Had to look up what FOP was, file -o- plate. Never used them as I think I have too many different sizes and types of chain.
Are FOP really progressive depth raker generators?
- Thread starter BobL
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Justsaws
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This is my third attempt to write this response and I am not doing a very good job of explaining my post. I hope you are able to understand.
As long as the raker is in the front of the notch and the guide is positioned over the raker so it hits the front would the angle remain more constant as the cutter wears. The newer designs have longer notches to accommodate this, hence the hardwoods/ softwood settings. The older designs just blend the best of the two over the length of the cutter.
The length of the guide remains constant and the only thing that changes is the position of the gauge over the raker as the cutter becomes shorter and the gauge is pulled back to position over the raker. .
The guide should be positioned in relation to the top of cutting edge instead of the back of the next cutter. That way the angle stays more constant.
Here is where a picture is worth a thousand words.
As long as the raker is in the front of the notch and the guide is positioned over the raker so it hits the front would the angle remain more constant as the cutter wears. The newer designs have longer notches to accommodate this, hence the hardwoods/ softwood settings. The older designs just blend the best of the two over the length of the cutter.
The length of the guide remains constant and the only thing that changes is the position of the gauge over the raker as the cutter becomes shorter and the gauge is pulled back to position over the raker. .
The guide should be positioned in relation to the top of cutting edge instead of the back of the next cutter. That way the angle stays more constant.
Here is where a picture is worth a thousand words.
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Cool Bob!
I understand the importance of cutting angle...that's why I put back-bevels on my block plane blades. Didn't occur to me that it would vary with a constant distance between cutter and raker.
I do have one question though...cutting efficiency also should vary as a function of the thickness of the shaving. It certainly does with my hand planes. At some point, would it be better to lose a little cutting angle (not as drastic as what you demonstrated) to reduce the thickness of the cut, or do you run out of cutter before that would become a problem.
If both have an effect, there should be some optimum reduction of cutting angle and corresponding increase in what is removed from the raker.
I understand the importance of cutting angle...that's why I put back-bevels on my block plane blades. Didn't occur to me that it would vary with a constant distance between cutter and raker.
I do have one question though...cutting efficiency also should vary as a function of the thickness of the shaving. It certainly does with my hand planes. At some point, would it be better to lose a little cutting angle (not as drastic as what you demonstrated) to reduce the thickness of the cut, or do you run out of cutter before that would become a problem.
If both have an effect, there should be some optimum reduction of cutting angle and corresponding increase in what is removed from the raker.
Correct!
It sounds like you might be confusing cutting angle with blade angle - these are not the same.
This is cutting angle. [EDIT]Its the angle made before any cutting starts between the surface of the wood the cutter tip and the raker top - I now call this Raker angle.
A plane blade angle is analogous to the degree of hook on a cutter ( this is called the top plate cutting angle in chain speak). Cutting angle is directly related to raker depth, increases in raker depth means an increased cutting angle. On a plane this is the same as increasing the blade depth.
The degree to which the chain can utilize a give cutting angle depends on a whole bunch of things like; type of wood, cutter hook and available power. To maximise cutting speed, what needs to be optimised is the cutting angle and the hook for a given power head power and type of wood with due regard to maintaining a sharp chain for as long as is reasonably required (see below).
The big difference between chains and planes are that planes are usually used as constant cutting device.
A plane blade bites across grain more or less once as it enters the wood and then generally follows the grain until it either reaches the end of the wood or fills the plan mouth with shavings or the operator eases up the forward and downward pressure and the blade then rises (relatively slowly) and crosses the grain again - this is also what happens when noodling with a CS.
When the chain is cutting cross grain it does not do this. It porpoises in and out of the cut and either cuts crescents or semi crescents.
My understanding of the sequence is
1) A cutter bites and is pulled slightly above the bar rails
2) the raker resists, then digs a little into the wood,
3) the cutter digs in further (meanwhile it is still being dragged along) and rises a little further off the bar,
4) the raker resists more, then gives a little,
5) the cutter digs in further (repeat 3 7 4 a few times)
6) eventually the cutter reaches its max penetration and lift off the bar.
7) The chain tension (forward and downwards) is so great it fractures the chip and pulls the cutter back down to the bar and a little half or semi crescent (chip) is now sitting in the gullet.
or in softwoods the the gullet starts filling up with sawdust so much that it pushes the cutter back down to the bar. Kinda like a plane throat jamming full of shavings
The ease with which a cutter enters the wood depends on the hook, lotsa hook means easy/further penetration but if it enters too far it can bog the chain. Not enough hook means it won't enter as far or as easily. Ideally the degree of hook should match the ability of the saw to perform step 7) above, but there are other trade offs with using too much hook. As well as becoming too grabby, to much hook means losing the cutting edge too quickly so more sharpening is required. Not enough hook means the saw will not self feed and will need to be pushed (I'm lazy so this is not my style). For my sort of very hard wood milling the optimum combination is one that allows me to cut one big slab without having to pull the mill out of the cut to touch up the chain - I will be touching it up between each slab anyway so as long as it gets me more or less through one slab that is all I need. I tend to use a light to medium hook and a medium cutting angle (6.5º)
Of course nothing happens in isolation. The chip sitting in the gullet is quickly broken up and some of the sawdust escapes past the bar, some escapes past the cutter and fills the gap behind the cutter and the following raker, and is eventually ejected as the chain exits the cut.
As the cutter wears there is more gullet (space for chips) so in theory (if your powerhead is up to it) a higher cutting angle will give faster cutting. However, in practice the raker and cutter are now not quite as tall so that reduces the gullet space available so this effect is reduced.
If the powerhead has enough grunt and the chain is up to it there seems to be almost no limit as to what the cutting angle can be. Some Aussie Lucas mill operators with 30HP V4 powerheads run 404 chains with rakers as low as 0.06 from new - which means practically no raker when the chain is near the end of its life. This is a cutting angle of 13.5º, it gives an ordinary finish but is one way of cutting slabs quickly. They tend to run very little hook because they don't want to sharpen their chains all that often.
It's the portability of powerheads that limits their power and the cutting angle and ultimately limits their cutting angle. If the cutting angle is too great on any chain the chain just grabs.
Sorry for the rambling response.
I certainly was.
Not rambling...very helpful. I knew the cutter porpoised, but never considered the raker penetration, and the oscillation that produces. Thanks Bob!
scotclayshooter
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Husky combi gauge is better I think, its more progressive. The pivot point is a little farther back then the FOP gauge.
I had a bit of brain fade one day and used the combi gauge for .325" on a 3/8" chain it made it really aggresive just the raker part BTW.
That'll do it !
BTW just based on a scaling factor, going from a .375" (3/8) chain to .325" should only increase teh cutting angle by ~1º which most saws should be able to cope with , what sort of saw was it?
Fun thread BobL - tired to rep you, but the rep Gods said I have to wait.
I think that the FOP argument is interesting, but as you point out, the relationship between the depth gauge and the cutter (top plate edge) still varies, only it varies differently than with a constant depth gauge setting tool (standard Oregon, STIHL type).
I keep thinking of the wood plane analogy. On my block plane, the cutting angle is fixed by the angle ground into the blade. I can adjust the depth that the blade sticks through the plane sole (analogous to the depth gauge height on a chain?) and I can adjust the length of the throat opening (analogous to the length of the gullet as the chain is sharpened?). Both of these adjustments make a big difference in how the plane cuts.
As the cutter is ground back, it takes a longer chip, so maybe a change in the angle you describe is OK?
In Carlton's book ( http://www.sawchain.com/images/complete book.pdf ), around page 19, they justify the FOP based on the way the cutter pivots when it hits the wood, and as the edge gets filed back. If the cutter only heeled back, letting the depth gauge rise up to the wood that would make sense. But if the top plate of the cutter then rises up into the wood, you would still end up with a longer, shallower chip.
In practice, if the chain isn't cutting after being ground back, I would just take the depth gauges down a few more file strokes.
***I would like to see a photo of how you use your vernier caliper to set depth gauges and a mention of how you determine the settings***
Philbert
I think that the FOP argument is interesting, but as you point out, the relationship between the depth gauge and the cutter (top plate edge) still varies, only it varies differently than with a constant depth gauge setting tool (standard Oregon, STIHL type).
I keep thinking of the wood plane analogy. On my block plane, the cutting angle is fixed by the angle ground into the blade. I can adjust the depth that the blade sticks through the plane sole (analogous to the depth gauge height on a chain?) and I can adjust the length of the throat opening (analogous to the length of the gullet as the chain is sharpened?). Both of these adjustments make a big difference in how the plane cuts.
As the cutter is ground back, it takes a longer chip, so maybe a change in the angle you describe is OK?
In Carlton's book ( http://www.sawchain.com/images/complete book.pdf ), around page 19, they justify the FOP based on the way the cutter pivots when it hits the wood, and as the edge gets filed back. If the cutter only heeled back, letting the depth gauge rise up to the wood that would make sense. But if the top plate of the cutter then rises up into the wood, you would still end up with a longer, shallower chip.
In practice, if the chain isn't cutting after being ground back, I would just take the depth gauges down a few more file strokes.
***I would like to see a photo of how you use your vernier caliper to set depth gauges and a mention of how you determine the settings***
Philbert
Thanks Philbert - I guess it makes a change from just yelling Husky - Stihl at random folk?
The change in cutting angle across the cutter varies with the top plate cutting angle and the width of the gullet.
When a 3/8 chain is new and the gullet is 6 mm. A 30º top-plate angle means the cutting angle varies from about 6º at the outside to 4.5º on the inside. With a 10º top plate angle as in a ripping chain the cutting angle is more uniform across the cutter edge. Most of the work is done by the outside corner of the cutter edge anyway - the rest just follows that.
Sure
A longer gullet is unlikely to change the chip length. The chip length is determined by the cutting angle and the degree of hook and the type of wood. From this point of view cutters are more like a chisel (cutting cross grain) than a plane cutting with the grain. The chip length is determined by how high or how shallow an angle the chisel makes with the wood - this is the combo of hook plus angle of chisel.
The cutter sort of rocks its way into the wood. Cutter bites, rocker resists, cutter bites more rocker resists more , cutter bites a touch more, rakers resists and then some sort of equilibrium is reached. The raker actually digs into the wood depending on its profile.
Sure that's what all the old timers did and I do that myself in the field. I only do the digital caliper raker checking at home in the evenings.
this is the threadhttp://www.arboristsite.com/showthread.php?t=69081
It looks slow but I am quite fast with it now.
scotclayshooter
Addicted to ArboristSite
The 262XP with an 8 pin, It cut well but its much smoother and more forgiving with a 7 pin.
Justsaws said:
This makes more sense to me.
It seems like we are talking about 2 different things in this thread: 1) a 'progressive' raker guide, where raker height varies with the width of the gullet / height of the top plate; and 2) maintaining a constant 'cutting angle' (BobL's term) - not necessarily the same.
This (red line) would be a simpler way to maintain a constant angle. A slight modification of the standard Oregon constant depth gauge - a constant angle depth gauge. Similar to some of the comments on that other thread that BobL referenced. Would work on full comp, semi-skip, skip tooth, and even (shudder) low-kickback chain.
But if you look at the illustration, you can plainly see that soon you would have no rakers!
Philbert
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Because the cutting edge moves away from the raker as you sharpen, the change in raker height has to be progressive to maintain a constant cutting angle.
The only way to register a guide like that would be on the blade edge, and if it is short enough to clear the links when you get towards the back part of the cutter, it might not reach the raker.
Phil, your red angle is too steep (its 1:2 - it should be around 1:8 or 1:10)and your line too thick to work out what is going on
Here is a new cutter with 1:6 slope (ie still very aggressive)
And then here is a cutter, with the same 1:6 slope, but now well and truly at the end of its life.
There is still plenty of raker left, and if a 1:10 slope is used then there will be even more raker left.
Here is a new cutter with 1:6 slope (ie still very aggressive)
And then here is a cutter, with the same 1:6 slope, but now well and truly at the end of its life.
There is still plenty of raker left, and if a 1:10 slope is used then there will be even more raker left.
I have fiddled with making this device but I just don't like to put a hardened steel plate (raker guide) directly on top of my freshly formed cutter edges.
RE: Post #35
Interesting difference that a line can make (admittedly, mine was crude).
I was assuming that my 'device' (line) would be like the Oregon depth gauge tool, with a slot in the end, so that you would file the part of the depth gauge fitting through the top of my fat line.
So why do you think that Carlton uses the back of the next cutter instead of this approach?
(And, of course you all know that Carlton, now part of the Oregon/Blount family, also offers a 'standard', constant depth gauge. Ray Carlton is probably rolling over in his grave!)
http://www.sawchain.com/products/newproducts.asp
Interesting difference that a line can make (admittedly, mine was crude).
I was assuming that my 'device' (line) would be like the Oregon depth gauge tool, with a slot in the end, so that you would file the part of the depth gauge fitting through the top of my fat line.
So why do you think that Carlton uses the back of the next cutter instead of this approach?
(And, of course you all know that Carlton, now part of the Oregon/Blount family, also offers a 'standard', constant depth gauge. Ray Carlton is probably rolling over in his grave!)
http://www.sawchain.com/products/newproducts.asp
Justsaws
Addicted to ArboristSite
Do you have access to Teflon sheeting? The stuff I am refering to is similar to wax paper but but extremely cut resistant except from the outside edge in. It is handy stuff for protecting cutting edges from the uglies.
You could always mill yourself one out of impregnated block. Might be a bit bulky but some sides to keep it squared and a handle would be nice. Face the file area HSP because the files wear it down fast despite what the manufacture says.
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Yep I am familar with this stuff.
It just so happens I turned a 2.25" (OD) 2" (ID) x 1/16" gasket for my coffee machine out of this stuff just last night!
I have also used a cylindrical block of it as a file guide for marking/making the teeth on a home made tenon saw.
And the wheels above the bar on my mill are also made out of this stuff.
As long as it wears down evenly it would be OK. I just realize I have a nice piece in my shed I will experiment when I get chance.
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Excellent sticky Bobl...you've illustrated in great detail the geometry I've always suspected to be the case....I've been taking my rakers down progressively for years now and lacked the proper nomenclature to get the point across to my peers.I will link heavily to this thread in the future,thank you.opcorn:
opcorn:
Justsaws
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