Cupping Band Blades...Too much Tension?

logwalker · September 04, 2008, 12:49:21 AM

Fellow Bandsaw Sawyers,

I have been sawing for several years and have been observing my blades develop a downward cupping that causes the blade to dive. I know there is a lot of controversy about rolling blades and whether it is ever necessary. But it is quite easy to see the cupping with a flat bar held to the band and the diving is a big pain.

I opened a new box of WM blades even though I have a large quantity of fairly fresh blades that will not cut straight. So out of the box I am setting the tension lower than ever before. I want to see if the 2500 lbs I was using before could be the culprit. I am using 2000 lbs and it cuts straight thru the knots and all.

Has anybody else made this connection or have any other ideas on how to combat the cupping I am experiencing? I am also considering making a handheld band roller that would slip over the band while mounted on the machine and reverse the cup. Is anyone using the Cook's roller and if so what are the results. Do the results last for several sharpenings?

Woodmiser recommends a psi of 2200 or 2300 lbs. That was for a 1 1/4" blade. I thought that if I went to 1 1/2" I should increase the pressure to 2500 or more. I think that might have been a mistake. I sharpen and set my own blades if that makes a difference.

Joe

bandmiller2 · September 04, 2008, 05:28:12 AM

Joe, I've wondered the same thing it seems bands tight around the wheels would put a cup in them.Whats the profile of your belt backs are they rounded or flat??Mayby thats an arguement for steel bandwheels they have just a slight crown not enough to deform a band.That sounds practical to roll the bands on the mill have convex and concave rollers and a method of clamping them togather in a controled manor,could be risky if not done right.Sorry I don't have real ansers for you Joe but I'am sure the flood gates will open.Frank C.

ladylake · September 04, 2008, 05:56:16 AM

I just sawed a dry old pine log cutting up to 23" wide. I started with a sharpened blade that dipped and cupped some not cutting to fast. Then I put on a brand new blade and increased the feed rate a little, it cut wavy and cupped on the down wave. The 3rd blade was just sharpened and set with more set, straight as a arrow. Those dry pine logs give me the most trouble of any wood. Steve

amberwood · September 04, 2008, 09:20:46 AM

You will need a lot more set on the old pine, we cut quite a bit with 1.25" WM blades and need to keep the set up at 025 to avoid problems.

DTR

Chuck White · September 04, 2008, 09:32:24 AM

Wood-Mizer at Hannibal recommends running the blade tension at 27-2800 PSI on 1 1/4 inch blades.

That's what I've been running all summer. No cutting problems. I'll have to check the cupping though.

I was told that regardless of the blade tension, tension doesn't break blades, constant flexing does.

pineywoods · September 04, 2008, 09:43:32 AM

Joe, I cut mostly dry pine and I had LOTs of problems just like you describe. Bout wore out the tracking adjustments to no avail. Two things--You need lots of set, minimum 25 thousands. Borrow a good micrometer and measure the diameter of the guide rollers, first right on the outer edge and then back against the flange. Mine were worn cone shaped, just a few rhousands. You can chuck the rollers in a lathe and true them up, but you have to use a grinder. Carbide lathe bits won't ever scratch them. I have a small collection of blades that just will not saw straight no matter what. Finally figured that one out also. After a blade has been sharpend quite a few times (theese are about an inch across) the tooth side of the blade actually stretches a little bit and you then have a blade that is shaped like a barrel hoop. Rolling stretches the back side to straighten the blade. Probably not worth the cost and trouble.

backwoods sawyer · September 04, 2008, 05:33:11 PM

I do not have a roller set up, so when I get a saw that is stretched, I just bench it. What I mean by that is I have two wooden rolls one slides to take the slack out of the saw. In the middle of the rolls, I have a long flat heavy piece of steal that I use as an anvil. I have good lighting behind it so that I can take a straight edge and look for cupping divots-bumps and other irregularities. I use a brass 8 oz square head hammer to tap the band flat, keeping the teeth off the anvil. I only bench a saw if it is not running at it's best.

logwalker · September 04, 2008, 09:00:09 PM

Backwoods, that sounds like a good setup. What I don't understand is that after being pulled over the belts on the sheaves, it cups in the opposite direction. So if I wanted to flatten it would I hammer the back edge of the blade? Joe

MartyParsons · September 04, 2008, 10:06:18 PM

We get into these discussions from time to time ;), I would a say the blade roller is not needed if you are using WM blades but if it works for you do it. Please understand what the roller does to the blade. There are lots of factors in blade profiles beyond set and hook angle.
I can only speak for PA Re Sharp be we have very few complaints about the blade cutting performance. We get requests to change the set on some blades ( mostly add more) to keep the lumber clean or some other issue. We are putting blades on many other mills besides WM and we have some tough customers. Just started working with a palett shop that has 6 heads running, sawing mostly Hickory and WO. They said WM blades would not out perform the blade they were using. But we got an order for more blades this week.
We have always ran the blade to max tension at shows and even when I saw for our own we run the bands a little over the orange on the gauge. We have another customer with a custom mill with a carrage system where the blade is stationary and the log moves I think the blade is 234" in length and 1 1/2 wide they are using 4 degree and 10 degree. The increased the blade tension and improved cutting performance but the idle wheel bearing would only last about 25 hours. Last week they were modifing the wheel to accept a larger bearing.
I guess if you called and said you were getting wavy and diving I would ask you these ? Is the band speed changing in the cut? Is the alignment of the blades correct? ( blade guide tool)
hope this helps.
Marty

WH_Conley · September 04, 2008, 11:56:36 PM

At risk of being told that I don't what I am talking about. I run WM and wolf blades at 3000+. Don't give them a chance to dip, If they do it is usually because they hit a nail or rock. Only problem that I ever had was that they got so thin that the teeth were hitting the guides, taking the set out.

With this theory about half the blades in a box will break at 3-4 sharpenings and the rest will run 8-10. Why? I have no idea.

deeker · September 05, 2008, 02:02:28 AM

Send the diving blades ( even WM blades) to Cooks and have them rolled flat. You will be shocked. Hard dry pine is what I am cutting right now, going to send a few of the blades to Cooks and have them rolled. Oh, by the way WM blades are not above diving or rising in the cuts.

I have most of my trouble with the wide ( 23-24") spruce boards. Hard wood on the edge from drying, and hard around the knots. The center of the tree (away from the bark) is softer and does funny things with the blade. Almost like a half frozen log.

Good luck

Kevin

logwalker · September 05, 2008, 02:58:05 AM

Hello Marty, I am glad you responded. I am using a 1994 LT40 Hd 15E. I have a bike speedo on the idler and I know nothing is slowing down. I use 1.5" with 10 degree hook and .045 thickness.The blade doesn't just dive at the knots or beginning of the cut but immediately and continuously thru the log. I can put on a new blade and it will work perfectly for several hundred feet and then drift only a little. I sharpen lightly and set it and still works great. But at some point before it is worn very far it will begin to dive. I then check it with a straight edge and it is obviously cupped in a down direction. It might be after sharpening 3 or 4 times or a few more. But the blades look great. Not burned or discolored looking.

I have gone so far as to readjust the guides into a slightly upward orientation and it works to a degree but not consistently among several blades. But then when I install a new blade it rises badly in the cut.

So why are they cupping to begin with? I will check my wheel belts carefully tomorrow to try and eliminate them. Something has to be causing this. I sure don't like to park a perfectly good sharp blade on the wall because it won't cut.

I should have called corporate in the beginning. But I wanted to see if others were having similar problems.

Joe

MartyParsons · September 05, 2008, 07:29:30 AM

The last mill I saw doing this the blade guide arm was out of adjustment, so it was related to an alignment issue. I would recomend you go throught the alignment procedure. If there is a step you dont understand call me or e-mail I will galdly help out. What about the 1 1/2 width blade. Are you using the wide rollers or do you have the high performance blade guides to help support the width of the blade? I just about always use 1 1/4 width unless we are running a 70. Again a personal prefference.
Yea I hear you guys about WM blades diving. If you feel the roller works use it. I am just trying to help not attacking you or another company. Dont get offended.
Marty

logwalker · September 05, 2008, 12:06:36 PM

Marty,

I am using the 1.5 guides, original style. I think they are within tolerance but will check them this morning. How could the guides create the cupping? Do you have any ideas on what to look for?

One other factor I can think of is my belts. I run the smaller version which fit tight in the groove. Just throwing out ideas. Joe

MartyParsons · September 05, 2008, 08:47:46 PM

Original style? What do you mean by that. Part # A04925 or 014299 roller. I realy do not thik the B56 belt would make any difference on the wheel for cupping issues. Is the belt above the wheel? WM recomends running the loose belt because it helps keep the saw dust from sticking to the wheels and you can remove them with out cutting the belt off.
Remove the roller guides idle side and drive side. tighten the band to propper tension and track the blade. How far do you track the 1 1/2 blade on the wheel. Note here: the more tension you pull accross the teeth the better the blade will cut, so if you run the blade further back on the wheel the better it will cut, but ( you know this was coming, You should not run the gullett on the belt. on a new mill the 1 1/4 blade will be flush with the back of the blade.
Ok now back to checking the blade guide arm, with two wheels and one blade measure form the blade guide arm to the blade (1 " strap that hold the guard) with a steel ruller that has 1/32 marks on it. run the blade guide arm out check measurment bring blade guide arm in check the measurement again it should be exact. Are the rollers tight on the arm? Can you wiggle the arm? These rollers are on cams and adjust the arm, it can be a little tricky ( most times this can take more than a few min to adjust) I also see the metal bent from the arm running into things like the log on return. Once you get the arm aligned up and down then do the same for in and out. Check the blade tilt before you put the rollers on with the blade guide tool. Install the rollers with 1/4 " deflection pulling blade down, space the rollers with 1/16 on drive side and 1/8 on idle side, check blade with Blade tool algin again and recheck 1/4 " deflection if it changed adjust it and then check blade tilt again. Adjust roller assemblys wo that they are tilted to the right 1/16. When nothing changes and the blade is running flat no tilt up or down, it should work great. Note again any part worn to make any of these adjustments change when the blade is cutting would cause cutting issues. The last one I seen they were cutting heart pine and you could hear the blade change sound and the idle side roller would stop the blade would dive up and down and cup, We changed the drive side mount ( worn) and adjusted the blade guide arm (it was coming up 1/8 " when the arm was in).

Hope this helps!
Marty

logwalker · September 06, 2008, 12:16:56 AM

Marty, It does help and it it sure great you can take the time to help.

As far as the alignment goes, I know I can get it closer than it is but the saw cuts perfectly with a new blade. It is only after the blade cups that it begins to wander. But I will check it carefully.

It seems to me there can only be a few causes for the warping of the band body. The wheels are the likely culprit. Too little set and the overheating that causes might be a factor. But from what I am hearing here, too much tension should not do it. I am quite surprised how well it is cutting with only 1900/2000 lbs. on the gauge. I didn't expect that.

The rollers are 1.5" style with no BC (bottom control pad). That is what I mean by original style.

Joe

backwoods sawyer · September 06, 2008, 12:22:20 AM

When I first got my mill, every adjustment listed above was off, the wheels needed crowned, every bearing on the guide, arm and wheels were worn out, the guide arm needed machined and both rollers were worn down on the front.

I switched from .045 bands to .055 bands while I worked all the problems out. I still prefer the .055 bands.

Do you have a top support for you band?

Tom · September 10, 2008, 11:37:22 PM

logwalker,
There are several threads on the forum about this very subject.

I havent' had the problem, but, I haven't run wide bands.

When the problem first began occuring, I understood from conversations with Manufacturers that it was showing up when wider bands were being used on narrow bandwheels. 1 1/4 bands will run fine ona wheel designed for it, but a 1 1/2 band put on that same wheel may cup. The reason was because the band wasn't supported on the edges.

logwalker · September 11, 2008, 11:46:44 PM

I think you may be right Tom. On this last set of blades I have begun to run lower psi. I am down to 1900/2000 lbs. I had been pushing the 1.5's to 2500/2700 lbs. My thinking was that being larger they should have more. That may be what caused this last batch to get put aside. I just can't get them to cut straight and they still look good with lots of life left. I sure wish there was a reasonably priced roller available.

There may be other benefits to the lower psi. As in longer bearing life. Maybe the belts too. Will check back with results in a month. I am not cutting much at the moment. Joe

Tom · September 11, 2008, 11:57:47 PM

I agree with your efforts at a lower blade tension. Logic tells me that a wider blade should have more beam strength, so, it might not need more tension.

I'm a firm believer that the first efforts should be spent on a "sharp" band. Having sharp teeth is more important than hook, set, or any of the rest of the stuff. Granted, tuning the band with all of the adjustments can't hurt, but if it isn't sharp, it won't cut.

ADAMINMO · September 12, 2008, 10:29:30 AM

On the Baker mills we run 1400 lbs on 1.25 blades and 1700 lbs on the 1.5 blades. We have had excellent blade life at these tensions.

logwalker · September 12, 2008, 12:16:49 PM

Adaminmo,
Those numbers don't tell me what actual blade tension is. That depends on the size of the hydraulic piston that is tensioning the idler. Do you know how your system compares with the Woodmizer?

ADAMINMO · September 12, 2008, 12:49:31 PM

I think it is fairly similiar. We are putting about 35k strain on the blade for 1.25 and about 40 to 42k on 1.5" blade when checked with a tension meter. I think I am correct on those numbers. I can get more info on cyl. size and stuff if you need that.