84" Alaskan Mill issues

[J Holtby]

Been having a few issues with the Alaskan mill, and I know I'm pushing it to its limits with a 84" bar, but wondering if anyone has been through this and has a better work around than I do!

 

Had a search through the forums already but as its a bit of a complex issue, not really hit on a similar issue, if its been discussed before, apologies

 

In short, the bar is, for want of a better description, 'sagging' or 'bowing'under cutting, and cutting a minor cup/trough into the wood. 

 

I have a feeling its simply flex in the Alaskans legs - as I push the frame along the top, there is resistance at the bar, the legs flex back slightly, pitching the bar down slightly, cutting down into the wood, and the easiest way the mill can accommodate the slight increase in thickness is the bar slowly growing a 'bow' along the woods length

 

To get around this, with 2 people we can evenly push both at frame and bar height, but when cutting solo its a real issue, sometimes the mill totally seizes and binds in the log (this has only happened a couple of times but a huge pain in the ass when it does!)

 

I've got a good router sled set up, so flattening the slabs isn't an issue, but reducing the error at the milling stage would be something Id love to improve upon

 

Cheers for any input, lashed up some pictures, hopefully the one with the level across will illustrate the issue

 

Joe

[Rough Hewn]

One way if find useful,
When putting the bar on the mill, put a plank under the bar to keep it flat whilst you tension the mill.
Are you using a reliable grinder to sharpen the chain?
Is that a granberg?
[emoji106]

[Big J]

It's more or less impossible to stop this on bars this length. It makes the cut much, much harder on the operator and machinery. It snaps chains, wears out sprockets rapidly and actually destroyed on almost new MS880 (which thankfully Stihl replaced). 

 

Wide cutting with chainsawmills was the final straw and I haven't touched a chainsawmill since. Up to about a 50" bar it's great, but beyond that you get bar sag.

 

What is needed is a bar tensioning system to eliminate this.

[trigger_andy]

84" with one Saw? How do you find that works out? (Aside from the obvious in this post) What kind of speeds do you get?

[CDMR]

You could find a shallower first cut would help. The deeper the cut the more leverage a sagging bar can put on the upper mount of the vertical pillars.

 

Big J's idea re tensioning could be worth a try too. How about a ratchet strap around the tops of the vertical pillars? As the bar sags they will want to move outward so it might prevent them from doing so.

 

Whether the mill frame will be happy to accept all these opposing forces, who knows.

[J Holtby]

Rough Hewn, yes, granberg chain, which Ive found great, but hearing good things about the hyperskip stuff, anyone know what its like?

 

Big J - what do you use now? bandsaw? some of the pieces Ive milled (forks/crowns of trees etc) are over 6ft, what bandsaws are out there that could handle that?

 

Trigger - it took about 15 mins to do that first cut, have to say the 880 is great, but wouldnt know any better!

 

CDMR - Yes, def more of a problem on the deeper cuts, almost unnoticable on 4" cuts, then progressively more so, a tensioning system ontop ala the old school handsaws is a interesting one, but think the main problem is 3 dimensional rather than just a tensioning issue

 

Our standard practice is to get the saw started and engine/bar/chain nice and hot. Then retension chain, loosen end bar clamp to let the bar 'grow' into place, and we make sure its flat as can be when nipping up, but its whats happening in the kerf that I believe to be the issue

 

Custom made mill for big stuff might be the answer and just use the Alaskan for smaller/lighter jobs?

 

 

[Rough Hewn]

I've upgraded to panther mills from chillaskans.
84" GB bar, 404 hyperskip chain, 80" panther.
Mainly use the 60" mill though with 56" GB bar,
Granberg ripping chain and stihl full chisel full compliment at 0 degrees.
Normally get a couple of millimetre dip but nothing to stress about.
I have had all kinds of problems when the chillaskan mill wasn't perfectly set up, and when
the aluminium wore, it went off.
Is your bar bent?
I had a 2-3mm bend on a 48" stihl duromatic made the cut really nasty.
Granberg mills are very well made but still flexible.
Especially long ones,
The panther is rock solid in comparison.
[emoji106]

[CDMR]

Does the dip get more pronounced further along the cut or is it constant?

[J Holtby]

It steadily gets worse along the length

 

Panther looks very solid, although the same fundamental design

 

I'm thinking I might knock up a basic purpose built mill just for deep/first cuts, with triangulated bar supports rather than just unsupported legs

[CDMR]

17 hours ago, J Holtby said:

It steadily gets worse along the length

 

Panther looks very solid, although the same fundamental design

 

I'm thinking I might knock up a basic purpose built mill just for deep/first cuts, with triangulated bar supports rather than just unsupported legs

Getting worse would imply it's the cut. So either the chain or chain/bar interaction. Is the bar out of parallel to the frame front to back perhaps?