Fixing twisted rails when milling.

[BobL]

All of the milling rails I've used, including ladders, have always been susceptible to some twist especially when they were used at over the 16ft mark. The way I have been checking for twist has been to use a crossed string stretched between the diagonals of the rails, or a spirit level and comparing the angle across each end of the rails. The spirit level method worked OK provided the log is reasonably level to start with while the crossed string method was ok for shorter logs

Yesterday I realized that my Wixey digital angle finder would probably also do the trick and make it easier comparing the angle between the two ends of the rails.

I made myself a large try square using some 1/4" Ally strap.
I place the square against the rails and zero the scale.


Go to the other end and adjust the angle to get Zero (see piece of wood under RHS rail).


I must make myself two moveable steel tabs that attach to the cross brackets at the end of the rail, that includes a threaded hole through which a bolt can be screwed to make contact with the log to make the angle adjustment.

[Steve Fryar]

With the mill I will eventually make,I have pondered over the same problem.In a scrap yard I found 4 adjusting legs used on the bottom of a scaffold.The bottom of the scaffold tubing goes over a coarse thread about 1ft long and into a adjusting nut with wings on it for hand adjustment.
My plans are to make a frame similar to the Lucas mills.With these things and a good spirit level I should be able to get the rails perfectly level.I like the coarse thread as well because a bit of dust or dirt won't make the thread bind.
Cheers,Steve.

[Exador]

With the Lucas, it's a simple job to eyeball the parallelism of the rails (similarly to using a pair of winding sticks)and I simply place a piece or two of offcut under the frame of whichever rail has a "low" end. It's not necessary to achieve level, just parallel. Would this not work with your BIL mill, Bob?

[BobL]

With the Lucas, it's a simple job to eyeball the parallelism of the rails (similarly to using a pair of winding sticks)and I simply place a piece or two of offcut under the frame of whichever rail has a "low" end. It's not necessary to achieve level, just parallel. Would this not work with your BIL mill, Bob?

With the digital angle finder the idea is also not to get the rails level but to get both ends of the rails at the same cross angle or parallel, which is why it is easier to zero the angle at one end and then just get the other end to be the same angle or parallel.

On the Lucas, the rails are a long way apart, usually a lot further apart than the diameter of the log so a bees dick out either way makes little difference over the diameter of the log.

Using an Alaskan rails on longer smaller diameter logs like this one

the rails are narrower than the log so that they might only be 250 - 300 mm part. When they are only this far apart, a bees dick makes a bigger difference across the width of the log since the log is wider than the rails.

Like this - I have exaggerated the bees dick so it is easier to see.


On the Granberg Website there is a video showing how they level the rails across the log at a number of different places along the rails. The digital angle finder would make this a bit easier.

[Exador]

I take your point about parallax leading to less precision, but I'd not have thought it was as big an issue as the length of the baseline: if the rails are longer, then the same absolute error at one end subtends a smaller angle, meaning the cuts are less twisted

That is to say, if a 2 m long rail is out of parallel by 2mm at one end the angle of twist is much greater than if the rails are 4m long with the same 2mm difference in parallelism.

If the rails are longer than the log, then the problem is reduced further.

[BobL]

If the rails are longer than the log, then the problem is reduced further.

Yeah - that sounds right. (scratches head) I don't know what I was having a problem with that 16 ft cedar log. I was using a sprit level and the slabs weren't coming out straight. I thought it might be because I didn't have it well supported underneath but that would just make the slab bowed. I think maybe it might have something to do with when I got to the end the mill was so low to the ground I was not keeping it level on the rails.

[Sigidi]

I Also find when slabbing the chain and bar make the most difference when getting varied results.

But having said this, a couple of mm difference across the face of a nice wide board or from each end is acceptable in rough sawn stuff???

Most slabs have to be dressed/planed prior to be used?

[Arthur Dyason]

The main disadvantage of the Canadian type slabbing mill is attaching the rail to the log and relying on the first cut being level. The Big advantage is lightweight and portability.

The EcoSaw, Lucas and Peterson slabbing systems all suspend the chainsaw bar from rails above the log and are therefore independent of the log and will always give a true cut depending on how good the operator is at setting up the mill in the first place.

I dont have examples of the other mills but below are some pics of our monorail and twinrail system. The Twinrail is best for larger bars over 1.2m but the acuracy over the width and length of the slab is within + or - 1mm and I consider the finish to be better than our circular saws.


this pic is of the twinrail system and shows a stack of slabs.


this pic shows the adjustable foot. These can be wound out to 500mm.


The Monorail setup and waiting for a log


The Monorail cradle. Any size chainsaw with bars upto 1.2m.


milling a 7.5m roof beam. Old Bloodwood log.


Like all our milling systems. Designed to mill the log where it lays.

I dont know about the other manufactuers but you can attach Canadian type cradles to our rail systems to use what you already have with minimum modifications. The longest rails tested so far are 16m for twinrail and 8m using the monorail although in theory we can go longer just havnt tested the maximum yet.

Hopes this gives you a few more ideas for your rail leveling.

arthur