Chainsaw bar warping (cupping) as I mill?

[whatwhat]

My 42" chainsaw bar is cupped after mill for just a little while. I have a pantherpros mill clamped onto it. I am suspecting it is getting hot and expanding during the cut.

Have any of you experienced this or have any advice on how to deal with this?

After it has cooled down it stays cupped in the mill until I take the mill off, then everything is straight again.

Thank you!

 

[BobL]

My 42" chainsaw bar is cupped after mill for just a little while. I have a pantherpros mill clamped onto it. I am suspecting it is getting hot and expanding during the cut.!

Which way - up or down?

Have any of you experienced this or have any advice on how to deal with this?!

Are you using an Aux oiler?

After it has cooled down it stays cupped in the mill until I take the mill off, then everything is straight again.

That's very odd.

What happens if you warm up the saw/bar out of the mill and then put it into the mill?

 

[whatwhat]

Which way - up or down?


Are you using an Aux oiler?


That's very odd.

What happens if you warm up the saw/bar out of the mill and then put it into the mill?

The bar cups upward so the slabs have a convex bottom.

No auxiliary oiler.

I'd never tried warming the bar up for a few minutes before. I usually leave the saw in the mill at all times.

 

[whatwhat]

I had something similar happen on this log, the chain would jump off the bar when at full revs. The log was from a school yard and full of objects first cut to the last.

That hole top right under the ladder is the beginning of a metal sludge hole. What I did was keep milling even though I hit an object, so the chain was not cutting as should making the bar hot from friction.

I was pulling and re clamping after every cut to get the bow out. I've cut other logs longer and the same width not hitting any objects and have not had that problem again.

Sharp chain & a clean log inner and outer would be my guess.

BobL has some very good posts regarding Raker Angles and info on Hook, which should be taken seriously as milling will never be the same again once put into practice


View attachment 447745

Interesting. I have found that reclamping doesn't seem to help for some reason. Maybe I need to cut slower.

 

[BobL]

The bar cups upward so the slabs have a convex bottom..

Lets see some pics of the mill.
Normally the bar wants to sag downwards but the weight of the powerhead normally helps balance or even remove the sag.
But if the CS head is too heavy for the mill, or too far away from the inboard clamp, the weight of the powerhead will force the bar to bend upwards.
Additional heating of the bar will just make it worse.
You may be able to apply tension between the top of the mill uprights to reduce the cupping but if the mill frame is too lightweight you may end up just bending the uprights.

.

No auxiliary oiler..

then install one as it will help keep the B&C cooler.

 

[whatwhat]

Lets see some pics of the mill.
Normally the bar wants to sag downwards but the weight of the powerhead normally helps balance or even remove the sag.
But if the CS head is too heavy for the mill, or too far away from the inboard clamp, the weight of the powerhead will force the bar to bend upwards.
Additional heating of the bar will just make it worse.
You may be able to apply tension between the top of the mill uprights to reduce the cupping but if the mill frame is too lightweight you may end up just bending the uprights.

. then install one as it will help keep the B&C cooler.

Here is the set up at full length the cupping happens if the mill is extended somewhere int he last third of the bar. I am thinking I may need a longer bar, just for strength. It cut just gets harder and harder to make as the cupping increases the thickness of the slab as I continue to cut. I feel like chainsaw milling shouldn't be THIS back breaking.

Let me know what you think.

 

[Robin Wood]

have you sharpened the cutters or tapped the rakers recently ?

 

[whatwhat]

have you sharpened the cutters or tapped the rakers recently ?

Yes I have. Stihl style ripping chain and I dropped the rakers to 0.30.

 

[BobL]

View attachment 448373
Here is the set up at full length the cupping happens if the mill is extended somewhere int he last third of the bar. I am thinking I may need a longer bar, just for strength. It cut just gets harder and harder to make as the cupping increases the thickness of the slab as I continue to cut. I feel like chainsaw milling shouldn't be THIS back breaking.
Let me know what you think.

Hmm . . . .090 - one of the heaviest and most vibrating powerheads there are.
Perch and clamp the mill on a ladder between two saw horses ( just like it was going to be cutting a log) and stand and take a photo directly behind the mill and level with the bar
How much wobble (up and down) is there in the powerhead.
Even a little movement will cause the bar to move up and down especially with the 090 vibe.
The weight of the powerhead will make the "down" amplitude bigger than the "up" amplitude which could be enough to cause the bar to dive.
You could try and provide some support between the mill uprights and then down to the 090 trigger handle (connecting to the wrap handle won't do much).
Something like a SS wire and a large turnbuckle might do it.


It also looks like you have removed the dogs?
If the 090 dogs are on that very heavy powerhead is really going to be hanging out in the breeze and cause a worse problem.

If your winch is pulling directly on the log from that position then this will contribute to the problem by constantly tipping the mill during the cut .
Have a look in Will Malloff's book on Chainsaw Lumber Making about how to attach a winch to a mill for minimum tipping.
Short bar on an 090 should not need a winch at all if the chain is sharpened right.

 

[whatwhat]

Hmm . . . .090 - one of the heaviest and most vibrating powerheads there are.
Perch and clamp the mill on a ladder between two saw horses ( just like it was going to be cutting a log) and stand and take a photo directly behind the mill and level with the bar
How much wobble (up and down) is there in the powerhead.
Even a little movement will cause the bar to move up and down especially with the 090 vibe.
The weight of the powerhead will make the "down" amplitude bigger than the "up" amplitude which could be enough to cause the bar to dive.
You could try and provide some support between the mill uprights and then down to the 090 trigger handle (connecting to the wrap handle won't do much).
Something like a SS wire and a large turnbuckle might do it.
View attachment 448484

It also looks like you have removed the dogs?
If the 090 dogs are on that very heavy powerhead is really going to be hanging out in the breeze and cause a worse problem.

If your winch is pulling directly on the log from that position then this will contribute to the problem by constantly tipping the mill during the cut .
Have a look in Will Malloff's book on Chainsaw Lumber Making about how to attach a winch to a mill for minimum tipping.
Short bar on an 090 should not need a winch at all if the chain is sharpened right.

I'll check out the wobble as you suggested.

I did add more pulleys in specific places for the winch to pull equally. Regardless, the cupping happens if I use the winch or not, unfortunately.

I did take the dogs off to get the maximum cutting width I could for that mill when I needed it.

What grinds should I be using on my chain? What cutting rate should I be expecting?

Right now it takes me ~15 min and an entire tank of gas and bar oil to finish one cut on a 36" diameter Poplar log, 8 ft long. That feels quite long to me.

 

[BobL]

I've never milled poplar so can't comment on cutting speed in this timber,

The 090 is a relatively high torque slow revving power head so to take advantage of the the high torque much lower than usual rakers are required.

This post explains chain angles etc
http://www.arboristsite.com/communi...nts-tips-and-tricks.93458/page-6#post-4107285

In this thread I talk about raker angles. This is NOT the angle on the top of the raker but the angle between the raker, cutter tip and the wood.
For milling you need to start at around 6º - standard chains start at around 5.5º and as the chain wears this angle gets smaller and smaller.
On an 090 in softwood you could get away with 10º but it would vibrate pretty badly. MntGun on this forum says he uses 9º in softwoods with an 066 so you could at least that.
Post some side on pics side of your cutters and we can comment on the grind.

 

[Robin Wood]

so i assume the cupping happened before you started filing the chain
or when it was still new
is the b&c new ?
take out the b&c from the power head and try sliding the chain along the bar
and see if it catches anywhere it between
it should slide freely and shouldn't stuck anywhere
let us know how it goess

 

[Kroll]

Hey yall! New to the site and to milling. Thanks to all that have shared here. Greatly appreciated! I have a 24" panther mill. Mine had problems out of the box. Square and flat issues but were easily fixed. Not bashing, I love it. Posting because lighter construction and heat were mentioned. I agree. Mine heats up because of exhaust, different from your set up I know, but the thin tubing on these do heat up easily. Thought I trashed my saw my first time out! When I shut it down after a couple cuts it creeked and popped for about 5 min or so. Turns out it wasn't the saw it was the mill as it cooled. Between the heat and some of the squareness issues I've experienced, might be something to look into.

 

[BobL]

Welcome aboard Kroll.

Hey yall! New to the site and to milling. Thanks to all that have shared here. Greatly appreciated! I have a 24" panther mill. Mine had problems out of the box. Square and flat issues but were easily fixed. Not bashing, I love it. Posting because lighter construction and heat were mentioned. I agree. Mine heats up because of exhaust, different from your set up I know, but the thin tubing on these do heat up easily. Thought I trashed my saw my first time out! When I shut it down after a couple cuts it creeked and popped for about 5 min or so. Turns out it wasn't the saw it was the mill as it cooled. .

Well I didn't think of heat being a issue, but it makes sense and if it is the case then it would just add to the other problems.
One way to test this is to make deep and shallow cuts.
On a shallow cut the exhaust will be closer to and heat up the mill much more than on a deep cut.

If it is the heat then an exhaust deflector should make a big difference help.
This is my deflector - not because my mill was suffering from exhaust heating but I just did't like the way the exhaust was bouncing off the log up into my face.
This pipe is also 3/4" ID compared to the regular opening of 9/16" - this helps keep the saw a bit cooler and it remains within the range of the H screw setting - it doe chew a bit more mix.

 

[BobL]

Something else I though of is;
if the bar is drilled and mounted though the drilled holes onto the mill and one of the bar holes (the inboard one) is slotted by an extra 1/4" the bolt can the slide along the slot to accommodate the mill expansion.

 

[Kroll]

Thanks for the welcome. I know my comment about the heat is a little thin concerning the op's setup. But just something i noticed with mine. Read back thru and saw the support you drew, didn't see it earlier. Good idea. Mine had a lot of flex, built a new skid bar with another cross piece on the tip end and fixed it. Drilled thru the sprocket too. Makes things a little easier to set up. I lack a lot of knowledge and experience in milling but learning as I go. I do like the mill but it does have its quirks. Took the time to figure them out before I tried to mill. And thanks for the muffler advice. Saw yours in other posts, very nice.