Testing inertia chain brake

[Bolt]

5 minutes ago, pleasant said:

Yes, I know Bolt, but comparing a chain brake test with a brake band system on a petrol saw against the kick back micro switch system on an electric saw is like comparing apples with pears. The test are completely different as although they both operate via the inertia of a kick back situation you cannot replicate the chain brake test on a petrol saw like in the video than you can with a mains electric- the mains electric saws need a physical pressure to the chain brake lever to operate as in a kick back situation.

 

Both work on inertia...but are tested in different ways. If the OP is suggesting the operation of the chain brake on his electric saw can be tested in the same way as the petrol one in his video he is incorrect....and I think that is what is worrying him?

OK.

 

It probably depends on what saw the has then.

 

He’s probably gone off to try and get a more succinct answer from a moble phone forum.

[GarethM]

2 minutes ago, Stubby said:

Ok . Thank you

Same thing was in the Wii remotes 🙂.

Kinda assumed if it was Husqvarna, they would have done something like that as they're heavily into robotic mowers.

[pleasant]

Well, he did state it was an electric chainsaw in his original post, so maybe that's where some confusion is coming from down the list of comments?

 

...and it has turned into a mobile phone forum 😁

[adw]

The answer is in the name, inertia, in early saws we had no brake, this moved on to a brake that did work by the hand guard hitting the back of the wrist if a kick back occurred, unfortunately in the felling position there is no way for the wrist to come in contact with the hand guard, so next stage was an automatic brake ( Swed o matic ) as Husqvarna called it, here the engine unit would move on the anti vib mounts and an adjustable button on the brake, or on the handle would actuate the brake, unfortunately this was dependent  on correct adjustment, and anti vib mount condition, so the inertia brake was born, weights are set in the hand guard, now due to the veracity of the kick back the guard tries to stay still as the saw body moves back thus bringing the brake on, Husqvarna now have what we call a knee link inertia brake, probably one of the most reliable brake there is, there is also the trio brake, this is a third way to bring the brake on, fitted to the rear handle this combats what is known as a slow kick back where the chain can run up the limb with insufficient inertia to bring the brake on.

So in my humble opinion the test in the video is absolutely correct, and should work with both petrol and electric/ battery machines.

End of todays lesson and apologies if insult any bodies intelligence.

[openspaceman]

A bit OT but some time back, on this forum, it was pointed out that an electric saw was directly coupled to the chain, so the brake had to stop the chain and the armature which has more momentum to overcome than the brake band on the clutch having to stop the drum and chain and slip the clutch.

 

It was in the context of a full power test on chainsaw trousers, the electric saw carried on cutting further.

 

 

[adw]

You are quite correct, we had to stop using an electric saw on the test leg, due to the addition inertia of the heavy  armature it could cut through the safety material.

[Bill C]

I've never taken a electric or battery saw apart but I suspect they have a brake band the same as any petrol saw around a rotor on the electric motor. The front brake guard/lever works the same on all types of saw, pushed forward by your left hand and Inertia. The inertia bit is worked by the weight of the front guard/lever, as the saw kicks back or in the case of the saw in the video the saw stops when it hits the wood the energy or inertia of the weighted front handle throws it over the spring cam and applies the brake.

[HillyJohn]

Stihl MSA 160 and above have a physical brake band around the outside of the drive sprocket, with a similar mechanism to their smaller petrol saws

[pleasant]

Would be nice if the OP came back to us and at least enlightened us with what make and model they have.

 

In all likelihood they have some generic chinese supermarket saw which has a more basic, earlier design of chain brake system fitted to the electric saw and is expecting it to operate as the latest brake does in the husqvarna video they have uploaded...which they dont. Even though it will still be an inertia activated chain brake.

 

We al all guessing here...myself included 

 

 

[tku]

Wow that is a lot of responses, thank you. This is clearly a lively forum! Sorry for not coming back sooner myself.

 

So the saw I have at the moment is the Makita UC4051A, which is a 2000 W mains-powered saw with a 16" bar. It's advertised in the Makita brochure as having an inertia brake but not on their website... so I asked their customer services and they said the brake was "manual only". So clearly Makita are confused about their own product even. 

 

I can confirm that this saw has the physical metal band that tightens around a drum upon engaging the manual brake using the front hand guard (so I believe similar to a petrol saw in that sense). Perhaps I need to be more "violent" in my nose-drop test, as has been suggested. I was already being considerably more violent than the man in the video though! The front hand guard itself doesn't seem to be weighted, so I presume there would be some internal weights to capture the inertial forces?

 

Cutting the electric does not stop the saw instantly, although most electric saws seem to have what they call an "electronic brake" or a "rundown brake" as well. This seems to apply a bit of reverse current to bring the chain to a stop when the trigger is released. This does not happen instantly though, it takes about 1 second. I don't think it's meant for kickback protection, just general safety and usability; a lot of modern power tools have this feature.

 

 

P.S. The Makita UC4051A looks identical to the Husqvarna 420EL (Husqvarna's only mains-powered chainsaw). I've also contacted Husqvarna and they say the the 420EL has an inertia brake and doing the nose drop test should activate it. I'm tempted to return the Makita and get the Husqvarna but I'm damn as near convinced they are actually the same saw rebranded one way or the other (Husqvarna ignored my question when I asked them if that was the case 😆)

Edited May 22 by tku