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Author Topic: Chain saw carving bars  (Read 4023 times)

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Offline Kevin

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Chain saw carving bars
« on: June 22, 2005, 06:14:40 PM »
Anyone have a narrow nose chain saw carving bar on a saw?

I know a guy that bought the 1/4" pitch drum sprocket, bar and chain and he's having trouble with it on a new  Echo saw.
I haven't seen it yet but it seems that something isn't quite concentric because as the chain advances it appears to be tight and then as you keep advancing it there's a whack of slop and the chain drops down off the bar and then tightens back up.
Everything matches so I was wondering if the narrow nose might cause this phenomena.
I told him to put all the stock parts back on and try it but I haven't heard back from him yet.
I know he sent it as is back to Echo in Cali and they said it was suppose to be like that but it sounds odd to me.

Offline sigidi

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Re: Chain saw carving bars
« Reply #1 on: June 22, 2005, 06:37:13 PM »
Sounds a bit scary to me, but then again I am a big fraidy cat about chainsaws ;D :D
Always willing to help - Allan

Offline jokers

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Re: Chain saw carving bars
« Reply #2 on: June 23, 2005, 09:19:09 AM »
Everything matches so I was wondering if the narrow nose might cause this phenomena...........................I know he sent it as is back to Echo in Cali and they said it was suppose to be like that but it sounds odd to me.

Hi Kevin,

With the physical relationship between the chain pitch and the nose radius unchanging, I don`t see how changing tension could be normal. It seems more likely to me that your friend either has a sprocket that is not concentric, excessive crank runout, or mixed pitch chain which shows an exagerated effect from the extremely small radius of the nose. I`m assuming a dime tip bar based on the use of .250 pitch chain.

My first bet is that the sprocket is out of whack, I`ve seen it before with a certain brand.

Russ

Offline Kevin

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Re: Chain saw carving bars
« Reply #3 on: June 23, 2005, 07:27:55 PM »
I have yet to take a look at it Russ but it just came back from the factory depot on the west coast and I can only assume they would have picked up on something like that.
We should know in a day or two, I'd like to get my mitts on it to run the sprocket by a dial indicator or a fixed object to see if it could be the shaft or a bearing.
They changed the drum sprocket at the factory but it still does the same thing that it was doing prior to him sending it out.

Offline jokers

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Re: Chain saw carving bars
« Reply #4 on: June 23, 2005, 11:41:03 PM »
They changed the drum sprocket at the factory but it still does the same thing that it was doing prior to him sending it out.

For some unknown reason I read into your first post that the saw had a rim sprocket, sorry.

I`m really curious now. I wouldn`t expect a bad crank bearing on a brand new saw but it could happen. The problem could be something as simple as an imperceptably bent crank when only checked by eye, get your dial indicator out.

Quote from: Kevin
I know he sent it as is back to Echo in Cali and they said it was suppose to be like that......

Apparently the boys in Cali didn`t see anything, how could they say that it`s supposed to be like that? When you said "as is" did you mean with the stock bar and chain or the carving set up? I`m reading this "They changed the drum sprocket at the factory...." to mean the stock pitch drum.

Russ

Offline Kevin

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Re: Chain saw carving bars
« Reply #5 on: June 24, 2005, 07:44:11 AM »
Russ the saw was bought stock at a local shop, the carving bar, chain and drum sprocket were ordered and installed by the carver.
He sent the saw with all the carving goods on it out to Cali because the local shop butchered his carb here.
He didn't have the proper clutch removal tool so he might have damaged something using a brass punch trying to get the clutch off but I would have thought the factory would have picked up on that.
They replaced the carb in Cali and changed the drum saying it was a little out but from what he says it hasn't changed the way the chain reacts on the saw.

Offline jokers

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Re: Chain saw carving bars
« Reply #6 on: June 24, 2005, 11:53:32 AM »
Interesting Kevin, be sure to let us know what you find.

I`m still having trouble accepting that the Echo factory guys saws the varying tension and stated that it is supposed to be like that. I wonder how closely they looked at the saw?

Dennis Greffard has been working closely with Echo in preparing a bunch of carving saws for the factory sponsored team, why not give him a call if you don`t figure this out soon?

Russ

Offline Kevin

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Re: Chain saw carving bars
« Reply #7 on: June 24, 2005, 05:00:30 PM »
Will do, thanks Russ.

Offline Kevin

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Re: Chain saw carving bars
« Reply #8 on: June 26, 2005, 12:59:12 AM »
I got the saw tonight and I don't see anything obvious but it is definitely out somewhere, maybe in the shaft or bearing but there isn't any movement or noticeable play back there.
I'll have a closer look at it tomorrow.

This is two and a half inches of chain travel ...



Offline Kevin

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Re: Chain saw carving bars
« Reply #9 on: June 26, 2005, 12:25:41 PM »
What I discovered is two opposing sprocket teeth have a difference in length of .013" which isn't much but because the chain is a loop the difference is twice as much causing the chain to run out .026" which is considerable.

Offline Kevin

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Re: Chain saw carving bars
« Reply #10 on: June 26, 2005, 09:31:49 PM »
Russ;
I had some additional info, the saw was sent back to the origin of purchase and not Echo, the saw is fine and it appears to be the after market sprocket.
The original stock sprocket that was on the saw has tolerances of .003" .

Offline Kevin

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Re: Chain saw carving bars
« Reply #11 on: July 08, 2005, 08:42:51 AM »
After one trip back to the distributors chain saw mechanic, three of the same manufactured after market sprockets and a trip to the local factory rep I got my mitts on the saw and discovered that the drum sprockets are garbage.
I ordered a GB sprocket which is far superior in tolerances and the saw is back in the hands of the carver doing what he bought it for.  :-X

Offline Oregon Engineer

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Re: Chain saw carving bars
« Reply #12 on: July 08, 2005, 04:44:44 PM »

Good you got to the bottom of the problem.

One little bit to add. If you pay close attention when moving a chain by hand around the bar you will see it naturally gets a little tighter and looser, or you may see more chain sag and then less chain sag. It's not a bad sprocket or crank, it is due to the "chordal action" or "chordal rise". See the attachment.

As a drive link or driver approaches its time to come off the drive sprocket it lifts a small amount (which tightens the chain), then as it leaves the drive sprocket it lowers (causing looser chain). The smaller the number of teeth the worse it gets. If you have a drive sprocket and a bar nose sprocket, then the two will combine to double the magnatitude of the tight and loose oscillations.


Due a web search under "roller chain" and "chordal action", there is some good information on the issue.

What was the name of the bad sprocket manufacturer???

Offline Kevin

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Re: Chain saw carving bars
« Reply #13 on: July 08, 2005, 08:22:51 PM »
OE;
Thanks for your input.
I clearly understand that we aren't working with Swiss watches here and there  is a slight variation in tension with all chains that rotate on a gear but if you look at the original picture you will see how drastic the variation was with this one manufactured sprocket.
There were two others just like it from the same manufacturer!  :D
I hesitate to say who the distributor is but the sprocket is made in the U.S.A. , I don't know which company is turning them out but I suspect several hundred will be sold to unsuspecting chain saw carvers all over North America.
The distributor is well aware of the problem although they don't believe it  :), I feel I've done my part.
I was at a logging show when I spotted the loose chain on this carvers bar and stopped to talk to him about it.
Everything was brand spank'n new, he had already had a chain saw mechanic look at it and had the original after market sprocket replaced by the time I got mixed up in it, he then sent the entire saw, sprockets and bar back to the distributors mechanic and they sent it back telling him to just loosen the chain if it was too tight.

...and I forgot to mention that I'm not even a chain saw mechanic !

end of rant.   ;)

Offline Oregon Engineer

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Re: Chain saw carving bars
« Reply #14 on: July 09, 2005, 03:24:14 AM »
Kevin,

When you found the .013" difference in tooth height I knew you got to the bottom of the problem! The other info I posted was just incase you started to look really close at the chain. The pictures ought to wake up the manufacturer.

You're not ranting. The .003" tolerance for the OEM sprocket is the correct range. The .013" difference in teeth height will cause excessive damage to the entire chain, bar, sprocket and saw system if it is run tight.

Often I see operators complaining about a rash of broken chains when it is a sprocket problem. It is easy to spot because usually the notch in the bottom of the tiestraps and cutters gets beat up bad from being lifted by the high tooth. 

If it is run loose then chain throwing becomes a real problem. Either way the craver will experience more wear and problems with chains breaking or coming off.

Can you post a picture of the problem sprocket and drum or any part numbers stamped on it? It might help a few other guys avoid the problem.

Offline Kevin

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Re: Chain saw carving bars
« Reply #15 on: July 09, 2005, 10:59:46 AM »
.013" was the good one.  :D
The original sprocket was worse than that.
I gave everything back to the carver but here's a picture of the sprocket,
no serial number only a part number so I'm not sure how they control different lots.



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Offline Oregon Engineer

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Re: Chain saw carving bars
« Reply #16 on: July 10, 2005, 01:20:51 AM »
Kevin,
Thanks for posting the sprocket. The part number should help others avoid the same problem.
Good Job!!

Time to do some camping!
Take care,


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