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Thread: Kerf Issues
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5th July 2013, 10:51 PM #1
Kerf Issues
It amazes me that people make so much 'noise' about kerf......
As Nifty mentioned - (https://www.woodworkforums.com/f132/b...ml#post1668304) he picks up 5mm in kerf over a swingmill.... now if we put that into real life perspective cutting 1" thick boards, this means a minimum of 5 layers need to be in the top third of the log before a bandsaw will pick up an extra layer as compared to a Lucas mill... so once the opening face is cut off, there needs to be 6" of log before flipping the boards and cutting them the other way through the mid third of the log - yes in the mid third of the log a bandsaw should pick up a board, but then we flip the cuts again for the bottom third and again a minimum of 5 layers are needed before an extra board is gained. Allowing 2" flitch top and bottom, adding the 6" layers for top and bottom thirds, then add the mid third of the log another 6" this gives a log volume of approximately 22" (or 550mm diameter)
Tacking this into consideration, cutting 1" thick boards, a log needs to be around 400mm diameter before a bandsaw will pick up 1 extra board due to kerf loss and further needs to be greater than 500mm before picking up more boards. Now if we talk about 2" thick boards this blows log size out to 550+mm before a bandsaw will pick up 1 extra board and now we are getting into 'not possible' territory for many bandsaws and when we look at an example to gain more than 1 2"board as compared to a Lucas the logs need to be outside the realms of many bandsaws capacity.
The tendency of others to 'extrapolate' the figures over a "years worth of volume" is essentially compounding an error, in real life the calculations start all over again when a new log is rolled in, the 'gains' can only be multiplied over a year if each and every log coming into the mill is the same size and we know that isn't possible As an example, if a bandmill mill uses 300mm logs there is no kerf gain on these logs - yes years ago we could all have had an almost endless supply of 600mm logs coming into the mill all day, but not now. Now we do have to mill down to this size of log - besides this is where bandsaws make a difference, small diameter logs are processed much quicker on bandsaws as compared to swing saws - but it isn't until the log gets bigger that a bandsaw gains on a swingsaw due to kerf, but due to the nature of the beast bandsaws don't cut BIG logs, therefore the kerf argument is moot...
My 2 cents has been spent - back to normal viewingI love my Lucas!! ...just ask me!
Allan.
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5th July 2013, 11:54 PM #2GOLD MEMBER
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Log handling is the greatest time waster in the milling process. I will not be sucked in to mill poles. Anything under 600 dia can go elsewhere.
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6th July 2013, 09:36 AM #3GOLD MEMBER
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... if you livesaw
and most importantly
... if you backsaw.
Backsawing is not a particularly attractive option on logs under 450 SED. More better to run them through and through if they're under 300mm, or take a top board(s), roll 180 degrees, take a new top board(s), and then deal with your center cant... or if you're in stuff thats behaving badly adjust your pattern to split the center cant through the heart then resaw.
A billet of 250 SED under bark x 2.4m minimum length is a compulsory sawlog under the western hardwoods region schedule of Qld Forestry. So learning how to deal with those sh!!ty little crown billets above the first branch becomes a matter of economic necessity. Apparently it's to help me transition to a plantation resource - that they haven't planted up here yet
http://www.fwpa.com.au/sites/default...lantations.pdf
is an interesting read about sawing patterns in small eucalypts. Yeah... it concentrates on the big end of the business... but that technology filters down, and perhaps most importantly, knowing what works for the big guys and adapting it to your level of equipment can help add a few % points to your recovery and dollars to your pocket.
The other thing is if you start thinking about the fastest expanding part of the hardwood timber market... overlay flooring... where you want to cut at 15mm GOS all the numbers change again.
As usual Allan, I agree totally with what you've said. I just see from a different perspective.
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6th July 2013, 01:49 PM #4Senior Member
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Is it not one extra layer of board not one extra board ,if milling for flooring /decking (100x26) and then one top one bottom and extra through the middle third the production of sawdust is also 2/3 more , think of it terms of large production mills .and i don't think most larger scale mill would put a log on a deck and go right cut that into all 4x1 ,6x1 the sawyer may cut stair tread material or square the heart for a post. personally i like both weather for one operation or large scale monsters
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6th July 2013, 06:43 PM #5Senior Member
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6th July 2013, 07:41 PM #6GOLD MEMBER
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If that's the accelerated drying one or the wood characteristics one then I have... if it's another and you can locate a link then I'd appreciate it.
Big problem with blown over plantations is... they aren't there any more. And the area under plantations up here - particularly hardwood - was never extensive anyway. I don't know if the carribean pine plantations around Cardwell are going to be replanted either... probably not. Mind, the only thing better for me then Cyclone Larry was Yasi... log access and orders to fill... it's an ill wind etc etc.
I have a lot of issues with plantation hardwoods... ranging from the ecological monoculture stuff through practical utilisiation to "why bother when the eucalypt estate up here is barely touched?" Then again, I have issues with most government policy decisions regarding forestry in North Qld for the last 30 years. Sadly politics drives policy and common sense gets shown the door, and this area is not where the voters live.
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6th July 2013, 08:32 PM #7
This is another interesting thread. Thanks Al for kicking away the discussion.
Let me comment from the outset that the circular saw is much easier to use than a bandsaw. No question about it. I think some of Al's comments come from the statements in other threads that bandsaws have a thinner kerf than circular saws. Again no question about it.
The question remains as to how much value we place in that. Certainly a bandsaw will produce more timber and less sawdust. The worth of this feature depends entirely on the value of the timber and the thickness of the boards. For example in New Guinea they introduced laws that banned the use of circular saws and only allowed bandsaws. However they were cutting balsawood and we know how thin some of that material is. The kerf was significantly thicker than the boards they were cutting.
Let's take a silly scenario of cutting 6mm veneers from a coveted species. With a circular saw each saw cut would be a lost board. I am not suggesting that this is commonplace. In my own case I went away from the bandsaw in favour of the circular saw as the advantages of the circular saw far outweighed any potential benefit from the bandsaw. However I was cutting building timbers.
A good bandsaw will cut large slabs quite easily down to the first third of the log. Then the log is rotated 90 deg. so all slabs from now on are going to be smaller width. Normal practice with a bandsaw is not to saw through the heart with hardwoods. It is of no use and probably is ratty. So we saw around it until the last piece of timber left on the mill is the useless heart.
FRG 7.jpg
When I started a comparison thread I listed potential advantages and disadvantages. No one feature should be taken in isolation. In fact even in the example above of cutting veneers you would need another means of resawing the thin sheets. I think Nifty, for example, mentioned he had a twin edger, which also has the added benefit of relieving growth stress.
Regards
PaulBushmiller;
"Power tends to corrupt. Absolute power corrupts, absolutely!"
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6th July 2013, 11:13 PM #8GOLD MEMBER
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Like you I own and operate circle saws. I intend to keep doing so, but in my case I have every intention of having a modern wide band resaw on my line in the midterm future. For me at least the economics - subject to change of course - stack up conclusively in its favour against automatic benches, given where I see both my resource and my market changing.
The keywords there are wide and modern... I have no real experience around narrow bands (but accept the popular argument that they don't do well in eucalypts), but I have played with wide ones. Theres been a lot of technological change in bandmills in the last 20 years. Metalurgical changes to the bands themselves, but also stuff like continously variable automatic tensioning and offset feeds have really changed the day to day economics of running one.
Of course, someone could come up with a magic alloy circle blade that could run a practical thin kerf and still cut straight and change my mind. I'm always open to new technology... a generation ago there were still mechanical pit saws in use up here for those logs too big for canadian twins, and the fact that grandad did it that way has no bearing on what I do today or next year.
As an aside, did you know that it costs about $30 AUD /square meter ($2640 m3) to ship that useless heart to China, have it veneered , dried, placed on a laminate backing, filled, sanded, polished, and delivered back here? Bunnings then sell it for somewhere around $50 a square meter ($4400 m3). Compare that with solid wood flooring prices.
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6th July 2013, 11:32 PM #9Senior Member
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perhaps the question that should be asked is what sort of recovery do you get from a bandmill.how big is the waste pile at the end of the day?whats the point of having a thinner kerf if you cannot maximise the amount of timber you recover.not having a go at bandmills just dnt know what they are capable of
p.s. i run a fixed mill and take everything down to palings and tomato stakescheers pat
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7th July 2013, 12:49 AM #10SENIOR MEMBER
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Good on ya Al for putting a different slant on the kerf "issue", did I say issue, there isn't one if you consider what you are sawing for!! I just found another old 2 cent coin in the back of my favourite chair so here we go again.
In the thread (bandsaw vs circular) I may have sounded like I was bagging band mills eg cost vs kerf. When I went into being a professional sawyer I saw it like this.... Every time a log truck pulls into my yard it costs me 2.2k. This time the logs might be good, next time average so I have to get back every stick I can get. So bandsaw looks like the best option, more homework to do but big deal.
if I had my time again I would have run a swing blade and horizontal band resaw.
over east you call it feedstock, here we call it flooring blanks. Take my Lucas and cut 110x110 blocks through the whole lot and then through the resaw to get my 110x27... Why? Because it does not matter how that block comes off I can BACKSAW my flooring blanks. Please... Fellas, not all timbers should be cut on the quarter ( I keep reading this on here and it gets to me) Go outside and look at your verandah beams if you don't believe me, and if they have been cut properly!
i stopped cutting professionally for a few reasons but one of them was because I could smell the sawdust but not see what I had cut. As long as it made grade I never wanted to see that timber again. Most of the members here have a true passion for what they have in the shed and what they will turn it into, that's a far cry from being a professional. So once again, apples are apples, off you have sawdust on your boots and a pile of timber in front of you, thank Mother Nature and appreciate it. As for the saw dust, if you own a blade mill you need to build a bigger vege patch than me.... Big deal... You grow the tomatoes, ill grow the herbs and we can trade....Deal??
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7th July 2013, 09:08 AM #11GOLD MEMBER
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20th July 2013, 09:34 PM #12
hehehehe
I am just going to say that both ways have their pros and cons, you cannot cut a full width slab with a circ saw like you can a bandsaw, well not as easily anyway. most guys who use bandsaws don't like cutting small logs, and I think the circ saw is the better option in this area (I.E. lucas or the like)
Honestly there is no better saw to cut a particular piece of wood than the one you have!!!
More often than not for me that means an MS660...lol.
Oh and gday yall I am still alive
TravisI am told that sharpening handsaws is a dying art.... this must mean I am an artisan.
Get your handsaws sharpened properly to the highest possible standard, the only way they should be done, BY HAND, BY ME!!! I only accept perfection in any saw I sharpen.
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21st July 2013, 09:07 AM #13
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