# Chain tension on longer bars when milling.



## Rob D (Feb 27, 2010)

Hi all. I was looking to see how others judge a correct tension on long bars. I have an 880 and find that I really have to use a fair bit of force to get good tension on the chain with bars 48"+ so that when you pull the chain off the bar it snaps back into place.

I find if the chain is not tight then as you're milling it jumps a little way off the back of the bar which to me does not look right.


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## dave k (Feb 27, 2010)

Hi Rob I was talking about you a few weeks ago with the supplier of my pal's band mill, it's a small world ! 
It's a tough one with the long bars as we all use different oils which make a big difference to running temps so chain strech is pretty subjective I go to the side of tight when setting cold and have no problems on 090 with 60" Stihl rolltip.
You should post up plenty of pics of your work with the Alaskans.


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## BobL (Feb 27, 2010)

Rob D said:


> Hi all. I was looking to see how others judge a correct tension on long bars. I have an 880 and find that I really have to use a fair bit of force to get good tension on the chain with bars 48"+ so that when you pull the chain off the bar it snaps back into place.
> 
> I find if the chain is not tight then as you're milling it jumps a little way off the back of the bar which to me does not look right.



The chain leaping up off the back of the bar like that under higher rpm is pretty normal even if is scary. That's one reason why I made my mill out of as much ally as possible so that when it does jump off there is usually little damage.

Here's what happened when the chain came off because I left the nose clamp loose.






It's interesting how it leaps off the more when its free running than cutting. The worse time I find is when starting the cut and the chain expands as it warms up quicker than the bar. Once the chain is fully in the cut it rarely comes off.

As for adjustment, the longer the chain the tighter is has to be and I'd like to have something more precise than "snaps back into place". I have been thinking about designing some kind of forceometer to do this consistently - anyone have any ideas?


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## gr8scott72 (Feb 27, 2010)

One thing I have found that helps me is when I first put a chain on, I will run it for a minute or so then I will retighten the chain and THEN I mount it on the mill.


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## gemniii (Feb 27, 2010)

BobL said:


> I have been thinking about designing some kind of forceometer to do this consistently - anyone have any ideas?


Get a pocket scale
http://www.tackletour.com/reviewberkleyscale.html for example.


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## BobL (Feb 27, 2010)

gemniii said:


> Get a pocket scale
> http://www.tackletour.com/reviewberkleyscale.html for example.



Could be a simple solution. I would now just need to work out how much force is needed to pull the chain say clear of the rails.


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## huskyhank (Feb 27, 2010)

As Scott wrote, running the saw a little, re-tightening the chain and then mounting it helps. But I don't have a 60" bar yet, it will be here soon. I usually run the chain where I can just move it with my hand without a lot of drag.


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## gr8scott72 (Feb 27, 2010)

huskyhank said:


> As Scott wrote, running the saw a little, re-tightening the chain and then mounting it helps. But I don't have a 60" bar yet, it will be here soon. I usually run the chain where I can just move it with my hand without a lot of drag.



Oh, an easy way to run a chainsaw with a 60" chain on it without fear of it hitting the dirt and not having to hold it up is using one of those stump vises. Like this:

https://www.baileysonline.com/itemdetail.asp?item=15246

Just be sure you have it tight!!:hmm3grin2orange:


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## BobL (Feb 28, 2010)

gr8scott72 said:


> Oh, an easy way to run a chainsaw with a 60" chain on it without fear of it hitting the dirt and not having to hold it up is using one of those stump vises. Like this:
> 
> https://www.baileysonline.com/itemdetail.asp?item=15246
> 
> Just be sure you have it tight!!:hmm3grin2orange:



That's why I have recesses in my service table - they hold the mill/saw on the table while turning, and warming up or cooling down.


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## gr8scott72 (Feb 28, 2010)

BobL said:


> That's why I have recesses in my service table - they hold the mill/saw on the table while turning, and warming up or cooling down.



Well, with the Husky, I have to take it off the mill to tighten the chain. Can't reach the screw otherwise. That's why I like to run it a little and then retighten it before mounting it on the mill.


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## gemniii (Feb 28, 2010)

gr8scott72 said:


> Well, with the Husky, I have to take it off the mill to tighten the chain. Can't reach the screw otherwise. That's why I like to run it a little and then retighten it before mounting it on the mill.


And not jumping on your husky, but for the edification of other readers:
That's why when I actually bought a saw for CSM I had to have an inboard clutch and a side chain tensioner.

The JD CS 62 I won has an inboard clutch and "inside" or "forward" chain tensioner. With a new chain I'd let it slop a bit before I went to partially dissassemble and tighten the chain. Always an excuse for a break.
With the Stihl 660 yesterday, new chain, had to re-tension 4 times, simply pop it on the side, loosen two nut's, rotate screw a bit, tighten nuts, good to go. No excuse for a break.


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## BobL (Feb 28, 2010)

gr8scott72 said:


> Well, with the Husky, I have to take it off the mill to tighten the chain. Can't reach the screw otherwise. That's why I like to run it a little and then retighten it before mounting it on the mill.



What about drilling a hole through the bar clamp like this?




We then took a screwdriver and ground the blade down so it passes through the hole - saves taking it out of the mill to readjust the chaion


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## huskyhank (Feb 28, 2010)

How about clamping the mill on a little bit away from the saw so you can angle a screwdriver in to reach the screw? Works for me on my 3120. I will likely drill a hole as BobL shows someday.


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## Rob D (Feb 28, 2010)

dave k said:


> Hi Rob I was talking about you a few weeks ago with the supplier of my pal's band mill, it's a small world !
> It's a tough one with the long bars as we all use different oils which make a big difference to running temps so chain strech is pretty subjective I go to the side of tight when setting cold and have no problems on 090 with 60" Stihl rolltip.
> You should post up plenty of pics of your work with the Alaskans.




Hi Dave. Yes it is indeed a small world! I'm usually an Arbtalk man (and still am!) but want to up my game hence trying to get more info. Looking at previous threads on this forum there's a wealth of knowledge on here. And other members look to be customising stuff 

Thanks for all the feedback. With the longer bars I do have the chain on quite tight. If not tight and the saw is revving high the chain seems to hover just above the back of the bar (this is what I meant more by jumping off the bar).

I'll try and get a vid of this up to be clear. But I find I have to use the exact right size screwdriver on the tensioning screw to get that last bit of tension on it as it needs a fair bit of effort.

I've had 3 MS880s and found this to be the case on each.... suddenly thought the other day "maybe I'm going for too much tension!"


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## BobL (Feb 28, 2010)

Rob D said:


> I'll try and get a vid of this up to be clear.


Yeah I know what you mean about the hover, it makes me a tad nervous when I see this too.



> But I find I have to use the exact right size screwdriver on the tensioning screw to get that last bit of tension on it as it needs a fair bit of effort.



Humm, . . . . . that doesn't sound quite right to me. I get mine to kiss the bar from underneath and then use maybe 1/8th turn more - I just use the screwdriver part of a scrench.

However, it would really be good to be able to quantify the tension. One should be able to hang a known weight from the middle of the chain so that maybe the middle drive link just clears the bar. I'll do the vector math on it tomorrow to see if that provides enough sensitivity.


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## Rob D (Feb 28, 2010)

Thanks Bob looking forward to seeing what you come up with.


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## Andrew96 (Mar 1, 2010)

I too thought this chain tension stuff on long bars was too subjective...and I don't even have a 'long' bar. Trying to balance a derailment (too much slack)...with bar wear/heat (too much tension) was too hard to do repeatedly. I use a little baggage scale we had already. The objective was to find a mass/deflection number that was just loose enough to stay in the bar nice...yet not derail if overheated (finishing the slab rather than stop and sharpen). That in my opinion was the two extremes...offer some small amount of slackness..with no chance of derailment even if overheated to a reasonable amount. 
I set chain tension, on a 660 with 36" bar, cold... pulling the chain from the cutter with 1kg of force...very close to my subjective tension (3-5mm deflection). Once hot (usually after my first cut) it might be close but I reset using only 500grams of force for the following real cut. That seems to be good for me. 500g moves the chain in the center of the bar 3-5mm away from the bar. So far, for each pass (I haven't milled in a few months now), I hook the baggage scale and see if I'm still 'about' 3-5mm off the bar. I'll do this until I calibrate my fingers and do a better job subjectively. Free spinning up the chain doesn't have it bouncing around causing you guys stress. Heated chain stays in the bar grooves for more than one slab.
This BTW is the same method you use to adjust the track tension on a snowmobile (hang known mass to obtain known deflection on warm track). Another belt type driven system that reacts wildly to heat variations..doesn't like to derail/nor be too tight. I just guessed a mass and deflection for the chain/bar. 
Maybe we can all have a go using a standard procedure and see if we cannot quantify this issue for various bar lengths...or teach me how to properly set chain tension if you feel mine is wrong. 
For me...36" bar, hot chain, 500g = 3-5mm deflection measured near center of bar. Or for you guys down in the states....1 lb. = 0.1" - 0.2" of deflection.


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## aggiewoodbutchr (Mar 1, 2010)

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.


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## rxe (Mar 1, 2010)

> What about drilling a hole through the bar clamp like this?



You, sir, are a genius! I've been cursing my 070s for a while now - this will solve the problem!


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## gr8scott72 (Mar 1, 2010)

BobL said:


> What about drilling a hole through the bar clamp like this?



It's a great idea but the chain seems to stay tight for me even between runs on different days. 

Really the only time I have to adjust it is when I put a different chain on there and I have to take it off the mill to do that anyways.


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## BobL (Mar 1, 2010)

aggiewoodbutchr said:


> 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.


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## aggiewoodbutchr (Mar 2, 2010)

BobL said:


> 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 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!


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## huebi (Mar 9, 2010)

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....


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## BobL (Mar 9, 2010)

huebi said:


> 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?


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## aggiewoodbutchr (Mar 9, 2010)

BobL said:


> 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.


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## huebi (Mar 9, 2010)

BobL said:


> 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


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## huebi (Mar 10, 2010)

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.


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## BobL (Mar 10, 2010)

huebi said:


> 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, . . . . ?


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## huebi (Mar 10, 2010)

BobL said:


> 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.


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## huskyhank (Mar 10, 2010)

huebi,

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


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## huebi (Mar 10, 2010)

Thank you!

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


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## huskyhank (Mar 10, 2010)

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


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## huebi (Mar 11, 2010)

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.


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## huskyhank (Mar 11, 2010)

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.


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## huskyhank (Mar 11, 2010)

More here:

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


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## BobL (Mar 12, 2010)

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.


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## huskyhank (Mar 12, 2010)

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


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## BobL (Mar 12, 2010)

huskyhank said:


> 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!


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## huskyhank (Mar 12, 2010)

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.


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## huebi (Mar 12, 2010)

BobL said:


> 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


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## BobL (Mar 12, 2010)

huskyhank said:


> 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.



Humm, . . . chain tension is not that big a deal for me. 

Time and weather still way too hot is the biggest deal for me right now. Today it was 106F (for you guys that would be like having a 106F day in the middle of September)

Probably the most restrictive deal for me is not having access to a loader to handle big slabs in certain situations. Meanwhile these logs continue to rot!

Double ender sounds like the way to go though. I might just make my own ?


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