Chain Brake Test

E

Eric_E

Location
USA
I'm looking for procedures for checking the proper operation of the chain brake. I was always taught, with the saw off and the brake off, to let the tip of the bar fall about 2 feet while holding the rear handle. If the brake snapped on then it was functioning properly. Anyone else taught the same? Heard something different?
 
Are you saying that gravity would engage the chain break by the 2 feet of tilt? I don't think that should happen. I check by running the saw full throttle with chain break off and then engagine it with chain in full rotation. If the chain stops, it works, if it doesn't, don't use the saw. You only have to do this test maybe once a day at full throttle...if you do it repeatedly my understanding is you could damage the saw. Anything that goes from a high rate of movement to 0 in a split second can't be good if done over and over and over.
 
Even one full-throttle (no-load?) stop could snap a crank, not to say it wouldn't be worth it under the right wrong conditions.

I saw in a Husky manual the bit about dropping the bar a couple of feet onto a stump or something similar while holding the rear handle. The brake should actuate when the bar tip hits the object. I don't think it's necessary to have the saw running, however, while performing that particular test. It's merely a check of the actuating system, not whether it will stop the chain. To check the actual brake effectiveness I'd say to rev the saw up under no load, release the throttle, and then pop the guard by hand.
 
I do it the same way you do glens...release the trottle just before engaging the CB but when you say no load, what are you referring to?
 
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I saw in a Husky manual the bit about dropping the bar a couple of feet onto a stump or something similar while holding the rear handle. The brake should actuate when the bar tip hits the object. I don't think it's necessary to have the saw running, however, while performing that particular test. It's merely a check of the actuating system, not whether it will stop the chain.

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Glen,

this is exactly the test I was refering to. Since the brake is inertia activated this procedeure should be enough to check the functioning of the system.

Has anyone heard of this or another method?

Phil,

I've never heard of the method you're describing, from what scource did you learn this?

Not trying to be jerky but, do you do this with your own saws or someone else's? Anyone else use this method?

The test in the Husky manual,("drop" type test), is to simulate a kick back situation I believe. Since the system is inertia activated this should be a good test.

I'm not sure about the full throttle idea. I wouldn't test the seat belts (inertia activated system) in my car by doing 65 and slaming on the brakes.

What have others come across?
 
i would test my own saws the way i dscribed, i want to see the brake physically stop the chain to know it works. You don't have to do this every time you want to stop the chain...once is enough. And this is how I have been taught to check the brake. We were warned that doing it too many times can damage the crank. You don't even necessarily have to run the chain full throttle...just have it spinning and see if it stops as soon as the brake clicks. But i wouldn't trust a test of the chain break whose only evidence of it working is a simple click and nothing else. Just my opinion. Everyone talks about how they dropped their saw from 20' and it still works and all this other stuff...these saws are designed to last (top brands being refered to) so engaging the chain brake with the chain spinning shouldn't destroy your saw...if you do it every five minute yeah something would prolly go wrong but i will still do this test.
 
Kevin,

Thanks for the link. I dug out a husky saw manual and found the same test.

I was speaking with a Stihl rep asking about this subject. I got the "cow looking at a new gate" look from him and others in the room. The discusion was about a 440 that has questionable chain brake operation.

Other opinions?
 
I know that some huskies have an inertia chain brake, I think it's supposed to activate the brake in a kickback event, at least that's when it's happened to me. To my (not so extensive)knowledge, Stihl doesn't have an inertia driven brake.
 
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when you say no load, what are you referring to?

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Cutting air.



All current saws have inertia-activated chain brakes at least as a primary mechanism. Some also have rear-grip releases which will activate the brake when not positively held and/or rear wrist guards which are also linked to the brake hold-open release.

I'm sure most of you know this, even if you'd describe it differently, but it sounds like some don't "see" what's happening, so bear with a word picture if you will.

The front hand guards have enough mass (some saws, certain small Echos come to mind, have additional weights affixed to them) that anytime the saw too-quickly moves backward/upward, the mass of the guard will make it want to stay where it was, thus tripping the catch holding the brake band open. Dropping the nose onto an immobile (-enough) object will simulate that action perfectly, though the roles are reversed: the guard is moving with the saw and when the saw suddenly stops, the mass of the guard lever wants to keep moving as it was, thus releasing the catch all the same.

It's like a Zippo lighter lid. It'll stay open until you overcome the cam, which you can either do manually or via inertia by quickly flipping the lighter body.

There two distinct actions which need to be independently tested: the activation (release) of the (held-open) brake and the function of the applied brake.

As with the Zippo, where the cam will lose its shape over extended time, the brake activation mechanism could (will) wear with repeated use. I believe this would tend to result in the sensitivity becoming greater than it need be, or that the brake would tend to activate too easily. Not really unsafe but surely aggravating.

If the void between the brake band and the clutch drum isn't occasionally cleared of its oily wood debris, the band will certainly not grip the drum as well as it could/should, increasing the time it would take to arrest the chain motion.

Again, I apologize if this seems insulting; it's not intended so.
 
I'd said "the brake activation mechanism could (will) wear with repeated use" and that sensitivity would thus be increased, causing premature (as it were) activation of the brake. I'm confident that the parts should be sufficiently hard that "repeated use" would mean way more times than probably even sitting on your couch and flipping it on/off endlessly while watching TV for a couple of months. In contrast, the cam in the Zippo lighter lid is intentionally made of a fairly soft metal so that it's what wears down instead of the brass case it's rubbing against.

Also, another possible reason for "premature activation" (wasn't there a thread discussing this on a Husky not too long ago?) might be a piece of sufficiently-sturdy crud getting in between the two parts (a cam and a spring-driven piston/rod, usually) which "set" the "trigger". That could conceivably prevent the cam from going far enough "over center" which would result in a "hair trigger" type of situation. That would be the very first place I'd look. You might want to set your mouse trap a little light, but probably not your saw brake. :)

Another continued thought: while checking the brake activation mechanism by dropping the bar nose onto something, the saw needn't be running, and in fact it would be better/safer if it weren't, IMO.
 
I saw this meatod of dropping at 2 foot done at a class. It is for the inertia activeated chain brakes. The instructer also showed us under extreme cuation how it works in an emergency, kickback and it did the job. Yes test with full throttle, and off with the drop. I do this to my saws before felling jobs just to give me the confidence it still works.
 
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