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Fletch Helical

Fletch Helical

Joined
Sep 29, 2009
Messages
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I just made my first knife for my scrap pile so it's time to figure out my second problem. I essentially miffed the plunge lines on this one, one side I managed to dig into the spine of the knife when cutting it in (not my immediate problem). So I'm done trying to grind in plunge lines for the time being. I'll cut them in with a chainsaw file at least enough to give me a "stop" when I hit the edge of the platen.... Anyway that's not what I'm looking to analyze here.

I attempted to go all mathematical on this one with grind lines and angles and whatnot. I used the grind angle chart from post #9 of this thread. I had a piece of 5/32 stock and wanted my plunge to be about 5/8'' high. So I came up with an angle of 7 degrees for my grind. I marked my center and then 20 thousandths to either side and away I went. However I still ground all the way up to the spine :confused:. What am I missing in my approach here? I thought just going with a 7 degree grind until I hit my marks would have been fine. How is it not working out like that?

Below is my first addition to the scrap pile. I was ment to be a fathers day present which I'll be starting over on. Might be for the best anyway I'm not really sure I love the design anyway. Maybe have to hit the drawing board again and modify it. Hopefully I can get it done in time.

crap2.jpg
 
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This is just a guess, but if the bottom of the plunge had been the dead center of the blade, that may have worked. Since you left about .040 on the edge, this may be what threw you off on your calculations. My only words of advice are knives are not that technical, try just using your eye and taking your time.
 
The chart assumes 0 edge thickness and has no 5/32 thickness

=DEGREES(ATAN((0.5*(StockThickness-Edgethickness))/BevelHeight))

Your edge thickness at .020 perside or = .040

calculating it out using edge thickness,
(or use the 1/8 thickness column on the chart -it's close to 5/32 - .040)

comes to 5.3 degrees


You used an even steeper angle of 7 degrees which should have given you an even shorter bevel height than that...

According to the math, your grind should have been much less than full height.
about 1/2 inch high.

Check the accuracy of your angle setting on your platen, how are you doing that?
 
I agree with Mike. The first knife I ever tried to make, I did all the calculations and determined exactly what angle I needed. Then I tried to grind at that angle from the beginning to the end. Needless to say, I didn't finish that one. Rahter, start at a 45 degree angle and gradually walk it up to where you'd like it on the flat of the blade.

I stopped worrying about angles long ago. I DO worry about geometry and work to get the right combination of thickness and grind height, but it's all by feel, touch, and sight, not by calculator.

--nathan
 
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12345678910 said:
The chart assumes 0 edge thickness and has no 5/32 thickness

=DEGREES(ATAN((0.5*(StockThickness-Edgethickness))/BevelHeight))

Your edge thickness at .020 perside or = .040

calculating it out using edge thickness,
(or use the 1/8 thickness column on the chart -it's close to 5/32 - .040)

comes to 5.3 degrees


You used an even steeper angle of 7 degrees which should have given you an even shorter bevel height than that...

According to the math, your grind should have been much less than full height.
about 1/2 inch high.

Check the accuracy of your angle setting on your platen, how are you doing that?
Click to expand...

I have the bubble jig so took a 3 degree wedge and a 4 degree wedge, put them together and set the bubble. I have my platen completely vertical and trued it up with a level when I mounted it. The only thing that should be the variation in the angle would be where I have the bubble jig mounted. I can set the angle of the grind to basically anything I need, within reason.

Nathan my feel and touch isn't that spectacular, that's why I like to use Fred's jig. It tells me what to do I just have to keep it there. Seems like this should have been fairly easy. Apparently I was wrong. I guess I can just start at a real hard angle and grind to my marks then switch to a lesser angle and walk it up the blade until it's the height I want.... But seems like this should have worked better.
 
Tryin to grind the whole bevel at once is the problem.If using fred's jig start with a 10 deg and grind to your center marks then move down in angle as you work your way up the blade.Go fom a 10 to an 8 to 7 then maybe even 5.
Stan
 
SBuzek said:
Tryin to grind the whole bevel at once is the problem.If using fred's jig start with a 10 deg and grind to your center marks then move down in angle as you work your way up the blade.Go fom a 10 to an 8 to 7 then maybe even 5.
Stan
Click to expand...


So if you want say a 5 or 7 degree angle you can't just start with that and go till you hit your marks? I figured if I needed or wanted an "x" degree bevel just grinding at that should hit my plunge height and thickness at basically the exact same time. Why doesn't it work out like that?
 
What Stan said. Start with a higher angle and work your way to the bevel angle you want. I have Fred's jig, but I haven't tried it out yet. I mainly picked it up for a handy tool for other applications/fabrication and for flat ground fals edges.

Your touch and feel will improve. Just give it time :).

--nathan
 
Fletch
No trying to grind the whole bevel at once is too hard to control,on doing flat grinds I work my way up the blade in about 1/8" increments till I get to where I want to be.
When I started I tried the same thing grinding the whole bevel at once,some folks may be able to do it but I can't.
Stan
 
Oh well back to the drawing board I guess.

Hey what do you guys think about the design? It's my first Wharnie, not sure I like the finger guard in it to be honest. Seemed to hit things like flat surfaces if you were trying to cut with much more than the tip I was thinking about just having the back of the blade be the finger guard and eliminating the thumb ramp too.
 
Fletch Helical said:
Oh well back to the drawing board I guess.

Hey what do you guys think about the design? It's my first Wharnie, not sure I like the finger guard in it to be honest. Seemed to hit things like flat surfaces if you were trying to cut with much more than the tip I was thinking about just having the back of the blade be the finger guard and eliminating the thumb ramp too.
Click to expand...

Well, my eye doesn't like the "hump" on spine--I think I'd like a continuous curve down to the blade. I also don't care for the guard. If the handle flowed right into the blade, I think it would look nice. Just MHO.

BTW, is this your first try with the bubble jig? I'm very tempted to pull the trigger on one. I've got a DE dagger and a 12" blade Bowie in the works that I think it might help me with.

PS Could you re-profile it and flat grind the whole thing down to match the plunge to save it?
 
Fletch, if you don't like the look of the guard, just deepen the index finger notch a bit, and it will serve the same purpose. Also, I agree that a smooth transition to the blade from the spine would look good. Take a look at my iteration of a wharncliffe I ground out a number of years ago, and you can see what I mean:

IMG_0566.jpg


I still haven't finished this one....:) It's sitting in a drawer right no for no good reason other than some minor flaws. I think I need to go ahead and give it away as I had planned a long time ago.

--nathan
 
silver_pilate said:
I agree with Mike. The first knife I ever tried to make, I did all the calculations and determined exactly what angle I needed. Then I tried to grind at that angle from the beginning to the end. Needless to say, I didn't finish that one. Rahter, start at a 45 degree angle and gradually walk it up to where you'd like it on the flat of the blade.

I stopped worrying about angles long ago. I DO worry about geometry and work to get the right combination of thickness and grind height, but it's all by feel, touch, and sight, not by calculator.

--nathan
Click to expand...

I'm with Nathan. Eye and feel. :thumbup:
 
Mr. Bad Example said:
BTW, is this your first try with the bubble jig? I'm very tempted to pull the trigger on one. I've got a DE dagger and a 12" blade Bowie in the works that I think it might help me with.

PS Could you re-profile it and flat grind the whole thing down to match the plunge to save it?
Click to expand...


Actually I've ground a few knives with the jig. This is the first one I did with actually marking center lines and trying to get all technical with everything. the ones I did when I didn't have a clue seemed to come out much better. A couple are ready for HT I wanted to make this one and send them all out at once and get them done in one shot.

Personally I love the thing bubble jig, I get very consistent grinds with every pass. I just think I screwed this one up because I was trying too hard. It's going to be the first knife I make that isn't for myself. I wanted to do a small edc type wharnie and have it be a fathers day present. My father isn't a big knife fanatic but he really liked how my WIP knife turned out. He carries a cheap-o little folding knife so I figured this would be a bit of a step up for him.

Regardless I'm pretty positive I'm not going to be doing the plunges on the grinder any time soon so I'll just hand file them in to my lines then hopefully they should be alright. If I have something to stop against with the platen I'm usually okay. I'll just start with the file and finish on the grinder.

Chances I can salvage it, or part of it at some point. However it's getting shelved for the time being and I'll work on a new one to hopefully have it done in time.
 
Hi Matt,

I walk the grind up the blade; that is the easiest way to get consistent grinds. Work the edge with a 10 or 12 degree setting and then move up the bevel in small increments. Stop when you attain the height you want.
Moving in 1/2 degree increments you are always grinding along a ridge along the side of the bevel which tends to remove the metal quicker than grinding on a totally flat surface. Once the grind intersects the edge; move up a 1/2 degree.


I have tried laying a blade out using thickness and pitch and then trying to grind to it; It is just easier to use the Bubble Jig as a reference and let the results speak for themselves.

Fred
 
Fred so are you saying if I want to mark my lines, grind to them and then walk the bevel up? I like the idea of marking the thickness of where I want my edge (which is why I bought a height gauge). I'm just trying to know what's the best way to get the thickness and bevel height I want.

Would grinding to the edge with say 10 degrees and then dropping down to a lesser degree work out alright do you think?
 
Fletch, that's the ticket. I get pretty close to edge thickness with a 45 degree grind. Then I continually work up the bevel height until it's where I want it, thinning the edge slightly as I go. It's all about controlling where you're removing the steel. Once you can control taking steel off of the edge vs. off of the top of the bevel while maintaining your flat, things go much easier. It's really just a slight change of pressure to the side of the flat you want to grind on while watching the edge against the belt and feeling the maintenance of the flat against the platen.

--nathan
 
Alrighty then! I just put a new blade on my band saw after having the one that was on there (original HF one) break right after cutting this one out. Time to revamp the design, play with a cardboard model then try this whole thing again.
 
I don't mark the edge myself; I just count the number of passes per side. Ten or twelve or fifteen degrees will work fine to develop the edge. As long as the edge is even from choil to tip it makes little difference. Stop when you hit .045 on the edge, you are at heat treat thickness. If you move up the blade a half a degree, you wont touch the edge again until you reach the finish height of the bevels.There is nothing wrong with marking the blade anywhere, edge or flat either one if it gives you something to reference too. Personally I use five degrees angle of approach to develop the edge. The main thing other than getting it straight and even is to not get it too thin. That's why I like the flatter angle.
After you grind with the jig for a while and get used to the different angles and the grinds they produce the choice of pitch will become second nature to you.

The thing about using the bubble, you know the sides are a mirror image of each other if you are using the same angle on both sides. It can't be any other way. That bubble doesn't lie. I can grind totally free hand, just using edge contact and subtle pressure to produce the flats but I can only get them close not like with the bubble where they turn out perfect ever time by using the bubble to reference the grind.
We don't all have the same hand eye control. And I do not care for convex blade grinds.
Once I have the edge established tip to choil I move up the flat towards the spine keeping the sides equal. If they are equal in height the edge will be centered.

People who have been grinding for years tell me its faster to grind with the jig because the grinding passes are made along the high point of the bevel until you reach the top where it becomes flat from edge to the top of the plunge cut.

Happy grinding, Fred



Fletch Helical said:
Fred so are you saying if I want to mark my lines, grind to them and then walk the bevel up? I like the idea of marking the thickness of where I want my edge (which is why I bought a height gauge). I'm just trying to know what's the best way to get the thickness and bevel height I want.

Would grinding to the edge with say 10 degrees and then dropping down to a lesser degree work out alright do you think?
Click to expand...
 
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