Chain Speed on Different Bars

firecracker_77 Posted By firecracker_77, Aug 25, 2013 at 5:25 PM

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  1. firecracker_77

    firecracker_77
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    So...this may be an obvious thought, but if my saw sprocket rotates at X rpm and I change the bar size downwards, the shorter chain makes a full revolution in less time. So if you dropped a bar size from 32 down to 16 inches, the chain is traveling at double the rpm? If that's the case, I'm getting a super short bar for my 441 and the thing will rip and tear.
     
  2. TreePointer

    TreePointer
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    Assumptions:for this discussion:
    1. Both bars have the same diameter tip sprocket.
    2. Both bars are run with no load (not in wood).

    The linear chain speed is constant. The rotation speed of the sprockets is constant. Both of these are determined by the speed of the drive sprocket, which is determined by engine rpm. The drive sprocket has enough power to make the difference in chain mass and friction negligible.

    Analogy:

    You travel at 65 mph on a mile track and a half mile track. For a given time interval, you will travel around the shorter track twice as many times as the mile track. Your wheels will not rotate faster on the shorter track.
     
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  3. StihlHead

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    Excellent analogy by TreePointer above.

    In general though, your WOT chain speed will likely increase some with the shorter bar (less drag and friction). Hence you may need to re-tune your saw when you put on a shorter bar to keep the engine from over-revving. The engine rev limit would also keep your original idea from becoming a reality (you would blow your 441 engine with 2x fast spinning loops).

    Also, there is no free lunch. Power is torque x revs, so if you get more revs, the torque drops and you will bog the saw a lot easier. The flip side is that with a shorter bar, you may have torque to spare, so swapping out to a larger rim will increase your chain speed w/o bogging. I usually use an 8 slot rim with 16-18 inch bars on my 361s, and with 18-20 inch bars on my 044. Inboard clutch saws are great for that. Try an 8 slot rim on your 441 with a 16-20 inch bar. They are pretty cheap, and more revs work well when doing some types of cutting. The power remains the same, but revs increase and torque drops. The default rim on the 441 saws is a 7 slot.
     
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  4. firecracker_77

    firecracker_77
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    I somewhat understand. Not completely.

    On a shorter chain, a specific cutter will pass through the wood twice as often on a bar half as long so it's moving twice as quickly?
     
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  5. StihlHead

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    You are stuck on your original track. It is not moving twice as quickly (or fast), but traveling half the distance.
     
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  6. TreePointer

    TreePointer
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    True, one specific cutter will pass through the wood more frequently on a shorter chain (it's traveling on the shorter track). That would be one cutter doing, say, twice the work in a given time period. While each individual cutter on a long chain will have fewer passes through the wood in a given time period, there are many more cutters doing work in that longer chain.

    To put it another way, the speed (linear chain speed, ft/s) at which a single tooth passes through the wood does not change when you chain bar length. The frequency an individual tooth makes a pass through the wood does change.
     
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  7. MasterMech

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    If you want it to rip and tear, bump the size of the sprocket up. If you've been watching the videos of my MS460 that I've put up, that saw is running a 20" bar with an 8 pin rim. It rips alright.... ::-)
     
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  8. TreePointer

    TreePointer
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    Bingo!

    There's your increased chain speed.
     
  9. JOHN BOY

    JOHN BOY
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    Try a 18 inch bar you'll be amazed. I agree with the statements above but also disagree to some extent that a 32 inch bar will also have more drag going throw the wood. Frankly i wouldnt run anything bigger then a 25 on the 441 , but thats just me.
     
  10. firecracker_77

    firecracker_77
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    That's great b/c it's the bar that came with it and I have bought a spare chain. I would never go bigger than a 25". I like smaller stuff... which is why I told them to downgrade my 290 to a 16" bar when I bought that one last October.
     
  11. DexterDay

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    Put an 18" and an 8 pin rim on that 441 and she will RIP!!!

    Changing to the 8 pin changes the gearing, which will increase the actual chain speed. But with a loss of torque. But by dropping 7" of bar length, you won't need as much torque. Once you step over 20", then slap the 7 pin back on...

    I like to run 20" 8 pin rim on my 460 mag... Makes me smile :) A lot.... ;)

    image.jpg
     
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  12. JOHN BOY

    JOHN BOY
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    Thats what i run on the 044 ,and nothing stops it. A muuffler mod on the 290 will really wake that saw up...there so restricted.:(
     
  13. firecracker_77

    firecracker_77
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    I would screw up a muffler mod. I'm not mechanical.
     
  14. MasterMech

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    If you can operate a handheld drill, you can do a MM on that 290. You only have to pull the deflector cover really to get it done. The more difficult part would be re-tuning the carb but I bet a dealer would do that for you for free, seeing as how you just bought that pretty new 441C-M and stuff. ;)
     
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  15. Gary_602z

    Gary_602z
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    Come on Dexter, nobody keeps their tools hung up and runs a saw with with a worn out bar like yours!:)

    Gary
     
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  16. amateur cutter

    amateur cutter
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    8 pin on my 046 with a 20" bar, is a really nice combo. I also run the 8 pin on the 064 at 24" with skip chain. Does well for me.
    I keep telling you guys, Dex buys His firewood, & polishes His saws for pics. Is that bench carpeted? A C
     
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  17. shawn6596

    shawn6596
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    I run a 670 ECHO with a 24" bar. It is my go to saw. I recently went to a skip tooth chain, and o-my. It is a monster. The oregon skip tooth was only $17. Also some how I lost the top of 2 cutters and I called the guy up and he offered to send me some replacement cutters. I love the chain so much I ordered 2 more and he threw the cutters in. It came to less than $45 for both chains and shipping. I ordered them friday and they were here today.
     
  18. HittinSteel

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    Appears it is!....... and it's cleaner than my living room carpet :eek:
     
  19. MasterMech

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    That's actually not a half-bad idea (the carpet), if you build saws for sale, cosmetic condition is everything when it comes to final value.
     
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  20. Jags

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    Another way to look at this is feet per minute traveled. With a long bar - the chain is moving at xxx ft per minute. Shortening the bar doesn't change this. Only a change in engine RPM or the Gearing (sprocket) can change this. At the same feet per minute - the chain is moving at exactly the same speed no matter how long or short the bar is (not accounting for resistance, etc.). The same amount of cutters are passing a given spot.
     
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  21. MasterMech

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    If the chain sprocket is able to haul say, 80 inches per second (that's roughly 55 MPH ;)), then the length of the chain loop does not affect that. Doesn't matter if you have 40" of chain or 60" in the loop, it still passes a given point at the rate of 80" per second. Only altering the drive sprocket size or the engine RPM will change that rate of 80" per second.
     
  22. lukem

    lukem
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    I usually line my workbench with a big sheet of cardboard (pallet slip-sheets that I get from work) for stuff that is really messy (tear down), or needs to be really clean/prevent scratches (final assembly). I throw out the cardboard like a dirty kleenex once I'm done. A couple staples with the staple gun in two corners keeps them in place nicely.
     
  23. MasterMech

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    I'm currently making do with a makeshift bench fabricated out of a damaged ping-pong table cut in half and screwed together. ;lol
     
  24. firecracker_77

    firecracker_77
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    It makes sense now.
     
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  25. firecracker_77

    firecracker_77
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    How many CC?
     
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