Cut starts to dive as i enter the log.

[joel logger]

Hi. Today i was milling with my brand new 72" double ended bar and helper handle with roller for the first time and i was having some trouble entering the log. Had my first cut set up on a 44" dia oak log and i was super excited to finally be milling some big stuff, but as the bar got about 2" into the log the cut began diving down and it only got about an inch before it completely pinched the bar. I figured id hit a nail but the chain looked fine. It was a brand new chain by the way. So i tried again from the other side, got about 2 inches deep and it got stuck again. I tried a bunch of things to sort it out, tightened up the chain as much as possible, shortened the bar clamps on the mill to reduce bar sag, i tried entering real slow on high revs but as soon as the chain hit the wood i could clearly see it tilting downwards as i applied just a tiny bit of pressure. The chain is definately a .063 gauge but im not so sure about the pitch. I suspect it could be 3/8 (i was very annoyed and completely overwhelmed by mosquitoes at the time so i didnt feel like digging out my beat up old calipers..), though the bar do specify 404. I tried both a 404 and a 3/8 sprocket but neither made any difference.
Saw is a 661 and a regular stihl ripping chain modified into a hyper skip. You guys have any idea what might be causing this issue?
And heres some pictures just for fun

 

[andy]

are the mill and bar perfectly parallel?
It may be the perspective of the picture but, it' looks like it's not parallel.

 

[BobL]

Mill geometry - Bar MUST be Parallel to Mill rails.
Cutters on one side of chain longer than the other side.
Rakers on one side lower than the other.
Worn bar groove causing chain to tip over in the cut
Mill winches can cause this problem because if they are not set up right then can tip the mill slightly - the best way is to ensure the winch cable is anchored to the power head and outboard end of the and then go down to the far end of teh log and back around using pulleys to the winch handle - have a look in Will Mallof's book on Chainsaw milling.

 

[joel logger]

Thanks for your reply. Everything was nice and square. Both post clamps set to exactly 10" and i never use the winch on the first cut for that exact reason, and when i do use the winch, i first put a nice thick steel plate with bricks on top of the mill so it wont lift the back end. One of the many tricks ive picked up while lurking on this forum. I've learnt alot from you BobL, thanks Now that ive given it some thought i really do think its the chain thats the issue. As i was very slowly entering the log on high revs i noticed the chain pulling out of the bar groove as soon as it touched the wood and got bent downwards. This chain really was brand new, the only thing i did to it, which i do to all my 42 and 48" chains is grind down 4 cutters in a row and leave the 5th. Ive had great success by doing that when milling the bigger logs. The cuts are way faster and the 661 dont bog down as easily. Now IF the chain is 3/8 pitch, and the bar i designed to run 404, could that potentially be causing this problem?

 

[BobL]

Now IF the chain is 3/8 pitch, and the bar i designed to run 404, could that potentially be causing this problem?

if it's a sprocket nose bar then a 3/8 chain wont ride properly on a 404 bar nose sprocket and you should notice that right away.

If it was an old bar and a new chain that was tipping over then it will most likely be the bar.
However with a new bar this should not be a problem - are you sure the chain is 0.063 gauge. Measure it, it might have been labelled incorrectly