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How to to flatten a forged knife blade


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Greetings, and Newbie question: (I hope this is in the right section)

I'm into my third knife build and for now I'm more concerned about learning techniques than producing high quality knives...that will come later.

I have a good, free source of used leaf springs, so that's what I'm using to learn on. My problem is that after forging and initial shaping, I'm having trouble getting the steel perfectly flat. It looks flat until I start grinding the blade, and then the unevenness shows up. Any suggestions on the best way to get the blade flat?

Thanks,

Eddie D
Eastern Oklahoma
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Hi Eddie, I am having similar issues, I figure it is probably a need for hand and eye and hammer to come to a better agreement with experience!

Some sort of flatter might make life easier for me, going to see if I can get hold of one - but in the interim until the "agreement" occurs -  I am leaving a fair bit of fat for grinding to make up for my lack of craftsmanship.

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Greetings Eddie,

.         It sounds elementary but does your forging hammer have s slight crown for drawing out? The finish flattting should be done with a flat face to limit the divots..Be sure to keep your metal up to forging temp and well brushed at the last stages of you blade formation . The temperature transferr to the anvil is very fast the thinner the blade ., Give it a wack and good luck. 

Forge on and make beautiful things 

Jim

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My best anvil for straightening a blade is one that has a slight swale worn into it---works nicely to push the blade just a bit too far so it bounces back to straight!

Also try counting hammer strikes on each side and use the same number for both sides; hard as we often have a preferred side to hammer on, but it makes a difference in keeping it straight!

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There's another possibility Eddy. You aren't noticing warp in the blade until you're grinding on it. It's entirely possible the blade is coming off the anvil flat but the thickness is uneven, this causes temperature differential when grinding and uneven temperature in thin stock tends to warp it.

How are you checking for flatness? Have you checked with a ruler? Tight drawn string? A chalk line works nicely because it will leave a mark on high spots.

Lastly, when you're grinding are you pushing against the belt/wheel? If so lighten up and take more time it'll cause less heat buildup in the blade. Once you get an even thickness you can start bearing down more without warping.

I'm not saying this IS what's going on but it is a possibility.

Frosty The Lucky.

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is this 3rd knife the only things you have done?  I recommend people start with basics to learn the basic things like how to move metal, flatten an edge, straighten a curve, etc but silly me what do I know :) with out any photos  who really knows anything

 

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Thanks for all the replies...lots good stuff to start working on.  I'm old, retired, took up blacksmithing about a year ago...just recently started making knives.  I have a basic understanding of heating, hammer control, drawing out, etc.  That doesn't mean I'm good at it...but I enjoy it!  Other than the self-made divots, my knives have turned out OK....not great, but OK.  Having read all these great suggestions, I think I'm starting out with jackdawg's method...."leave more fat for grinding".  I believe that will alleviate my immediate problem.  I know that's just a work-around until my skills improve. 

Great Forum!

Eddie D

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That is an old established method!   There is an old saying "If a good blade you would win you must forge thick and grind thin"  So far the earliest I have tracked it is to Moxon's "Mechanicks Exercises" published in 1703 and much of it written earlier.

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Leaf springs are funny critters sometimes.  Some of them really want to return to the curve they had even after the heat and beat.  I'll sometimes heat them, reverse the bend in them, and leave them that way for a day or two then straighten and anneal before ever trying to forge.  Once you do get them the way you want, then several normalization cycles with checks for straightness and adjustments where needed helps get rid of that tendency to return to the original shape.  Other than that .... yeah, forge thick and grind thin.

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16 hours ago, SpencerDirks said:

True enough why use a crutch when you don't have to.

It's not a matter of a "crutch"; it's a matter of using the appropriate tool for the job. Flatters are fantastic tools for removing hammer marks from surfaces intended to be smooth, but not so great for straightening out bent pieces (especially ones that are probably going to be ground smooth anyway).

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On the other hand what improves hammer control is using the hammer and trying to do a better job with it. (Given that the hammer face is dressed appropriately!)

So a bunch of hours hammering on a project that doesn't suffer from control issues is a step towards the goal---and you get another tool!

I might advise working on some Christmas projects for a bit of monolithic bi-avicide

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Spencer,

Flatters are a lot of steel to move and if the heat treat is off, they're liable to spall and/or chip on you.

It's not gee-whiz impressive looking, but I took an old 3lb double faced hammer head and annealed it completely.  I tested every surface I could touch with a file to make sure there weren't any hard spots.  Then I ground one side flat and polished it.

I trimmed down a length of wood till it was just snug in the handle hole so it wouldn't be hard to replace the handle if it broke.

Since it's only used on fairly flat and clean stuff, the soft and polished face hasn't shown any wear.  I check the struck end for signs of spalling but I haven't had any yet.  When I do, there's plenty of stock to grind them out.

I found that it takes quite a bit to overcome it's mass to make it useful.  After grinding and everything, it's between 2 and 2.5 lbs.  I can't get much to happen striking it with a 3lb hammer, but switching to the 6lb hand sledge does a really nice job.  The face is about 2" square so it's small enough I can use it solo, but large enough that it's more efficient that just planishing with a flat faced hammer.  Since the flatter requires a fairly hard strike to make it work, it's less touchy about hammer control.  Plus it's dead handy for stuff like flattening the boss area on a pair of tongs. 

I have found that a "butcher" block type wire brush is excellent at getting the scale off quickly.  Flatting over scale just pounds blemishes in.

I can't say I'd recommend the annealed hammerhead flatter for working with a striker.  The heavier blows involved would quickly mushroom the head and potentially collapse the sides of the handle eye.

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On 11/1/2016 at 8:10 PM, Jackdawg said:

Hi Eddie, I am having similar issues, I figure it is probably a need for hand and eye and hammer to come to a better agreement with experience!

Some sort of flatter might make life easier for me, going to see if I can get hold of one - but in the interim until the "agreement" occurs -  I am leaving a fair bit of fat for grinding to make up for my lack of craftsmanship.

An honest and modest fellow. I commend you.

On 11/2/2016 at 1:23 PM, ThomasPowers said:

That is an old established method!   There is an old saying "If a good blade you would win you must forge thick and grind thin"  So far the earliest I have tracked it is to Moxon's "Mechanicks Exercises" published in 1703 and much of it written earlier.

That is such a great quote. I love it!!!

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  • 4 weeks later...
On 03/11/2016 at 3:14 AM, Steve Sells said:

is this 3rd knife the only things you have done?  I recommend people start with basics to learn the basic things like how to move metal, flatten an edge, straighten a curve, etc but silly me what do I know :) with out any photos  who really knows anything

 

I wish I knew about this when I started!!

Can someone create and public the forge bible pretty pleaseee

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threads of inport are pinned to stay at the top  of the page, all were suggested to be read before posting, and  few do,  there is an entire section called Knife making classes,  and I wrote a book, I cant force anyone to read any of them tho

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