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Drawknife from a file #1: planning handles

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Blog entry by RobynHoodridge posted 508 days ago 1718 reads 0 times favorited 5 comments Add to Favorites Watch
no previous part Part 1 of Drawknife from a file series Part 2: roughing out the blade form »

I was thinking of using an old file to make a drawknife blade.
It’s pretty much the same size and shape.
And made of the right steel.
One would have to create a bevel and thus cutting edge. And flatten one face. Without overheating the steel. Like so:

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But there’s a bit of a problem with a file – it doesn’t have handles or tangs to add handles to like a drawknife has.
Of course, it’s possible to dedicate part of the file to becoming tangs:

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But files aren’t that long, and you’d have to end up with very little left for the blade. (though there’s a trick to use to maximize blade length. Ask if you’re planning to make one this way)
So I was contemplating ways to add handles to a file-derived blade.
I thought of doing this:

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Which is merely a few inches (in this case about 18 cm) of mild steel flat bar (5 mm by 20 mm), welded or bolted onto the flat blade.
And I was planning dimensions and angles etc.. To know where and how to bend the steel strips, and come out with a functional knife.
For instance, a traditional drawknife has “broad shoulders” to make it possible to angle the blade to the wood and slice more than wedge it apart.

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But I could achieve the same thing by adding handles at an angle instead of imitating the traditional shape.

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Which would save me some effort making handles imitating the elbow shape of traditional drawknives to add to the simple file-derived blade. Doing it this way of angling strips outward, it’s basically just a matter of welding on strips of flat bar which has one bend in it to take care of the up-down orientation of the blade for comfortable use.
And i’m pretty sure that the way drawknives are shaped (broad shoulders) is a result of how blacksmiths would have forged the first drawknives. Taking a plate of steel, adding some cuts, then unfolding the shape, before refining things.

Cut; bend; then shape things like the bevel etc..
So copying the shape blindly wouldn’t have any purpose.
.
But contemplating adding flat-bar strips to a straight blade, I was pondering a few things.
Whether to add them to the top or bottom of the blade. Would the added strips for the handles get in the way more if placed on one side than the other?
Which direction should the handles be bent? Above or below the blade? One direction might be helpful for “bevel up” cutting, but a hinderance for “bevel down” work.

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Pictures of each possible arrangement were all swirling around in my mind at once. Blades and strip handles at all angles, and all sorts of options for each way of using the knife. And i’d had a bit of coffee so I was hazy. And they sorta melded for a second. Superimposed.

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And because I was also thinking of how I was going to add wood to the flat strip handles to make them comfortable to grip, there were wooden rods floating around the same picture space in my mind too, and those also got superimposed.

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Which left me imagining two strips leading from each end of the file-derived blade to the ends of a wooden handle oriented not in-line with the blade as is common, but perpendicular to that.
This is how lots of handles for pulling upon look out in the world, right? Have you seen the handles on a TRX exercise contraption, or pull handles in the hardware store? So why not on a knife that you pull on?
,,, Of course my blackboard drawings above are of a side-on view. Which wrongly implies that the handles would somehow jutt out straight in front of the blade. But remember i’m also planning to have them splaying outward. Here’s how they might look in a plastic model of the idea:

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And an idea of what the resulting drawknife might look like:

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In making this model I experimented a bit with ways that the strips of steel bar would be attached to the flat blade. With the idea to weld the pieces together:

Welding high carbon steel is possible. And it will remove the hardening only very locally ot the weld, so that welding the strips on well away from the cutting edge won’t ruin the blade.
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I also experimented with ways of bending the strips to create an angle of the handles or grips to suite, in this case, bevel-up cutting.

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A handle ‘perpendicular’ to the pulling force won’t want to slip out of one’s hand when pulling on it. (The reason that drawknife handles are pear-shaped.)
If I put my hands out in front of me and grab at nothing (to simulate the most natural or comfortable position for them), they end up with an imaginary grip on handles that are more vertical anyway. So shouldn’t my more vertical drawknife handles be more comfortable to use?
And how about the control they’d offer? As much or more as handles jutting horizontally toward the user, surely? -Since they’d be equivalent levers rotating the direction of the blade, and thus direction and depth of cut.
These things are complimentary too. Not having to grip so hard upon a handle which wants to pull out of your grasp will allow muscles action to go toward fine control of the cut.
Since there would be two ‘tangs’ coming off of the blade rather than one, and the handle would be in the strong shape of a triangle, there should be less chance of flexing between the handles and blade for better control. Though I don’t honestly think that’s ever really a concern with traditional drawknives. Just showing what my brain was running through when analysing the new handle design that’s come about from fuzzy superimposition.
Depending on how the wooden ‘grip’ part of the triangular handles were affixed, they could probably be more easily replaced than those that are friction-fit upon a peened-over tang as is common.
There’s even the possibility of introducing variation in how the knife can be used. By swapping out or adjusting the angle of the grip in the triangular handle arrangement.

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Perhaps most importantly for me though, is that the perpendicular handle design is achievable with my flat blade derived from a file. More than achievable, it’s probably easier to do considering the tools at my disposal (grinders, vise, and welder – rather than forge, chisels, and hammers). So without involving a blacksmith, and using standard materials easily available.
Not that one has to use an old file. I was contemplating whether a guillotine blade, or indeed a large planing (jointer or thicknesser) machine blade would make a good drawknife blade. And such things would also be flat and without tangs.

But why not such handles on a drawknife? – I did ask.
Well, every design has good consequences and bad consequences. A knife with a handle perpendicular to the blade will take up more space in storage / cartage. It also jutts out below the direction of the cut (depending on how exactly you shape the strips). So that the piece being worked on couldn’t be too much wider than the blade (couldn’t slip under the handle). But if we’re honest this would be an issue shared with most other handle designs, and very wide stock isn’t really the quarry of the drawknife.

I’d welcome any insights into major flaws with the handle design i’ve conceived. But for now I can’t see any big issues. And the extra comfort, control, possible variability, replacement of parts, and the ability to make it with common tools and materials, make me think that this might be a better handle for drawknives. There’s no reason for us to use modern tools and fabrication means to create a product that is exactly as it would be if made the old-school way.
Perhaps this is one you might try if you’re going to make your own drawknife like I am. I’ll let you know how it goes when i’ve made the first one.

-- Never is longer than forever.



5 comments so far

View 1yeldud1's profile

1yeldud1

285 posts in 1640 days


#1 posted 508 days ago

As a tool maker who has altered files for manufacturing process setups please note: Files are normally around 60 rockwell in hardness. It would be very tough to weld to a file and to keep if it from breaking at or in the weld zone. Possibly if you were to make a frame with handles and attach the file as a cutting edge – this could possibly be accomplished

View Bluepine38's profile

Bluepine38

2876 posts in 1683 days


#2 posted 508 days ago

That handle arrangement looks like it might be easier to use for those of us who have slightly abused and
worn out some of our joints. Have just picked up a 12” piece of small planer knife to make into a draw knife.
If I heat the ends of the knife before I weld the handles on it should work OK. This is how we used to weld
cast iron to steel. Those old forges were a good tool to have.

-- As ever, Gus-the 75 yr young apprentice carpenter

View David Kirtley's profile

David Kirtley

1276 posts in 1595 days


#3 posted 508 days ago

If you are going to do it, why not go ahead and set up a small forge? It is not that hard. In essence, it is a matter of getting a piece of metal hot to soften it and hitting it with a hammer. People have been doing it for quite a few years. :)

Heat treating is a little touchy but you can always do it again if you miss the right temperature. A good book is The Complete Modern Blacksmith but if not available there, lots of demonstrations on Youtube.

As far as the ergonomics, I honestly think it is unlikely to make an improvement. While simple, the standard designs are the result of hundreds of years of product development and “usability testing.” The biggest problem with your design is that you don’t always use a drawknife from one direction. Sometimes you use it bevel up, others bevel down. Sometimes you skew the blade, sometimes you use it perpendicular. The handles you show will get in the way. Also, you don’t want the handles centered on the blade. They should be offset.

-- Woodworking shouldn't cost a fortune: http://lowbudgetwoodworker.blogspot.com/

View RobynHoodridge's profile

RobynHoodridge

126 posts in 927 days


#4 posted 508 days ago

1yeldud1, you speak the truth. Welding hard high carbon steel is not recommended.
But here’s why i was going to do it anyway:
First, because i was hoping to leave the welding bit to someone called “speciality welding” near where i live. Not because they should somehow be able to do what others can’t. But because they’d be able to do a longer, better, weld than i would, with more contact, more join, between the parts. Under the theory that more of a weaker weld would add up to a functional joint. And i feel i’m okay with this because the drawknife isn’t going to be under high impact stresses, or indeed any high stress. So when i said it’s “possible”, i should have said “it will weld, but leave a joint that’s more brittle / fragile than usual”
The other reason i might be okay with welding to the old file is that i’ve done it before, very quickly and in a disgusting manner with a stick welder, and this joint held up longer than the blade itself did:

Though it should be noted that the weld probably didn’t get a full testing because the blade was seriously compromised. -

Which brings me to David’s question of “why not build [and use] a forge?” Well, because I failed at it. So i’m scared to repeat my mistake. Scared. The file-derived blade in the picture above was annealed, then shaped, then hardened in my make-shift forge. And as you can see, it ended up so brittle that it simply snapped right accross the depth of it. In short, i don’t want to go to all that effort again only to waste it. I will play more with treating metals. But until i have learned, the shortest way to a functional drawknife is not this.

I like your suggestion of ‘preparing’ the contact points of the blade for welding by heating them Bluepine38. Special care about heating only very locally, maybe needing access to oxy-acetylene kit, but maybe the best option?
I would love to add handles without any welding. I’ve contemplated a way to make ‘bolt-on’ ones in fact. But i just don’t like the possibility of any play between blade and handles. I may revisit it though, and make it more like what 1yeldud1 has suggested where more of a framework embraces the blade. Maybe welded into this, maybe bolted in. A bolt in design could allow you to flip the blade over and turn it from a decidedly ‘bevel-up’ knife to a decidedly ‘bevel-down’ knife. Not that someone would do this on the fly.

Sorry David, i just don’t agree that something has to be good just because it’s been used till now. Or at least not ubiquitously best. And even if my ‘perpendicular handles’ serve a small and specific cohort, i’m going to try. I don’t mean to imply that we’ve been using a flawed design for hundreds of years. It’s always possible for two designs to serve the same purpose. You haven’t felt the difference. I made the plastic prototype specifically because one can’t really tell these things until there’s a physical specimen in one’s hands.
I totally agree that the biggest issue with the prototype handles i’ve made so far is that they can only really be used one way up. I’m working on it. But i don’t see how they’d “get in the way”? I’m also not sure what you mean by offset handles (not centered on the blade). Should they be above or below the plane of the blade? Cause there are plenty of examples of drawknives with handles in the same plane as the blade. In fact my prototype’s handles aren’t exactly centered. And you could alter the design to position them wherever you choose.

-- Never is longer than forever.

View David Kirtley's profile

David Kirtley

1276 posts in 1595 days


#5 posted 508 days ago

That’s ok, I would be the last one to knock someone from testing new designs. Ask me about my CNC router that I have been changing designs on for the last 10 months or so and still don’t have built. :) That said, there have been very few improvements in hand tool ergonomics in the last few years. When people were using these all day every day, bad designs got weeded out quite quickly.

As to the blade/handle relationship, longer drawknives usually have handles that are less bent as you have room to work with on the blade. The shorter they are, the more they tend to have them bent more. They tend to have the handles below the cutting edge to counteract the tendency for the blade to dive as it is cutting. The bevel of the blade will create a downward pressure. Pulling from below the cutting edge counters that force.

As far as getting in the way, many times you skew the drawknife to decrease the effective cutting angle. The edge can be a lot closer to parallel to the workpiece.

There are a variety of drawknive shapes. Some for removing bark. Some for carving. Some for general shaping. They have differences in how they are used and the orientation of the handles goes with it.

-- Woodworking shouldn't cost a fortune: http://lowbudgetwoodworker.blogspot.com/

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