Multiquip Sp-6065 operation manual Engine Power, Cutting Power & Sheave Size, Blade Shaft Ratios

Engine Power, Cutting Power & Sheave Size

The cutting capability of your saw is a relationship between engine power (as reflected in the engine RPM) and the speed (RPM) of the Blade Shaft. The gasoline engine of the SP-6065 runs at 2800 RPM (full load). If 2800 RPM was a desirable Blade Shaft speed for the average conditions in which you work, we would use the same size sheave on the engine shaft and the Blade Shaft; and the ratio between the two would be 1 : 1.

1 : 1		1.4 : 1
Blade Shaft	Engine
	Blade Shaft	Engine

Fig. 4 — Blade Shaft Ratios

If, however, for your cutting conditions, you need a Blade Shaft speed slower than the engine speed (and this is usually the case), then we need to INCREASE the ratio between the two speeds by putting a larger diameter sheave on the Blade Shaft.

If, for example, you know from experience that you need a Blade Shaft speed of 2000 RPM for the size of blade you normally use (see the Blade RPM vs. SFPM Chart, below):

2800 (engine RPM) ÷ 2000 (desired BS RPM) = 1.4

This is the ratio 1.4 : 1, which means that for every 1.4 revolutions of the engine, the Blade Shaft only turns once.

Ratios greater than 1 : 1 also have the beneficial effect of increasing the torque of the Blade Shaft by the same factor (1.4 in our example) . The manufacturer advertises that the Deutz BF31011 diesel engine develops 123 ft. lbs. of torque. To find the theoretical torque of our example saw setup:

123 x 1.4 = 172.2 ft. lbs.

Actual torque of the saw will vary somewhat. In general, more torque means more cutting power.

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