Progressive grinding or whats your angle.

Fred Rowe

Well-Known Member
This thread was originally posted in 2009. If you have not seen it previously it contains some good food for thought.
Progressive grinding assures that as you grind up the blade the abrasive will make contact with the peak left by the last grinding angle. The steel is removed faster each time the angle of approach changes.



I used a 4 inch by 2 1/4inch by 5/16 inch section of planer blade for this demonstration.
The first picture shows the blade section, end on, before it was ground.

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The second and third pics shows the grind on the left side of the blade using an angle of approach of 10 degrees.



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The forth picture shows the results of switching to a 5 degree angle of approach. The grind moves up the blade and moves to intersect the edge that was ground at ten degrees.
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This next picture shows the grind at 4 degrees angle of approach, the grind moves up the blade and moves to intersect the edge.



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I jumped from a 4 degree angle to an angle of 2 1/2 degrees, relative to the belt surface, to show the amount of grind line change caused by changing the angle of approach by 1 1/2 degrees.

The last picture shows the grind at the 2 1/2 degree grinding angle.
As you can see the grind has gone completely across the 21/4 inch blade section.

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The straight edge shows the ground side to be perfectly flat across the ground bevel.

When you grind blades by degrees, two things will happen, one is the grind goes faster because you are grinding across the high points left by the previous angle of approach. The second is you will end up with a perfectly flat bevel.

So whether you want a flat scandi grind blade, ground at 12 degrees or a wide chopper, three inches across, ground @ 2 degrees we are all looking for the same results, flat even bevels.
If you have questions send me a pm, happy to answer any questions you might have.

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Happy grinding, Fred
 
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It takes a pretty steady hand. I think the pics help people to visualize whats going on where the steel meets the belt.

Fred
 
Sorry if this is considered thread necromancy, but it raised a question for me. I use the Bubble Jig, and I do progressively grind as that just seemed the thing to do.

For a full flat grind, I just progressed until I had the angle that just about took it to the spine. Also for a scandi, I started steep til I hit my edge scribe line, then brought it down to 12.5.

But my question has to do with those times you don't want a full flat grind. Let's say you want a partial flat up to a scribed line maybe bisecting the point, is there a flat grind calculator you can use with your blade thickness and width to give you the correct angle to work for? Otherwise it winds up eyeball, and maybe its because I'm still learning all this, but if I take it up past my scribe line that ruins the geometry. So then I sand the flats back ... then I adjust angle and try again ... then have to sand the flats ... pain in the neck. I just oversanded one side of a blade, to where its slightly curved now, trying to get a nice straight grind partial height. I was trying to leave some flat so when I put a swedge on, it makes a nice clean triangular shape on the flat.
 
Rob,

You are quite welcome. I have one posted above the lay out bench I can glance at when designing a grind.

Fred
 
I have one posted above the lay out bench I can glance at when designing a grind.

Fred, that raises another question I had, and let's see if I can make this make sense. The blade profile itself impacts the contour line of grind as well, or can. For example, let's say you're doing a scandi at 12.5 and you want an even distance between the edge and the top of the grind. Am I wrong, or does it seem as if the curve of the blade is too steep or too shallow, you can lose that even appearance unless you change the grind angle or adjust the profile of the blade? I guess it would be even more obvious if you were trying to keep an even grind line on like a high flat but with a recurve or deeper bellied profile.

If that makes any sense ...

So how do you personally use the chart when you design a grind?
 
Fred, that raises another question I had, and let's see if I can make this make sense. The blade profile itself impacts the contour line of grind as well, or can. For example, let's say you're doing a scandi at 12.5 and you want an even distance between the edge and the top of the grind. Am I wrong, or does it seem as if the curve of the blade is too steep or too shallow, you can lose that even appearance unless you change the grind angle or adjust the profile of the blade? I guess it would be even more obvious if you were trying to keep an even grind line on like a high flat but with a recurve or deeper bellied profile.

If that makes any sense ...

So how do you personally use the chart when you design a grind?

Good morning,

Just like the bubble, I use it as a reference to make sure I am in the ball park.
If you stopped by my shop and we had the day to work this would be the best advise I could leave you with.
In order:
Profile the blade.
If the blade is to have distal taper, do it now.
Finish the ricasso and take it to 400.
Attach the bevel clamp and align with the layout line.
Establish the edge from plunge to tip, make it as even as possible.
Reference the chart for the blade width you are grinding so you
have a ball park idea of the finish angle on the bevel.
Progressive grind the blade working from the plunge. Don't be
concerned about the belly of the blade or the tip at this time.
Focus on the straight flat section of the bevels.
Once these are close to heat treat stage, remove the clamp.
Use the flat bevels you have developed as your guide to finish
the tip along with the radius area behind it.

You'll find this process to be very efficient and it produces excellent results.

I realize this is not a concrete answer to your question, but I believe it is the most useful one I could give.

I have ground 500+ blades using the bubble and it is second nature to me.
After you get a few more blades under your belt it will be the same for you.
Regards, Fred

I almost forgot the most important thing, have fun when you work.
 
Fred, thank you very much. I'm going to print the whole thing out and pin it to my bench, but this stands out to me:
Don't be concerned about the belly of the blade or the tip at this time. Focus on the straight flat section of the bevels.
That really really makes a lot of sense.
 
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