How I fixed my Norwood sawmill (long post)

[arky217]

Let me start by saying that this post is not meant to bash Norwood sawmills.
I think they make a decent sawmill and there are a lot of features
about it that I like. But I think that it has a definite design flaw
in the way the carriage is raised and that flaw, coupled with the lack of a plumb adjustment
on the bandwheels, can cause the problem that I experienced.

If you have a Norwood sawmill, specifically the LM29
(and it might apply to the other models as well), then you might
check to see if you could be experiencing this same problem.

I have the Norwood model LM29 sawmill; I got it a couple months ago.
I have milled about 2 dozen logs thus far.
I check the lumber frequently to see if it is sawing evenly.
The boards always seemed to be the same thicknes end to end and side to side.

Then one day, as I was sighting down a 6"x10"x12' beam that I had just sawn,
I noticed that it did not seem to be straight; it seemed that it was bowed concave
in the middle and not just on that one side, but on the other side as well.
So, I checked it with a string and sure enough,
it was thinner in the middle than on the ends. I measured the 10" dimension and it was
exactly 10" on each end but in the middle it was less than 9 & 3/4". Also, at 3' into the cut
and at 9' into the cut, it was about 9 & 7/8".
Then I checked the 6" dimension and it also was gradually thinner in the middle than on the ends.

In other words, the blade was gradually diving to the middle of the cut
and then (because of the increasing pressure from the tension of
the blade) it gradually rose back up to the original dimension".

I then check a number of boards that I had previously cut and though most were the same
thickness in the middle as the ends, I noticed that they all seemed to be bowed outward
a little on one side and bowed inward a little on the other side.
But it was the beams that I was cutting that were bowed inward on both sides and thus
thinner in the middle than on the ends. The wider the cut was, the more pronounced
was the diving.

I then realized that the boards had a consistent thickness because the diving on the 
previous cut matched the diving on the present cut. That's why they were the same thickness
in the middle as the ends but showed a convex bow on one side and a concave bow on the other side.

The beams, however, were bowed inward on both sides due to cutting on one side and then flipping
the cant and cutting on the other side, thus the blade diving took place on both sides resulting
in the middle thickness being less than the thickness on the ends.

At this point, I knew that I had to find out why the blade was diving in order to keep
from continuing to mill boards that weren't consistent.
I tried a couple of new blades; same problem. Then I tried more tension on the blade
and then less tension; same problem both ways.

(To tension the blade, Norwood recommends to turn the tensioning handle 4 & 1/2 turns
after it contacts the tensioning spring. 4 & 1/2 turns seems about right, but I tried 4 turns
and then 5 turns; diving problem didn't go away.)

Then I happened to think to check the blade itself for level and was surprised to see
that it angled down quite a bit. Why would that be, I wondered. Well, I then checked
the plumb of the band wheels and was surprised again to see that they were out of plumb,
angled downward over 1/4" from top to bottom.

Well, what do I do now; there is no bandwheel plumb adjustment on the mill. Then I thought
to check the level of the carriage platform itself and discovered that it too was angled downward
over 1/4" from the back edge to the front edge.
I then checked the uprights that the platform rides up and down on but they were exactly plumb.

I discovered that when the platform is all the way down, resting on its bottom with slack in the cables, that
it then is only slightly angled downward. But when the platform is raised (the cables are
attached to the platform more toward back, away from the bandwheels, rather than in the middle), then it tilts so much
that it angles downward over 1/4", thus angling the bandwheels downward, thus angling the blade downward.

This seems to be a result of a combination of excessive clearance in the plastic blocks that travel the uprights
and the lifting point of the platform being more toward the rear than in the middle.

(In my opinion, all bandmills really should have bandwheel plumb adjustments and they also should have
level adjustments on the guide rollers.)

My solution to solve the problem was to insert shims between the platform and the plastic blocks that
ride the uprights. It tooks several tries and I ended up cutting 3/8" washers in half and inserting
halves between the front of the lower plastic blocks and the platform and the other halves between the
rear of the upper plastic blocks and the platform. (See the pictures below)
The right thickness of washers to make the platform exactly lever was 0.1"

When I finished, I tightened everything up, put on and tensioned a blade, and then checked everything.
The platform is now exactly level, the bandwheels are exactly plumb, and the blade is exactly level.
Tried a few wide cuts and now the diving of the blade is no more.

So, if you have a Norwood sawmill, you might want to check if it is diving as it goes toward the middle
of cut and rising again as it finishes the cut. If it does, perhaps your blade is also angled downward due to this same problem.

I'm going to include this post in an email to Norwood to see what their response is. I'll follow up with
what they say.



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[RAYAR]

Those should be built in adjustments. Good that you were able to get your mill squared up and true.

[pineywoods]

Arky, I have seen similar problems on norwood mills. I do a bit of sawmill repair for other sawyers. Had 2 different norwood mills come to my shop with like problems. On one, the driven bandwheel lateral alignment was out of specs. There is an adjustment there, but it was up against the limit, not enough adjustment range. On the other the idle wheel was way out of plumb.(no adjustment except to bend the head frame)..Don't even think about it...Remove the drive belt and a few covers and the axle carrier can be slid all the way out of the square tube it slides into. It's a very loose fit. On the square tube that carries the bandwheel axle, you will find some small metal tabs brazed to the tube to take up the slack. Grinding these down until the pieces fit for correct tracking is the factory adjustments. These little tabs wear from vibration and rust, causing alignment issues. Stacked thicknesses of beer can shim in the appropriate places took care of the problems.

[wbrent]

Interesting. I have the same mill. Usually when I have a discrepancy in thickness it's because the rails need to be re levelled. I'm just sitting on gravel so things settle with the seasons. But now I'll check what you checked too. 
Wonder if you played around with blade tracking in terms of where you allowed it to run on the wheel. I think the manual says to run it so the gullet is about flush with the front edge of the belts. I think mine is further forward of that. Wonder if playing around with that would change the angle of the blade?  Just a thought. 

[ladylake]

Interesting. I have the same mill. Usually when I have a discrepancy in thickness it's because the rails need to be re levelled. I'm just sitting on gravel so things settle with the seasons. But now I'll check what you checked too.
Wonder if you played around with blade tracking in terms of where you allowed it to run on the wheel. I think the manual says to run it so the gullet is about flush with the front edge of the belts. I think mine is further forward of that. Wonder if playing around with that would change the angle of the blade?  Just a thought.

 I'm with you, if the tilted head was causing the blade to dive in the center why would it come back up at the end of the cut.  Sounds to me like more support is needed in the center of the mill.  Or dealing with stress in certain logs.  Steve

[arky217]

Interesting. I have the same mill. Usually when I have a discrepancy in thickness it's because the rails need to be re levelled. I'm just sitting on gravel so things settle with the seasons. But now I'll check what you checked too.
Wonder if you played around with blade tracking in terms of where you allowed it to run on the wheel. I think the manual says to run it so the gullet is about flush with the front edge of the belts. I think mine is further forward of that. Wonder if playing around with that would change the angle of the blade?  Just a thought.

I'm with you, if the tilted head was causing the blade to dive in the center why would it come back up at the end of the cut.  Sounds to me like more support is needed in the center of the mill.  Or dealing with stress in certain logs.  Steve

The straightness and levelness of the rails and bunks was the first thing that I checked after I noticed the diving problem. They are spot on.

I think that the reason that the blade rises again after diving for so far is that the diving causes so much strain on the blade that it begins to pull up again. This is just my opinion, but I've observed that on other posts about diving problems, that pictures show that the
dive goes so far then rises up again. Some pictures on some diving posts even show several dives and rises within the same cut.

As far as log stress causing the problem, I think that can be ruled out or else all the logs I cut before the fix would have had log stress and all the logs that I cut after the fix would have been stress free. That is hardly likely.

As I said at the beginning of the post, it is not meant to be a bash against Norwood.
I really like the mill; it has several features that enhance the milling operation.

However, the way the cables pull up more on the rear of the platform coupled with the
play in the plastic blocks that ride the uprights causes the platform to tilt downward, thus
tilting the bandwheels downward, thus tilting the blade downward.

Bottom line, the fix of making the platform level completely solved the diving problem as
evidenced by carefully measuring the boards and beams from several logs after the fix.

[Hilltop366]

Wondering if the saw was loaded ie put a typical log on the mill and move the saw to the middle of the log bunks is the mill still straight and level?

Thinking there could be a difference depending on the ground, something to watch out for.

[arky217]

Wondering if the saw was loaded ie put a typical log on the mill and move the saw to the middle of the log bunks is the mill still straight and level?

Thinking there could be a difference depending on the ground, something to watch out for.

Absolutely, the rails are setting on a solid foundation.

When measured with a string, there is not even a 1/32" difference
in height from end to end.

I have cut enough logs now after the fix to know that the downward
angle of the blade was indeed the culprit.

The cut is so straight now that when I cut both sides of a cant,
no matter where I measure the thickness, it is less than 1/32" different,
whereas before the fix, there was as much as 5/16" less thickness
in the middle of the cant than on the ends.

[arky217]

There is a guy that has a Youtube channel called 'Koality for Life'.
He also has a Norwood LM29 sawmill; I have watched a number of
his videos and he has some good tips for the Norwood LM29.

Well, I emailed him the link to this thread, thinking that he might want
to check his mill to see if he has the same problem.
He did have the same problem and he made a Youtube video
showing him implementing the same fix that I describe above.

He shows putting the shims in the same places that I did and
that it solved the problem for him as well.

Here is the Youtube link:

Norwood sawmill fix

[hamish]

Firstly I have been running my ML26, virtually identical the the LM26 since 2010.  

Points to consider........

1.When the sawhead is at its lowest position, there should be no slack in the cables. Check cable routing or take up slack in the sawhead turnbuckle/yoke bolts.  Which will also eliminate the forward pitch of the sawhead.

2.Check your bed and cross bunk alignment, anybody than can say its within 1/32" aint wearing there glasses, even if on a concrete pad.  Rails have to work with the crossbunks to all be true.  Foundation/anchoring and alignment are key.

3. Any and all diving issues I have encountered even in the nastiest logs have been bed or blade related.
I mainly cut Eastern White Pine and Spruce with alot of knots, but only cut about 20-35K BF a year.

Get Milling!

[dudders]

I had the same problem with my Trekkasaw.  Uncanny how it would dig in and then rise out again.  Luckily for me, it's a fairly straightforward adjustment on the wheels to get the blade running absolutely level.  Once level, or at least square to the rails, it cut true.  Now looking for a new mill, I'll bear this aspect in mind.

[OH Boy]

Arky,
Thanks for replying to my post about this same issue and pointing me in the right direction. This makes perfect sense and I'll check it out along with making sure the bed is all level. 

[cmcguigan]

The problem is because the deck material isn't thick enough to resist the pulling force the cables put on it.  I just rebuilt my deck and have noticed the area where two bolts attach the lower pulley to the saw head deck will end up dimpled in.  This in turn throws everything else off. Also if the hardware holding the pulley to the deck is tight it will do the same thing.

I swear if I had a dollar for every hour Ive spent tweaking my hd36v2 I could have bought a woodmizer.