Chain speed calculation discrepancy and PPE - Help me understand

[CFar45]

When looking at PPE (ie. chaps/pants/boots), chain speed is often used as a reference in determining the effectiveness of protective equipment. However, I’ve noticed some discrepancy in chain speed calculations between manufacturer, safety organizations (ISO) and my own calculations.

For example:
From Stihl ms400 manual:
ISO max chain speed = 28.9m/s
Chain speed at maximum power (according to Stihl, I assume) = 21.7 m/s.


Why the (significant) discrepancy between ISO calculation and Stihl calculation? What am I missing?

To further confuse the issue, when I plug the numbers (3/8 pitch, 7 tooth, 14000 max RPM) into the formula on Madsens, I get 31.12 m/s. (Converted to m/s using online calculator)

Just trying to understand as I assess PPE.

I understand that my leg doesn’t know the difference between 21 m/s and 31 m/s and the damage is going to be the same for practical purposes if chain meets unprotected body part.

I also understand that in general, the more robust the PPE, the better. But PPE manufacturers use chain speed as a reference to help the consumer determine appropriate level of protection…. for example, class 1 vs class 2 vs class 3 chainsaw boots….

So I’d like to better understand why Stihl says 22 m/s and ISO says 29 m/s.

Thanks in advance to those here who are smarter than me!

 

[2dogs]

You will get a better response in the CHAINSAW forum. This forum is more forestry related. Good luck.

 

[rwoods]

Not a matter of smarts, a chainsaw does not make its maximum power at its highest rpm. I don't know how ISO measures things, but if you take it at face value - a chainsaw's maximum speed is much higher than it is at maximum power. I understand that it is not usual for a 12,000+ rpm saw to make its maximum power at 9,500 rpm.

As stated above, your question will likely see more action in the chainsaw forum.

Ron

 

[ray benson]

Max speed - no load
Max power - probably in the 9,000 to 10,000 rpm range

 

[CFar45]

Max speed - no load
Max power - probably in the 9,000 to 10,000 rpm range

Thanks all. That makes sense.