Thread: 1/10th rule

Originally Posted by pjt

Does this sound right BobL?

yep - that is supposed to generate the ideal cutting angle (but maybe that's for softwoods - see below)

So tried it out on the bit of cadagi and had no problems, not huge chips but not dust either, so I gave the rakers a bit more ....Attachment 119362 just to see how much I can get away with like to see them chips.
Normally I would have left the rakers alone until the the cutters where a ways further down, just goes to show how quick things can deviate from the ideal

Here's what I actually do.
If the gullet is 7.8 mm the supposed raker is 0.78 mm, but I usually make the raker a little deeper still, maybe 0.85 or even 0.90 mm.

The reason for this is I know that as I continually touch the cutters up while slabbing the next few logs the raker depth will decrease and maybe even go past the ideal into what I call the powder zone. So probably the 1/10th rule is a minimum - it also depends on wood hardness - see below.

Even though I measure my rakers with a set of digital calipers I don't sit there and get them all exactly the same, if they are within ~0.15 mm that is good enough and as I said above I would tend to go over. I know if I have done them too much because the chain becomes very grabby.

I also realized recently that I got my soft and hardwood fractions the wrong way around. Most people don't realize that depending on wood hardness the raker actually digs a little into the wood and changes the cutting angle. With softer woods the raker digs in a longer way creating an even higher cutting angle so with softer woods a raker depth 1/10 of the gullet, is probably enough. With harder drier woods the raker hardly digs in at all so the raker depth needs to be compensated even further. So my ideal fraction are now 1/10 for soft and maybe 1/9 or even 1/8 for hardwoods.

I really noticed this a while back when I switched from lemon scented to Marri. It's getting to the point where I will set up chains with different raker depth, maybe one for harder and one for softer woods.

OK - that's the depth - now for the raker profile. We know that a dead flat raker puts more load onto the saw because the leading corner will continually grab in the kerf. If the raker is more pointy or with less and less of a flat it will dig further into the wood. The final cutting angle established by the cutter is determined by a combination of raker depth and raker shape. I'm tending to make my rakers even pointier (or perhaps more rounded) these days which increases my cutting angle. I have no idea what the best combination would be - will add it to the todo list

Thanks again Bob for more good pointers, especially about the raker digging into softwood more than a hardwood.
With the aggressive raker height I have noticed the digging in/bogging down at the start of a cut and at the finish, until I establish the cut it is a bit grabby, there's always a trade off
As far as profile goes atm I will generally make it to the same general round shape... maybe with a couple of facets depends how fussy I am being
Peter

Originally Posted by pjt

Thanks again Bob for more good pointers, especially about the raker digging into softwood more than a hardwood.
With the aggressive raker height I have noticed the digging in/bogging down at the start of a cut and at the finish, until I establish the cut it is a bit grabby, there's always a trade off
As far as profile goes atm I will generally make it to the same general round shape... maybe with a couple of facets depends how fussy I am being
Peter

Yep - so have I, especially at the beginning with the 60" bar and all cutters freshly sharpened.
So I start my cuts like this.
Instead of going straight at it like A, I alternate between B and C till the bar is inside the log, by then I'm usually good to go like A.


It takes the load off the saw till the very sharp edges of the cutters are are worn off a little.

I tend to keep the saw straight like A all the time to get as smooth and even a cut as possible. Only if I am close to the end of a big slab and the chain is getting blunt do I revert back to alternating between B & C, this takes the load off the saw. It feels like it's cutting faster but it isn't. Also if I pause to slip a wedge in or adjust something I no longer WOT the blade back into the kerf - I squeeze the trigger and ease it back up to full RPM. This reduces the marking on the slab.

I don't have the same problem at the finish though?

The digging in is more technique my end, I recently added some wheels wheels.jpg
I start by put a wheel on the log and start like A but if I'm not careful it pivots and grabs and bogs... technique I think
And at the end of the log if I'm not watching when the wheelAttachment 119623drops over the edge of the log it grabs and bogs
Note the theme with the wheels and brackets
Peter

Originally Posted by pjt

The digging in is more technique my end, I recently added some wheels
I start by put a wheel on the log and start like A but if I'm not careful it pivots and grabs and bogs... technique I think.
And at the end of the log if I'm not watching when the wheel ]drops over the edge of the log it grabs and bogs

Ah yes, I know exactly what you mean, I don't think that is a raker or chain sharpness problem - that happens to me whether the chain is blunt or sharp.

Note the theme with the wheels and brackets

Yeah, nice wheels, I like the clamping adjustments, will have to use that idea some time.
Now you need a wheel above the bar on the vertical upright of the mill.

Good idea Peter, the wheels. What diameter do you recommend - maybe a touch bigger?

In practice I found I needed 4 wheels.

Like this.


Here's another view with the 880


When milling the top half of the log, like A, it's better to have wheels well below the bar like the black ones.


When milling near the middle of the log (B) it's better to have wheels level with the bar (Like PJTs) or the black and white ones in B that are either side of the bar.

When milling the bottom half of the log, like C (white) wheels) above the bar up near the rails work best. If not the log mashes into the inboard mill upright and bogs the saw. Because the slab thickness can vary the wheels above the bar need to be adjustable in the vertical direction to enable them to sit just below the rails.

My adjustable wheels look like this.


An alternative to wheels are vertical rollers.

The wheels and brackets I originally made for my bandsawAttachment 119717andAttachment 119719 then they started turning up hereAttachment 119718 and Attachment 119721I just made a heap of them cos they r quite handy and it maintains a certain uniformity to my mods.

The ones on the saw r spare (were) so for a trial I used them..Yep TT the lead one could be a touch larger in diameter (made from 50mm stock, the turned dia is 44mm same dia as the 6002 ??? brgs(I forget) on the bandsaw guides and the brackets have a 44mm center distance, (just this uniformity thing i have)) as could the trailing but I was trying to keep things compact to give me as much bar as possible. the trailing one could nearly not be there (just an observation in use as it doesn't do much work) however when both r rolling along the log it keeps the saw moving smoothly and has reduced my effort to control the saw.

The leading one with the way it is setup is good cos I can have it below the bracket for the top of a log or transfer it to above the bracket for the lower half of a log, a 2 second change, it doesn't need the edges either.

Bob I did look at a center wheel but I think I thought it was going to rob too much bar length, I still do like the idea of a wheel up against the side of the rail...that system would possibly have less pivot/bog probs
Last post I said I start like A make that B however on a couple of starts today it was more like A which worked OK think it's mostly a case of gently gently, and the finish I pull the saw so it pivots on the rear wheel (so the front wheel doesn't drop over the edge) I complete most of the cut and if I need to I can lower the wheel over the edge and all good

Originally Posted by pjt

The leading one with the way it is setup is good cos I can have it below the bracket for the top of a log or transfer it to above the bracket for the lower half of a log, a 2 second change

That's a very good system. The only time I don't see it perhaps coping is if you had to cut deep (say 6" slab on the lower half) then the wheels may not reach up high enough to stop the mill upright hitting on the side of the log. I must make a sliding bandsaw gizmo thingy like yours some time. I was doing a bit of bandsawing on the weekend and could really have used a set up like that.

Bob I did look at a center wheel but I think I thought it was going to rob too much bar length, I still do like the idea of a wheel up against the side of the rail...that system would possibly have less pivot/bog probs

I tried that and it didn't really help and just tore the log rails off the log so I had to tek screw them down.

Last post I said I start like A make that B however on a couple of starts today it was more like A which worked OK think it's mostly a case of gently gently, and the finish I pull the saw so it pivots on the rear wheel (so the front wheel doesn't drop over the edge) I complete most of the cut and if I need to I can lower the wheel over the edge and all good

Yep - Yep, and . . . . Yep

A good point Bob, I did ponder the best height of the wheel when I originally looked at it and I concluded that the best place is same height as the bar, (no induced turning moments) to overcome the possibility of the bar hitting there's a couple of things I can do .... so far I just take the wheel out of its bracket and flip it over, (have to take some pics) I could raise the height by ~24mm by flipping the bracket and wheel then add in a longer shaft or angle the wheel and bracket toward the log more or add a longer bracket (inbuilt adjustability thing I like to design for) or a larger different wheel, I picked up some inline skate wheels from the tip shop which might find a new life ... and I can still do this to the rear one as well

You blokes are just fiddle fanatics hey? I gotta get me a shed before I can fiddle with anything

Originally Posted by pjt

A good point Bob, I did ponder the best height of the wheel when I originally looked at it and I concluded that the best place is same height as the bar, (no induced turning moments)

Yep I agree this is generally correct, except when the bar is cutting (and the wheel rides on) the curvier part of the log. What I find happens here is the wheel wants to keep riding op or down the curve which adds additional tension to the mill.

to overcome the possibility of the bar hitting there's a couple of things I can do .... so far I just take the wheel out of its bracket and flip it over, (have to take some pics) I could raise the height by ~24mm by flipping the bracket and wheel then add in a longer shaft or angle the wheel and bracket toward the log more or add a longer bracket (inbuilt adjustability thing I like to design for) or a larger different wheel, I picked up some inline skate wheels from the tip shop which might find a new life ... and I can still do this to the rear one as well

Longer shaft and bracket arm sound like the way to go. Seeing as you are fiddling in that area you could also make part of the marked bracket arm in the picture out of round stock that could be locked in place so you just flip the wheel above or below the bar.

Do u mean something like this BobL?Attachment 119798 I can flip this up or down on my bandsaw fence.
More wheel pics, first cut, just a thought the edge on the wheel might be helping to stop the mill riding up or down, as can be seen it does dig inAttachment 119801
first and second slabsAttachment 119799Attachment 119800Attachment 119802
4 inch thick slab with the wheel on the btm side, needs to be turned overAttachment 119803
Wheel flippedAttachment 119804
Peter

Originally Posted by pjt

Do u mean something like this BobL?
]I can flip this up or down on my bandsaw fence.

Yep

More wheel pics, first cut, just a thought the edge on the wheel might be helping to stop the mill riding up or down, as can be seen it does dig in

Yep - my wheels are like roller blade wheels so they ride up more easily

Good stuff.