Board gets wider at the end of a cut with the CSM

[MAI]

I've been cutting some boards with a logosol big mill chain saw mill. Saw is a Stihl 660 with a Logosol narrow kerf ripping chain. The big mill has a rail that you fix to the log and slide the saw along in a jig. I'm finding that the thickness of the boards is about equal at the sides of the start of the cut but not at the other end. At the end of the board the closest edge is again in good agreement with the thickness at the two sides of the start of the cut but the width on the other side of the cut at the end is generally wider ie the saw is cutting deeper into the log on the far side at the end of the cut.

Looks like operator error on my part but I'm not sure what I'm doing to cause the increase in width on the far side at the end of the board.

Grateful for any advice on what I'm doing wrong and how I might fix it

MAI

[BobL]

Logosol will deny it but its a basic flaw in the design of any horizontally mounted CSM that is holding the bar only on one side.
Alaskan or mills that hold the bar level on both sides are much less likely to have that problem.

There is a root cause and that is your chain is very slightly cutting more on the underside than the top side.
This could be due to a
- sloppy bar groove
- uneven wear on the bar rail
- greater top plate cutting angle on the lower side cutter
plus a few more I can provide if I stop and think about it
This means the chain lays over in the groove and preferentially cutting on the down side.
It does not take much to do this and once it starts it will just compound because it feeds off itself and will get worse and worse.

An alaskan mill is much more forgiving on these matters as holding the bar firmly at both ends will help force the chain to stay flatter.

I note that newer models of the Logosol mill have an outrigger to hold the outboard end of the bar level. This should work much better,

[MAI]

Thanks for the comments, Bob.

The saw was bought new for the CSM (Stihl had a great offer last year and the shop threw in a bunch of stuff) and only used for about 10 hours so the bar should be OK I would hope. I've used both new chains and chains I sharpened with similar results. The bar is the 63cm which logosol claim should do accurate cuts. They recommend cutting on an angle if possible which should reduce the tip bend and for wider boards with a 90cm+ bar they recommend attaching a jig at the other end of the bar as you suggest.

What makes me think it's something I'm doing wrong which is at the least contributing to the tendency for the increased width, is the way the width gets bigger right at the end of of the cut ie the width at the far side of the log isn't too bad for most of the length. Although the longest board I've made was only about 3m so maybe the problem would have been more pronounced on a longer log.

It's as if I'm doing something different with the saw handling right at the end of the cut which is causing/contributing to the problem. But dunno what that would be. I could get someone to watch to see if there's anything obvious I'm doing different. Clearly what we need is an Institute of Chainsawmilling like the Institute of Sport so we can get slow-mo biomechanical replays of the CSM operator in action to help perfect that technique

Cheers

MAI

[BobL]

Does it do it this on shorter boards?
If not it could also be some sort of a temperature thing.
Have you checked if the Mill rail has a slight twist in it at the point where the bar starts to dip?

Are you using Aux oiling. I do this even when using a 25" bar.

[MAI]

Does it do it this on shorter boards?
If not it could also be some sort of a temperature thing.
Have you checked if the Mill rail has a slight twist in it at the point where the bar starts to dip?

Are you using Aux oiling. I do this even when using a 25" bar.

Thanks again, Bob.

I've had the problem with both a short rail (~1m) and the standard 2.8m rail. I don't think they're skewed but I'll run a square over them. Maybe I should do some more milling with a range of lengths, focus on handling the saw for the end of the cut the same as the start and middle and do some careful measurements of where the extra thickness starts. And check the bar to see if it is warming up.

I'm not doing auxiliary oiling. I thought that was more for longer bars (90cm+). I use a chain lube oil for the Huskie and Stihl. The lube oils are supposed to be a bit stickier than (new) engine oil which is what I use in a small electric chainsaw used for cutting firewood.

Any pointers to a good reference that demonstrates how to attach an auxiliary oiler?

Cheers

MAI

[BobL]

. . . . They recommend cutting on an angle if possible which should reduce the tip bend and for wider boards with a 90cm+ bar they recommend attaching a jig at the other end of the bar as you suggest.

First thing I would try is milling them straight across or on the reverse angle.