Bubble jig use...

[dirtyphil]

I am on call at the hospital today and have some time to grind. Figured I would bust out my bubble jig I’ve had for months but never learned to use. My freehand grinds aren’t terrible but they’re not the greatest either.
My question is this: is there a recipe for the size, width and thickness of the stock being ground? Should I go 10 degree then 5 then 2? Should I use them all while changing belts the higher I go?i saw a video that I can’t find where he said, “for 1/8” stock I start with this degree followed by this then this,” I just don’t wanna grind too thin before heat treat. Trial and error? I am using an esteem 2x72 if that makes a difference. Thanks, Phil

 

[E.Carlson]

Since you are starting, I would go 10, 5, and decide where to need to go from there, depending on your knife. You don't want to over shoot it, so I would probably do 3.

 

[Ken H>]

Just saw the post before me while I was writing this one up. Yes, some folks will grind a higher angle down to the scribe line, then slowly walk the grind line up. It seems to work better for me to set the final angle, then grind the correct angle all the way up.

Well, you can always do a simple calculation. Take how high your grind will be on the blade. The thickness of blade, less the .020" or so you might wish if your grinding pre-HT, then take half of that. angle required = arctan (thickness/grind height)

example, say you've got the 1/8" blade you mentioned, and you wish the grind height to be 1.2"

.125" blade thickness, let's figure .025" left on edge for pre-HT grind, so half of that would be .050"

then arctan (.05/1.2) Using your calculator; to get arctan press "shift-tan" (press the shift key, then the tan key)

shift-tan (.05/1.2) = 2.39 degree. If you use the 2⁰ block that comes with and grind at exactly 2⁰, your grind height will be 1.4" up the blade.

Sounds a bit complicated but once you get the hang of it, fairly simple

Ken H>

 

[E.Carlson]

I tend to start at 5 degrees these days but I've been using it for quite a while now.

 

[Stromberg Knives]

I've been using the Bubble jig for quite a while now.

When I fully grind post HT, I start at around 10 degrees and step down a couple of times until it's where I want it. I've found it saves on belts, because it avoids getting a large surface area to grind at once.

But when I grind most of a blade pre HT the steel is so soft so I set it at my final angle and just grind away.