Hmmm... Crowned cuts....

[GoManGo]

We have been running our home brewed bandsaw mill for about 40 hours now, and we are facing a very flustering problem.  The cuts are crowning up in the center, and no matter how much readjusting we do, its still present.

A brief history since my last post...  :P

We moved the sawmill from the construction site to its new home, and started pumping out the boards from fresh fallen white fir. We ran into several problems and fixed them as we went.  (new pillow block inserts, and other annoying issues...)  Still getting the occasional broken blade, and I once attempted to saw threw a log dog, but  other than that, everything is working great.  I found that the blade tension is best set on the fly, by slowly increasing tension at operating speed until flutter is at a min.  When we stated doing this, we stopped breaking so many blades.  And now this problem....

It started right after blade change.  We shut down, and re-leveled the saw rails, and adjusted the blade. the wheels are running at 90 degrees to the track, and the blade is flat, but after ripping off a 1/4 inch slab, the same crown was present.  I did notice a slight buildup on the roller guides on the side where the blade exits the log.  The buildup seems to be normal, and didn't seem to cause any issues in the past.  I ran a straight edge across the log, (about 25" knotty white fir) and found that the crown starts about 6" into the cut.  The crown doesn't seem to get worse threw the cut, but is consistent.  I tried really poring on the lube to see if the buildup was the problem, but doesn't seem to matter.  We are using a 50/50 chain bar oil / diesel for lube. Any ideas??  ??? ???

[Kevin_H.]

Any time we have a problem with a crown in the cut it has always been a blade issue, with the set being wrong on the teeth, Most of the time it was from grazing something with the blade and messing up the set on one side of the blade making it rise in the cut.

If you havent already, you may try changing the blade and see if that makes a difference.

[GoManGo]

We tried changing the blade, and the issue was still present.  Thats when we readjusted the guides.  Is it possible that we need to have a slight dive in the blade adjustment?  Im afraid that if we do this, we will need to lower both blade guides to create enough pressure to get the blade to change its pitch without riding hard against the front guide bearings, and totally missing the rear one.  As it is now, the guides hardly deflect the blade at all.  

[ronwood]

GoManGo,

On the Woodmizer the blade guides deflect the blade downward about 1/8 in. Might try that. Also when your blade is tension does it run parallel to the bed. I have a alignment tool that I clip on the blade that is around 12 in long. The tip of the alignment tool should not be more than 1/32 in off front to back. Per Woodmizer manual. If you need a picture of the tool let me know and I will post one.

Ron

[D._Frederick]

GoMan,

When sawing soft wood, you should have more set in the teeth, I have found that 0.022 - 0.025inches per side works best for are soft woods. You should have 1/8 to 1/4 down force on the guides and the back of the blade should be within 0.025 inches of the support roller. The blade should be parallel to the saw track. If you are running carbon alloy blades, you may not have enough blade tension.

[Tom]

Whatever you do, don't introduce lead into your blade.  You will be chasing ghosts forever if you do. That is like treating the symptom rather than the illness.

The guys are right when they say to keep everything square.  The down pressure/deflection recommended still leaves the blade square with the mill but is for control purposes.

When I experience "crowning" it is a combination of dulling teeth (or hard wood) and too little band tension.  The blade enters and exits in the right spot but rides up in the middle of the board. Sometimes it gets sucked down.  I've also noticed gumming of the blade when it happens.  I don't know it this is a cause of the crowning or a result.  The heat generated by the rubbing of the side of the blade could be the cause of the gumming.

And yep.......  hitting something in the log will dull teeth too :D

I've changed blades and still experienced bad cutting before only to find that there was a tack or wire at the beginning of the log and I hit it with both blades. grrrrrr.

[sandmar]

Also,have seen waves and dives when there is buildup on the blade wheel belts even though the blade is kept washed clean. Just  knock off the build up and clean the blade...back to normal..this is on a Woodmizer

Sandmar

[JD350Cmark]

Hey Sandmar,  hows that new WM?  Still working on those lots?  -Mark

[sandmar]

Hey JD
Yep .....got 5 lots worth { a whack} cut into logs and hauled here..they are either cut or staged to be cut. Should be clearing 5 more lots starting next week so........gotta get these out of the way to have a place to put the new ones ;) Haven't had time to cut in about a week...getting a rental house ready for new tenants.They will be moving in Sat............I can almost taste the sawdust now ;D
How is your new mill working out??? Fun ain't they!!!

Sandmar

[GoManGo]

Ronwood
Would love to see that tool if you could post it for us. (Have been using a standard level) We found that the stationary guide is about 1/8th inch higher than the adjustable guide.  This was tracked to an issue with slop in the blade tension slide assembly.  When we tension the blade, it pulls the blade guide up when the slop is pulled out.  We will try to do some really fancy heating and pining, or even cutting and re-welding to eliminate the slop.  I just hope we don't get it so tight that the blade tensioner jams.

D Frederick
We are using Woodmizer part number B3751589S Thickness-.045, Width-1.25, Length 158, HookAngle-9.  Not sure what set this blade is using, but it was what Woodmizer recommended for knotty soft wood.  We are running out of blades very quickley trying to get this thing up and running, and would appreciate any advice for my next blade choice.  We are just about done sawing the white fir, and will be starting into douglas fir in a week or two.  After a couple units of doug fir we will be needing to get a very smooth cut on cedar for shakes.  

Tom
The crown is consistant after about 6 inches into the cut.  The center is high, but the edges seem to be right where they need to be.  Everything is the same distance from the rails when measured on the outer edges.  Its just when we put a straight edge on the log that we notice the crown.  This seems to happen with all logs, but we didnt notice the crown in the smaller logs.  Everything was working great at first, and after about 40 hours of use, it started happening.  

[ronwood]

GoManGo

I will take some pictures in the morning and try and get them posted sometime during the day.

[steveo_1]

Hi GoManGo sometimes ill have a little rise in the blade bout 6 " into the cut and have noticed that if i slow the feed down while entering the log,then after say 6 " speed back to normal.It usually stops the wander,not sure whats causing mine to do it either but i think it has something to do with the sudden change in RPMs.Just something you can try to see if it stops it.

[LeeB]

Are you getting crown along the length of the board or acroos the width? If across the width, you may be feeding too fast. LeeB

[D._Frederick]

GoMan,

If the crown is along the length of the cut, check your track, it may have been knotted out of alignment.  
Steveo is correct, you should not enter into the cut at maximum sawing speed, it will cause the blade to wander at first.

[Tom]

That little hump at the beginning of the board is caused by your guides losing control.

It can be caused by entering the log too fast, dulling teeth, guide not supported in the back. It makes a hump because the blade is recovering.

Put on a sharp blade. (having been passed through a sharpener doesn't make it sharp)

Check the log for dry ends (that dry wood is harder to cut.)

Check for the back roller or flange on the guide being close enough to the blade to eleminate bending.

On roller guides check for enough down pressure.

On flat guides check for too much gap to the blade.

A really well sharpened and set blade will cure most ills.

[D._Frederick]

GoMan,

I guess I don't know what you have for band wheels, your saw teeth shouldn't be touching the wheel surface, it will take the set out of the teeth.

[GoManGo]

I guess what my biggest problem is, I have a total lack of experience.  I have never actually seen a sawmill in operation, let alone operated one.  We built this mill with bits and pieces around the farm here, and from what I am told, did a really nice job.  Now to learn how to use it properly.... hehe  ;D ;D

D._Frederick
Please refer to my last post to see the saw, and the band wheels.   The way we aligned the blade is to the center of the blade starting from the gullet and ending at the back of the blade, so the teeth should never come in contact with the v-belts.  I'm not sure if that theory is correct or not, as the guards obstruct the view during sawing.  I guess it could be possible that the blade gets pushed back during loading in a big log.  

The crown is not present in the length of the cut, but is side-to-side.  Today the mill was dragged back up here to the welder, and we have begun the hard daunting task of re-bracing the saw assembly to try to eliminate some vibration still present in the drive wheel.  it seems that even the slightest shimmer in the drive belt is reflected to the blade.  when we got it up here, we discovered that the blade guides, when slid in and out change in elevation, and may be changing in pitch as well.  we are going to concentrate on that in the morning to see if we can do a bit of heating and bending to eliminate whatever slop is causing this.  Its possible that the actual guide arm itself might be slightly bent.  if that's the case, might have to replace it.

Ronwood

Thanks for going out of your way on this.  Sounds like a really handy tool.  Is the Woodmizer manual somthing that is available online, or do I need to actually own a Woodmizer to get it?  I would like to see the procedures outlined by them for calibration.

Feed Rate....

I was judging the feed rate on the engine load.  When the engine started to load, I would try to maintain the same pressure to maintain that engine load.  Its possible that we could be over feeding the saw, but once again... this is where the lack of experience falls into play.  I was trying to get as much production as possible out of the saw, but I don't want to sacrifice quality, or broken blades for production.  I just feel that 2376 Board Feet in 40 hours of operation is a bit slow.  Is this what I can expect?  What type of board footage, starting with just green logs, is average in 40 hours for a manually fed saw?  

[LeeB]

If I read correctly you are getting this problem onreally wide boards which tends to make me beleave you are either feeding too fast or don't have enough power(drive belt possibly slipping). Could also be your guides in as you say they have a litttle slop. 2400bf in 40 hours on a manual mill is about what I get by myself cutting 4/4. What size motor you using? LeeB

[GoManGo]

Yeah, the problem is usually just on really wide logs. We are running a 22 horse Wisconsin two cylinder.  I guess I should slow the feed down a bit and see what happens after we get the mill back together.  Thanks for the advice.

[woodmills1]

See if you can either view on the web, or obtain a copy of the little sawblade booklet that timberwolf puts out.  It really is full of lots of good info on blades, blade use and sharpening.  Try this, use one of the blades that gave a crown on a large log, but try it on a much smaller log.  If there is not a problem with that blade on the small log then you have either too much feed speed or the blade you are using is just not right for larger logs.

I cut a lot of 8x8 red oak for a barn a few years ago and was getting a slight crown on the finished product.  The customer was fussy so I had to find away to fix it.  I cut all of the pieces to 10x10+ then put on a new blade and trimmed them to 8x8.  It seems the small amount of dirt and debris in the bark was enought to dull the blade to the point that there was a crown after a few cuts.

[Tom]

If your guides aren't true, then that would be the first thing I'd look at.  The slipping band blade or power belts would be the second.  That slows the FPM of the band and will cause lots of strange stuff.


https://forestryforum.com/cgi-bin/board/YaBB.pl?board=sawmill;action=display;num=1078813785;start=0

I found your old post to look at the pictures.

I still think that tensioning of the blade may be a viable target.
That blade flutter is indicitive of a Lo-o-ong blade, and/or loose tension.

Here is an idea that has nothing to do with your problem: ;D

Instead of the "back wheel" on the guide being at a 90 degree angle.  Think about trying it twisted up about 10 degrees or so counter clockwise.  It's just a thought but it looks like it may give you more surface wear and also help to pull the blade up tight against the upper roller.  If it works, you might be able to get rid of the lower roller. This is just a WAG that entered my mind as I sat here.

[ronwood]

GoManGo

Below are several pictures of the alignment tool. It has a small clip that attaches to the saw blade. Should be able to make one.



Second picture




Per PM from Tom Good info !!   8) 8)

If you balance that alignment tool by centering the clip, you will find that you will get a more accurate alignment.  It won't pull the blade down with the weight of the tool.

Centered, you don't have to move it, just move the head back and forth over the bunk.  There is enough length that you will still be able to determine whether one end is  higher than the other, with ease.  

Tom Once again thanks for the input

[D._Frederick]

GoMan,

Since you are using Vee belt pulleys for band wheels, you should not have tracking problems that is taking the set out of the saw teeth. I have read that too small diameter saw wheels will remove set, if you are 19 inches or larger you should not have a problem, WM has used this size wheels for yours.

How much saw dust is left on the boards? Crowning and and lot of saw dust results because of not enough set. Since you are using WM blades you could have 1100lbs to 1200lbs stress for blade tension.

[GoManGo]

Well D._Frederick.  Its hard to say how much sawdust is left on the logs.  At times, the cut is really clean, but other times is totally covered.  I noticed that there seems to be some connection with my feed rate.  If I really push the saw, the logs are spotless, but if I take it easy, the sawdust is pretty bad.  As for tension.... we are working on a way to measure the pressure, but for now... hehe, ummm, yeah.  We just wing it.  

Tom,
We have redesigned the blade guides since the first post.  We are no longer using the bottom roller.  As for the 10 degree offset guide, sounds like a good idea.  

[FeltzE]

I encountered a problem with blade tracking on my mill that caused me a lot of headaches and can goe easily unchecked.

One of my guide wheels slipped slightly aft of the other creating greater backpressure on one which resulted in the blade flexing and climbing or diving. All other alignments looked fine. I readjusted the blade putting down pressure on the guides, checking level, increasing set, and still had a problem with wavy cuts which gets worse with width of cut.

You can move the guides both aft then track the blade on the drive wheels (keep your covers on for safety) without releasing tension after the band is properly aligned (tracked) bring the guides forward to a position just about touching the blade. then realign them for horizontal tracking. Equal back pressure on both guides will make for better tracking of the cut. So make sure they are properly set.

Eric

[Timbo]

The blade that is crowning upward on you can be 1 of 3 things . I am considering that you have sharp blades and the set is at least .020 per side.
What your band is telling you is that it is easier to saw up that to saw straight away. Which it is showing you that the least path of resistance is slightly up rather than straight away. These 3 check points will help you.
1. Check Roller guides for wear in the front edge. If there is .010 to .015 wear then a blade that has a tendency to rise up will be much worse. Always adjust the guides  to hold the band straight with you log bunks.
2. Check the flattness of your blade. Flattness from the back edge to the front gullet. A straight edge razor is good to use. If you see a dish that looks to be .005 to .010 in the middle of the band, this could be all of your problem.  I do like to see at least .001 ot .003 of dish in the band on the roller guide side of the band. But if there is more that .003 it will be a riser or Crown the lumber. This can be altered by hammering or rolling.
 3. Your bandwheel could be tilted back at the top away from the log slightly. The bandwheels have a direct relationship with the band flattness and these two determine where the least path of resistance is. Of course you want this to be straight away. If you tilt your bandwheels forward at the top at least 1/16 of an inch to 1/8 you will change the pressure points of your saw and hold the front edge down. The roller guides should always hold the blade flat, parrallel with the bunks.    
To help you understand the relationship with the wheels, I will give an exagerated example. If you tilted the wheels 3 inches back at the top and tried to hold the blade flat with the roller guide the band would saw up, extremely up.If you tilted the wheels 3 inches forward at the top toward the log and tried to hold the band flat with the roller guides the band would cut down extremely down. So there is a perfect spot with the bands that you are using that will be straight away. Remember a band sawing up is not refusing to saw, it is actually sawing under harsh heat conditions by running up overthe crown and down to the other roller guide, and it is saying rather loudly that it is easier with the present adjustments to saw in this direction. Simply change the least path of resistance  to straight away and your problem si solved.  Call me if you need some more help  334-692-5074 .

[Wes]

I had alot of problems with WM softwood blades breaking , they cut great but broke after 200-300bf, and nothing i did fixed the problem. I think they were too heavy for the blade wheel diameter, I see now that they no longer carry the style that they sold me, I e-mailed them direct and never got a response on this so it was an expensive lesson. :(

 I went back to using WM standard blades on softwood and they work just fine as long as they are sharp. ;D

 Wes

[Tom]

Welcome to the Forestry Forum, Tim.

[Larry]

Welcome Tim.
I read your newsletter as it is filled with a lot of good pointers.  I understand the dish concept on the band but never could figure out how you get it.  Do you run the bands through some type of roller or does the band steel come that way?

[D._Frederick]

Timbo,

Glad to see you here, always read you news letter, has valuable info for us band operators.

[Timbo]

We controll the flatness or dish with a roller. I have taught many people all over the U.S. to hammer with a ball peen hammer over a block of steel. However we have just developed a hand cranked roller, just like the roller we use in production. This roller makes it easy to control.
Most people don't realize that flatness is more important than larger or  lower set. When flatness is controlled the set can vary as much as .005 from one side to the other, as long as there is enough set on each side to give clearance for the body, (for the prevention of heat).

[smwwoody]

Great to see you here Tim.  Do you roll all the bands you get in to sharpen?

Woody

[Timbo]

Hi woody

we roll all the blades that have a wrong curvature. which is most of them. You might also like to know that we check all of the new blades going to sawmill before they ship. Most of those have to be rolled just a little. The extra  time is worth it.

[Buzz-sawyer]

Is the effect of rolling...more resharprning out of the blade? or better performance?

[Timbo]

The effect of rolling the steel of the body is actually forging the steel and makes it stronger. it will when used properly make the band cut straighter and cooler, which will also allow faster.

[Buzz-sawyer]

So the strengh (resharps) , and performance should both improve...