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Comparison of 13/29 and 10/30 Profile Blades Cutting Softwood

At the recent International Distributor Meeting held at the European headquarters in Kolo Poland, Wood-Mizer gave a demonstration of the difference between using their 10/30 general purpose blade and the new 13/29 blade that has been designed for cutting softwoods.

Both blades were our special ''Double-Hard'' blades, which feature our unique induction hardening process on the tips of our normal blade stock. This has the advantage over other manufacturers in that once you have sharpened through the hardened tip you are still cutting with Wood-Mizers special blade steel which has exceptional durability and sharp life.

The purpose of the demonstration was to show that the 13 degree profile performed better than the general purpose 10 degree in both dry and green spruce and also to demonstrate that most operators are not cutting as fast as is possible while still maintaining high degrees of accuracy of the cut. 300mm wide cants of dry and green Spruce and Pine were prepared and a special test headrig was used for the demonstration.

The Test Headrig is exactly the same as our production LT70 Series heads, except that we can control feed speeds, blade speeds, and we can measure the maximum and average current draw while cutting. In addition we use a long straight edge and feeler gauges to measure any wave or crown in the cut, and we use three grades of sieve to measure the size of the sawdust grains being produced during each cut. In each 300mm cant we cut using both the 10 degree and the 13 degree blades and gradually increased the feed speed by 2m/min until an unacceptable level of deviation in the cut was reached. Our measure was +/- 0.5mm.

1. Comparative Speed of cut between 10 degree and 13 degree blades

The tests showed that in both green and dry Pine and Spruce the 13/29 profile blades were able to cut at an average of 10m/min faster than the 10/30 blades at the same level of cut accuracy. 2. Actual Speed of Cut

In Green Spruce and Pine the average acceptable cutting speed was about 32m/min.This is a speed that very few operators cut at for fear of ''wavy'' cuts. We demonstrated that even in Grade 2 & 3 logs this cutting speed gave an accuracy of cut within our +/-0.5mm tolerance. At slow cutting speeds the performance of the blade is not very good, with a lot of very fine sawdust being produced, which is the result of cutting the same wood over and over again. As you in crease feed speed, so each tooth only cuts the same piece of wood once and the sawdust chip size increases and the blade performs much better. The trick is to cut as fast as possible and to keep the feed speed constant.
In dry Pine and Spruce the maximum feed speeds that could be achieved were about 8m/min slower than for green Pine or Spruce.
Out of interest we prepared a green Pine cant with a width of 120mm and cut as fast as we could. At 48m/min the cut was still straight, and the operator was almost having to run!! Unfortunately our test rig was not programmed to be able to go faster than 48m/min and so we do not know at what speed accuracy would have stopped us, but we believe that we can cut at about 50m/min in green pine and spruce on 120mm wide cants.
All of the tests were carried out with our standard LT70 Series Head with an 18.5kW motors and our standard roller double block guides.

When using 13/29 blades, operators must practice cutting at higher speeds than they have become used to in the past with the general purpose 10/30 blades. The 10/30 blades perform very well in Hardwoods and are an excellent general purpose blade.

To consistently cut at between 30 and 40m/min in green softwoods you really need to use a remotely operated mill and to combine the sawmill with material handling equipment to bring logs in and to remove sawn material.

The 13/29 Profile blades will significantly increase your productivity in Softwoods, and should be used for softwood sawmilling especially on our top end LT40 and LT70 Series mills.

This article was published in the 'Wood-Mizer Today' company newsletter.

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