Thread: chain cutters rakers etc
3rd Nov 2009, 11:35 PM #1
chain cutters rakers etc
I started a thread a "bush fix" to which Bobl has been replying to about my current chain, so I thought I'd post a new thread, took some more pics and measurements....
Gullet width is about 12.5mm
about 12.5 mm.jpg
the raker height is about 0.5mm below the top of the measuring gadget
about 0.5mm below.jpg
this makes the raker depth about 0.65+0.5=1.15mm and it looks about right by eye from this pic
definatley over 1mm.jpg
applying the 1/10th rule this would mean that my raker is still a lttle high by 0.1mm but who's counting
so I measured the angle, at this point I'm not real sure how this cutter angle is measured....I set my rule up paralell to the btm of the cutters and the protractor blade lined up with the cutter and raker
measuring the angle.jpgcutter to raker.jpg
which is about 4°
about 4° with rule level with btm of cutter.jpg
based on what BobL was saying this isn't enuff angle
so I set my rule up paralell to the btm of the gullet
rule inline with cutter gullet.jpgrule inline with gullet and blade inline with cutter and raker.jpg
which makes the angle about 8°
I'll have to check but I think Bob was saying that the angle should be 6° ...which makes wonder about the 1/10th rule seems to disagree with maintaining an angle of 6° ......but some of my measuring is a bit agricultural, (by eye),
Yep should be 6°....comments Bob or anyone...
I took a video of me milling a raintree fork with the chain the way it is, apart from just a quick touch up, seems to be quite ok to me, lots of chips, not grabby, is a wide cut which helps not grabbing, as soon as I can load it.....
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4th Nov 2009, 12:04 AM #2
Not quite the right angle Peter.
I can measure the ratio for this cutter direct from the photo in my graphics program and it is 10.2/1 or an angle of 5.6º
See also how important the rounding off of the raker becomes, a few thou' difference there and the cutting angle is stuffed up no end! People that leave their rakers flat have to drop them a lot more to get the optimum cutting angle
Sawchain files his rakers almost triangular so that this reduces this problem.
BTW I recalculated what a 6º cutting angle translates to in terms of a ratio,
Using a 1/10 rule actually gives 5.7º
To get a 6º cutting angle a 0.026" raker is needed for a 0.25 gullet and a 0.058 is needed for a 0.55" gullet and these ratios are more like 1:9.5
I use 10:1 because it's easy to remember but like I have said before I tend to file the rakers a little more so they are within 0.005' but on the deeper side of where they should be.
So If I'm targeting a 0.035" raker I try to get them all between 0.035 and 0.040", certainly no lower than 0.035. The 0.040" rakers are then at an ratio of 8.75:1
5th Nov 2009, 01:01 AM #3
Thanks again Bob, twice in one night ...the 6° is taken from a line along the top of the rakers down to a point on the raker and as u say that point can vary depending on the shape of the raker and that then ultimately affects the cutting angle.
I have noticed that the top of the raker gets a shiny spot ahead of the flat top portion which I normally file to set the hieght, I'll have to give the raker a few more facets to keep the flat portion short and the general shape as it should be.
all good stuff...
5th Nov 2009, 11:07 AM #4
It's all a bit of a trade off between how flat and rounded and angled the rakers are, and how dry and hard the wood is.
Let's stick to green wood for the moment.
1) If the raker is too square or has too much flat top (ie orange line) the leading raker corner penetrates into the wood too much and continually has to crush or compress wood as the chain cuts creating unecessary friction. Since the depth the raker penetrates into the wood is determined by wood hardness flat tops also create different cutting angles for different hardness woods.
2) If the raker top is flat and angled to around the cutting angle (ie green line) that reduces the square raker corner problem but increases the flat contact area with the timber, and while it will give a more consistent cutting angle between soft and hardwoods, the greater contact area also means increased friction - but probably not as much as flat topped rakers.
3) If the raker top is angled to greater than the cutting angle (ie brown line) this gets us back to where the raker now starts to increase penetration again and is the same as being too square plus the chain will also become very grabby
This is why on average a nicely-rounded, no-flat-spot raker works best across the range of wood hardness. Virtually all commercial chain is set up with rounded cutters with a radius or curvature to suit northern hemisphere softwoods and can be improved on with a bit of care.
In very hard, dry wood, more triangular shaped rakers (ie brown line) do not penetrate much and so are one way to minimise raker friction. BUT before you all rush off and try this and wreck your chain, just try increasing the radius of curvature of the raker and keep the starting angle below the cutting angle, ie try the red and then the blue arcs etc a bit at a time and try it out and see how it works. If you rush in and generate pointy (well they should never be pointy anyway) shark fins your chain will become super grabby and you can never recover the chain from it without removing most of your cutters. Also be carefully moving from dry hardwood back to green softwood.
I tend to file mine around the red and blue line, ie just slightly greater radius of curvature than usual
all good stuff...
6th Nov 2009, 12:43 AM #5
Thanks again Bob, I for one am learning little by little and I expect others are too,
6th Nov 2009, 02:41 PM #6
Check out this raker profile used by one of the CS gurus over on the arboristsite.
As you can see, he uses a filoplate like gauge and then rounds the raker over a lot more than usual. It's quite triangular in profile so it's pretty aggressive and would just shred north american softwood. It would be interesting to try something this pointed in Aussie hardwood.
6th Nov 2009, 10:34 PM #7
Some things change and improve .... methods, machines and whatever but gravity is still gravity and wood is still wood and whether it is old or new knowledge it is still worth taking on board what others know and do, I appreciate your input and am gaining knowledge all the time
The next chain will have the best looking rakers this side off .....well maybe not but they will get more attention!
10th Nov 2009, 12:39 AM #8
** WARNING - ULTRA GEEKY LONG POST ON RAKERS ESPECIALLY FOR PJT **
I have not used an filoplate (FOP) or their look alikes but, following discussions and some of the images posted on the aboristsite, I wonder if FOPs are really true progressive raker depth makers after all.
So I put the following up for your consideration. This is complicated and it took me some time to write so if you don't understand it I don't blame you!
Compared to conventional raker gauges which generate the same raker depth irrespective of the cutter or length or gullet width, progressive raker generators make even greater raker depths as the cutter wears (or gullets get wider)
The whole idea of using progressive raker depth is to maintain a constant cutting angle (not to be confused with top plate filing angle).
This picture shows what I mean by constant cutting angle - it's the angle between the wood, the cutter edge and the top of the raker.
The idea of a constant cutting angle is to produce the fastest cutting speed during the whole life of the cutter.
Cutting angles for new cross cut and ripping chains are similar, around 6º , and determine the size of the chips being made, with higher angles making bigger chips , and very low angles making powder.
Operators should consider varying their cutting angle to suit the size and hardness of the wood, and also the power of the saw.
Higher angles (7- 7.5º) suit wider softer woods and bigger saws, while 6º works for harder wood and smaller saws. Some Lucas slab millers use 10º on their chains .
OK, now lets look at how an FOP works for rakers.
Side view, I have flipped the image so it is consistent with my next one
In the next picture I have exaggerated all the angles so that things can be seen more clearly.
The Black line represents the FOP as would be set up for the current cutter length. The resulting cutter angle is 9.6º
As the cutter wears, as to be expected the FOP drops (blue line) but if it still pivots around the base of the back of the adjacent cutter as shown here the cutting angle does not remain constant - it gets shallower (in this image it drops to 7.3º) .
The red line shows what true constant cutting angle would be (also 9.6º). It has to be parallel to the black line to maintain the same cutting angle because the line across the top of the cutters remains parallel to itself at all times.
If the FOP remains tucked up against the back of the adjacent cutter, the result is the FOP can only make approximately progressive raker depths and shallower cutting angles as the cutter wears.
The difference - between the red and blue lines shows what else is needed to be removed from the raker to create a true constant cutting angle - I agree it's not much but there is a difference especially when the cutter is very worn so as the cutter wears an even greater amount of extra raker will need to be removed to make a true constant cutting angle.
So all this suggests to me that although FOPs are better than regular gauges, I will probably stick with my old method of using vernier calipers to set my rakers even though it is a lot fiddlier.
Another couple of good reason to use calipers are
I can change my cutting angle to whatever I want at the time, whereas one FOP only permits a fixed slowly dropping cutting angle as the cutter wears.
FOPs cannot set raker height accurately on skip chain.
Clear as mud?
10th Nov 2009, 09:21 AM #9
Bob, I see where you're coming from (and it wasn't so technical mate, understood it fine) It's a pity I don't have a better camera, so I could take some good pics of a fresh chain, as compared to an old chain - rather than file one tooth on a new chain all the way back to make it an 'old' tooth.
I used one to 'true-up' a badly sharpened chain, about half way through it's life and it has returned the chain back to my cutting line up, I was pretty happy with it - although doesn't take a lot to make me happy, normally a bit of Pig will make me happy
10th Nov 2009, 10:22 AM #10
10th Nov 2009, 11:01 AM #11
10th Nov 2009, 12:04 PM #12
While I see where you;re coming from, Bob, I do wonder how much difference it makes to have the rakers perfect or otherwise. I used to spend as much time doing my rakers as my chain, being careful to get them just right, but a tree-lopper friend put me onto the idea of simply running them over with the chain grinder, which I now do about every third or fourth cutter touch-up. I simply take them down to a mm or so below the cutter and leave it at that. I sometimes file the front edge to round it off, but it doesn't seem to make a huge amount of difference to my saw or the cut if it's not done.
I do pay more attention to the lucas chain, but it's still only a matter of rounding off, rather than taking any great pains.
What sort of performance difference do you expect to see between my method (the rough-as-guts, she'll-be-right-mate way) and yours in crosscutting logs up to about 600 diameter?Cheers,
10th Nov 2009, 12:29 PM #13
10th Nov 2009, 12:29 PM #14
Some difference worth having comes.
a) in milling bigger harder wood, I try everything I can to have to avoid pulling the CS mill out of the cut halfway down the slab to resharpen the chain.
b) when the cutter gets more than half way worn I think it becomes more important than when it is new.
c) when using a smaller saw in bigger wood.
Old timers never did any measurements they just kept filing the rakers until it felt right - what they were really doing without realizing it was progressively filing the rakers. Most of us weekend warriors don't have the exposure to gain the experience that comes with extended use over time so quantifying the process and knowing what to do from the beginning can save a lot of learning time.
I admit I over analyse things but this then allows me to understand the processes in detail, and I then go back to being more pragmatic and depending on what it is ,I usually use a "close enough" is OK method.
10th Nov 2009, 12:50 PM #15
Wouldn't it be fairly simple to make up a basic jig from a piece of strip, with another strip fixed underneath bent at 6° (or angled as desired)? First bit sits along the top of the chain registering on the tops of several cutters, lower strip butts up against the cutter and angles down past the raker. Reckon this would be pretty easy to knock up and should keep the cutting angle constant. May try to make one up this evening (or at least a half comprehensible diagram!!)....
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