I’ve had mixed results with a Hitachi B600A bandsaw. This is a 3″ resaw with VERY expensive blades. The machine is variable in how well it cuts. It often wanders on the bottom edge. I’ve tried all of the usual suggestions for truing the saw without marked success. Going to their website, I see that the B600A is long out of production and that all newer models have a backer bearing on both the top and the bottom. The B600A only has a bearing on the top.
It seems to me that this would make the saw bottom move back under pressure and thus bow out the blade. This may be why the veneer I cut varies in thickness top to bottom.
I’ve bought a bearing and some steel profiles to try to weld up a mount for a second bearing. Am I off base, or might this really be a problem?
By the way, it was new and CHEAP about 17 years ago. It was in the Whole Earth Access in Berkeley and the roof leaked. The table had surface rust and looked bad, but cleaned up with steel wool and oil in a few minutes.
Replies
You might check out the 12/02 issue of FWW; they ran an article I found quite helpful on setting up a 14"bandsaw for resawing. I am not familiar with the model you have but I found generally that a stronger tension spring, a good resaw blade and maybe most important was a fence that was adjusted to compensate for blade drift eliminated the problems you mentioned on my Jet 14".
I've used one with carbide, with the ceramic teeth, and the steel teeth. I'm left unimpressed. I think that if you have to resaw it's an adequate tool but new blades are necessary to get good cuts. It's an expensive machine to use because of the blades. The wandering cut is caused by heat, not lack of bottom thrust bearing support. Heat is caused by the slight dulling of the tips and/or too fast of a feed rate. As the blade heats the leading edge expands causing it to twist and wander. The only fix is to put a shiny new blade in and slow the feed rate.
By the way, I won a lunch on a bet I couldn't wrap that beast of a blade into thirds. I did it much to the surprise of the loser of the bet.
Lee
Furniture Carver
Lee,
I think I would have taken the other side of that bet and been among the lunch buyers. Wow; coiling a 3" blade.
I have a 1" carbide on order for a new toy (they are actually arriving together tomorrow) but I din't think I'd be able to third it. Any special tricks here?
You don't want to store the 3" baldes folded into thirds. On a blade this size it's far better to not put a twist in it. Folding the things is just a parlor trick meant to impress friends and attract women. Oh, and win a lunch or two.
I posted the technique I use to fold blades in the thread of that title. Actually, unfolding the bloody things is a lot scarier.
LeeLee Grindinger
Furniture Carver
It seems as if somebody might actually be reading some of my posts! Thank you Lee.
There is another alternative -- putting "back" in the blade. If, instead of cutting the edges of the blade square for the weld, cut them on a slight taper (so that the back edge is longer than the front/toothed edge). A situation will be created where strain on the blade will be maintained on the front/toothed edge when it expands with friction and cutting force heat.
If the front and back edges are the same length, and the heat generated by cutting and frictional forces expand the front/toothed edge disproportionally to that of the back, the front edge will wander because it is no longer stiff. As such the teeth will follow paths of lower density wood (eg earlywood) or get pushed to one side by sawdust spilling from the gullet. When it becomes very bad, it appears as if the blade is "snaking" in the cut.
I don't have the coefficient of expansion for steel handy or I would provide it. Basically calculate the total possible blade length expansion based on a 300 degree F change in temperature. This increase in blade length should then be "added" to the back edge by an angled cut. Reweld/rebraze the blade as before.
A good saw shop should have capacity to do this and the cost of rewelding the seam should be a minimal expense. If any of the filers have doctored bandsaw blades greater than 3" wide, they should immediately understand what you are attempting to do.
Additionally, you may not need to construct a "complete" guide for below the table. The guides on the large bandsaws in primary mills only push the blade away from the normal tracking plane of the blade.. AS long as you can align the top guide with the bottom guide (and keep the blade perpendicular to the table surface) you will not have to restrain the blade from moving outward. The strain (tension) you apply on the blade should keep it running true.
Slowing the feedrate, new blade/old blade, may be the wrong approach. The friction generated in cutting is generally less than the rubbing friction of the blade passing through the kerf. Too slow a feed generates a very fine chip/particle (sawdust) that can spill from the gullet and push the blade to one side or ta' other. Underfeeding will dull a blade faster than normal cutting.
Edited 2/26/2003 5:18:53 PM ET by NIEMIEC1
I just learned a bunch; thanks. Does one do this on a 1" carbide? I am stepping up from a 14" Delta and will appreciate help.
I certainly think that putting back in blades could be done with all sizes greater than 0.5". The carbide should provide an excellent cutting blade as it is a formed tooth and as such will cut the entire width of the kerf (as opposed to a set tooth blade that cuts only one side at a time). Additionally because each tooth is shaped by grinding, it is likely that you will not have a poorly set tooth with greater side clearance than the rest of the teeth -- this should equate to a smoother cut.
Since the blade will now be a section of a cone rather than a section of a cylinder, you will probably have to put some tilt in the top wheel so that it tracks correctly. The only possible problem that could ensue is if you overfeed the blade and the tooth dives into the cut. With the top wheel tilted forward there will be nothing to keep it from coming off the wheel. The shrouding of the machinery should provide adequate protection.
I would further recommend that you obtain a blade that has the greatest pitch (tooth spacing) as possible so that your teeth cut rather than rub. More teeth do not necessarily mean a smoother cut -- the key is to have an appropriate feed rate that produces a chip that does not spill from the gullet (ie larger than the tooth side clearance) and such that you do not overfill the gullet. Gullets will generally hold about 60% of their volume in sawdust.
In the large mills, guides (one-sided) are set so that they constantly put adequate pressure on the inside of the blade forcing it outward. Generally these blades are cutting green wood and use some sort of lubricant (oil in water) to reduce friction. You can probably do the same with a ball bearing that is wide enough to support the blade but narrower so that the teeth protrude beyond the bearing.
Stepping "up" from a Delta 14-inch? That must be some toy... what are you getting? (Just curious, and prepared to bring lots of resaw work to your shop.)
David"The world that was not made is not won by what is done" -- Mundaka Upanishad
Bring away. Assuming that I have the new DC in by then. What I received yesterday was the Agazzani 20". Nice toy, it seems. So far, have just cleaned it and fiddled with the guides, etc. The instructions are worthless. Took me 4 hours to figure how to turn it on. And, the bride is out of town this weekend, so guess what I'll be doing?
The prob. with the DC is ceiling height. It will fit, but just barely, and will require a lot of moving this and that. This spring I hope to add an outside entrance to the basement, and if so, am trying to have a landing that is 8 feet tall, and will hold the DC. If I can do this, then the piping configuration is one way, if not, then another. Resawing kicks up a ton of dust. I have an older DC now, of course, but what it misses is much. Oh, what the heck; bring it on either way.
Stanley, you know I hang on every word you type but it's going to be a really hard sell convincing me you are the one who figured out the band saw blades expand when they get hot. It's pretty common knowledge. Your idea of welding the joint at an angle won't work. The tension you need for this idea of yours needs to be the entire length of the blade and a weld such as you describe will tension only the length at the weld. It would go through the machine with a horrendous CLUNK, CLUNK, CLUNK. This is assuming it would even stay on the machine.
I think a better solution would be to try to control the leading edge and let the back do as it wants. You figure that one out and you could probably win yourself a patent.
LeeLee Grindinger
Furniture Carver
Lee -- it isn't my idea but instead an idea that is used on every bandsaw in the primary mills of the PNW and the South. Seemingly it is not one of those practical ideas discussed in most books on wood machining and appears only in those dealing with saw doctoring.
I failed to note that it was a 3" blade. For a 3" blade to cut properly, it may require tensioning (in its correct usage where the inside of the blade is stretched with metal pressure rollers). This is done so that the blade will run only on the outside edges (called the tire) so that the strain on these areas will be greater. Without tensioning, at any strain level, it is almost impossible to keep the blades on the wheels.
When back is put into a blade and the weld is properly dressed (smoothed) it does not go clunk, clunk clunk. It runs perfectly smooth and will track properly if the top wheel has some tilt. Adjusting top wheel tilt is exactly what the tracking screw adjustment does.
And while it may seem odd, if you take a section of a cone that is parallel to the base of the cone and cut that section along a line that runs perpendicularly from the base to the tip of the cone, you will see that at the cut, an angle will be formed such that it is not perpendicular to either edge.
You can test this with two strips of paper -- take strips that are about 1" wide. Join one where the ends are perpendicular to the back edge and one in which both ends are slightly angled (say 3 degrees). When the ends of each of the pieces are taped together and placed on a flat surface, one will be a section of a cylinder and the other will be a section of a cone.
And it is by this principle (of putting back in a bandsaw blade) that the strain is maintained on the front edge.
I've heard from bandmill owners that they resaw on their bandmills. They say it's quite accurate resawing to 1/4". I wonder if there is crossover technology that isn't getting employed. Actually, the only resaw for shops I'm aware of is the Hitachi. The blades are only a hundred inches or less long so there aren't nearly as many teeth as a band mill, perhaps that's the limitation. I've never been impressed with the Hitachi for the reasons I've stated earlier but there are few choices for the shop that needs a resaw.
LeeLee Grindinger
Furniture Carver
Lee -- Part of my frustration as a wood technologist is that there is very little apparent crossover between the technology employed in large bandmills (eg primary sawmills) and cabinet shops and ESPECIALLY portable sawmills. It is almost as if individuals want to believe that cutting dynamics change for the wood somewhere in between.
It is very frustrating when I get into a discussion regarding cabinet shop bandsaws and individuals become very hostile and confrontational defending their ideas when they are completely contrary to accepted wood machining theory/dynamics. The fact of the matter is that for all the expertise among woodworkers, most have never read anything that gets into the basics of wood machining theory/dynamics -- something that I find incomprehensible.
The reason that the Hitachi blades have fewer teeth is probably because somebody followed the accepted ratio of bite is to feed speed as pitch (tooth spacing) is to blade speed and designed the blade to match machine capabilities.
You mentioned an apparent tolerance of 0.25" regarding sawing accuracy. Based on recollections now 7 years past, primary band headrigs running 60' long 12" wide blades at feed speeds around 9000 fpm were cutting lumber from logs to tolerances a quarter of that or better. The goal of most mills then was to produce saw-sized lumber, both consistently smooth and accurately sized such that they could eliminate planing and thus planer losses. Most of the time when I would get with a group of sawfilers talking about these issues, I was smart enough to keep my mouth shut and my ears open because some of these guys had devoted their entire lives to doctoring saws.
I guess I take a different view, Stanley. I belive all companies that produce tools are in a juggling act, juggling quality against cost. I believe that in the end they honestly try to deliver the best quality for the best price.
Cutting green logs is quite different from cutting dried lumber. I cannot believe that if Woodmizer (as an example) felt they could produce a band saw for the workshop that outperformed the ones currently out here for a comparable cost that they would not do so. Profit is a strong motivator.
The real reason Hitachi resaw blades have fewer teeth than a bandmill is that the blade is shorter.
LeeLee Grindinger
Furniture Carver
Lee -- I return to my original premise that very few individuals who consider themselves woodworkers have done any reading or research in wood machining theory/dynamics. For example, what is your background on this subject? And further I think that many/most machinery ventors are likewise ignorant on the subject.
I have done a fair amount of research dealing with portable sawmills and without one single doubt believe that the bandsaw blades that portable sawmill owners use are completely inappropriate for the application. And this is not some personal opinion -- through my contacts from OSU, I talked with four individuals who are considered pre-eminent authorities in sawing technology -- Eb Kirbach (formerly of Forintek West/ UBC, Warren Bird (president of CalSaw), Rich Budke (president of Systematic) and Carroll Sizemore (Cascade Southern) and they all agree with me. I likewise think that the results speak for themselves -- very low throughput and horrible quality (size tolerances and surface smoothness).
SEveral issues are preventing change -- the first is the fundamental lack of knowledge (even though everyone seems to have their own pet explanations). Secondly, most operations do not have any systematic QC programs that allow individuals to evaluate the performance differences between various options (even if they were available). Also extant equipment, would have to be modified if change was to be implimented. Finally it has only been recently that different technology has been available.
The only way that change will occur is that if consumers begin to demand different options. And for this they, at least in the beginning, will have to pay a considerable premium. In the long run, there will be a positive result because less resource will be used, production rates will increase, and with smoother and more accurate cuts, less time (labor) will be spent on secondary machining processes (like sanding).
If a company is currently making a good profit doing what it is doing, what impetus is there for change. I cannot count the number of times I talked to various mill personnel about implimenting change in sawmills and heard the response -- if it ain't broke, why try to fix it. To produce a better bandsaw blade, the manufacturers would have to retool and then they would have to convince their vendors that they need to support this new technology, who in turn would have to then convince the consumers that they should now begin to pay 6 to 10 times the price for a replacement sawblade for their bandsaw. That involves considerable risk especially if their competitors take the approach that all this new stuff is unnecessary and foolish. And since most individuals do not know sawing dynamics/theory, it is likely that they are not going to set up their machine centers in an optimum manner so it is likely that performance will still be less than ideal. Yeah sure -- that's going to happen.
And to clarify a point -- the only difference between green wood and dry wood is the amount of water in the wood. As far as cutting dynamics are concerned this equates to an increase in density and therein related strength properties. The wood however is exactly the same -- there are not two separate and distinct machining theories to explain the differences -- just minor changes in variables.
I hate to say this because I truly respect your skills and your business acumen but for you to say that the reason the Hitachi blade has fewer teeth (greater pitch) is because it is a shorter blade is absolute nonsense.
Stanley, relax buddy, you're preaching to the choir here. As I said, every company out there is juggling the quality to cost issue. That's what you're saying too.
Longer blades do have more teeth. A 100" (that's a guess) blade for a Hitachi resaw has fewer teeth than a 1300" blade for a small band mill. Where's your sense of humor? Fewer teeth means each tooth is doing more work. More work means they dull more quickly. Yeah, yeah, yeah, tpi and pitch and blah, blah, blah, I'm sticking to generalities here. Relax.
Lee
Lee Grindinger
Furniture Carver
OK
Be aware that only one industrial sector invests less money in R&D than the Forest Products sectors and that is mining.
And if you are looking for progressiveness in good ol' USA manufacturing, might I remind you of the Automobile industry both in the '60's and for a matter of fact currently -- which in my thinking is 'give 'em what WE WANT'. Henry Ford's motto was 'give 'em any color they want as long as it is black' and I don't see that much difference in attitude now.
Very interesting, after watching a TLC program, I think it was monster machines, I came off with the impression that mining was pretty high tech. Have you seen the optical sorting systems that they use in diamond mining? Now that is one cool machine. The way things are going, almost all of the mining machinery is controlled from the surface. Now as far as the forestry industry goes, I have no reason to doubt you. However, I think we might see a change in the future as the global economy grows to such a size that it demands a more efficient process.
As long as much of the primary processing industries are controlled by large multi-national corporations and they continue to have good profits, do not expect to see a whole lot of change vis a vis technology -- unless of course it is related to replacing workers.
Hi Stanley,
A question.
If you cut the blade weld line crooked and rejoin by about 5 degrees each cut = 10 degrees misalignment, and when hot, the front expands by such an amount so that the leading and trailing edge of the blade are the same length and the blade tracks neatly, how do you track the blade when cold? Does this breed of bandsaw have some form of automatic tracking?
Cheers,
eddie,
imagining a horrible thump, thump, noise for the first ten minutes and dramatically shortened thrust bearing life.
Edited 3/8/2003 5:02:30 AM ET by eddie (aust)
If the front edge is shorter than the back edge and the configuration of the blade section is a cone rather than a cylinder, then for the blade to track correctly, there must be tilt in the top (idling) wheel. The tilt will push the top of the top wheel forward and the blade will track more toward the front edge of this wheel (rather than on the back edge). The wheels are crowned (arched rather than flat). The level of strain on the blade will keep the blade tight to the wheels with the strain forces evenly distributed across the blade and the blade would follow an appropriate track.
When the blade expands due to heat generated from the frictions of both cutting and rubbing, the blade will either remain on that same track (this assumes that the straining mechanism [what you likely call the tensioning spring/mechanism] will compensate for the blade elongation, or the blade will move slightly backward and up the arc on the wheels' crown.
Based on what is happening to the big blades on the big mills, I believe that both stituations are happening simultaneously -- the blade track is changing slightly and the overall straining of the blade is changing or maybe slightly dimininishing.
This should not cause any problems. Small shop band saws have bearings to control any "pushing" of the blade backwards. These bearing will likely keep the blade from coming off the back of the wheels. If the back the blade goes beyond the top of the arc (including the top wheel tilt) as long as the front edge of the blade remains in front of that arc, this front edge will carry the strain and the blade will track. Remember that it is the front edge of the blade that is doing the cutting and it is the edge that you truly need to have strained and 'stiff'.
If the front edge AND the back edge of the blade both lose the strain, then you are in real trouble but this will likely occur, if and only if, the straining mechanism is malfunctioning or there was not sufficient strain on the blade to begin with.
There is one downside to putting back into a blade. When blades are overfed, the teeth dive into the cut. The tooth (as a wedge) is literally driven into the wood and when this happens the blade track moves forward -- instantaneously. If a sawyer, in the big mills overfeeds the saw, the blade will come off the wheels and it is termed a wreck (as would be expected with 60' feet of steel,12+" wide travelling at 9000 feet per minute). With forward tilt on the top wheels, there is nothing to prevent this from happening (unless of course the back edge of a wider blade is on the back side of the crown and this edge has sufficient strain to keep it tracking behind that crown).
From my perspective, it is almost impossible to overfeed most small shop bandsaws. In my 30+ years of experience, I have only done it once and the blade broke rather than it coming off the wheels. If it were to come off the wheels in a forward direction, there is housing to protect the operator and, once it is off the wheels (especially the bottom power wheel), there would no longer be any power (force) tranferred to the blade (and it would stop). As such, I do not believe that for a properly operated and enclosed machine, there is a significantly great safety risk.
I would think that it is almost impossible to have any mechanism that would "adjust" tracking. From my perspective, the tracking mechanism compensator would have to be extremely sensitive and extremely flexible. Under most normal operational conditions, the variation in cutting forces and tracking forces and god knows what else would be both too slow and most likely more likely to over compensate such that it would cause more wrecks than it would prevent. Good mills have good teamwork/cooperation between filers and sawyers; and sawyers are truly very skilled operators making sure they neither underfeed (and overheat a blade) nor overfeed (and wreck it). And beyond insuring proper machine operation, sawyers also need to know how to evaluate a log to maximize both grade and recovery under the demanding and fast paced conditions of modern mills. 'Tis why headrig sawyers are truly the prima donnas of the mills -- they know how good they are and they certainly expect others to acknowledge their expertise.
I hope my explanation is sufficiently understandable. If you think about it for a while and do some visualization, it should make sense.
Being brand new to resawing and having purchased my first bandsaw, 14" with riser and 1 hp, I need to resaw 7" curly maple. I have a new Timberlake 3/4 3-tpi blade. My first attempt with a 1/2" 3-tpi was a disaster and I think I ruined the blade. The cut wandered, cupped, and finally was burning the wood. I tried tensioning every which way with equally bad results. I hate to admit that I did so many things wrong but despite tuning everything according to all of the tips I could read up on, things went badly.
I realize experience is a great teacher but I need a primer on how to get started with some chance of success. Thanks for any help.
Doug
I'm not an expert in resawing at all, but here are two things that I've read about in terms of resawing that you can try.
1. Build a point device for your fence. This is a rounded device (like a half dowel) that you attach to your fence exactly in line with the blade. The wood goes against the point and if the blade wants to wander you simply change the angle of the wood that is being resawn. You can put a pencil mark on the wood to help with tracking.
2. Take a piece of 2X lumber and make a pencil mark parallel to one side. Without the fence, push the piece of lumber against the blade and change the angle of attack so that the blade follows the line. Stop after about 8 inches and keep the board exactly where it is. Put a pencil mark on the table. Adjust the fence so that it is parallel to this line. This is the deflection of the blade, and when you resaw it should track pretty well and cut true.
Of course, there are other setup items on the saw, but the above are to ways two resaw pretty accurately.
John
Edited 3/11/2003 4:35:55 PM ET by johnhardy
Bandsaws appear to be relatively simple machines but in reality they are not. A quite jotting down of critical variables (off the top of my head) yields 14.
It is relatively easy to change the strain (tension) on the blade and hope that it will solve all the problems. Likewise there are equipment manufacturers that will be more than willing to sell you their "special" blade but in reality, while it might work better than your current one -- the blade per se may not be the cause of your problems.
Since you have not provided any information concerning blade variable particulars, I cannot make any specific comments about hook angles, pitch (tooth spacing), tooth configuation, gullet capacity, side clearance, etc., etc.
One issue I will always raise however deals with feed rate. If you are feeding the stock too slowly, the tooth bite will be very small and the sawdust produced will be extremely fine. If the particle size is smaller than the tooth side clearance, instead of being retained in the gullet through the cut, the particles will spill. When this happens, they can deflect the blade and increase the frictional rubbing forces of the blade in the kerf. The more heat, the more likely the blade will loose the strain on the cutting edge and therein snake in the cut. And the hotter the blade, the more likely it will cause machine burn.
As someone mentioned above, lead (the angle between the plane of the blade and the angle at which it actually cuts) could be a factor but it is very likely that more than one variable is creating your overall problems. Listed below are the variables I wrote down:
Bite, feed speed, bladespeed, pitch (tooth spacing), hook angle, tooth configuation, side clearance, gullet capacity, lead, depth of cut, guide pressure, strain, back and HP. Species and MC are also factors.
And rather like a circumstance when an unexperienced driver has an accident, the tires may get blamed but may not be the real cause just because they are at the interface between the vehicle and the road.
Thanks. My first assumption was exactly as you stated: it appears to be a simply machine. I have learned it is not, both from my early failed attempts and reading the posts on this subject. I take full responsibility for the inadequacies of my attempts.
I think I have gained some infoprmation that I can now go back and try it again, this time with more of a plan of how to start and what to look for if it isn't working.
Thank you for your posts and sharing the collective knowledge.
Doug
Thank you for such sharing all this information on band saw blade dynamics.
This is part of what I like about knots – the sharing of knowledge
Ian
Oh come on Lee..... LOL.... Just kidding... having read all the posts you are absolutely correct... As usual....... ! Dang its hard to argue with you !
If it's so hard to argue with me why do so many people do it...and win.
I guess I need to pick my battles more carefully.
LeeLee Grindinger
Furniture Carver
The thermal expansion for steel IIRC is .000006" per degree F per inch. I'm not sure how long the blade is though so I can't come up with a final number.
If you use a hypothetical blade length of 100 inches and consider a 300 degree F temperature increase, this would equate to an 0.18" change in length. If I were to want to put 0.18" back into a 1" wide blade, then I would mean that you would cut the blade ends to a 5.143 degree angle.
If you wanted to be more conservative and consider only a 200 degree F temperature increase (between the front of the blade and the back), then the angle for each end would be 3.434 degrees.
I used the following equation -- Thermal expansion coefficient x number of degrees x 100" (blade length).
To determine the angle of the cut for the butt weld, you divide this value by 2 (0.18" divided by 2 equals 0.09"), and then obtain the Inverse Tangent of 0.09/1.
To determine the width of the blade measure the perpendicular distance from the bottom of the gullet to the back of the blade.
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