Flattening the Bar on a Chainsaw Slabber

Troubleshooting a slabber that likes to crawl up or down in the cut. November 16, 2011

Question
My Lucas slabber is crawling down the in-cut if I push the feed speed at all. I have to go ridiculously slow to prevent this. I thought it was the bar so I flipped it over and it did the opposite (crawled up the in-cut). I have a new chain and reground bar and it’s still the same. Any ideas would be appreciated.

Forum Responses
(Sawing and Drying Forum)
From contributor G:
I have only use my slabber twice, so take this with a grain of salt. But if you flip the bar and the error goes the other way then it is the bar. I assume you re-shimmed the bar each time to compensate the bar's tendency to bow down. How about over shimming the bar so it is slightly up in the center? The only other thing that caught my eye is the design of the slabber. With the way it is held on the drive side, it looks to me that it would not be that difficult for the slabber to rotate under cutting pressure which would cause it to dive.

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From contributor O:
Can I ask how one can tip the center of the bar by shimming, when it is held only at the ends? I do understand how one could tilt the bar up or down relative to the length of the log, using shims, but not just the middle. So far as bar sag goes, isn't chain tension (higher tension pulls out sag) the only remedy? I'm very interested in this topic as I'm getting ready to go on the road with my new Peterson swing mill and slabber. In my years of chain saw milling with Sperber and Alaskans I never encountered anything critical about bar alignment.

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From contributor G:
On the Lucas slabber the bar is held at both ends. Each end has a fastener that when tighten squeezes the bar. When a shim is placed on one side of the bar (the outside relative to the fastener) and the fastener is tightened the bar will curve up. The curve will be closest to the end that is being tighten. Therefore a small amount of shimming at both ends will flatten the bar. The factory does this for the slabber owner, but because the bar was taken off it is likely that the shimming needs to be checked and re-done. I believe the sawmill owner's manual covers this adjustment.

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From contributor M:
If the bar has a lot of cutting on it or has run without enough oil the rails on the bar may be spread or worn wide allowing the chain to tip to one side or the other. It's normal wear and tear. Oil is cheap. The rails can be closed and the bar ground at a good saw shop so the surface is again flat and snug to the chain.