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The Newbies Arena Are you new to knife making? Here is all the help you will need.

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  #1  
Old 08-14-2016, 08:51 AM
shiny shiny is offline
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Determining the grind width from stock thickness

Hi guy's,

I would really appreciate some help with a calculation: I like to calculate how wide the grindline/bevel should be to establish a 22.5 degree angle on a puukko. Stock thickness is 0.125 inch (3.2 mm). The blade is 0.787 inches (20mm) wide. I ended up a tad to small on the belt grinder I am not used to . I will just finish this knife as practice. No problem.

This calculation is something I am not very good at I have seen a lot threads, but I just don't fully understand most of them. Often they are about calculating an edge on knifes that already have an established bevel...

thanks in advance!
Shiny
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  #2  
Old 08-14-2016, 09:19 AM
damon damon is offline
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if splitting the hairs down to .5deg. means so much then buy a jig or a milling machine that can be set to exactly what you want. no math required.

personally I do a different style. id flat grind a knife that small from edge to spine.

if its just the appearance of that style of knife youre after.... stop your grind line 1/3-1/2 way up.

as for functioning geometry... set your grind at less than that, and then when you use some sort of sharpening jigs you can dial in your 22.5deg. edge.
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  #3  
Old 08-14-2016, 09:34 AM
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Ray Rogers Ray Rogers is offline
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Your grind would be .32 inches high to form a 22.5 degree zero edge on a Puuko style blade according to this calculator:

http://www.calculator.net/triangle-c...its=d&x=71&y=9

That grind is ridiculously short, of course. I've made knives for 20 years and have talked to a lot of knife makers and never met one who bothered to calculate any type of edge geometry except as a curiosity. It really is a waste of time unless you're trying to program a CNC machine. 22.5 degrees is sort of silly anyway as you won't be able to get that half degree anyway, lucky to get within one degree. Not that it matters, you'd never notice the difference when cutting with a 21 degree edge compared to a 22.5 degree edge.

Just grind it until it looks good to you and then test it. You'll have an edge that is less than 22 degrees and it will cut better and be as durable as most zero grinds ....


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  #4  
Old 08-14-2016, 10:56 AM
shiny shiny is offline
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It's not about a few degrees more or less actually... That is not my intention... Well if I could achieve it exactly that would be good, I guess. I am just wondering, because a utility knife like a puukko, that's meant for wood carving and hard use should have an angle somewhere of about 20 degrees isn't it? For me personally that is hard to eyeball. But that's just me. I have woodcarving knifes and a bushcrafter that have scandi grinds. They have very short grinds. It doesn't look good. I agree. But they wedge the wood away from the cutting edge and make good whittling knifes though. They don't dig in like a flat grind does in wood. It's indeed a trade off I guess between looks and functionality. I like it to keep an edge for a long time. That's more important for this knife then looks however. I am using A2 for it.

As for a jig, yeah that would be handy. As soon as I have my own workplace with a grinder I will probably make one. Although I would prefer learning to freehand grind eventually... Much more versatile. I just need some practice with angles for this type of knife.; with flat grinds it's an other story. You just grind till the spine.
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  #5  
Old 08-14-2016, 11:31 AM
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Ray Rogers Ray Rogers is offline
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It's not just you, I doubt there are any of us who can just look at an angle on an edge and really know what it is. But, now you know that if you grind about 1/3 of an inch up on that blade you'll be near 22 degrees at the edge. If that suits your purpose then that's what you need to do. The higher up you grind the narrower the edge angle will become. If you grind all the way to the spine the edge angle will be about 9 degrees ...


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  #6  
Old 08-14-2016, 12:24 PM
shiny shiny is offline
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Quote:
Originally Posted by Ray Rogers View Post
It's not just you, I doubt there are any of us who can just look at an angle on an edge and really know what it is. But, now you know that if you grind about 1/3 of an inch up on that blade you'll be near 22 degrees at the edge. If that suits your purpose then that's what you need to do. The higher up you grind the narrower the edge angle will become. If you grind all the way to the spine the edge angle will be about 9 degrees ...
Cool thanks Ray!
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  #7  
Old 08-15-2016, 09:09 AM
dtec1 dtec1 is offline
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hey shiny I used to use the same calculator that ray posted a link to eventually I found this one http://www.csgnetwork.com/righttricalc.html I find it a lil easier (for me any way every one is different) this one I use now is a "right" triangle calculator. so the one ray posted is if your thinking of the whole blade for me I find it easier to think of one side at a time and I think the "right" triangle calculator a lil easier for that. I also try to find the angle for how high I want the line to go up and not the other way around if that makes sense for example if you look at that link....say the stock is .187 thick but you want to leave a lil thickness at the edge so lets say .187 - .02 =.167 now if you think of one side at a time divide .167 by 2 = .083 so .083 is "SIDE B" on that calculator and now say you want the grind line to come up .5 so .5 is "SIDE A" so if you plug those to in and hit "calculate" it will show "ANGLE 3" is = to 9.43 so that is the angle you want to grind one side on so if each side is done at 9.43 the total 18.86 I may be explaining it very complicated but for me it makes it easier thinking one side at a time .....also you can figure out side b if you plug in side a and angle 3 as long as you have 2 of the sides or angles you can calculate the rest... try it both ways and see what works for you and of course in reality you cant grind something at exactly 9.43 of a angle but then you got something to shoot for...when I do a full flat I do it complete free hand if I do bevels half way up I have been using the bubble jig lately its not like a normal jig very close to freehand its more of a guide than a jig to me. I can do it freehand but it makes it quicker to get the sides even with the bubble jig...try differnent ways and see what works I used the one ray put up but thinking of it as each side different using the other calculator ended up being easier for me different strokes different folks
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  #8  
Old 08-15-2016, 09:32 AM
damon damon is offline
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after reading all of that... lets see if I'm understanding.....
you know what your thickness is.....
you know how high up you want your grind line to come up the side....
YOURE DONE! mark your lines and get to work.
and all the math and such is just for fun?
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  #9  
Old 08-15-2016, 09:59 AM
shiny shiny is offline
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Ah, thanks Dtec. That bubble jig looks like a nice way to have a little help. So simple, yet so smart. I like the way it does not make contact with the belt. Maybe a little at the plungeline though? Does it?

Thanks for explaining the angle calculator you use. To be honest it still didn't settle in my brain. It's not something I am very good at obviously (can not be good at everything). But generaly I would say thinking of one side at the time would probably be a bit more palatable for me as well. When I make another knife for which I like to know the approximate angle I will surely use the calculator link you posted and read your description. That's the beauty of a forum like this; everyting that is posted keeps stored for later times. I love it! Thanks again.
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  #10  
Old 08-15-2016, 12:07 PM
damon damon is offline
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http://www.bing.com/videos/search?q=...0435&FORM=VIRE

I know there are other jigs out there too. try several of them.

might also look into an online college course in geometry or trig.

"precise mathematics and complicated specific tools are the best way to get into quality knife making." that has become a common mindset lately. putting so much focus into gadgets to "do the work for us"

maximizing the heat treat will go a lot farther toward a better knife than NASA precise angles.
yes you want the to be consistent on both sides of the knife, but that's something that takes practice. (and sometimes some creative use of verbiage) even though with that style of grind there is little risk of the grind causing any warping issues during heat treat.

sorry if I sound a bit S.A. but I see this same issue in the hand engraving forums too. people get soooooo fixated on "sharpening templates" and "best geometries" that they spend more time chasing down gadgets and numbers, when just practicing will help them more. cutting tools were made for centuries without all the fancy toys. yes they can be very helpful.... I'm a bit of a tool whore at times myself sometimes. but lately its been more focused on does the tool open up my capabilities or restrict them?

grinding jigs do one thing..... set one angle for only a straight blade. and for a "scandi grind"... after a bit of practice youll be able to freehand grind one faster than itll take to set up the jig in the first place. its not as hard as you might be thinking.

and as ray always says.... make one, and take it out and test it. use it HARD and see how it preforms. study how it works, and where it does or doesn't fail... look at if the success/failure is an issue caused by geometry of heat treating. then make some more.... test... repeat as necessary.
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  #11  
Old 08-15-2016, 02:00 PM
dtec1 dtec1 is offline
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damon. I found that calculator when I first started before I was any good at freehand. I made one of those jigs you can make from a piece of angle iron (search youtube you will see what I am talking about) with that sort of jig it was very helpful to know the angle. eventually after a few blades I wanted to learn how to freehand and I did...however the way I did it free hand is like you said mark the center line mark the height line , grind to center then grind towards height, done. after seeing the buibble jig in a few videos I got curious because it is NOT like any other jig out there I am not sure if you have seen it basicly you know those file guides that you put at the pluge lines...just like that but its "extended" for lack of a better word so you have room to put a lil level bubble magneted to the file guide thing the hole thing clamping the blade in the file guid thing and setting the level bubble takes less than 3 minutes. with that I know the angle so I can start grinding at the right angle and continue all the way through and that makes it a lot quicker than grinding free hand when you "grind to center line then back" (for me anyway) also its more accurate and makes it pretty much imposible to get the sides un even (unless your really really bad at this if so I sugest you find a new hobby) BUT like I said it is not like other jigs the blade is still in your hands you move it just like free hand it just gives you a guide IF you look at the bubble sometimes once I get the bevel going I don't even look at the bubble any more. it can be used on every kind of blade that I can think of curved or not straight pluge lines or swept, plunge lines angled or not flat grind scandi grind what ever. I really don't look at it like a jig , its not a jig kinda holds the blade for you this doesn't...I don't know if you have seen it in action try to you tube "bubble jig fred rowe tutorial" if you haven't it is soooo simple and easy and makes work quicker and more accurate but has the flexability so you can decide to go to free hand at the drop of a dime without taking off anything just don't look at the bubble that's all......if you cant tell I think the thing is absolutely genious.... SHINY to answer your question like I said just like a file guide like you would use if you were doing the bevels by hand with a file so you can keep the plunge line straight. so no it doesn't contact anything obviously the side will bump up agenst the platen if you are doing a straight plunge without the belt hanging over the edge of the platen but even if you do have the belt hanging off the side so you can get that swept look it doesn't contact much it might rub up agenst the side of it but if your asking because your wondering if it will wear by hitting the belt ....no I have done many blades with it and no wear whatso ever . if I remember right I think it is made from hardened o1 steel that may help with not wearing to but I wouldn't worrie about that maybe if you grind 15,000 blades you might get some wear but by then you got your monies worth lol
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  #12  
Old 08-15-2016, 03:28 PM
damon damon is offline
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File guides..... different story.... AWESOME TOOL!! aside from keeping plunge cuts even, I use it for truing up with a file the steps where guards will go, as well as setting up bolsters and keeping everything even. when cleaving up plunge cuts ill track the bely off the edge a bit and let it crawl up against the guide. 320-600 belts don't seem to have any affect on the guide in the past 6 years.

bubble.... if it helps you... go for it. from what youre saying I'm still not convinced. you look away from the blade, and an oops is more likely to happen. what youre thinking is an unnecessary step of grinding to the centerline (with edge down) serves practical purposes. 1: easier to see exactly where youre grinding, and where to stop. 2: grinding edge up without beveling to your center line, will scrape the grit off your belt (I'm sure you'll notice how much your face gets showered with chunks when you do this)
3: time saving..... 3 min to put it on.... one can put a scandi grind on 2 blades in that time.

I'm one of those oddballs who likes to "feel" the materials as I'm working them. I'm slowly getting better at cleaning things up closer on the grinder, but I cant get away from the files and sand papers. I have greater control that way. I do some cheaper knives up just before shows that are done freehand and all on grinder. they are not as perfect as the ones I spend the extra time on, but they are still good using knives, and I can let them go for nearly 1/2 the price. never had anyone ask if the angle on the grind was 20deg, or 22.5deg. I make it look decent, feel great, and WORK. (slicing through cardboard, or 10oz leather like paper always impresses)
had one guy buy one of the cheap ones on a sat.... went home, used it.... came back on sun and bought a nicer one too. (#### I wish we all had more customers like him)

ok looks like I got off topic.
my dislike of things like that is when people become too dependent on them right from the start.
(learned lesson as jeweler..... bought fancy stone setting jig.... learned how to set stones right... realized I waster $400 on a tool ill never use again)
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  #13  
Old 08-16-2016, 08:30 AM
dtec1 dtec1 is offline
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I guess I wont be changing you mind...the thing I like a bout the bubble jig is it shows me the angle I want but yes I can still feel where the bevel is and I can see the bubble and the blade at the same time so no "oops" from that and basicly if I don't want to follow that angle for some reason or once the bevel is straight enough I want to just keep following that I just ignor the bubble and its basicly a file guide...
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