Hi guys
I have one question from my friend which has WM LT70.
From the last week, his LT70 is working very strange. As you would see in pictures below the final cutting result is very bad.
The strange thing is that these bad cuttings apply only on the soft type of wood (spruce), hard one like oak it is OK.
As you would see it below, this unusual "scratches" on the wood are appearing for few inches, then they stop, and appear again and stops etc.
What we have checked (from my side by remote is this):
1) we tested 7 different NEW and also resharpened blades (WM, other, Vortex).
2) we checked guide rollers
3) we checked power belts
4) we checked driven and idle wheel bearings
5) we checked free movement of sawmill head
6) we checked blade tension
7) we checked a guide arms
I was not present with those checkups, but I know, he is very strict and precise man and he double checked everything.
Do you maybe have some other suggestions about what else should we look?
Any advice will be appreciated.
Thank you
(https://forestryforum.com/gallery/albums/userpics/45032/20180620_183017.jpeg?easyrotate_cache=1529526071)(https://forestryforum.com/gallery/albums/userpics/45032/20180620_180956.jpeg?easyrotate_cache=1529526070)(https://forestryforum.com/gallery/albums/userpics/45032/20180620_183006.jpeg?easyrotate_cache=1529526071)(https://forestryforum.com/gallery/albums/userpics/45032/20180620_183017.jpeg?easyrotate_cache=1529526071)
Going too slow.
Hi
I do not think so. He has more than 2500 hours of experience and he knows how to work with it.
Electric or gas/diesel? If not electric, I'd check to see that the engine is running at the right rpms. There is some sort of harmonic issue going on, I suspect. Typically, that sort of washboarding is from going too slow, and it's often seen right in the beginning of the cut.
Quote from: Dave Shepard on June 20, 2018, 04:47:51 PM
Electric or gas/diesel? If not electric, I'd check to see that the engine is running at the right rpms. There is some sort of harmonic issue going on, I suspect. Typically, that sort of washboarding is from going too slow, and it's often seen right in the beginning of the cut.
Diesel engine. Yes, you are right, we did not check if Kubota is running with full power.
Probably harmonics and the cause could be from several sources some of which have already been mentioned. #3 above stated "power belts", and I am unsure whether you/he meant drive belts or bandwheel belts? The drive belt tension needs to be verified to insure that it is not slipping and causing a reduction in the blade speed.
Has he tried changing the fuel filter? Could be starving for fuel when under a heavy demand.
My LT40 does that when I cut too slow.
Here is a very similar picture from member @Scottasheppard (http://forestryforum.com/board/index.php?action=profile;u=38553) 's gallery:
(https://forestryforum.com/gallery/albums/userpics/48553/20180618_084635.jpg?easyrotate_cache=1529355700)
I would say that he was entering the face slowly and then speeding up. Nothing really wrong and I have made this pattern many times.
Is there sawdust build up on the V-track frame rails? Spruce sawdust is kinda sticky when the sap is running (this time of year), and can build up and lift the head ever so much as it passes. Oak wouldn't be as sticky and probably wouldn't build up the same way.
There was another recent thread here on FF where the V-track frame rails of the saw weren't aligned so well, and causing issues halfway into the cut. After I read that, and went out to saw a couple of times, I noticed this was happening on my mill too, but I don't have segmented tracks (portable mill on continuous rails). So, when I started blowing off the sawdust every couple of boards, I stopped getting weird cuts like this.
Although lines on a board should be given some attention if its not what your looking for....
I always say its part of a bandmills character like the circle lines from a circle mill.
As long as my boards have a consistent thickness a few lines are not bad. :)
I've only been milling wood for a few months but I've been building furniture full time since 2010 i bought my wood exclusively from David Widehead Poston.. My customers love the saw marks... I've asked the old Goat to put an old blade on the mill... love the character and the $$$
Just maybe it might be the side pitch,It seems to be that some teeth have more than others, my 5 ¢ .That is what I figure ,But I never got set the blade to make sure ,Cause mine does that to.I'm going to check the settings when I can .I never really noted that till now so maybe that is something to look into. :P
Not sure if the LT 70 has the blade vibration dampener bolt in the guard above the top of the blade or not. Something to check.
WM blade vibration dampening block in Sawmills and Milling (http://forestryforum.com/board/index.php?topic=80931.msg1231642#msg1231642)
What causes this? in Sawmills and Milling (http://forestryforum.com/board/index.php?topic=92888.0;all)
Have the blade guide rollers been removed and blade checked for levelness on the idle and drive wheels? I had a similar vibration issue and it turned out to be that the carriage rollers were so worn out, the head was wobbling up and down thru the cut, leaving marks.
I find that when I get those marks, that the entry point of the band into the log is always on a curve (round edge of the log) greater than say 45°
As MM posted "I would say that he was entering the face slowly and then speeding up" I tend to lead into the log slowly with my LT35HD and get that chatter until I turn up the speed and get moving on EWP. The chatter does not happen on oak which I start into even slower. Ross had told me to go ahead and get moving right away but guess I am just unnecessarily concerned the band is going to crumple up against the guide on first contact.
Does this happen all the time no matter what band he is using? Has he tried a band from a different box?
I had a brand new box of turbos that had bad set from the factory and made the lumber look just like that. I'd try a different box and see if it is still doing it.
Quote from: Chuck White on June 21, 2018, 10:10:35 AM
I find that when I get those marks, that the entry point of the band into the log is always on a curve (round edge of the log) greater than say 45°
(https://forestryforum.com/gallery/albums/userpics/10919/20180622_074332-756x1008.jpg?easyrotate_cache=1529674686)
Sawed this off the top of a cant last night.
I'd say there is steel in Chuck's words of wisdom.
Glad to hear that someone absorbed what I've been saying for...... how long!
Thanks T.A.
Some of the other things members have said are likely to be true too, I'm not arguing that point!
In my experience I've found that it's not so much the curve of the log, but rather the bark. In cedar the stringy bark gets underneath the blade and causes vibration. I debark all my logs, so I no longer have that issue.
I can see where the curve of the log could make a difference due to one side of the blade having more teeth biting than the other.
There isn't much difference in that regard. How much wider is the log when you drop down 1/8" ? 5" on the top side of the band becomes what, 5 1/4" on the bottom side? I would blame sapwood and bark in that instance. I know Turbo 7s won't cut straight going through narrow sapwood and bark.
Too slow & / or not enough tension.
I'd say you have a flat spot on a bearing. It is definitely in the large bandwheels. Something isn't coming around square and flat.
I noticed you checked quite a few things, and lots of good suggestions made. however, I have observed that most times it is due to high speed blade bounce, sometimes due to harmonics, sometimes due to foreign matter on the band wheels, sometimes due to incorrect tension, or even not removing tension after sawing and slightly flat spotting the tires.
Generally, this is easy to spot because if there is blade bounce it will manifest itself as the characteristic ridges as soon as the band enters the cut, especially with a soft log and sharp band. Also, as soon as enough sawing force is applied to the band (speeding up), the bounce will be dampened out and the ridges will smooth it. Slow down, they will reappear.
If this is suspected, then it will be bouncing or vibrating well before a cut is started, so it's easy to spot in advance. Engage the band full speed and look at the band as it's running. It should look as stable and flat as a laser beam, no shaking, boucing, fluttering, etc. If the band is running and sitting dead quiet, then the cuts will be dead smooth when entering a log. Of its doing a high speed flutter or bounce, then that flutter will cause ridges in the cut and the blade vibrates up and down. Sometimes simply applying more band tension will help round out of mask whatever is causing the vibration. Sometimes other things cause it like sawdust packing between the band and wheels, or under the wheels. Either way, most times it's a symptom that is detectable and fixable before the first cut.