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Assessing your twist fit & going off your rocker

I’ve written in past posts about adjusting tang twists and horizontal balance but in discussing this in the scythe forums it became obvious that the concepts aren’t as obvious as they might seem, and that I hadn’t really covered them in any detail, other than to refer people elsewhere (chiefly www.scytheconnection.com) for further information.

For starters, the terminology is all a bit fraught with difficulty because it can be ambiguous. Peter Vido refers to horizontal balance, and by it (in the context I’m speaking of) he means the way the blade presents to the ground when you’re holding the snath in your ‘natural’ way. He means whether the point is too low, or the beard is too low, or whether both are sitting about right and the belly of the blade is what’s actually sitting on the ground (just in case my explanation is including even more unfamiliar terms, I’ll include the annotated picture over there to the right…)Anatomy of a scythe - glossary

The trouble is that other people, when speaking of horizontal balance, can be referring to something closer to the blade’s balance point when held horizontally; the point at which if you were to hold the blade up (unattached) with a ruler or similar, on the underside of the blade, it would balance nicely. That point is usually somewhere around a quarter to a third of the way along the blade. While this “horizontal balance” characteristic contributes to how the rig behaves overall, it’s of far less importance to the rig’s behaviour than the “horizontal balance” Peter refers to.

I propose using the term “twist fit”, rather than “horizontal balance of the blade” because (once you understand what I’m on about) it describes the problem and solution, and also doesn’t include any reference to the blade or snath, which I think is important because the problem is never just about one or the other, but rather about how the two are matched, or mismatched.

The way to test whether your twist fit is good or poor is (as Peter outlines) to hold your snath without a blade first, and then hold it with the blade fitted. The first part of the process is in this video and the following photos:

The lay of the snathAs you can see clearly in the photo (and not so clearly in the video), the end of the snath, as I hold it, presents to the ground at an angle that’s a long way from flat. It’s Close-up23 degrees, to be more precise, as found using a zoomed up version with a digital protractor.

The main reason this angle occurs is the way the grips on the Canadian snath are set, combined with how I like to hold them. The grips are angled downwards, and I prefer to keep my wrists relatively straight, which means I roll the grips forward. The day I made this video and took these photographs, I also asked Tony to hold his snath as he normally does, and was very surprised to see that the end of the snath was parallel to the ground. Looking at his hands, I could see why – he prefers to hold the bottom grip as close the stem as possible, and even puts his thumb up on the grip stem itself.

Similarly, if I hold a snath with relatively “peg-like” grips (like a Marugg or a Scythe Supply snath), I find the end of the snath is much closer to level.

Now, when you consider that a blade has to be fitted to the snath, and that the tang of the blade itself has its own angle, the whole ‘twist fit’ thing should become a little more clear. Here’s my 75cm Falci, model 100, which I have heated and twisted to suit me:

Falci

That’s a photo taken with the blade sitting on a flat surface, with me poking my finger down on the spot where I’d like the blade to sit on its belly, to keep it in position. The angle here is just over 21 degrees – just 2 degrees off being identical to my snath hold. It’s worth noting that I came to this setting by trial and error – I have heated and reset the tang twist on this blade several times, until I found the spot where I was happy with it. So this is, to a degree (yes, pun intended) independent confirmation that the snath twist governs what you need from your tang twist; that is, with this blade I worked at the problem backwards – by finding the angle that worked, and then measuring it, rather than measuring the angle of my snath and then setting the tang to that angle.

This particular blade was particularly problematic for me, because it had a very flat tang to start with. It wasn’t quite flat, but it was “over the point” (meaning that if you ran a straight edge along it, the straight edge wouldn’t touch the body of the blade at all, but rather go over the end of the blade). Here’s another “over the point” blade to demonstrate what I mean:

"Over-the-point"

That’s a Russian (“Arti” brand) blade, which is around 96cm long. It wouldn’t matter how sharp I had this blade, or how I had the hafting angle, it would give me lots and lots of trouble if I attempted to mow a paddock with it just by clamping it onto my snath and going with it. Effectively what I’d be doing would be setting the blade up so that the point wants to be 23 degrees lower than the beard, which over that length of blade would be a lot of drop… more like a plough than a scythe:

 

...that's digging 38 cm deep!

…that’s digging 38 cm deep!

 

Of course, I wouldn’t really end up mining for iron ore with such a setup. What would actually happen is that the blade would lay on the ground and the grips would therefore be rotated back out of my comfort zone. But as I tried to mow, as my hands tried to get into their usual position, I would find I was inclined to dig the tip in (which indeed I am with this blade, if fitted ‘as is’).

The angle of the grips, and your preferred way of holding them, will affect how the end of the snath is rotated. The tang also has a rotated face, and unless your preferred snath rotation and the tang rotation happen to be exactly the same angle, once they're clamped together the point of the blade may be too high or too low.

The angle of the grips, and your preferred way of holding them, will affect how the end of the snath is rotated. The tang also has a rotated face, and unless your preferred snath rotation and the tang rotation happen to be exactly the same angle, once they’re clamped together the point of the blade may be too high or too low.

It’s worth noting that there’s probably an argument to be had about whether a longer blade may actually prevent this nose diving effect, since its length provides a ‘self-correcting’ tendency; that is, you’re actually fighting against the stabilising leverage of the longer blade on the ground, such that if you’re keeping the beard of the blade more or less on the ground, you’d really have to be doing something drastic to get the point to dig in (like lift the whole rig a bit). I suspect that – just as there’s a length shorter than which an unmatched tang twist has little effect on the rig’s overall usability – there’s probably a longer length at which the tang twist becomes less of an issue for the tip digging in and rather just becomes purely a comfort issue because the length of the blade simply forces you to modify your grip by way of leverage exercised by the blade on the snath. But I digress…

So, how do you go about fixing an unmatched twist fit, where your preferred snath hold presents the end of the snath at a very different angle than the tang has?  You’ve basically got three options:

  1. Wedge your blade (see below)
  2. Heat and twist your tang to match the angle of your snath hold
  3. Shave/cut off some timber from your snath to match your tang twist
Looking up the snath from the blade end.

Looking up the snath from the blade end. Used this way, the wedge lifts the point.

We’ll do option 2 for you when you buy a blade, if you tell us your preferred angle. We also adjust any tang that is obviously too flat or elevated for our snaths, as a matter of course. So, for you, we probably won’t get it spot on, but it’ll be a good start. We also supply some wedges to get you started with experimentation – again, you’d be very lucky if the wedges were spot on for you, but they’ll be a good start. Option 3 is kind of scary from our point of view as timber is really hard to fix if you stuff something up – only recommended if you’re really comfortable working with wood, you’ve tried a dummy just to test your result, and so on.

Unfortunately, there’s yet another thing to be mindful of when taking all this into consideration: a poor twist fit isn’t the only possibility to think of when trying to diagnose a nose dive or a floating nose that’s too high. Consider the following three blades (one of which you’ve already seen above):

Despite the middle blade’s tang being almost an exact match to my preferred snath hold, I still get a nicer overall mowing experience in rough terrain/tougher mowing, with the other two blades. As far as I’ve been able to ascertain from experimenting with different models, this is because a relatively flat blade (as measured from the beard end of the blade to the point end – more on that below) exacerbates any problem with twist fit or, perhaps more accurately, a blade with a more curved profile in this axis will compensate for a poor twist fit, simply because both the beard and the point of the blade are already sitting further off the ground. I’ve found the easiest way to compare this curve along the belly of the blade (which Botan Anderson and Benjamin Bouchard refer to as ‘rocker’) is to place the blade upside down on a table with the tang overhanging the table, so that the blade is touching in three places: two at the beard end – the beard end of the edge and the beard end of the rib – and the third at the point:

Of course you can't see much from this angle - this is just showing you the setup.

Of course you can’t see much from this angle – this is just showing you the setup.

Comparing my 21 degree tang twist Falci blade (which is a 75cm 100 model) to another 75 cm Falci blade using this method (and looking at it from edge-on), you can see the difference is quite significant (click to see animated comparison):

Comparative "rocker"

Peter Vido has noted that it’s an accepted specification within the industry to measure this curvature just by turning the blade upright and pressing down on the beard such that it contacts the surface underneath. The equivalent of “rocker” is then measured simply by the height of the point from the same, level, surface.

You’ll get away with more in the area of a poor twist fit if your blade has more rocker/a deeper belly/more curve across the belly lengthways. Both a more exaggerated rocker and a better twist fit will improve your mowing experience noticeably in harder, clumpier, or more uneven mowing. You probably won’t notice a poor twist fit too much if you’re mowing lawn or light pasture, and less rocker may even be advantageous in such circumstances as you’re likely to get a more even stubble with the edge being a more uniform height across its length.

And of course there’s a lot of personal preference that comes into all of this. Indeed, when I tune a blade for myself, if Tony uses it, he wedges it to compensate for what he thinks is too much tang twist – he likes his tangs flat, because that’s how he holds his grips. People always do their own thing…

That’s why we can’t possibly hope to fit a rig to someone unless we see them mowing with it. Note that this applies to any rig that anyone sells you – the human body is highly variable, so there is no such thing as a mass-produced “perfectly fitted” rig. You need to experiment to find what works best for you.

Here’s hoping this has taken you one step closer to the mower’s bliss!