A couple of years ago, I bought a Sasmo/Kopo brand screw chunker that came up for sale locally. I wanted a chipper anyways, so thought why not. Finally, 2 years later, I was able to try it for the first time with the help of someone who has a tractor.
The purpose of this post is to share what I learned operating it for a day, have some notes written down for my own reference later, and hopefully gain some advice from the Scandinavians or any others that know how to use a screw chipper. I reached out to Laimet for some literature but didnāt hear back.
Firstly on the setup, the tractor had 60 hp at the PTO. Min 42 inches required between the lower arms. Google translate informed me the writing on the chipper was Finnish. Very heavy construction, seemed well built. Was surprisingly quiet compared to the knife-on-wheel chippers. Seems to be direct drive from pto to conical screw (has a big flywheel too).
Itās strength lies in eating the larger diameter pole wood. It consumed any tree we fed it through itās roughly 6"x6" opening, so long as it didnāt have large branches jutting out at right angles. It pulled off small branches as it sucked in the log but stopped pulling in the log if it had larger branches jutting out. The tractor did not bog down. However, we were using coniferous trees and soft maple so perhaps it would require more horsepower for true hardwoods.
We had to force in smaller trees and branches (screw didnāt pull them in), and the chute got jammed (small branches and needles caused ābridgingā Ha!), which required shutting down and clearing out the debris. We ended up running it without the chute.
Here I am sort of pushing on this soft maple tree but later learned I can just let it suck it in if it is large enough diameter. It also ate the sawmill slabs you see beside.
I adjusted the āanvilā I will call it, the plate that the screw pushes the wood against as it consumes it. Bringing it to within 1/4 inch seemed to pull more of the smaller stuff through. I need to test other configurations (larger gap at front, anvil closer to screw, etc). I donāt know what Iām doing in this area. Three bolts allowed the adjustment.
On to chip size. This seemed to vary mainly on the wood moisture content. Perhaps also based on the species. It seemed the dryer the wood the more big chunky chips I got. I understand most people chunk their gasifier wood when it is green. The dryer wood seemed to hold together through the screw. The wetter wood seemed to pull apart and fracture more, which I believe was the cause of more fines I observed. It also caused these stringy lengths of wood to appear - the wood did not shear off cleanly, so a length of bark and sapwood was produced. This phenomenon is also documented on the fluidyne website where they tried a Laimet chunker. The screw size I have made chips smaller than I was hoping, but still bigger than a conventional chipper. They are also flatter than Iād hope. It was a gamble buying something I did not understand but it does chip up wood just fine. I wonder if PTO speed would affect chip size.
If anyone knows how I can get it to feed smaller diameter branches (< 1 inch or 2.5cm) that would be a plus (so maybe I can use it as a yard waste chipper with small tractor). Otherwise, all in all it is a great machine for making chunky-ish chips from large diameter straight wood with few right angle large branches. I doubt I could ever get one, but I think a screw with wider spacing is really what Iād need to make big chunks like the square-baler-chunker guys do. The space between the screw blades is 1 3/4 inch.
Here is a dry-ish (cut early summer and laying in the bush 2 months) red maple chipped up and screened through 3/4"x3/4" screen (just what I had on hand). The black container with grey handles on the left are the āfinesā that fell through the mesh. The white bucket is what did not pass through the mesh. The lower square bucket is an assortment of chips from the white bucket laid out, along with some of the outlier large chunks. I estimate these extra large chunks make up less than 5% of the chips. I estimate the fines make up less than 10%.
Here are some up close pictures of the chips. The measuring tape is in inches. There are quite a few that are very thin, even though they are a good width/length.
Outlier XL chips:
Some thinner chips:
chips that did not fall through 3/4 mesh:
Fines:
