Chain tension on longer bars when milling.

[Rob D]

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.

 

[dave k]

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.

 

[BobL]

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?

 

[gr8scott72]

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.

 

[gemniii]

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.

 

[BobL]

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.

 

[huskyhank]

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.

 

[gr8scott72]

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:

 

[BobL]

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.

 

[gr8scott72]

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.

 

[gemniii]

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.

 

[BobL]

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

 

[huskyhank]

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.

 

[Rob D]

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!"

 

[BobL]

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.

 

[Rob D]

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

 

[Andrew96]

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.

 

[aggiewoodbutchr]

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.

 

[rxe]

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!

 

[gr8scott72]

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.