'Invention' of Square Ground Chain?

[SierraWoodsman]

Good illustration, hadn't seen than one before, but it makes good sense as to why it works the way it does.
A square working corner has the ability to support those thinner/more efficient edge geometry's-(within reason of course).

 

[Terry Syd]

OK, there is an assertion, but I don't see the explanation. The illustration would have been better if they had pointed out WHICH fibres were not being cut. Maybe someone can help me out, which fibres are not being cut in relation to the position of the round cutter?

EDIT: If it is the wood left in the 'corner', that wood is taken out in the next cut. The depth of the cut remains the same between semi and chisel, what gets left in the 'corner' gets taken out in the next cut. The total amount of wood fibres being cut is the same for semi and chisel.

There is also the issue that the semi-chisel is taking a short-cut across the corner. By analogy, think of being on a walk and coming to a corner lot where you turn. The distance is shorter to take a short-cut across the lot instead of walking all the way to the corner and then down the next street. The chisel chain must be striking more wood than the semi-chisel each time it cuts, but the depth of the cut remains the same. In other words, there should be more resistance against the chisel cutter than the semi-chisel.

 

[Philbert]

Maybe someone can help me out, which fibres are not being cut in relation to the position of the round cutter?

This is new to me too Terry. Have heard it a couple of times but did not understand what they were getting at.


The fibers next to the blue line first get cut to a radius by the curved edge of the semi-chisel tooth. In the next pass, some of the same fibers get cut again by the side plate cutting edge, to make a kerf with flat sides. On full-chisel chain, these fibers get cut square the first time.

If this is true, there would be an efficiency by not cutting the same fibers twice. It might be a very small amount, but when multiplied by 700 'bites' per second, it may account for some of the difference between these chains. Of course, any chain has to be sharp and matched appropriately to the powerhead.

And, of course, this is an illustration and not to scale. It would be more of an issue with chipper chain than 'micro-chisel' cutters.

Philbert

 

[Terry Syd]

Yep, I understand that the corner is left and that corner it is cut out on the next cut and a new corner is left, which means the depth of wood removed is the same. Where's the extra cutting of wood fibres that they are referring to?

I'm beginning to think that the reason semi-chisel cuts slower is the way the EDGE of the wood chip is more slowly cut compared to the top plate - the optimum cutter being square chisel corners which cuts the corner at the same time as the top plate starts cutting.

I don't know at this stage, but I'll be interested is seeing how my modified semi-chisel works. If it does cut faster, then it MAY support that theory.

 

[Chris-PA]

This is new to me too Terry. Have heard it a couple of times but did not understand what they were getting at.

View attachment 337241
The fibers next to the blue line first get cut to a radius by the curved edge of the semi-chisel tooth. In the next pass, some of the same fibers get cut again by the side plate cutting edge, to make a kerf with flat sides. On full-chisel chain, these fibers get cut square the first time.

If this is true, there would be an efficiency by not cutting the same fibers twice. It might be a very small amount, but when multiplied by 700 'bites' per second, it may account for some of the difference between these chains. Of course, any chain has to be sharp and matched appropriately to the powerhead.

And, of course, this is an illustration and not to scale. It would be more of an issue with chipper chain than 'micro-chisel' cutters.

Philbert

The thing is, the next cutter comes along at a slightly lower point. It is not moving to the side, just down. It has to cut the fibers that the previous cutter didn't, which are the ones below at any given point along the edge. I don't see how the shape matters at all in this context, nor how it implies that fibers must get cut twice - just keep moving that shape down, and it cuts fresh fibers every time regardless of shape.

I buy that semi may be slower, but this explanation doesn't fly for me.

 

[Philbert]

I can't say for certain that it is the truth, but the theory makes sense to me. I will try to explain it one more way.

Let's assume that the wood is incredibly uniform. And that, due to the depth gauge settings, each tooth cuts exactly 2 new fibers with each pass on it's way down (consider the Left side only, as shown).



Pass 1: Full-chisel cuts fibers #1 and #2. Semi-chisel cuts fibers #1 and #2.
Pass 2: Full-chisel cuts fibers #3 and #4. Semi-chisel cuts fibers #3 and #4 and re-cuts fibers #1 and #2.
Pass 3: Full-chisel cuts fibers #5 and #6. Semi-chisel cuts fibers #5 and #6 and re-cuts fibers #3 and #4.
(Etc.)

The additional re-cutting puts more of a load on the powerhead, slowing down the cut. This would be in addition to any other speed advantages, or increased depth of cut per 'bite' that may result from the different shape profiles. We need the Myth-Busters guys in here . . .


Philbert

 

[Chris-PA]

OK, you've convinced me - only if severing the fibers takes more energy than shaving off the chip below, but that may well be the case.

I was thinking of it in terms of a homogeneous material where cutting is cutting, but that is not a realistic way to think of it.

 

[Terry Syd]

OK, I can see it too. It is the radius of the curvature of the corner that determines how many fibres it has to cut on a pass.

 

[MustangMike]

Philbert, Your illustrations showed it perfectly. The bottom 3 grains are cut with the round tooth inside the blue line, then as the chain moves down, in addition to cutting the new chip down, the side cutter re cuts those 3 grains in line with the blue line, wasted cutting. In addition, the curved side of the tooth has more surface area (the shortest distance between two places is a straight line). The more surface area you have, the more friction on the chain, the more power it takes to move it.

No wonder full chisel works so much better, and this year I am going to try square file.

 

[Metals406]

One really just has to examine his chips when using either profile. The semi profile does more tearing of fiber, while square does more severing of fiber.

Take a peek at your chips next time.

 

[SierraWoodsman]

One really just has to examine his chips when using either profile. The semi profile does more tearing of fiber, while square does more severing of fiber.

Take a peek at your chips next time.

Very good point! Love them chisel chips. Here's a couple pic's using square chisel with the wood grain / against it.

 

[madhatte]

It also appears that the contact patch of the semi-chisel cutter is larger, which makes for greater drag. The chisel profile does a better job of getting out of its own way. Still, semi-chisel surely cuts longer when dulled. Once the point on a chisel chain is dulled (round or square ground), its cutting efficiency drops to nearly nothing, as the top plate is doing ALL of the cutting, since the blunted corner is blocking the side plate from grabbing the severed fibers. With no corner to lose, the semi-chisel can cut, albeit slower, until the top and side plates are both dull.

 

[Terry Syd]

This has been a great discussion on chains. I hadn't considered the extra fibres needing to be cut when using semi-chisel. Once I looked at it, the mod to the side plate angle takes on more significance.

A 30 degree top plate angle gives a 60 degree side plate angle, that seems way too steep. A square ground chisel has a side plate angle around 45 degrees. However, when I look at the top plate angle with 'hook' the angle is much smaller. I don't know what would be a good working angle for a semi-chisel side plate, but I'm going to keep tweaking it and see where it takes me. After a while I should find what works and what doesn't.

If I can find a better angle AND an easy way to create it, I may be able to set up a faster cutting work chain. At this point in the learning curve there is too much work involved to justify it, but maybe after I get a few things figured out, I may be able to simplify the filing process.

 

[MustangMike]

Generally, it is a trade off. If you change the angle to cut faster, you go dull faster. The recommended angles generally provide the most useful life, and keeping it sharp keeps it fast.

 

[lankat]

I thought Joseph Cox invented the Cox chipper chain. I have read the patent. As far as I know he never invented the full chisel chain but I would like to know who did. I did a google search and found nothing. Does anyone know who invented the square full chisel chain