Pushing the limits of Lo Pro

[Coralillo Lo Pro]

Got that part now I put my hands on a saw and thought it thru. There is notable tension on the nose sprocket but no, Lightning is wrong in one major way. He’s suggesting the drive sprocket load was transferred to the nose sprocket which makes no sense at all and defies the laws of physics and chainsaw functioning. The nose sprocket is a pulley and the chain would not turn if all the load was there. The rim sprocket as the drive is still carrying the vast bulk of the load. If the chain is tight enough it forces it forward in the rail counterbalancing that nose tension and completely overcoming it. If the chain is loose it bunches up and potentially derails, why you can cut w loose chain w bottom of bar cutting but w top of bar invites disaster. As Tony’s experience bears out, w a reasonably snug chain the tension effects of top bar cutting as far as nose sprocket wear are relatively inconsequential. Debris is the major culprit in nose sprocket wear. Shooting noodle shavings directly into the nose sprocket would definitely overheat it. They don’t all spit cleanly free off the tip. Noodling seems a terrible idea no matter which way you go at it. It’s 100 degrees every day here. Easy enough for me to try top bar milling in fine sawdust hardwood to see if I experience any especially bad nose sprocket heating. Glad for the discussion and helping me think out all the pros and cons, but not the absolutism of declaring people right that aren’t.

 

[SeMoTony]

May not be thinking this all the way out but as nose is just a carrying sprocket not a drive sprocket, don’t see any load difference there from physics of cutting w bar top vs bottom. Heat in nose sprocket would seem to be result of friction of sawdust spewing into it. Noodling would dramatically increase that. Yes, a lot will spit off the tip but even carried partially around that drag will really heat up the sprocket. So could totally see it resulting in a wear issue. Normally the vast bulk of debris ejects out the power head side so the nose sprocket sees little of it. But spitting all directly into nose sprocket it sees all of it. For fine dust of hardwoods probably not an issue. For noodling and softwoods could see it being a major friction issue.

Physics says an object in motion stays in motion (on same path) by leaving safety guard off the nose sprocket, chips spewed about 12 foot using ported 661on a maple ,cutters are not attached to chips or dust as ¥using top of bar ms460 42" b&c 34" ash log. Stopped mid slice to show the type angle used to not have 90° to grain. The push of the cutters was part of feed along with the bit o down hill on this healthy ash below
From doing I learned more n more
G'day gents

 

[Coralillo Lo Pro]

Physics says an object in motion stays in motion (on same path) by leaving safety guard off the nose sprocket, chips spewed about 12 foot using ported 661on a maple ,cutters are not attached to chips or dustusing top of bar ms460 42" b&c 34" ash log. Stopped mid slice to show the type angle used to not have 90° to grain.

No argument there. Exactly result I’d expect in hardwood. Would take large shavings like noodles stuck in the teeth to not spit free from centrifugal force. I see the effect of top bar cutting on both nose sprocket wear and saw power as about the same as running a slightly more snug chain than is max efficient. But as that decreases side to side chain slop it can actually mean faster cleaner milling w your saw bogging less so I normally run w some extra friction anyway. We can talk theory til blue in the face but real world milling results are the only thing that matter. Yours seem good.

 

[Lightning Performance]

Lightning and jd are 100% correct. When cutting with the bottom the chain is pulled tight by the drive sprocket, the too side has little basically no tension on it. Top aide cutting the inverse is true, the drive sprocket is still pulling the chain around the bar, but now your work is on top, meaning the chain is fully tensioned around the nose of the bar to where your cutting. Any slop in the chain will still be in the top side before the area where the chain is engaged in the wood.

That rain "roll" or curl on top seems to pull in chip is my best guess. This is likely why the nose started getting hot. The added load is one factor but the open slot area is probably a bigger one adding to the friction dragging in the crumbs. A camera there filming might shed more light on that. All my drivers normally turn black on both sides from pitch. Cutting with the top turns them shinny silver. It might be a good way to clean off the pitch on dirty chains or completely weld it on the drive links. It definitely fills the rail slot under the drivers with packed in chips and dust.

 

[Coralillo Lo Pro]

That rain "roll" or curl on top seems to pull in chip is my best guess. This is likely why the nose started getting hot. The added load is one factor but the open slot area is probably a bigger one adding to the friction dragging in the crumbs. A camera there filming might shed more light on that. All my drivers normally turn black on both sides from pitch. Cutting with the top turns them shinny silver. It might be a good way to clean off the pitch on dirty chains or completely weld it on the drive links. It definitely fills the rail slot under the drivers with packed in chips and dust.

One of the most interesting engineering/physics equations I’ve pondered in chainsaws. Even an engineer I consulted who worked on the SR-71 Blackbird admits this is complicated. The understandable tendency is to view this as a static forces pulley problem in which case it seems obvious. Initial load is all focused on top of nose sprocket rather than bottom of rim sprocket. But it’s not a simple static load and tension pulley system. It’a dynamic system with a high speed drive, the “effort” force to overcome the load. I started only talking about drive loads as “load” when that’s more precisely effort. Lightning is correct that top bar cutting does transfer the initial load to the top of the nose sprocket vs bottom bar cutting the initial load is felt as pull by the bottom part of the drive sprocket. If you totally bog the saw down to a stop top bar cutting there will be a lot of force on the nose sprocket. But then it will be a static load without the sprocket turning to create friction and heat. If you partially bog it down heavily, I could see it creating a lot of heat. But in a high rpm chain loop system driven by the effort forces of the drive sprocket which dramatically overwhelm load forces (chain drag from cutting), a whole new set of tension points are created in the loop. It all gets hazy to model at this point. But comparatively, forces at this point tend to equal out, they’re just redistributed in the loop. Imagine a chain driven exercise bicycle w a spinning wheel. If you’re pedaling high speed and someone places light drag pressure on the chain, it doesn’t matter really if they do it on top of the chain or bottom of chain. Will still slow you down the same amount. Bottom bar cutting creates a tight chain on top of the bar - thus still a tension on the nose sprocket - and the sag of loose chain bunches up before the cutting edge contacts on the bottom side. So I had that wrong about which was worse for derailing chain, they both should be about the same, just different places. Maybe bottom bar cutting worse actually because w looseness at front underside of bar, centrifugal force of nose sprocket will want to spit chain outward due to that looseness instead of being pulled around the sprocket.

 

[Lightning Performance]

One of the most interesting engineering/physics equations I’ve pondered in chainsaws. Even an engineer I consulted who worked on the SR-71 Blackbird admits this is complicated. The understandable tendency is to view this as a static forces pulley problem in which case it seems obvious. Initial load is all focused on top of nose sprocket rather than bottom of rim sprocket. But it’s not a simple static load and tension pulley system. It’a dynamic system with a high speed drive, the “effort” force to overcome the load. I started only talking about drive loads as “load” when that’s more precisely effort. Lightning is correct that top bar cutting does transfer the initial load to the top of the nose sprocket vs bottom bar cutting the initial load is felt as pull by the bottom part of the drive sprocket. If you totally bog the saw down to a stop top bar cutting there will be a lot of force on the nose sprocket. But then it will be a static load without the sprocket turning to create friction and heat. If you partially bog it down heavily, I could see it creating a lot of heat. But in a high rpm chain loop system driven by the effort forces of the drive sprocket which dramatically overwhelm load forces (chain drag from cutting), a whole new set of tension points are created in the loop. It all gets hazy to model at this point. But comparatively, forces at this point tend to equal out, they’re just redistributed in the loop. Imagine a chain driven exercise bicycle w a spinning wheel. If you’re pedaling high speed and someone places light drag pressure on the chain, it doesn’t matter really if they do it on top of the chain or bottom of chain. Will still slow you down the same amount. Bottom bar cutting creates a tight chain on top of the bar - thus still a tension on the nose sprocket - and the sag of loose chain bunches up before the cutting edge contacts on the bottom side. So I had that wrong about which was worse for derailing chain, they both should be about the same, just different places. Maybe bottom bar cutting worse actually because w looseness at front underside of bar, centrifugal force of nose sprocket will want to spit chain outward due to that looseness instead of being pulled around the sprocket.

Here is a good add on. The particulate we know adds drag and steam to the equation.

I've thrown the 404 166dl twice milling from the top never from the bottom. That tells me my chain was infact too loose and it is probably not a good idea even with the big Cannon belly bar on there. The bar had a nick in it once near the nose. It never touches the rest of the rails. Lucky it was still new then and dressed out after the first season.

You can see the chain carry all the load on the roller race noses. It will lift sometimes off the nose in the cut when those pipe saws run well.

 

[Coralillo Lo Pro]

Here is a good add on. The particulate we know adds drag and steam to the equation.

I've thrown the 404 166dl twice milling from the top never from the bottom. That tells me my chain was infact too loose and it is probably not a good idea even with the big Cannon belly bar on there. The bar had a nick in it once near the nose. It never touches the rest of the rails. Lucky it was still new then and dressed out after the first season.

You can see the chain carry all the load on the roller race noses. It will lift sometimes off the nose in the cut when those pipe saws run well.

Good point, and I think most people’s experience is similar w throwing chains. The “pushing” and bunching up of the chain in front of the drive sprocket from top cutting may be a lot more problematic. The nose sprocket is tightly abutted w w the nose rails. The drive sprocket isn’t to the tail rails. So would more likely throw chain when bunching up at drive sprocket end. So my gut feeling on that probably was right in the first place. Hadn’t thought that all the way through.

 

[Lightning Performance]

Good point, and I think most people’s experience is similar w throwing chains. The “pushing” and bunching up of the chain in front of the drive sprocket from top cutting may be a lot more problematic. The nose sprocket is tightly abutted w w the nose rails. The drive sprocket isn’t to the tail rails. So would more likely throw chain when bunching up at drive sprocket end. So my gut feeling on that probably was right in the first place. Hadn’t thought that all the way through.

In a heavy peice of 45" wide oak running full comp 404 LX you can watch the chain climb right up off the bar as it leaves the power head. That bar is nearly 4" tall exiting my cases. The GB 404 40" roller nose does the same thing cutting from the top but is smaller with no belly. It acually clears the whole bar if the chain isn't very tight. That bar is mean in anything. Welded nose from factory and there is no repair for it or so they thought. I'll add a bearing and just make it longer when it finally does wear out. So far so good and I got it used with a 138dl links of 3/8 on it so the nose has plenty of clearance now. 404 drivers ride on the internal roller.