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Face centered vs. log centered pith - revisited

Started by kelLOGg, August 06, 2016, 09:43:34 PM

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kelLOGg

There has been a lot said about this but I still need to ask the pros.

My 2 questions are in regard to sawing beams.

1) How do you decide how level the log to make the opening cut?  If you are not going by the face pith on what basis do you level?

2) The opening cut reveals the pith in the log but that only shows where the pith is in the plane perpendicular to the opening cut. It seems to me that a second cut 90° to the first is necessary to reveal the pith in a 2nd plane perpendicular to the first in order to know where the pith goes in 3D space. Has that been addressed or did I miss it?

Bob
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

5quarter

    Hi Bob... If the pith is centered in the log on both ends and the log is straight, then there should be little or no deviation of the pith in either plane. you simply level the pith to the bunks, drop your blade to 3" above the pith (to make a 6x6, for example) and make your first cut. rotate 90° and repeat.rotate 90°, drop your blade to 6" above the bunks (or 3" above the pith) and make your third cut. rotate 90°and make your 4th cut without moving the blade. Even if the pith is centered at one end and off center on the other you should follow the same  routine. you may get a little wane on the small side of the off center end, but your beam will be more stable that way. Logs with sweep don't make good beams. saw them into blocking or some other lowly purpose. good logs make good beams.  ;)
What is this leisure time of which you speak?
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scsmith42

Bob, when I'm cutting timbers we center the pith in both directions.  If we're using the Peterson, we measure from the track to the pith on each end, raising a bunk and leveling as necessary.  We then measure from the guide rail on the track to the center on each end, and use a sledge hammer to shift over one bunk (or the backhoe forks) until both piths are centered.

On the Baker, we raise the toeboards as necessary to center the pith from end to end, make the first cut to start squaring the cant, rotate the log and repeat.  The we lower the toeboards, rotate the log for the third cut and fourth cuts, leaving us with a cant with centered pith on both ends.

We try to avoid logs with sweep or lots of large limbs when milling timbers.
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

kelLOGg

5Q and Scott,
That's the way I have been doing it, but in a long thread, Customsawyer describes using the grain pattern to show where the pith wanders (if it does at all) in the log and saw according to that. However, he was sawing 2 x 4s from a large cant, not sawing a beam. Maybe his description applies only to small dimension lumber cut from sweepy logs and not for making beams. I was thinking maybe his way would enable getting straight beams from logs with some sweep or wandering pith but it is beginning to dawn on me that that is not what his post was about. So there is no better way to saw beams than to center both piths as seen on the faces as I have been doing, and, of course, that means you gotta have straight logs for beams. No other options! Have I got it right now?
Thanks,
Bob
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

5quarter

What is this leisure time of which you speak?
Blue Harbor Refinishing

scsmith42

Quote from: kelLOGg on August 06, 2016, 11:20:48 PM
5Q and Scott,
That's the way I have been doing it, but in a long thread, Customsawyer describes using the grain pattern to show where the pith wanders (if it does at all) in the log and saw according to that. However, he was sawing 2 x 4s from a large cant, not sawing a beam. Maybe his description applies only to small dimension lumber cut from sweepy logs and not for making beams. I was thinking maybe his way would enable getting straight beams from logs with some sweep or wandering pith but it is beginning to dawn on me that that is not what his post was about. So there is no better way to saw beams than to center both piths as seen on the faces as I have been doing, and, of course, that means you gotta have straight logs for beams. No other options! Have I got it right now?
Thanks,
Bob

Yup, you have it right.

Once you make your opening cuts on two faces of a log you can read the grain direction by the location of the center of the cathedral grain. 

This is useful when sawing 2 x 4's so that you can mill them so that they will deflect sidewise relative to the 4" cut while drying, since it is easy to push them back straight with bracing or blocking when they are installed in a wall or as rafters on a shed.



Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

BigZ La

So from reading this I surmise that it's better to cut beams from smaller logs rather than cutting multiple beams from a larger log, is this correct. Thanks

kelLOGg

I think it is better to cut them from logs large enough that the pith can be completely avoided. So, for four 6 x 6s, e.g., it would take a log of diameter of ~28" small end. Or, have logs as straight as an arrow so the pith is contained in the geometric center. Wait until others chime in to get a better answer :-\

Bob
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

Brad_bb

Boxed heart beams will be more stable.  I can attest that Free Of Heart or Split Heart beams will bow on you.  Can twist too.  They come out best with boxed heart.  If you're cutting Ash borer stricken Ash, they are usually partially dry already and more stable than typical full green.  I prefer a log just big enough to get the beam you want, due to the aforementioned effect of multiple beams from one log.  The exception might be, if you take a beam from the center, like an 8x10 or 8x12, you may get 4" thick FOH brace stock from either side of the beam(4x8).  These pieces may want to bow, but if you're cutting brace stock, you're going to be cutting shorter pieces so it will matter less.

I also like to cut them 1/2 inch or a little more oversize for planing.  If I can let the beams start to dry for a period of time, great.  I then plane them after that.  If you have the luxury of being able to leave the cants stacked and stickered for a year, they'll dry on the outside helping to keep them more stable. Then plane them.

If you're going to cut and raise/use them quickly (green) you can plane them right before you cut he joinery.
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Engineer

When I was cutting pieces for my house, I centered the pith on both ends of the log so that on the first cut, the pith was the same distance (tried to keep +/- 1/4") from the bunks.  This is where toeboards really come in handy, especially on big logs.  In only a couple of circumstances, I cut free-of-heart clear timbers from a really big log, and in those same circumstances, the timbers were fully restrained in all directions by other parts of the timber frame.  Basically they were forced straight. 

I really don't like the look of off-center cathedral grain, or runout grain, so I normally cut lumber by centering the pith too.  Logs with a big sweep would either become firewood, or in some circumstances, flitch-sawn with the sweep parallel to the bunks. 

drobertson

If you boys can center the pith on both ends of a beam consistantly, then I'm pretty sure I'm out of that league. I reckon that's why they cost so much.
only have a few chain saws I'm not suppose to use, but will at times, one dog Dolly, pretty good dog, just not sure what for yet,  working on getting the gardening back in order, and kinda thinking on maybe a small bbq bizz,  thinking about it,

Engineer

Quote from: drobertson on August 08, 2016, 04:36:15 PM
If you boys can center the pith on both ends of a beam consistantly, then I'm pretty sure I'm out of that league. I reckon that's why they cost so much.

It's actually pretty easy to do, especially if you have hydraulic roller toeboards.  My old LT30 didn't have toeboards at all, so I was using shims and wedges constantly to center the pith.  Nice thing about it though, is you only need to worry about it on your opening face and your second face.  After that, everything is parallel to the bunks.  It's a lot easier to demonstrate than it is to explain.  Surprisingly, I can't seem to find any YouTube videos or any instructions online about how it's done.  Basically, you want to simply maintain the same measurement from the bed of the mill to the center of the log.  It does take some trial and error but most anyone should be able to get within a quarter inch or less.  A framing square and a tape measure become your best buddies when doing this.

Kbeitz

Quote from: drobertson on August 08, 2016, 04:36:15 PM
If you boys can center the pith on both ends of a beam consistantly, then I'm pretty sure I'm out of that league. I reckon that's why they cost so much.

I think its easy... Just  measure from your track to the center of the log on the BIG end.
Then you could put a jack on the small end and raise it to the same  center measurement.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

drobertson

Thanks for the encouragement! I might suggest coming on down and showing me on some of these SYP, 16' plus. I have to figure that some folks don't quite get it, but I reckon a rookie is always a rookie!
only have a few chain saws I'm not suppose to use, but will at times, one dog Dolly, pretty good dog, just not sure what for yet,  working on getting the gardening back in order, and kinda thinking on maybe a small bbq bizz,  thinking about it,

Magicman

Right David.  If you center the pith on some Pine logs, there will not be anything left for the cant.   ::)
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kelLOGg

Since cathedral grain tracks and locates the pith within the log I would expect that at the very ends of the log the cathedral grain would always be centered in the face of a cant provided it has been sawn with the pith centered at the ends. If the log is straight the cathedral grain (and hence the pith) maintains that center position down the log. If the log has sweep I would expect the cathedral grain to deviate from the center position at the end of the cant and follow the sweep. That's what I expect but it is not what I find in the pics below.

The 1st shows the centered pith and the cathedral grain also centered at the end of the cant. However, the 2nd pic (of an adjacent face of the same cant) shows a centered pith but the cathedral grain is not centered at the end of the cant. This is unexpected to me. Can anyone explain? These are 6 x 6s.
Bob




  


Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

Tom the Sawyer

Kbeitz

It is that easy, only if the edge of the big end is sitting directly on one of the bunks.  If it overhangs the bunk even a few inches, raising the heart at one end will lower it at the other end.  Illustrated in that milling walnut for figure I posted last week.
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drobertson

You bet!  The center, (the pith) in SYP as I have seen, is very difficult to keep centered on both ends of the log/cant. And from what I have seen many times, its not that critical.
only have a few chain saws I'm not suppose to use, but will at times, one dog Dolly, pretty good dog, just not sure what for yet,  working on getting the gardening back in order, and kinda thinking on maybe a small bbq bizz,  thinking about it,

Kbeitz

Quote from: Tom the Sawyer on August 08, 2016, 09:21:42 PM
Kbeitz

It is that easy, only if the edge of the big end is sitting directly on one of the bunks.  If it overhangs the bunk even a few inches, raising the heart at one end will lower it at the other end.  Illustrated in that milling walnut for figure I posted last week.

Your right. I have bunks about every 24" so thats not to much of a problem on my mill...
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

Brucer

kelLogg, on your second picture look at how the growth rings are distorted. Something caused the rings in one spot to grow a little thicker. You can follow the path that extra growth took -- up and slightly to the left.

DanG trees never grow perfectly straight and perfectly round ... which is good because it's our ability to "read" a log that puts us a cut above the ordinary joe. (Pun intended  ;D).
Bruce    LT40HDG28 bandsaw
"Complex problems have simple, easy to understand wrong answers."

WDH

Yep, logs are almost never perfectly round. 
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

kelLOGg

These logs I am sawing 6 x 6s from are not perfect specimens for beams but I am trying to get what I can from them. (Some I am having to cut in half) The one in the pic had an off-center pith and I ended up with wane because I centered the pith in the beam. In such a non-ideal log should I still expect to see the cathedral grain locate the pith? I ask because in the 2nd pic in reply #16 it certainly does not, so I think the answer is no. Interestingly, in all the other faces the cathedral grain is almost directly above the pith.

I'm probably beating this to death but I think I am on the cusp of learning something so thanks for putting up with it.
Bob
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

Okrafarmer

If you have the time to do it, and this really doesn't take much, if any, more time than using a tape measure, I found a good way to check the height of the pith. Just run your saw blade up to it, center the blade on the pith. Take a reading on your height scale (for instance, it might say 10 ¼ inches). Pick the blade up and go over top of the log to the other end, and put the back of your blade against the pith on the other end, and read the grade scale. Suppose it says 9 ½ inches. In a case like that, I would say I'm within an inch, so there's no real need to tweak it, since that's generally within the margin for error for pith wanderment in most logs. If I felt like it, I might tap the lower end up with a toeboard just a tad (remember, a tad is four smidgens) just to make myself feel like I made it a wee bit better.

If you find you're off by more than that you find acceptable, you can make an estimate of how much you need to raise the lower toeboard (assuming that end is not directly on a bunk), then check it again using the same method as above.

This approach works well with portable bandmills.

Otherwise, if you don't like this approach, just eyeball it intuitively and get better at it over time until you're a pro, just like a golfer does.  :-X
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drobertson

I am posting this as a sawyer that custom saws. This often times equates to limited logs, scaled footage with a hope to achieve the required lumber for the project. Its production with a slant, slow enough for personal service, but time wise to make money. Every log is different, period,
only have a few chain saws I'm not suppose to use, but will at times, one dog Dolly, pretty good dog, just not sure what for yet,  working on getting the gardening back in order, and kinda thinking on maybe a small bbq bizz,  thinking about it,

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