Band technolgy

Larry · December 19, 2005, 05:47:22 PM

I'm out in the shop re-sawing dry 10" to 12" wide white oak crotches today. Sounds like tough sawing on your mill right? Well I'm re-sawing on a shop bandsaw...1-1/2 horsepower motor. Feed is quite fast...no waves or cup and going through wild grain straight as an arrow.

Band is 1/2" wide, .021 thick, and 8 degree hook. Don't have the tension cranked up big time either. I think the big difference is it has a variable pitch. Four different tooth spacings between the red marks and than the pattern repeats...hard to see in the pic but I measured it with the calipers. Brand is not particularly important as there are several companies in the race, with contenders. The only drawback I can see is how would you ever re-sharpen anything like that?

Guess my point is I think us sawmill guys are being neglected in favor of woodworkers as far as band technology goes. Wonder how you would get somebody like WM or Lennox interested in doing something for us...or maybe they already have. :-\

Tom · December 19, 2005, 05:53:05 PM

If the pitch isn't too far off, a sharpener like Woodmizer's will handle it OK. The reason is that the blade is moved by an arm that is pushing on the tooth whose back is being ground and the face grind of the tooth depends on the full extension of the arm. So, it has the capability of following pitch.

I've missed teeth on a blade from having hit a nail and it didn't cut any better. :D

what do you suppose the variable pitch is supposed to be accomplishing?

Larry · December 19, 2005, 06:08:45 PM

Quote from: Tom on December 19, 2005, 05:53:05 PM
what do you suppose the variable pitch is supposed to be accomplishing?

Don't know Tom other than it sure cuts a lot better than the fixed pitch bands. I have some old sawmill books that talk about pitch, gullet area, and feed speed. I can read the words but I don't understand what they are talking about. :-[

getoverit · December 19, 2005, 06:29:37 PM

I did a google, and here is what they say about the variable pitch blades:

"Premium variable pitch blades offer high heat, wear and shock resistance. Variable pitch allows a broader range of applications and reduced vibration when cutting. This combination results in the longest blade life among competitive blades."

"Hooked VariableTooth
Designed for:
- Low Vibration Cutting
- Solid Materials"

the strange part is that they are generally talking about cutting metal with them :-\

Tom · December 19, 2005, 06:45:07 PM

I called google and went off to school too. :D lI think the variable pitch is more of a metal cutting blade. You're right, I didn't find any instance of it being recommended for wood, although it might be the ticket in something like knotty pine or even Loblolly, where there is a drastic difference in the amount and hardness of early wood as opposed to late wood.

The suggested remedies for variable teeth were for (metal) thin stock, pipe or tubing. Pipe and tubing have two entry points and variable teeth on the blade would help to make sure that they weren't both being approached by a tooth at the same time. The accomplishment would be breaking up the harmonics and minimizing vibration.

Knowing the manufacturer might help in determining what he intended the blade's use to be.

You might be having good results because your wood is dry and there is a diffeence between a shop bandsaw and horizontall sawmill's blade speeds. I doubt that there would be a signifacant difference in a log where one of the main problems is filling gullets with sawdust. The smaller gullets of the diminished pitched points would soon fill and be relatively non-functional throughout the rest of a cut through a log, which could be a distance of 20" or more.

All this to say I'm just guessing. :D I use 7/8" pitch raker blades and they do just fine.

highpockets · December 20, 2005, 08:04:06 AM

Tom,

I am planning to build another blade sharpener. I am interested in your comment about your grinder cutting the back side of the tooth and the front. I can't exactly get this in my mind of what is happening in the sequence of movement. I have never seen the WM Sharpener up close.

About six years ago I built a sharpener and used a chainsaw blade sharpener base, etc. I added a small gearmotor with a cam to move the blade and also drop the wheel. I wasn't completely happy with it. I did use a straight a.c motor and had no way of controlling the speed. I now have some variable speed motors which I am going to use. Anything you can add would be appreiciated.

Tom · December 20, 2005, 12:29:02 PM

If you get a chance to watch a WoodMizer sharpener, do it. I wouldn't change a thing on it except for, perhaps, the blade rests. And what they have is easily modified.

I wonder if Wood Mizer might have a video clip on their web-site. If they don't, it would surely be a good addition.

They don't tout their sharpener enough and it's a shame. The thing is a good one. Except for the electronics, it's bullet proof. I've run the fool out of mine for fifteen years and the wear is negligable.

They have one thing on there that is nice and that's a microswitch for stopping the sharpener when it has made a revolution of the blade. It works by sticking a littling magnet on the blade that trips the switch when it comes back around.

I run mine on AC but it is actually a DC device with a converter that makes DC from AC. If you are in a bind and need to take it to the woods, all you have to do is hook it up to your truck battery and everything will work but the Little Giant water pump. I've done that a time or two and it sure was convenient.

Having the water bath sure makes for a sharper tooth. I seldom have a burn mark. A metalurgist may say that I'm wrong but it sure seems to be.

highpockets · December 20, 2005, 04:16:11 PM

Tom,
I totally agree on the coolant. I have a machine shop and can appreciate grinding with something. I just built a jig for sharepening me 20 planner blades on my bridgeport mill. I use a mister. Do you have any photos of the WM sharpener?

Kirk_Allen · December 20, 2005, 04:42:34 PM

Tom, talk to me about this micro switch? Does your unit have that? I was not aware of that feture but it sounds great. I couldnt find anything in my manual about it.

highpockets · December 20, 2005, 05:11:31 PM

Tom,
I reread you description of the sharpener then went to Wm site and looked at their sharpener. The photo is not that great but it got me wondering if the arm rides a tooth profile and controls the wheel depth?

Tom · December 20, 2005, 05:56:34 PM

Kirk,
Yes, my sharpener has it. It is a little device that is behind the blade on the right side of the blade clamp and is attached to the electronics VIA a telephone cord. If you put a little magnet on the back of the blade, it will pass between the blade and this little switch just before hitting the clamp. The magnet trips the switch and everything stops. ;D

Highpockets,
The arm is attached to the rotating cam which changes the rotating action to a horizontal action and the blade is pushed by the arm coming in contact with the tooth. As the cam turns the arm is disengaged and dragged back over the back of the next tooth where it drops off of the point into the next gullet and contacts the face where it pushes the blade toward the stone once again.

The push arm is made from a piece of "all-thread" which allows it to be lengthened or shortened and that determines the amount of material taken off of the face of the tooth. Also it allows the stone to be centered in the gullet to get a good back grind.

The depth of the gullet is controlled primarily by the shape of the cam. A bearing/cam-follower , through a linkage, causes the head to rise and fall in a proper pace to create the general shape of the tooth and gullet. The stone can be raised or lowered to present this motion to the blade. A finer tuning of the shape of the tooth is caused by the shaping of the stone. It controls the shape of the transition curve from the face to the gullet and, to some extent, the height of the tooth. A properly shaped grinding stone will produce a smooth transition, a deep gullet and a tall tooth.

The rake of the tooth is controlled by an axis on a bolt that allows the motor and grind stone to be swiveled.

highpockets · December 21, 2005, 06:25:43 AM

Tom,

Thanks for the info. It sounds pretty much like what I built the first time. One thing I did not have was a wheel with enough width to do what you are talking about. I was also lifting the wheel off with an eccentric (arm pinned to the shaft) instead of a cam. I know it is basically the same but the timing can be better with the cam if it is designed right, I think.

Mine allowed the wheel to drop down the face of the tooth, but it lifted off as the tooth started to move. I am not sure if this makes sense to you but it does to me. I know what I'm looking for now. Thanks.

Cedarman · December 21, 2005, 07:42:09 AM

Tom, how fool proof is your magnet switch? Once in awhile mine won't trigger the stop. So I am a little gun shy. But It sure is nice to turn it on and walk away for awhile and set blades.

Tom · December 21, 2005, 09:01:53 AM

Mine works every time. I adjusted it so that the switch would be close to the magnet, Painted the magnet to make sure the correct side was attached to the blade. I guess there is a correct side. I figured the switch had to be pushed or pulled and one side of the magnet worked better than the other.

I make sure that the magnet doesn't get dragged along the blade by one of the uprights on the frame.

If the wire connection is good, there isn't much to go wrong.

iain · December 23, 2005, 04:55:48 PM

Vari pitch works GREAT for resawing on a shop band saw
Matrix steel even better
the reason its vari is to stop harmonics, but when resawing deep dry stuff, if you get the feed right the the harmonics come back, which can be good and bad

iain

Larry · December 23, 2005, 05:21:13 PM

Thats what I'm finding out iain. Using a carbon Woodslicer I'm getting veneer that only needs light sanding and thinner slices than anything I have cut in the past. Lenox appears to be the leader, but there really good bands are only available in high dollar carbide and to a lesser extent bi-metal.

Lenox also has bands with a different set than what we are used to on our mills. Bandmills use a raker set with a 3 tooth sequence of left, right, straight. Lenox has carbon re-saw bands with 5 tooth sequence (left, right, left, right, straight) and also a 7 tooth sequence. So what advantage is that?

Guess I'm just curious as why things work.