Problem with striations when milling with W-M LT40

[York Woodwright]

I encountered a problem with the quality of my milling today. Normally, I'd phone the good folks at Wood-Mizer's Canadian office, but they are at a farm show this week. Hence, I am hoping a forum colleague can help.

I have an LT40 (made in 2013) with 300 hours. It has auto clutch and hydraulics.

This morning, when I began milling Basswood into 12/4 slabs, many of the boards had a distinct pattern of striations on the surface. There were intermittent areas having the normal, flat surface, interspersed with sections showing this grooved or striated appearance. The distance between the striae was dependent on the rate at which the head was moving forward.

I checked the drive belt tension, which appeared to be at or very close to the recommended 14 lbs for 7/16" deviation. I changed blades, to no avail. I tried altering the rate at which the milling head moved and did numerous other things short of standing on my head, all of which failed to induce or clear the problem. Thus, I do no know the etiology of this conundrum. At times, I wondered if the entire mast/milling head assembly was moving or vibrating a bit, but I could not convince myself that it was any different than yesterday when things were just fine.

In the past, the only problem I have had with the mill was that I blew the rear seal on the Kohler 29 hp motor last winter when the crankcase ventilation tube was plugged with ice (at -22C). The mill has worked well since then, and I have not previously encountered this situation.

Your suggestion or insights are most welcomed and appreciated.

Charles


 

[Brucer]

Sometimes you will get marks like that when the blade starts to resonate. That's when a bunch of different factors combine to match the natural frequency of the blade.

One fix ... change the natural frequency of the  blade:
- change the blade tension.
- change the position of the outboard roller guide.
- use a thicker/thinner or wider/narrower blade.

Another fix ... change the factors that cause the blade to vibrate at a certain frequency:
- narrower cut.
- harder or softer wood.
- blade with different tooth spacing.
- blade with different tooth angle.

And one more fix ... damp out the vibration:
- flood the blade with lubricant (and I do mean flood).

Not all these fixes are practical. Sometimes they have worked for me and sometimes I have to put up with the marks.

[47sawdust]

On occasion I have had that problem too.It sounds like you have tried to to eliminate the source.My only thought is have you tried another log to see if the striations go away.Some logs ,like people, have a mind of their own.
I've got a piece of siding on my house that has a very obvious washboard pattern in the middle of the board,I'm probably the only one who notices it.It gives me a chuckle to see it,perfection is allusive.

[Peter Drouin]

Cutting to slow, tension on blade too low.

[bkaimwood]

I have had that on occasion while milling also...every time it has happened, it has been caused by the log...I never worried about it, cause its rough cut lumber...I wouldn't sweat it too much, it'll probably be gone next log you do?

[Sixacresand]

York Woodwright, Keep us posted on your remedy.

[4x4American]

x2 what Peter said.  Saw faster and crank up tension on blade to 3000psi or better

[York Woodwright]

Thanks guys. I appreciate your time and help. I'll report back at the end of the day.

Charles

[drobertson]

It might not hurt to check the little set screw between the two band wheels, should be set close to 1/16", also make sure your guide rollers are not wobbling. 

[Magicman]

It might not hurt to check the little set screw between the two band wheels, should be set close to 1/16"

That is a good tip David and an often overlooked item.  It's purpose is to eliminate/reduce blade oscillations.   

[barbender]

I get those marks when I saw too slow. I haven't sawn very much basswood, but with how soft it is, I can see where the blade would really "bite" into it, and contribute to those waves if you don't keep the feed speed up.

[Dave Shepard]

x2 what Peter said.  Saw faster and crank up tension on blade to 3000psi or better

I agree, and basswood is really bad about it for some reason.

[4x4American]

It might not hurt to check the little set screw between the two band wheels, should be set close to 1/16", also make sure your guide rollers are not wobbling.

Please enlighten me on these set screws!

[YellowHammer]

It's a 3/8 inch nylon sets crew that is in the top housing of the band wheel cover. It's designed to limit band bounce or otherwise damp out vibration. If the band is bouncing too much it will hit the nylon screw and smooth out.

Among the other fixes for band resonance is to clean the bandwheel belts.  The bounce can be seen well before the band touches the wood so you don't have to be making sawdust to diagnose it.

Sawing fast is one pretty sure way to damp it out.

[Ga Mtn Man]

It's a 3/8 inch nylon set screw ...

Mine came with a metal set screw, just FYI.

[drobertson]

I run pretty much maxed out on tension myself, however can see this occur at any given moment and it's visible before entry,.  I've never sawn bass wood, so this situation is out of my realm, but see it often with pine, only issue is the knots, high speed can do more damage than the minimal variations from oscillations in my opinion. Mine seems to occur, when it occurs just before the knots, where there is a major grain change in the growth rings around the knot.  So I figure it's part of the process, hard to fix what's tight, aligned, and running true until it happens.

[Magicman]

My blade damper is a steel bolt with locknut.

[4x4American]

Huh.  Well boys I looked but didn't really see this set screw.   ???   What does it adjust?  Or is it just there to take up slack?

[Ga Mtn Man]

Open up the middle blade cover and you'll see it in the middle, just under the blade.  It is just a bolt sitting under the blade body, to dampen vibrations.

[4x4American]

ohhh I didn't realize it was in the middle blade cover!  I didn't look there.  Thanks Paul

[York Woodwright]

I spent much of my day studying the numerous helpful suggestions. I did not undertake rigorous scientific analyses, choosing to abandon methodologies such as multiple linear regression analysis, in favour of my personal method of statistical analysis known as CNOEBI. It stands for 'complete neglect of everything but intuition'.

In approximate order of importance, the factors are:

1. Wood species. This is clearly the most important factor. As a number have suggested, my problem is peculiar to Basswood. I milled six different Basswood logs, all of which were afflicted with these linear striations. I then put a lumpy log of Sugar Maple on the mill, and the striations immediately disappeared. (See photo below.)

2. Rate of feed. This is the second most important factor. When the mill head was moving as fast as I dared, with sawdust pouring out of the chute, the striations disappeared. When the feed rate was slowed to a more moderate level, the striations recurred.

3. Width of the board. The wider the board, the worse the striations. I hypothesize that this effect is related to the rate of feed, inasmuch as I could mill the narrower boards more quickly than the wider ones.

4. Blade tension. This is a factor of lessor importance, but nevertheless it made a perceptible difference. The greater the tension (to the maximum of 3000 PSI on the gauge), the less marked were the striations.

5. Lubricating fluid. This made a very slight but perceptible change. When the cooling stream was at full tilt, as if coming from a garden hose, the striations were slightly less pronounced.

6. Debarker. The striations were present both with and without the debarker. However, they appeared to be slightly less pronounced when the debarked was used, suggesting it played a minor role in dampening the vibrations.

7. Bandwheel belts. There was surprising little dust or material on the belts. After cleaning them, there was no perceptible change in the striations. However, this does not preclude the possibility that sawdust-impregnated belts or other belt-related disorders could be a culprit.

8. Heartwood versus sapwood. Cuts through sapwood appeared to have the same degree of striations as those through the pith of the tree.

9. Blade type. This factor remains unexplored. I have only two types of blades, -9 and -10 degrees, and both were associated with the striations.

10. The set screw. I haven't had a chance to explore this factor. In fact, I haven't even found the set screw yet. But thanks to Ga Mtn Man's instructions, I'll look again tomorrow.

I am most appreciative of all the assistance you have afforded me. Thank you so much!

Charles

And after all the Basswood milling, here was the lumpy log of Maple. It made my day.


 

[Green Man]

I believe that that is the sign of sawing sawdust. Basswood is very soft- but the fibers bind in the cut and are spilling to the side of the blade. 10 degree blades and widen the kerf till it cuts smooth. I bet some snow on the ground would help firm it up too.

[4x4American]

you can really fly through basswood.  btw, we know these striations as washboarding or the washboard effect.  that crotchwood sure looks good!

[Sixacresand]

Open up the middle blade cover and you'll see it in the middle, just under the blade.  It is just a bolt sitting under the blade body, to dampen vibrations.

I did not have clue that it existed, but I hobbled out to mill, threw opened them middle cover and there it was.  I got to read up how to adjust the height  or how close to the blade it needs to be.  It appears to be <1/4 inch.  I never paid attention to striations because I know it is rough lumber.  This has been a interesting thread, worth reading.  Thanks for the posts, everyone.

[Ga Mtn Man]

The gap should be approximately 1/16".  Honestly, I've never noticed that it makes any difference but I'm sure WM wouldn't go to the trouble of putting it on there if it didn't do something.