Chain tension on longer bars when milling.

[BobL]

I don't have a scientific answer to your question but my 66" and 72" bars require as much tension I can physically put on them to keep them from jumping off. As others have said, tension-run-tension is the method I use. I keep an eye on it and if I see the chain coming off the back of the bar in the cut I'll stop and re-tension. 12'+ of chain whipping around is not my idea of fun.

Good to see you're still around aggie. Done any more milling lately?

When I first used my 60" bar I was very concerned about chain jump so I deliberately over tighten the chain but after seeing the amount of extra chain and bar wear I was getting I've since gone back to using just a firmer than usual tension. Maybe the 076 just wasn't delivering enough lube at the time.

I get a jump very occasionally on but usually it's because I have been a bit sloppy in adjusting the chain tension. The worst one so far was earlier this year where the jump resulted in the chain coming off the drive sprocket mid slab and the sprocket ground away the tips of about 6 drive links.

Big dry logs are the worst for chain jump on log entry, they're already hard enough to begin with, but that exposed end grain seems even harder, plus they are often dirty and termite infested so they go blunt quicker. This means by the time the mill is near the end of the cut the chain can be blunt and heat up so much it expands and comes off the bar in the cut. BTW I can see the effect of the chain being blunt on any log pretty clearly on my engine temp gauge with the temp being 10 - 15º above normal. Also I can a similar effect with aux oiler on or off and even the chain being too tight.

The approach I have come up with for the chain jump on entry is to, buck the first 6 inches off dry logs and semi-flood the chain with lube. I start the mill at an angle at about 7500 - 8000 rpm, with the nose going in first so that bit of chain that rises off the back of the bar is fully buried first, Then I ease the rest of the bar into the log and finally when the back of the bar is buried in the wood I ease back on the lube and then hit WOT.

 

[aggiewoodbutchr]

Good to see you're still around aggie. Done any more milling lately?

When I first used my 60" bar I was very concerned about chain jump so I deliberately over tighten the chain but after seeing the amount of extra chain and bar wear I was getting I've since gone back to using just a firmer than usual tension. Maybe the 076 just wasn't delivering enough lube at the time.

I get a jump very occasionally on but usually it's because I have been a bit sloppy in adjusting the chain tension. The worst one so far was earlier this year where the jump resulted in the chain coming off the drive sprocket mid slab and the sprocket ground away the tips of about 6 drive links.

Big dry logs are the worst for chain jump on log entry, they're already hard enough to begin with, but that exposed end grain seems even harder, plus they are often dirty and termite infested so they go blunt quicker. This means by the time the mill is near the end of the cut the chain can be blunt and heat up so much it expands and comes off the bar in the cut. BTW I can see the effect of the chain being blunt on any log pretty clearly on my engine temp gauge with the temp being 10 - 15º above normal. Also I can a similar effect with aux oiler on or off and even the chain being too tight.

The approach I have come up with for the chain jump on entry is to, buck the first 6 inches off dry logs and semi-flood the chain with lube. I start the mill at an angle at about 7500 - 8000 rpm, with the nose going in first so that bit of chain that rises off the back of the bar is fully buried first, Then I ease the rest of the bar into the log and finally when the back of the bar is buried in the wood I ease back on the lube and then hit WOT.

I haven't noticed any unusual wear but I know I'm getting plenty oil at both ends. The first few times I used my 72" GB bar I tried just a heavier than usual tension but I was throwing chains pretty often. Since then I tighten them as snug as I can get them on the initial adjustment with out risking damage to the tensioner. Once the chain is warm I don't go nearly as tight on subsequent adjustments if they need them. The 66" WP/Cannon is not nearly as bad as the 72" because of the belly shape but it still requires a fair amount of tension to prevent the chain from whipping too far off the back of the bar.

You are absolutely correct in your point about too much chain tension. I learned that lesson once when I changed from a 72" to a 42" and out of habit cranked it down. LOTS of smoke real quick!

 

[huebi]

In this video you can see starting at 0:17 a tension mechanism witch works fine for longer bars. The cutting length of the saw is about 75".
http://www.youtube.com/watch?v=32_kTPHUfA4
The tension is held by a compressed round piece of rubber.
I think about a design for standard Stihl Duromatic hard tip bars.
It should also include a mechanically driven oil pump to automatically serve the cutting side of the bar with enough oil. Needs some hard design work....

 

[BobL]

In this video you can see starting at 0:17 a tension mechanism witch works fine for longer bars. The cutting length of the saw is about 75".
http://www.youtube.com/watch?v=32_kTPHUfA4
The tension is held by a compressed round piece of rubber.
I think about a design for standard Stihl Duromatic hard tip bars.
It should also include a mechanically driven oil pump to automatically serve the cutting side of the bar with enough oil. Needs some hard design work....

Thanks Huebi and welcome to AS.

We are not so much worried about "how to tension" chain but "how much to" tension chain.

The video also shows some "scratcher chains" which look very interesting. Anyone know anything about these?

 

[aggiewoodbutchr]

Thanks Huebi and welcome to AS.

We are not so much worried about "how to tension" chain but "how much to" tension chain.

The video also shows some "scratcher chains" which look very interesting. Anyone know anything about these?

http://www.holtecusa.com/holtechome.htm


I left them a message asking for more information. I'm not positive that tooth pattern will work well in an end cut application. My guess is it will be pricey too. I'd be willing to try it if it not outrageous.

 

[huebi]

Thanks Huebi and welcome to AS.

We are not so much worried about "how to tension" chain but "how much to" tension chain.

The video also shows some "scratcher chains" which look very interesting. Anyone know anything about these?

Thank you to make things clear for me. I agree. I think to get the right tension is not too hard. If it's too much tension the chain gets hot and chain and bar will be damaged soon. If the tension is too loose the chain will get some slack on the back side and might jump off the bar. OK, that would be easy if there wouldn't be the heat of the running chain cutting wood. I think a solution to keep the tension right over at least one long cut is needed. The idea is to compensate the chain elongation over time from being cold to being very hot at the end of a cut through dry and hard wood. I took some photos of the stuff I have.

This is the top view of a Holtec tension mechanism. Wheel diameter 100mm.

This is the side view of a Holtec tension mechanism.

This is a very old Stihl tension mechanism with a spring in the black handle on the left. Wheel diameter 72mm.

Back view with oil pump driven by the tension wheel.

Tension Wheel with blue chain bar on the left.

For more pictures just have a look at the directory:

http://www.nagios.us/wood/chain_tensioner/

Sorry for the big pictures

 

[huebi]

I just found out how the chain tension is adjusted on a Holtec saw. On the first picture in my last post you see the chain tension mechanism. This is the picture I revere to.
On the photo the case for the guide skid is missing. The parts are from left to right: Adjustment handle, brass washer, rubber spring, case (missing), guide skid with guide wheel.
On a 74" chain bar the handle for chain tension adjustment handle is screwed in until there is just no gap between all the parts and the chain is positioned in the groove of the guide bar. Now the tension is increased another 4-6mm. This is the minimum tension you need to operate the chain saw safely. The tension is right if you pull the chain off the groove in the middle of the bar with a force of 100 N and the chain is lifted off between 2 cm and 4 cm (0.8" to 1.6"). The chain must always be movable by hand.
As posted at the beginning of this thread they also use a scale to measure the force to get the gap between chain bar and chain.

 

[BobL]

The tension is right if you pull the chain off the groove in the middle of the bar with a force of 100 N and the chain is lifted off between 2 cm and 4 cm (0.8" to 1.6"). The chain must always be movable by hand.

Thanks huebu.

Which part of the chain are you referring to, the bottom of the drivers, or the bottom of the ties or, . . . . ?

 

[huebi]

Thanks huebu.

Which part of the chain are you referring to, the bottom of the drivers, or the bottom of the ties or, . . . . ?

I'm referring to the ties. so the gap between the ties and the surface they glide on is 2-4cm wide. But keep in mind that there is the elastic rubber spring in the tension mechanism.

 

[huskyhank]

huebi,

I re-sized your photographs so they are easier to view.

 

[huebi]

Thank you!

I changed the links in my posting to the smaller pictures.

 

[huskyhank]

That looks like a great solution to tensioning the chain on long bars.
Do you get good results when you use this?

 

[huebi]

I did not use any of the above for myself.
I got the worn Holtec stuff from a mechanic working on theses machines. He told me that it lasts for at least a year under heavy industrial conditions with low effort on maintenance.
The smaller green box is the military edition of the front handle/tensioner/oiler of a two men chain saw made by Stihl a few decades ago.
I try to get the Holtec tensioner on a normal chain saw bar. I like the rubber spring more than the steel spring in the Stihl mechanism. And most of all spare parts are available from Holtec.

 

[huskyhank]

Here is a video showing a Holtec portable saw in use.
The orange thing on the end of the saw bar is what huebi posted photos of.

http://www.youtube.com/watch?v=hBWW_TM0KA4


It seems to me a tensioner like this would work great on a CSM.

 

[huskyhank]

More here:

http://www.youtube.com/watch?v=32_kTPHUfA4&NR=1

 

[BobL]

I've thought many times about using something like that ype of chain tensioner, but the problem with that is it eats up valuable cutting width.

 

[huskyhank]

Yes, but if its on a 60" or longer bar maybe the convenience and better performance would be worth it.

 

[BobL]

Yes, but if its on a 60" or longer bar maybe the convenience and better performance would be worth it.

Might put it on the ToDo list for the MonsterBIL mill!

 

[huskyhank]

I'm kinda wishing (now that I have my 60" single end bar) that I had a double ender to be able to use a nose tensioner. I guess I'll see soon enough how aggravating a 60" bar can be. My 42" is no big deal.

 

[huebi]

I've thought many times about using something like that ype of chain tensioner, but the problem with that is it eats up valuable cutting width.

Hello BobL.

I can see your concerns. My thoughts about the separate chain tensioner are these: Only if I have a long bar I need an extra chain tensioner to keep the tension of the chain not too hard when the chain is cold and not too loose when only the chain is hot before the bar heated up, too.
When I use a long bar in a saw mill the tip of the bar must be guided in some way. Therefore I need a guide fixed on the tip. Here I will always loose cutting width. Necessarily I may not need more space of the bar to clamp the tensioner on it than with the normal clamp. I definitely need a longer chain. But that should be all impact on the saw mill.

Regards,
huebi