Help - woodmizer bed rail alignment issue.

[Poweredward]

Hey guys, I am having a problem with the bed rails on my LT35HD,  when following the woodmizer alignment proceedue it asks you to move the head over each bed rail and set the scale to 15" and measure from bed rail to blade ,should be 15" and should be out 1/16 on the outside side of the bed rail.  All this checks out prefect.  I had some trouble sawing , 1st and last board would be taperd out by about 1/4-3/8 on one end.  I put a 6.5 foot level over the bed rails and they are not level with each other.  I double checked the measurement from bed rail to blade and it's still in.   I am not sure where to go next.  My local woodmizer rep said it's a set up issue,  I currently have it set up in a garage cement floor only on the front and back legs no weights on the side supports.

[Chuck White]

Welcome to the Forestry Forum, Poweredward!

Only thing I can think of is to recheck the "set-up" procedures!

I don't have my (LT40) book right here, but I think it says no pressure on the front and rear outriggers, just solid contact and minimal ground pressure on the loader-side outriggers!

[terrifictimbersllc]

It is helpful to understand the two basic reasons for what you are seeing that can commonly happen even when the mill is aligned properly and perfectly adjusted. 

What you are seeing can be caused by the mill rail (& consequently the bed) not being straight, or by the cant bending as it is being sawn, or most likely,  by a combination of the two. Both are routine occurrences in sawing. 

To understand the first one, about mill rail straightness,  imagine the cant (the thick very long wood beam, for example a 16 ft 7x7), being perfectly straight and rigid, but the sawmill rail, due to its weight and the weight of the mill and head that affect its straightness, is not straight, but instead arched one way or the other, or perhaps sagging or arched upward at one end because of jack pressure, or downward as the heavy head travels over it and it is not immovably supported.  This straightest is affected, and straightness achieved, by adjustment of its four supports along its length.  If the rail is not straight, it cuts in an arc.  For example if it were cutting a perfectly straight beam that does not flex, then if the front end of the main rail is a bit low, it would cut the beam a bit thinner at that end.  You could see this by sighting the main rail with the head at the back end and seeing that it is sagging at the front, or perhaps by seeing that there is a gap between the front support and the bottom of the beam. One would jack or shim the mill foot at that point to raise the front end of the rail.  It is pretty easy to change the thickness of the beam at either end by 1/8 or 3/16 by raising or lowering the front or back mill supports.  Tor some reason my mill or milling practice more commonly gives beams thinner at the front end and right within less than 1/8 at the back end. So I am commonly raising the front end jacks a little. Maybe this is because the head is more often at the front than anywhere else and the weight forces the front foot into the ground more than the others. 

Some techniques to detect what is going on with the mill bed straightness are 1) sighting the straightness of the rail by eye, 2) sighting the beam straightness before and after a very thin cut (downplays role of stress change in beam), to see for example identical arcs or straight lines before and after the cut, 3) raising, either by shimming or in the case of fine adjustment outriggers, jacking up the mill rail a little at either end and also making sure center outriggers are tight to the ground, to see corrections in beam thickness, and 4) techniques involving checking straightness of the mill bed itself using string, long straightedges, or perhaps a laser. 

In my daily sawing, when lumber gets long, say 14 ft or over, I keep track of mill rail straightness by a combination of 1-3 above. 

Understanding the role of cant bending due to stress changes when boards are sawn off is much easier when I first have a good understanding that the mill rail is straight.  Then I sees lifting of the cant at either end or in the middle.  These lead to thick and thin boards, or in the case where beams are the target, to beams that are not the right thickness at either end.  Flipping the cant and making final trim cuts when accurate beams are the target are what help.