Bands saw blade diving on knots and wider parts in the same log

[BobL]

I'm trying to get the bandsaw mill cutting straight again and seem to have run into a brick wall.
It was cutting "OK when I last used it a few years back but since getting back to it, every time the blade starts cutting something harder than the rest of the log, like a knot or branch union, or even just entering a wider part of the log the blade dives about 1/4" or so in the cut.
When the cut comes back to straight grain or narrower wood it comes back up again.
Today I finally lashed out and threw a brand new Lenox Woodmaster blade onto the mill so it can't be the blade..
Checked and double checked blade tension, all angles and settings etc.
Any idea gratefully appreciated.
Thanks

 

[woodchuckcanuck]

Only advice I can offer is

1. To slow your feed rate into the knots.
2. If you can, reduce your engine speed to about 2800-3000 rpm.
3. Blade tooth hook angle should be correct for type of log being sawed.
4. Blade tooth set should be correct for type of log being sawed.
5. Correct blade tension (you got that covered).
6. Sharp blade (you got that covered).

 

[BobL]

Thanks Jim,
New blade is supplied by reputable supplied who supplies blades to statewide sawmills to run in our hardwoods.
Most of the wood we cut is pretty hard but I started a few months back cutting up a a pine log and it seemed no different.

RE: Position of blade on wheels/tyres.
The tyres are 1" wide V-belts and the band is 2" wide.
On my home WW bandsaw I run the bottom of the blade gullets almost in the middle of the tyre, but I didn't seem to need to do that before when I used the BS mill.
I've tried moving the blade on the wheels so that the edge of the wheel/tyre is within 1/16" of the gullet but it doesn't seem to make any difference.
If I move the gullets even closer to the wheel edge the back of the blade strikes the inside of the Band guard.

 

[Leeroy]

Bob I hope you can get it sorted out. Bearings or blocks for blade guides?
What WW stand for?
Not sure this info on tensioning is relevant, but I've never heard of this method :
http://www.suffolkmachinery.com/six-rules-of-sawing.html

 

[woodchuckcanuck]

WW likely means woodworking.
Assuming you've run 2" blades on 1" wheels/tires before with no issue, I would look to the blades. If your blade is only diving (downward I assume) then you should check the inside set. Its quite possible the inside set is insufficient. Or, the outside set to more than it should be. Is it happening with softwood only, hardwood only, or both?

 

[Bobby Kirbos]

If you can in some way, reverse the cutting direction (not the feed, but the cutting direction of the blade)....
Roll the band ... make what is currently the outer face of the band the inner face. This will also flip the teeth. If the band continues to dive in the same direction, the problem is likely NOT related to the band or the cutters. If the "dive" changes direction with the flip, the problem is likely the band or the cutters.

 

[grizz55chev]

Maybe you need more lubrication during the cut, increase the water feed.

 

[nwhunter]

The back edge of the band needs to run on the wheel, there should be more tension put in the band on the back edge of the band, I would not run a 2" band on a 1" wheel as it would put an excessive amount of the cutting edge forward of the support from the wheel, resulting in the band dodging.

 

[CWME]

I ran into that issue with some knotty hemlock this past spring. I increased my tooth set and the issue cleared up for me.

 

[billstuewe]

Hi Bob! long time since I have been around. I retired in Feb of 2010 and my hobby woodworking became a nice business. I now have a Woodmizer LT40/36hpG. Sometimes it is just the log that causes wavy cuts--especially at knots and other hard parts. The only things that helps is, as woodchuckcan noted: A good sharp band , reduce feed rate and the right tension. I will even increase the tension a bit.
Bill Stuewe
www.billstuewe.com

 

[Franny K]

The back edge of the band needs to run on the wheel, there should be more tension put in the band on the back edge of the band, I would not run a 2" band on a 1" wheel as it would put an excessive amount of the cutting edge forward of the support from the wheel, resulting in the band dodging.

He said an one inch belt I am guessing the wheel is wider than an inch, for a 1 1/4 inch band the wheel or pulley sheave is about an inch and the belt is 5/8. We probably need a clarification here.

BobL are you running roller blade guides and if so how much downward deflection does the fixed one and the moveable one have?

 

[BobL]

Thanks to every for all their replies and suggestions.
Sorry I have not got back to you all sooner.

Bob I hope you can get it sorted out. Bearings or blocks for blade guides?
What WW stand for?
Not sure this info on tensioning is relevant, but I've never heard of this method :

I'm using super hardwood (Wandoo) blocks as guides.
WW is woodwork.

WW likely means woodworking.
Assuming you've run 2" blades on 1" wheels/tires before with no issue, I would look to the blades. If your blade is only diving (downward I assume) then you should check the inside set. Its quite possible the inside set is insufficient. Or, the outside set to more than it should be. Is it happening with softwood only, hardwood only, or both?

Yes have run any 2" wide blades successfully on this mill. I doubt it's the blades as I've tried two new ones from reputable supplier.

If you can in some way, reverse the cutting direction (not the feed, but the cutting direction of the blade)....
Roll the band ... make what is currently the outer face of the band the inner face. This will also flip the teeth. If the band continues to dive in the same direction, the problem is likely NOT related to the band or the cutters. If the "dive" changes direction with the flip, the problem is likely the band or the cutters.

When I say dive, it was both dipping and rising. Mainly diving on entering a knot or branch union and rising back up to normal or a bit less after it cut through the knot . Anyway your suggestion is a Good idea and will give it a go if I need to.

Maybe you need more lubrication during the cut, increase the water feed.

Water is flooding the blade, plus every few feet of cut I usually add a few squirts of chainsaw B&C lube.

The back edge of the band needs to run on the wheel, there should be more tension put in the band on the back edge of the band, I would not run a 2" band on a 1" wheel as it would put an excessive amount of the cutting edge forward of the support from the wheel, resulting in the band dodging.

The blocks are ~2" wide (and 2" long and about 1.25" thick) and start providing support just under the gullets to past the back of the blade. Its worked very well in teh past.

I ran into that issue with some knotty hemlock this past spring. I increased my tooth set and the issue cleared up for me.

I've tried this but maybe I need to add even more.

Hi Bob! long time since I have been around. I retired in Feb of 2010 and my hobby woodworking became a nice business. I now have a Woodmizer LT40/36hpG. Sometimes it is just the log that causes wavy cuts--especially at knots and other hard parts. The only things that helps is, as woodchuckcan noted: A good sharp band , reduce feed rate and the right tension. I will even increase the tension a bit.
Bill Stuewe
www.billstuewe.com

Yeah have played around wth the tension a fair bit, from 25% less than recommended to 30% more than recommended. Nothing

He said an one inch belt I am guessing the wheel is wider than an inch, for a 1 1/4 inch band the wheel or pulley sheave is about an inch and the belt is 5/8. We probably need a clarification here.

BobL are you running roller blade guides and if so how much downward deflection does the fixed one and the moveable one have?

The mill did come with rollers but they last about half a dozen cuts before the bearings gumed up with sawdust. The previous mill owner replaced the rollers with blocks and we successfully used these blocks for 4 years . The blocks only provide down force and support the blade from the gullets to the very back of the blade. Downward deflection is ~1/4"

Some of the blade dives were so deep the blade would eventually no longer even be in contact with the guide blocks.

The wheels are just over an inch wide and have a deep V-groove that holds a large V-belt. The belts are very loose in the groove and they have always been like that.

Now just to make things entertaining, today it cut straighter than it has cut since I got back to this mill, Blade dive was down from the usual 1/8->1/4" to 1/16->1/32"
What did I do in the meantime?

The first thing was to fix the throat width adjustment. I noticed it was packed with rust and sawdust not well secured so liable to twist. This is now clean, shimmed, greased and secured.

Then I added hard wood plates to support the blade at the guide blocks from underneath.
At both the inboard and outboard sides, the blade effectively passes through a pair of blocks with about 1/32" of extra gap.
If the blade goes for a dive the plates will prevent it going too far. The wooden plates are about 1/2" thick and secured to the back of the top guide blocks by 1/4" thick piece of angle. The hardwood plates ar fastened to the angle with 1/4" counter sunk brass screws so of the wood wears the brass screws won't do anything to the blade.

I cut 4 slabs and was pleased enough, but still I think there is more I can do.

Thaks again to all.

 

[BobL]

Not many photos taken but this is one of the least wavy/divey cuts from earlier in the week.
At least the wood is purdy!

 

[Franny K]

I suppose we should establish if the thickness of the band blade is the same as four years ago. The wheels look large enough to run kind of thick bands,

I have observed that sandwich type guides seem to be used in line with the way the blade comes off the band wheels and roller guides control the band with a downward deflection.

From your picture, turn it so the opened face is vertical and where the blade enters as soon as possible if wave cut is an issue is my current tactic.

From a design prospective I note that Cooks and Baker for their 2 inch blade width models keep the same blade direction but put the log stops or squaring arms on the other side, the enter the cut side. They also put the fixed guide on that side and the moveable one on the exiting the cut side.

The part about the bearings of roller guides gumming up is puzzling as I have never had a bearing issue but the ridges in the roller guides can clog and be frustrating.

You are saying your belted band wheels are an inch wide in total, ?5/8" belt for a crown, I would think for best results the crown of the band wheel should be pretty much the width of the blade from the gullet back.

 

[BobL]

Thanks for the feedback FK.

I suppose we should establish if the thickness of the band blade is the same as four years ago. The wheels look large enough to run kind of thick bands,

Yes they are the same blades

I have observed that sandwich type guides seem to be used in line with the way the blade comes off the band wheels and roller guides control the band with a downward deflection.

Initially there were two rollers (I still have those and as I said have tried several times to use them bt they gum up.) replaced by 2 downward trusting guide blocks, now there are two sandwich type diodes

From your picture, turn it so the opened face is vertical and where the blade enters as soon as possible if wave cut is an issue is my current tactic.

Yep - understand, problem is the carriage log and squaring arm stops are over on that size and would have to change things around - hoping not to have to do that.

From a design prospective I note that Cooks and Baker for their 2 inch blade width models keep the same blade direction but put the log stops or squaring arms on the other side, the enter the cut side. They also put the fixed guide on that side and the moveable one on the exiting the cut side.

Interesting. Thing is the mill has cut very straight in the past.

The part about the bearings of roller guides gumming up is puzzling as I have never had a bearing issue but the ridges in the roller guides can clog and be frustrating.

Yeah it's very strange. I even replaced the bearings with sealed types but they still got gummed up. On my WW BS I only clean the roller bearings every couple of years. I also cut up large beef bones for our dogs with this saw so the rollers get covered in beef fat, the BS tyres also pick up a lot of fat and the get scrapped off every month or so but the bearings never get gummed up

You are saying your belted band wheels are an inch wide in total, ?5/8" belt for a crown, I would think for best results the crown of the band wheel should be pretty much the width of the blade from the gullet back.

Yes its kind weird. On my woodwork Bandsaw I've always (for ~15 years) used the Snodgrass set up method where the bottom of the gullets matches the crown on the wheel. Works really well, I can't do this on this mill as the back of the blade would be touching the wheel guards.

 

[Franny K]

Yep - understand, problem is the carriage log and squaring arm stops are over on that size and would have to change things around - hoping not to have to do that.

I was meaning use a level or square to get the opened log face vertical. Depending on the squaring arms or log stops and the turning method this will vary in difficulty.

 

[BobL]

After last weeks improvements, yesterday I decided to have a go at a partially cut that I had trouble with a couple of weeks back.
I did a number of cuts with the mill, most were OK and then I got a bit greedy and the rise and dive came back although not as bad a before.

I keep forgetting to take photos but here are couple of the worst ones taken by the boss from a couple of weeks back.

Same log but from the other side.
The shadows and log width changes exaggerate the dive so what looks like a massive dip is actually also a change in log width.

Still trying to work out "Why" things improved.
I think it's a accumulation of factors - slower cutting, slightly higher band tension, blade support from underneath,

 

[BobL]

After watching me struggle for months trying to get the old mill to cut straight the arborist/boss has decided to spring for a new small mill.

He recently got a big order for smallish (60 x 80mm and 60 x 40mm, x 1.8m long) dressed hardwood lumber - there are massive and growing lumber shortages here.
He's really lashed out and bought a spiral headed thicknesser/planar combo machine.
Earlier this week we (me and the boss) prepared a dozen or so samples and the amount of work to produced dressed to size from roughish cut lumber was not lost on the boss which is why he wants to get a new mill.
We'll still use the old mill to break up larger logs while a second operator puts the cants through the smaller one.
I'll be still driving the bigger mill and trying my best, but I won't have to stress too much about getting straight cuts.
He's looking at a few different mill brands but availability is probably going to be a final determining factor.

 

[rogue60]

Sounds like it could be a packing problem allowing the band to wander when it hits knots or a wider cut. Normally to much heat makes a band wander but you have plenty of water for cooling. To much feed speed will also make a band wander.
Bandsaws aren't the greatest things at cutting straight when the going gets tough especially in our hardwoods.
If you weren't so far Perth im in QLD you could have our old Bandsaw for scrap money to tinker with.
We used to cut Hoop Pine, Cedar, Silky Oak etc..

 

[BobL]

Thanks for the offer. I have a not that I'd be tempted. I used to have a large collection of old wood and metal working machinery that needed restoration and have only after ~10 years managed to get rid of them.