Thread: chain cutters rakers etc

Bob I can see where you are coming from with the cutting angle now, but although this would be good to allow for the optimum amount of sawdust / chip to be carried in the gullet it doen't allow for the power increase needed in the saw to take more bite (raker depth) which this method is doing unless it was on a mechanical harvester or lucas type slabber where power is not much of a problem.
regards inter

Yep, I undestand what ur saying there Bob, and how the filop does give u a progressive raker depth but not quite maintaining the consant 6° for the life of the cutter.
I still have a few thoughts tho

By maintaining the 6° angle there has to be increasing amounts taken off the rakers as the cutters are filed back, this should give u a deeper cut/bigger chips/faster cut rate (assuming everything else is equal) shouldn't it?

Now if I understand correctly the cutting action is as follows.....the top round of the raker rides on the surface (lets assume hardwood) of the timber that has been cut by the previous cutter....the cutter then takes a cut (assuming that the cutter is sharp enough to take a full depth cut) the depth of which is determined by the raker height or (how much is filed of the raker) as per this pic say about 1mm
Attachment 121801

As the cutter is filed back the gullet does get wider and the cutting angle gets shallower but I wonder all that is happening is that there is now a bigger gap between raker and cutter and as long as the same depth of raker is maintained we should get the same rate of cut at new chain as at worn chain shouldn't we the raker is still riding along the previous cut and the cutter is still taking the same depth of cut, Yes/no?

Do the arboristsite guys say that to achiieve a constant cut rate throughout the life of the cutter (chain) u need to maintain the 6° and do they say that if u maintain a constant raker depth that ur cut rate will slow down

Peter

Originally Posted by pjt

As the cutter is filed back the gullet does get wider and the cutting angle gets shallower but I wonder all that is happening is that there is now a bigger gap between raker and cutter and as long as the same depth of raker is maintained we should get the same rate of cut at new chain as at worn chain shouldn't we the raker is still riding along the previous cut and the cutter is still taking the same depth of cut, Yes/no?

Do the arboristsite guys say that to achiieve a constant cut rate throughout the life of the cutter (chain) u need to maintain the 6° and do they say that if u maintain a constant raker depth that ur cut rate will slow down

It's not just the arboristsite guys saying this, it's the Carlton chain engineers.
Look at pages 3-5 on this document.
http://www.sawchain.com/images/complete%20book.pdf

The constant raker depth approach is a result of people thinking that CS cutters act like little planes and cut constant depth strips of wood. This came about by looking at the long strips or noodles that CS produce when ripping with the grain. But even the plane analogy is not right, one does not start of using a plane with a cutting angle of 30º and then over the life of a blade drop it to 15º - also we don't increase the plane mouth by a factor two or more over the same time.

When cross or end grain cutting, chain behaves quite differently than we think, (have a look again on the Carlton chain manual). The sequence of events is like this
1) The cutting angle in combination with cutter hook enables the cutter edge to initially grab the wood.
2) The cutter bite is resisted by the raker which in turn digs a little into the wood which then allows the cutter to bite more which drives the raker further into the wood. The cutter sort of rocks or rattles its way into the wood at the cutting angle
3) This rocking action actually lifts the cutter up off the bar - that's another reason why chains should not be too tight.
4) The extent of the cutter penetration is determined by
- hardness of the wood
- cutting angle
- power of the saw.
5) The cutter cannot keep biting in at an angle indefinitely because the chain tension eventually becomes so high which together with the continual pulling of the chain by the power head breaks off the cut wood as chips.
6) The freed cutter then drops back to the bar.

This is all explained in the Carlton Manual.

The cutters cut by porpoising up off the bar in groups of two or 3 at a time and cut thin curved arcs or strips of chips. If anything its more like whittling than any other process I can think of.

If the cutting angle is too low the maximum thickness of the curved strips is less than if the cutting angle is optimised. If the cutting angle is too high the chain becomes too grabby and won't cut.

When the cutting angle becomes too low the cutter approaches the wood at a shallow angle and takes a finer shaving since it does not have time to penetrate far enough into the wood before the power of the saw pulls the cutter back down to the bar making more dust in the process. Some operators have found that their saw cuts better if they drop the revs when using and old chain. This is probably because the lower revs allow a shallow cutting angle cutter time to bite a bit more wood.

The other factor to consider is cutter wear. Taking thousands of fine shavings means the cutter edge is skating along the surface of the wood much more than it needs to. This just wears the chrome plating further and further back from the cutting edge and increases chain wear faster than necessary. I have seen the Cr plating stripped up to 3 mm back from the edge of worn cutters that have run constant raker heights for the entire life of their cutters. The operators have filed the cutter edges to razor sharp and set the raker to 25 thou and gone and cut hard dry wood expecting to get the same time between sharpenings as they did when the chain was new. Instead of stopping when the talcum powder started flying they pushed it too far and ruined the chain.

there's a good bit of reading there, I have wondered whether a cutter does leave the bar during cutting, my thinking tho was that it would leave the bar for a longer period, but as the info says it does the porpoise thing
And I also thought that once engaged in the wood a cutter stayed there to produce a continues strip of wood, but not so, noodles would tend to be a lot longer than they usually r
A few noodles, I was long grain cutting here
Attachment 121881Attachment 121882

chips from crosscutting
Attachment 121880

some white cedar I was cutting
Attachment 121883

Good pics Peter.

Cheers

Very interesting reading bob. The idea seems to be a bit back to front because the leading cutter has to start biting first which would be a result of the depth gauge setting parallel with the bar, then it could drag the tooth away from the bar & start the porpoising action and its probably a combination of all those things which allows both methods to work for the types of depth gauge tools being marketed today.
regards inter

Originally Posted by InterTD6

Very interesting reading bob. The idea seems to be a bit back to front because the leading cutter has to start biting first which would be a result of the depth gauge setting parallel with the bar, then it could drag the tooth away from the bar & start the porpoising action and its probably a combination of all those things which allows both methods to work for the types of depth gauge tools being marketed today.
regards inter

Don't forget there is no difference between the two methods when the chain is new and it only becomes significant after about 1/3 of the cutter has worn away and really significant in the last half of the cutters life. It is not in the chain manufacturers interest for you to keep using the chain to it's maximum potential as it wears - they would rather you bought a new chain

All this talk about the cutting angle, admittedly mainly by me, got me thinking. What about a digital angle finder (DAF)?

A new 3/8 chain has a gullet of ~0.25" and a raker depth of 0.025", the resultant cutting angle should then be 5.7º

Put short bar in vice and zero DAF, mark position on bar.


Put chain on bar and locate at same position on bar where DAF was zeroed.



This is a new chain that has had the cutters touched up but the rakers have never been touched, hence cutting angle is less than optimum.

Here is one of my old square ground chains - note the poor profile of the left side raker nevertheless the angle is approaching optimum.


Here is my well used ripping chain.

With a 6.2º cutting angle the gullet is around 0.41" so the raker depth is around 0.044"
Last time I used it this chain was cutting well.

The DAF body appears to be made of some kind of Zn? alloy so it should be soft enough not to damage the cutter edge but I'm thinking of adding some sort of sacrificial angle in brass to the base to protect the cutter edge a little more. When the piece of brass angle becomes too mangled I would just replace it.

The DAF has to be held near vertical along the other axis but that could be achieved using a bubble level. While not perfect it appears to be easier than the caliper method especially as it is a direct measurement.

Before going on my milling holiday I measured and set all my rakers on my 60" milling chains using the DAF idea as per the previous post.

To read correctly, a DAF needs to be held square across the cutter and raker. What I found was freehand holding a DAF leads to an uncertainty in measuring the cutting angle of about +/- 0.3º. Also the DAF also has rounded corners and inset magnets recesses which limit the contact area over which the cutter edge - raker angle measurements can be made which leads to further variations.

To get around these problems I clamped a rebated block of wood onto the bar for the DAF to lean up against and so the chain can still slide past easily onto the bar.
Like this

This diagram shows on the left a side cross section of the DAF. The two arrows show the contact area that should be used. If a cutter or raker encroaches into the inset magnet recesses or rounded corner areas, an incorrect angle reading will be made.

Measuring the cutting angle is then
1) Remove chain from bar and zero DAF against a marked position on bar
2) Replace chain and mount block of wood as shown
3) Move cutter of interest above marked position on the bar
5) Place DAF down onto cutter edge,
6) Lightly push back of DAF flat up against block and rotate DAF down till it makes contact with the top of the raker.
Care should be exercised to ensure the DAF does not make contact with adjacent rakers and cutters.

It's a bit hard to see but here is what it looks like but here is a reading before filing..


On my ripping chains I measured an average angle of about 4.5º but the range of angles was between 2.9 and 5.2º - ie all over the place.

The raker of interest is then slid a little away from the wooden block and filed, then slid back over the marked position and remeasured.
Repeat until you get 6º


After while you get good at guessing the number of file strokes needed to reach 6º. I work out that each full rounding file stroke removes about 0.3º

A few times I got a bit vigorous and a couple reached 6.7º , so all were between 6.0 and 6.7º ie a lot better than before. With a bit more practice I reckon I could get the range down to less than 0.3º.

When I bunged the chain onto my mill . . . . . .


Conclusion:
The DAF is a marked improvement usability wise over a Vernier Caliper because it directly measures angles with a single measurement. Apart from the rebated block of wood and a clamp, no jigs are needed and I will be moving to doing all my milling chains with the DAF in the future.

BTW I also tried using a FOP for the first time and found out it does not pivot about the base of the next cutter but the top of the vertical side of the raker being filed. This means it is truly progressive raker depth generator.
BUT
The greatest angle I could get from it (as measured by my DAF) was a filing angle of only 4.7º on a new chain - which is rather on the wimpy side! I'll be using the FOP for my firewood saws but for milling I'll be DAFing.

The DAF method has the added advantage that you can also set whatever cutting angle you like.

I also got a FOP and found the same thing Bob, I checked my current chain, some a little high some a little low but in the park, the other thing I noticed was that it gives a good visual indication of raker shape, from my pics u can see there is a bit of variation, I'll be paying a bit more attention to this now.
Bob, as yet I haven't worked out the use of the shaped cutout near my thumb in the FOP, Do u have any clues? cutter shape/angle checking

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Attachment 128500 Attachment 128501

Attachment 128502 Attachment 128503

Attachment 128504 Attachment 128505

Pete

Originally Posted by pjt

I also got a FOP and found the same thing Bob, I checked my current chain, some a little high some a little low but in the park, the other thing I noticed was that it gives a good visual indication of raker shape, from my pics u can see there is a bit of variation, I'll be paying a bit more attention to this now.

The angle is more important than shape which is why an FOP is better than regular gauges, but the FOP only makes and angle of 4.6º which makes small chips, but 6º makes much bigger chips hence cuts faster (if the powerhead has enough grunt)

I have written almost half a book on the subject of cutting angles and FOPs on the arborisite and the subject has been made a sticky in their chainsaw section - see here "www.arboristsite.com/showthread.php?t=114624"
I have also used some of your excellent pics to illustrate some idea, I hope you don't mind? Post number 51 discusses raker profile and also uses some of your excellent pics.

Bob, as yet I haven't worked out the use of the shaped cutout near my thumb in the FOP, Do u have any clues? cutter shape/angle checking

Do you mean this?


If so it's used to file the cutter like this.

The file is held parallel with the angled front of the FOP for the "correct top plate angle".

FOPs are reasonably quick for rakers so I have started using them on my firewood saws but the angle is too shallow for milling
One reason I don't like FOPs for cutters is because they really require one hand to hold the FOP leaving only one to hold the file.

I prefer to file two handed with a file guide like this.
[ame="http://www.youtube.com/watch?v=5qE0iN_P-6E"]YouTube- Broadcast Yourself.[/ame]

BTW That's 15 cutters touched up in 54 seconds or 3.6 seconds per cutter.

For the 60" chain with 95 cutters thats about six minutes of filing, plus a few seconds to tap the filings out of the file every 20 cutters or so, and time to scratch myself and walk around to the other side of the mill, so make it ~7 min all up. Sometimes I go for 3 strokes instead of 2 but it only adds another 1.5 minutes to the process. If I push it I can go faster but usually I allow myself 10 minutes for touching up.

With the 42" bar it's ~4 minutes of filing plus tap and scratch time, ie about 5 minutes.

Given it takes me 5 minutes to swap chains (and then I would still have to sharpen) this is why I sharpen on the mill. I usually take the chains off to do a raker reset or to get all the cutters back to the same length on an electric grinder.

another answer attach a v6 commodore motor and just file the rakers clean off...lol.

Honestly if it is pulling a nice chip who cares if it is a poofteenth different from cutter to cutter. If it isnt pulling a chip file a bit more off the raker till you are getting a nice chip without the saw bogging too much. Honestly I find the "optimums" that manufacturers put on the box your chain comes in are just a guide, a ms 660 stihl will pull a bigger raker cutter difference on a 20 inch bar than will a ms 361 so sorry bob the ratio goes out the window.

Personally I use the numbers on the box as a guide and probably a bare minimum. If your saw can pull a bigger chip, and you are not getting too bad a finish go for a bigger difference. all it will effectively do is increase the load that your powerhead is pulling and increase your cutting speed. however it will also reduce the quality of your finish should you go too far.

Honestly it doesn't take rocket science to cut wood...lol

Originally Posted by Travis Edwards

. . . . . . . .Honestly it doesn't take rocket science to cut wood...lol

Yep agree 100% - but this is not rocket science - I'd call it about grade 9 geometry

Originally Posted by BobL

Yep agree 100% - but this is not rocket science - I'd call it about grade 9 geometry

agreed bob, was just trying to stir the pot though. The way I feel today after sweating it out cutting slabs yesterday I am temporarily over chainsaws...lol

Honestly some improvements can be made through correct geometry but at the end of the day like I said if it pulls a good chip without bogging excessively or powdering then it is pretty close to the mark. I find that some chains when new are a little too aggresive on some saws and are better after they have been touched up a time or 2 but on a bigger saw the same chain works just right. Horse power and amount of teeth in the cut play as big a part or bigger than + or - a degree or a couple of thou here and there. The type of timber also plays a part and in HARD timber more aggressive angles generally work better where as for softwoods the opposite can be said.

An example of this is with circ saws in jarrah you would run a 30 to 35 degree hook angle but in pine you would run around 15 to 20 degrees.

Truly this is as close to a hard and fast rule as I would commit to and you will find that different timbers under different conditions require a different set of circumstances to obtain the "OPTIMUM" outcome or performance from your saw.

At the moment I am happy with the performance of my granberg style chain but if you compared it to the true granberg the only real similarities are the fact that I have 2 scribers and 1 raker tooth, and even though it performs very well in blackwood does not mean I would not have to make adjustments to it in different timber, Say redgum for example. Redgum is much denser and does not compress as easily under the rakers of the teeth thus it may require a greater raker depth to take the same tooth bite.

basically if it works do it, if it doesn't try something different.