Rim or Spur sprocket ?????

[Ax-man]

Just curious as to which type of sprocket is preferred on a chain saw by some of you guys??

Myself I prefer a spur over a rim, to me it gives the saw a little more bite in the wood. But rim has the advantage when it comes to maintence and is cheaper.

Is their any big difference in running a 6 tooth over a 7 tooth sprocket???

 

[timberwolf]

I did not even think there was such a thing as a 6 tooth rim sprocket, you just dont have room between a standard 7 drive spline and and the botom of the drive links if bent into the smaller arc of 6 driver circumfirance.

Brian

 

[SilverBlue]

Rimm. When they are ready to be replaced I grind them and get a faster chain speed.

 

[glens]

I prefer rims to spurs for a couple of reasons.

If you could measure it, I'm sure you'd find rims to be somewhat smoother-running.  Hang a chain over a spur and rotate the spur by hand and watch the point on the side where drivers are picked up by the spurs.  You'll note the rivets walking nearer to then away from the center of the sprocket as each driver is picked up by a spur.  Now do the same with a rim and you'll note somewhat less variation in the radius.  The variation in the radius (not entirely avoidable, yet is somewhat less with a rim) causes an oscillation in the chain speed.  The math shows that with 7 teeth, the tangential point through which the rivets pass varies by 10%.  Going to 8 teeth, it drops to 7½% while 6 teeth comes to about 13½%.

"I grind them and get a faster chain speed"&nbsp; <i>What?</i>&nbsp; Reducing the diameter <b>will</b> <i>reduce</i> the chain speed in and of itself, but moreso since the reduced pitch diameter will be at odds with that of the chain.

Glen

 

[Ax-man]

Rocky.

What I meant by the " bite in the wood " comment was that the saw has a slightly smoother feel and a tad bit more aggresiveness when using the single piece spur compared to the two piece rim. I 'm just curious to see if any one shares this same opinion when it comes to sprockets or am I putting more into it than is really there.

In regards to the 6 tooth, 7 tooth question it was more directed toward the spur sprocket, chain speed wasn't the answer I was looking for, although it is relavant to my question.

I'm more interested in knowing if giving up some chain speed, in favor of more torque with a 6 tooth, to offset some adverse cutting conditions like cutting softwoods like willow and cottonwood or in tight, confined cutting areas to reduce the kick back factor. Is the difference beween the two enough to warrant the use of one as opposed to the other. This is more what I was after when I posed that question, I should have ellaborated a little more.

SilverBlue,

Interesting comment

When you grind it can you get it perfectly round and a smooth enough surface as to not put put additional wear on the drivers???

Aren't you also removing metal that could lead to failure of the rim???

 

[Kneejerk Bombas]

Originally posted by RockyJSquirrel
And a 6 tooth rim would bring your chain speed down too slow.

Wouldn't that depend on the application?

What if you where running a a Makita 12 volt cordless chainsaw, with a 4" bar? I'm not sure it could pull a big 6 tooth sprockt.
On the other hand, a pp090 with a 16" bar, probably wants a 10 tooth.

 

[SilverBlue]

Grinding Rimms

I made a special rig on my drill press and an adjustable grinding wheel. Yes it comes out nice but I don't grind that much off.Have gone down to .125 without problems.

 

[geofore]

sprockets

Smaller saws under 65cc spur, unless they are Power Ported, then under 50cc. Over 65cc, rim. I think you mean 7or 8 tooth not 6 or 7 tooth. The aggesiveness you think you feel with the spur is the wobble factor, the chain runs smoother on the rim. The rim tends to line the chain to the bar better, the less wobble you feel, it's not more aggressive it shakes more.

 

[Ax-man]

Thanks for the neat replies it clears up some questions on sprockets I've had for a long time.

Geofore, I wasn't wrong on the 6 tooth 7 tooth, on the smaller Stihl's they will accept either one. I have some in the shop right now ( 6 tooth ) be glad to post the part no. for you if you want.

Thanks again for the info it will definately come in handy next time I go sprocket shopping.

 

[NeTree]

Definitely prefer all rims. WAY cheaper to replace.

Wonder what a 10 tooth would do on my 394 with the 20" bar?

 

[robedic]

335

Then why are rim sprockets not available for smaller saws like my 335 xpt?

 

[sedanman]

If your smaller saw has appeal to the carving crowd then there might be a rim system for it. Bailey's has rim set-ups for some unlikely saws...Stihl 017 for example. Carvers like 1/4" chain and sometimes a rim sprocket is the only way to run it.

 

[NeTree]

That's a very good question, and I have wondered the same.

I THINK you can change SOME of them over to a rim sprocket, but I'll leave that for the techies to answer.

Anyone?

 

[ricksvar]

I have two saws with rim sprockets and two with spur.I've given thought to the idea of chips becoming lodged in the teeth of rim sprockets resulting in uneven wear and increased vibration.Has anyone experienced these problems with rims?

Rick

 

[z4lunch]

Quote...Wonder what a 10 tooth would do on my 394 with the 20" bar?

Steve here... The chain will derail, if the tail of the saw bar isn't tall enough to accomidate the large spocket. I run a 9 pin on my stock 090.
Beside running a modified tall tail sawbar, I also run the bar as close to the sprocket as I can. If not the chain can still derail.
Steven