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I Forge Iron

Knife Making Class Log 114: Grinding and Harmonics


Steve Sells

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Rich Hale

 

First is a way I clean my abrasives Both flat and belt I have used a rubbery item that knife suppliers sell for it,,, For a couple of years now I have used an air hose,,,blow it off while running works great It really shows where to remover stockpost-2529-0-19625900-1362025370_thumb.jp About them belts: When you put a square edge to a belt it removes grit as it works,...more so than a rounded or less sharp edge.  post-2529-0-99433900-1362025383_thumb.jpI grind blades with the edge up But before I do that I take that edge
off with the blade edge down post-2529-0-73795400-1362025390_thumb.jp So it looks like this This blade is prepped for heat treat,,it is SS and I send them outpost-2529-0-94155300-1362025375_thumb.jp Same blade as one earlier There are a few things I have also done on this blade,,,,,I use two different SS types,,,this one has two center punch marks on the tang,,,not near the guard location,,,,The other steel I use gets one punch I also have stamped and H on the tang, That helps me get this blade back from a large batch

 

I have rough ground the hollows with it and left cutting edge of a dimes thickness Now for a quick update on a billet I started a while back post-2529-0-36482600-1362025397_thumb.jpThis is the one with .030 1095 and .003 pure nickel,,,welded in a can and has over 50 layers The can is off now and you can see where the nickel was not cut exact same as 1095 and overhangs a bit,,I r ough groung that off,,,then for kicks dipped one end in etchant, I drew that out triple its length and cut twice and stacked and rewelded, it is almost ready to pattern now, power hammer hit a stumbling block today will be back up next week,

 

mike-hr

Do you pay attention to the direction a belt runs? Specifically, with the engineered grit on orange blaze belts.

 

Rich Hale

No I do not but just got a few different brands and they have an arrow,,,

 

steve sells

One thing to get more life is after you think the belt is worn too much flip it over and I can get a little more work, when desperate, but its best to forget cost of belts when using them replace as needed.

 

Rich Hale

If a belt seems a little dull flipping it makes it work a wee longer

 
Steve Sells

Keeping with our 2 subject per chat I am going to cover large blades. not really getting into swords. but large blades are not the same as small ones - as we get longer there are harmonic nodes that come into play and we can't just make a blade large with out planning for the vibrations we will get from them,   for the most part it is not a real problem if we are aware of them and pay attention, but if you just cut a edge on a flat bar of steel like many first time knives are there is gong to be a big problem.  First will be the weight, they will get heavy.  Second as parallel sides running long lengths its asking for vibrations to be set up.  Easiet way is the distal taper we already covered early on in this 100 series that breaks up the parrell sides a bit and it also lightens the blade. And third it will make the blade less tip heavy, leaving it feeling more like an extention of the hand rather than a block ot steel pulling down like a base ball bat (or cricket bat for you brits) The last sword I did was o.31 inch at the guard and about 0.125 about 2 inches from the tip.  A long bowie may be 0.25 at guard and 0.125 near tip.  12 inch blade lengths start this vibration problem, shorter ones are not much of a problem, but long have a tendancy of when you make impacts they have enough mass and length to vibrate more and this feels BAD in the hand, so as we get longer it is a needed matter of function to have good smooth distal tapers, but how do I get them in?  Hand hammering! I work on profile of bleds, and then the sides as I work down the length getting close to where I want.   I almost never do a full reduction in thickness at once pass, I mentioned in a earlier lesson that I try to work maybe 1/3 the reduction at a time after finishing the length start over and get more, this helps prevent burning the already thinned areas while I am getting the new thicker area heated.
 

After I get the blade close to where I want it ( remembering we remove about .030 off all sides to remove decarb after heat treat) I will bonk (thats a technical term) the new blades against a block of wood and try to feel vibrations 1/3 the way from guard toward the tip seems to be a sweet spot for causing this so I try to impact it there to see how bad it is.  If its pronounced I thin that area more, if not I check a few other areas, its not much,  just a few more passes with the grinder/belt sanding machine only a few minutes can tune a OK blade and make it a great feeling blade.

 

mike-hr

You're saying, you can remove the tuning fork effect, by the distal taper?

 

Justin11045

i had made a 26ish" blade before, the first time i hit something with it it felt like my arm was going to vibrate off kinda like a stinger while playing baseball

 

steve sells

Yes that is the basic way to do it, to keep the max vibration point away from the hand and make it the null zone of vibrations instead


Rhettbarnhart

so this makes chopping nicer?

 

steve sells

Yes Rhett, and the tuning fork effect is very accurate description and exactly the same reason.  The vibrations you experience is what I am talking about,  they are harmonic vibrations.   I can explain things in math but what it means in simple terms is the Tuning fork effect, some can be very annoying,  Us paying attention to the distal taper is the START of how to relocate and perhaps remove them.  The wide tapers effect this as well,  one reason why some designs people come up with dont work well on sword, knives and in between, these have been used by mankind for thousands of years,  what works is repeated for manufacture what does not work well is dropped.   I covered enough for now I will get permission some day and I have graphics I would like to post, but no answer from the maker of those yet.  they are showing and explaining in more detail these nodes I mentioned. the floor is open to comments and questions now,

 

mike-hr

I suppose I can assume that many of those fantasy video game blades haven't gone through massive harmonic vibration simulation tests..

 

justin11045

Of course they have those are counter weights to reduce vibration with all the crazy stuff coming off of those things

 

Rhettbarnhart

i just made a bowie with a 6in blade would these vibrations play a part in this knife?

 

steve sells

all metal will vibrate the larger it is the more pronounced it will be I worry in all my blades after learning about it, but in reality less than 12 inch not likely to notice much larger and we had better start to watch out for it.   Justin made a point i want to touch on: the counter weight is for balance but it also plays a part in the vibration, that IS correct and we can use that to help us also

 

Rich Hale

As as aside, rifle barrels have the same harmonics A pile of identical barrels may have them in different forms


justin11045

Thats why "free floating" is used to help with accuracy in barrels A pile of identical barrels may have them in different forms he vibrations will rub the stock and cause all sorts of problems but thats a whole nother monster


steve sells

If you have parallel edges and sides there will be more vibrations than it its all tapered smoothly some subtle bevel adjustments can effect them also I am just giving you all a start of what to look for, we can cover more in 200 series class

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Harmonics do play a big part in proper swordmaking.  If you make the grip a node, (0 point), then the sword will stay in your hand even when struck or striking a hard object  If you make it a peak then the sword will want to leave your hand during use---not a good thing!  

We've all probably have hit something and had our hand "buzz"; not pleasant and indicative of bad harmonic node placement

Note this is one of the aspects that are in play when we say that swordmaking is not the same as knifemaking; weight is another as using swords were and should be quite light making use of tapering along almost all dimensions and structural designs with fullers.

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