Difficulty Cutting Even Bevels...What's Wrong?

T

tychoseven

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Aug 9, 2005
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I'm working on a few nessmuks made from lumber mill bandsaw blades, and I'm putting scandi grinds on them. I cut the initial bevels with an angle grinder, and then return with a file to flatten the bevels. I clamp the blades to the edge of my work table with the base and tip of the edge at the end of the table so that when I flip the blade over to do the other side, the angle remains consistent (I have a static reference point). I am using a jig to ensure the file remains at a consistent angle, but for some reason when I finish, one bevel will be taller than the other. That is to say, it appears to be at a different angle than the other bevel. On some blades the difference is as much as 1mm, but on others the difference is hardly noticeable.

I can't determine where the problem is at. The base of the file jig is clamped to the table, and I check the angle after every side to ensure the same angle. My blades are clamped securely to the table in the same place every time. I mark the bevels with a red sharpie to monitor my progress and ensure there are no low spots. I scribed the centerlines on each of the 5 blades at the same time using the same technique and tools. The only thing I suspect is the angle grinder, which I used freehand to establish the bevels. I don't understand how that would influence the bevel size, as both sides are being cut with a file at the same angle and if one were taller to begin with, the upper portion would not be cut at the same rate as the edge.

Aesthetically uneven bevels don't bother me, but I'm concerned the edges will warp when I heat treat.

I'm new at this bladesmithing gig and am completely stumped by this problem. Clearly my spatial reasoning skills are not up to the task. Anybody have some suggestions?
 
Simplest solution for a blade already filed would be to adjust the angle on the jig to raise the bevel on the low side .This would be the last cut with the file.

To diagnose the problem, without actually seeing the setup is a bit dicey,but:

The center line you scribed is just an eyeball closeness. A few thousandths off at the intersection (edge) will equate to a few millimeters off at the bevel top.

When you file the bevels it should be the be the height that you use to know when to stop, not the center line. If the edge is way off center when both bevels are the same, then the clamp board is not absolutely parallel to the plane of the jig base.

The file cuts deeper into he top of the stroke (edge of the material closest to the handle). That means that you file a little more on the edge side when doing one side , and a little more on the spine side when you flip it. Unless you did each side with extreme care, and reduced the file to a finishing file at the end of each side, it would create what you are getting. ( Not sure this applies to your jig setup?)

Unless the jig and clamp surface is unbelievably preciser and true, it is unlikely that it would make identical left and right cuts. So use the place where you want the bevel to stop as your guide.There are so many variables in a jig that it should never be used to replace the eye and brain. File...look.....file more....look again.
Stacy
 
My guess would be it has something to do with a different way you are filing from side to side...possibly holding the file in opposite hands?

Also, do you do one side completely, then flip it? You may be getting flex in the blade due to the distal taper you put in unless you are supporting the tip. That flex can push the blade down, causing the grinds to go higher...
 
Thanks guys, I think I've worked it out with your help. I had to draw some pictures to help me understand, but my centerlines were not exactly in the center :foot:

For some reason I couldn't visualize why the bevels would be different sizes when I was cutting at the same angle. Once I worked it out on paper it all made sense. I was so caught up with the angle that I overlooked the problem.

Good lesson for me, and I was able to easily correct my mistakes.

Thanks!
 
One way to get those center lines more "centered" is to simply scribe two lines. If your piece is 1/4" thick, make the scribe set a line at just under 1/8," flip the piece over and scribe from the other side at just less than 1/8" (same setting.) You will end up with two parallel lines. The true dead center line is equidistant between those scribed lines, but since youre doing your primary bevels anyways, youll want some meat on the blade for HT. If you scribe those lines right, youll stop at each of the two parallel lines and be left with your proper pre-HT thickness and even height bevels.
 
David Schott said:
My guess would be it has something to do with a different way you are filing from side to side...possibly holding the file in opposite hands?

Also, do you do one side completely, then flip it? You may be getting flex in the blade due to the distal taper you put in unless you are supporting the tip. That flex can push the blade down, causing the grinds to go higher...
Click to expand...

I am having some trouble getting the edge straight on my first knife, which happens to be a long blade. I have been doing BOTH of these things! :o Good advice.
 
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