sugihara bar cracked

[SteveA]

That's quite a summary��

 

Yes, and useful for putting in the item condition section on eBay when he sells it on.

[agg221]

Yes, and useful for putting in the item condition section on eBay when he sells it on.

 

Sorry, not with you?

 

Alec

[Goaty]

Sorry, not with you?

 

Alec

 

I think it's sarcasm at how stuff gets listed on eBay, stuff is sold as in good usable condition when it's actually had it's usable life.

[agg221]

I think it's sarcasm at how stuff gets listed on eBay, stuff is sold as in good usable condition when it's actually had it's usable life.

 

Fair enough - I would have thought you just list it 'spares or repair' and sell it for twice what a new one would cost

 

Alec

[Forest2Furniture]

Thanks for the pics - I need to have a look at where I clamp my mill to the bar.

 

 

It may be perhaps down to the powerhead being too far from where the mill clamps to the bar but am assuming like most of us you clamp the mill as close to the saw dogs as possible to get max milling width?

 

 

 

Yep, as close as possible.

 

I'll be buying a new one next week

[Forest2Furniture]

I have shown the pictures to one of our fatigue experts. Obviously we can't be definitive from the photographs, but we did make the following observations:

 

The cracks are initiating at the edge of the bar. There are various initiators here - such as the sharp change in section at the edge of the rails and the profile at the bottom of the groove.

The point of clamping provides a change in section, effectively creating a tight bending radius between the clamp and the bar, as the saw vibrates, creating a fatigue situation.

Notably, failure is not at the outer edge of the clamp, but within the clamped region, effectively at the apex of the bend on the bar rails if the mill was held in operational position with the powerhead hanging under its own weight. This may indicate that the chain action is a factor (effectively another cyclic loading), rather than purely vibration from the powerhead.

On right hand rail it appears that the surface is no longer flat, but rather is worn down in the region of the crack. Do you regularly flip the bar, or would you happen to know if this has been predominantly the upper side when milling?

 

One possible scenario drawn from the above is that, when milling, the powerhead is hanging mostly free under its own weight, or is being habitually pushed slightly downwards. This is putting a bend on the bar, which ends where the clamps are so there is a slight change in chain direction and a point of peak stress which coincide. Over time, the chain running round this radius causes fretting, which initiates a notch at an already sharp change in section on the rail edge. Failure then occurs from the notch due to the stress cycle of constant load from the powerhead weight + cyclic load from the vibration of the engine.

 

If the above scenario is correct, some factors which will have a bearing are:

 

Sugihara bars are more likely to suffer from it because they don't wear so fast. If the rail wears faster than the notch propagates the problem doesn't arise - notably this is the same issue as caused the failure in rail track at Hatfield, where lighter trains didn't wear out the rail fast enough to stop the cracks propagating.

Failure is more likely if you don't flip the bar regularly - it will effectively halve the life.

Failure is more likely if you use a winch than if you push carefully from the powerhead, as the downward force will be greater and vibration will be less damped (by your arm!)

It may be advisable to keep an eye on the bar at this particular point, for signs of wear, and dress back the rails if wear is observed.

 

Hope this helps.

 

Alec

 

Thanks for that Alec.

 

Yes I do use a winch and yes I do turn the bar.

As I have a system that locks the throttle open I don't hold the power head and so as the unit is hanging down slightly this seems to be the likely cause of the damage.

I'll look into making a harness that attaches to the mill and supports the powerhead that should help take off the strain.

[Forest2Furniture]

New bar arrived today.

Thanks to Rob & co at chainsaw bars great service as always.

[SteveA]

I think it's sarcasm at how stuff gets listed on eBay, stuff is sold as in good usable condition when it's actually had it's usable life.

 

oops, sorry for my late response.... to confirm yeah I was just being a silly nincompoop (with a feeble attempt at sarcasm).

cheers, steve

[Rob D]

New bar arrived today.

Thanks to Rob & co at chainsaw bars great service as always.

 

 

No prob Patrick - let me know how you get on and hopefully the same issue does not happen again.