Performance of Simonds Band Saws on Head-Rig

The Benson Lumber Company of San Diego, California, is using Simonds Wide Band Saws exclusively for the headrrg.

Head-Rig Operation

The mill has one Summer 9-foot head-rig which uses a No. 15 gauge, l4inch saw traveling' at a speed of about 9000 f.p.m. The length of the saw is 53'6" and. the tension is set to the curvature of a circle 4O' in diameter.

Logs cut by the head-rig consist of. 90/a fft and lo/o hemlock, and range from 12" to 5(' in diameter and 14' to 30' in length. They are floated down in rafts from the Columbia River, Oregon, and as these rafts are broken up some time prior to sawing the logs are allowed to float in San Diego Bay, thus becoming saturated with salt water. They are raised by conveyor directly from the water to the head-rig. Few knots are encountered and the logs are entirely free from nails.

The cutting speed of the head-rig is from 250 f.p.m. for the larger to 330 f.p.-. for the smaller logs, the latter figure representing the maximum speed of table travel. The average cutting speed is 300 f.p.m.

The average hourly production of the head-rig is 10,000 board feet as shorvn by actual records tor July,1929. The mill operates about t hours a day for 275 days a year.

At the head-rig the logs are cut into 2" to (' flat board slabs and some to 8x8. Slabs go to circular rip saws and to a horizontal l0' band saw for resawing.

Saw Maintenance

The length of run for a Simonds saw between grinds ranges from 3 to 4 hours, with an average of.3l hours per grind. With each change of saws the head-rig is out of production for approximately 5 minutes. The mill has four saws fer the head-rig, used in rotation.

Grinding of saws is done on an automatic Covel grinding machine with a lo-inch Norton grinding wheel. Saws are passed around this machine 3 to 4 times pe1 grind, removing about .0115 inch of metal. After grinding the teeth are touched uf with a hand file, a total of about 30 minutes being required for grinding and touching trp. Swaging of points and shaping of edges are done every second or third grinding, the time required being approximately 15 minutes.

Saws are tensioned every fifth grinding, requiring about 3rl houfs of belch work.

Salvs are given about 170 grindings before discarding so that the set of four last approximately one year. They seldom wear out but are discarded after about 2 inches of width is removed, because of the rapid accumulation of rust caused by salt water.

Costs

Saw expense is set up on a cost-per-grind basis. The first cost per grind is $1.32. All maintenance labor is charged at the rate of $.70 an hour. I-;abor costs for grinding, touching up, swaging, shaping, tensioning and changing saws on the head-rig' are calculated in accordance with the time requirements discussed above. In addition the down-time of the head-rig during change of saws is charged at the rate of $2.80 an hour.

The total saw cost per grind, excluding the fixed charge and polver cost of the grinding machine is $2.52. Based on average production per grind the saw cost per 1000 board feet is $.072.

Savings

Simonds saws are effecting a saving in sawing cost at the rate of $.021 per M board feet, or $.735 per grind. Based on the average daily output of 90,000 board feet the daily economy is $1.89 and the yearly saving, $519.75. Simonds band sarvs are also used in the mills of the Benson Timber Company at Clatskanie, Oregon, owned and operated by the same management.