the box are also parallel to the long axis of the roll. I'll be getting around to testing the effects of my hammering on the hardness later this week hopefully.

Okay, here's some more heresy. I took one of the pictured blades and my surface hardness tester and using the N30 scale I measured Rc hardnesses of 62, 64 and 64 in the region of the back of one of the pictured blades. I'm really surprised.

test points marked.jpg

Originally Posted by rob streeper

Isaac,

I gather that the Disston works used mechanical hammers to work harden the blades followed by some hand work on an anvil to true them up.
In my experiments I have run two lines of hammer strikes, more or less continuously down the length of the blade. I'm using a 5 lb. cross-peen sawyers hammer. The first pattern of strikes I run down the centerline of the blade. The second along the back side of the blade. I have found it fairly easy to control the flexure of the blade. After the hammering I grind the blades to remove the marks. I intend to test the hardness of the hammered areas but just haven't gotten around to it. I will post the results on the hardening thread I'm currently doing battle on.

Cheers,
Rob

I never heard about the mechanical hammers. Do you happen to remember where you heard that?

What little I have found about Disston and tensioning is rather vague, to say the least. It always sounded like one of those black arts that was handed down from master to apprentice with little, if any, documentation.

I'm curious as to what you wished to accomplish with tensioning. An increase in hardness or yield strength? Changing the stiffness of the blade? Straightening/flattening the blade? Something else (I had another possibility in mind, but can't think of it right now. Stupid, faulty memory...)

How hard and often did you hit the blade? Why along the back of the blade and not along the toothline?

Boy, do I have a lot of questions on this topic. Hope you have lots of time, because I will ask them as long as somebody is there to answer them or talk about it.

Originally Posted by rob streeper

Okay, here's some more heresy. I took one of the pictured blades and my surface hardness tester and using the N30 scale I measured Rc hardnesses of 62, 64 and 64 in the region of the back of one of the pictured blades. I'm really surprised.

I too am surprised. If I understand this correctly, those measurements were taken where you hammered the blade. Are you getting the same hardness measurement in unhammered regions? If so, and assuming a uniform hardness across the blade, then something doesn't seem to add up; verything I have ever read and experienced says that high carbon steel of that hardness is brittle, not springlike.

Originally Posted by Isaac S

I never heard about the mechanical hammers. Do you happen to remember where you heard that?

What little I have found about Disston and tensioning is rather vague, to say the least. It always sounded like one of those black arts that was handed down from master to apprentice with little, if any, documentation.

I'm curious as to what you wished to accomplish with tensioning. An increase in hardness or yield strength? Changing the stiffness of the blade? Straightening/flattening the blade? Something else (I had another possibility in mind, but can't think of it right now. Stupid, faulty memory...)

How hard and often did you hit the blade? Why along the back of the blade and not along the toothline?

Boy, do I have a lot of questions on this topic. Hope you have lots of time, because I will ask them as long as somebody is there to answer them or talk about it.

Isaac,

Look here in the second paragraph. http://www.workshopoftheworld.com/tacony/disston.html A statement is made that the blades were subjected to: later steam pressured hammers were used(on the ingots). The process of flattening continued in the rolling mills,... and The next step was "smithing,"—hand-hammering the blade to perfect flatness and subjecting it to several stages of grinding and filing.
This may suggest that Disston saw blades were in fact created by a process we would likely refer to as hammer forging. Forging generally is reckoned to produce stronger and more consolidated material than does casting for instance. The differences between forging and modern rolling mill working may or may not be important, unfortunately we'll never know.
As to the work I'm doing on the blades I am planning a deeper analysis. In a nutshell I'm hammering the blades in a line parallel to the back curve of the blade with overlapping hammer blows from both sides down the centerline of the blade and about 3/4" away from the back edge of the blade. I then grind away the dents producing the plates pictured above. I'll post the results here.

Cheers,
Rob