log deflection

[brdmkr]

I have a bunch of small SYP that I am going to need to mill someday.   The Lucas works fine with big stuff, but is a bit slow with small logs.  I and others (DanG) have been thinking about things that might make this go quicker with my Lucas mill.   I recently had a new idea (a very rare thing for me) that might work (kind of a log on a rotisserie), but it relies on end dogging the log with support ONLY on the ends.  So, to work, the log would have to be relatively stiff.  What I am thinking of would only be useful for cutting posts (4 x 4 or 6 x 6).  Does anyone know of published tables that would provide data as to how much deflection you could expect in the middle of a log of a given species, length, and diameter?  If the log is too limber, there is no need for me to continue to pursue my idea.

[raycon]

Start with the log beam calculator in the forestryforum tool box.   Even though you have a round shape and the calulator looks like its setup to for square/rectangular beams you'll get a safe approximation of deflection.

[beenthere]

Roll out some of those logs onto supports just under each end, and see how much deflection you are going to be faced with. It would help if the sawcut line was vertical instead of horizontal when the log is 'deflecting', but that isn't likely.

[Lud]

Just brainstormin'.........
            Couldn't you use a pneumatic lift bag to fight the deflection?   Even a 'propriately sized inner tube would let you test the hypothetical validity of the concept 9and DanG cheap too! :D

[brdmkr]

That might work, but you'd have to be careful with the vertical cut.  Might have a blowout ;)

[Lud]

Put a sacrificial piece of slab wood on top of whatever bladder  you used.


Another way would be a couple of cheap floor jacks with the even piece of slabwood fixed to their tops.  It's underneath the pinned SYP, spanning the 1/3 to 2/3 marks.  You pump up to support,  ie. eliminate deflection,  and release to drop back down for rotation.

How's that one?

[broker farmer]

Lud, could you explain to me the principle of "log deflection"?

[brdmkr]

Broker farmer,

I am not sure that is really even the right term.  What I am referring to is the tendency for a thin log to bow in the middle when supported on the neds.  I am trying to think of a way to quickly mill smaller logs into 4 x 4 or 6 x 6 posts using my Lucas mill.  DanG and I have been discussing a mechanism of his design, and I recently thought of a different approach as well.  However, this newer idea requires that the log be pretty stiff as if can only be supported on the ends.  Lud is describing a way that I might be able to have sort of a variable middle support that can be raised or lowered to affect different dimensions of the log as slabs are removed. 

Of course, right now I am just in the studying phase :P.  However, I think that either of the approaches will likely work as deflection on a 10 - 12 ft syp should be minimal for a 4 x 4 (If I am interpreting the beam tool in the FF toolbox correctly). 

[Lud]

brdmkr is considering venturing  onto the thin ice of using a swing arm saw to cut small diameter logs and has speculated on pinning them at each end .  Kind of like putting a spindle on a lathe.  But with a log getting smaller by cutting boards off of it,  there's a point where it would begin to bend at the weakest point, usually the middle,  and that would be deflection.  My thoughts were towards giving a temporary support to the middle of a pinned log that could get out of the way if the log was being rotated.

[Lud]

Hey brdmkr,     How do you like the floor jacks attached to slab wood method?  Let's you fine tune the support for the specific stick you're  cutting.

[beenthere]

Seems the hyd 'log turner' like WM's would be just the ticket, or something similar.  Knowing when and where the deflection was removed would be the tough thing to figure out. But do-able.

[Lud]

But the swing bladers don't have those options because they don't have the rails and mass underneath the logs.  They have to "farm engineer" a base for the little sticks to make them hold still for their suspended saws .  More fun for tinkerers! ;D

[brdmkr]

Lud,

You have a complete understanding of the issue.  I had not thought about a floor jack, but I had considered a scissor jack.  Same concept I suppose.  The Lucas works just fine on the small logs.  Problem is that they take just as long as  a big log.  It is really hard to get fired up about the productivity.  You are also correct about the fun for the tinkerers. 

[Ron Wenrich]

Why not use an old circle mill carriage?  You can advance your log for your cuts, hold it in place with the dogs, and support it with the bunks.  All you have to do is move your swing arm up and down, since your left and right adjustments will be made with the carriage.  Dogs will help eliminate the deflection.