Question
I recently purchased a Hitachi cb75 for res-awing koa and other tropical woods and from the beginning I have been having a problem with the blades. Maybe it is not a problem but a nature of the machine. This machine is not altered in any way and I am using the stock guide blocks that were supplied. It seems as if what it happening is that the blade sets up some sort of frequency vibration in the cut and removes a lot more material than it should. It also leaves a pronounced wobbly cut pattern. It generally only does this during the first 1-2 inches of the cut and will straighten out on its own. Some blades I have used are better than others; although some will not cut smooth for 5-6 inches and will occasionally do this "dance" further down the cut seemingly with no reason at all. I mostly re-saw koa into 3/16ths or 5/32nds. Most stock is 4 to 10 inches wide and 21-36 inches long.
The only way I can minimize this is to crank the tension down all the way but then I see blade tracking problems after re-sawing for a couple of hours and turning off the machine for a few minutes to take a break , upon restarting the machine the blade will wander out of tracking about 1/4 inch and then slowly return to its original setting. Once, after the blade I was using had about 12 hours on it, I restarted the machine and the blade came off the machine and cut through the blade guard before I could shut it off. It destroyed the blade and was quite scary. Has anyone else experienced these problems and if so are there any remedies?
Forum Responses
(Solid Wood Machining Forum)
From contributor P:
What size blade are you using? I have a 3" rip blade on mine.
If you aren't using the Hitachi 3" Stellite tipped blade (either every tooth or every other tooth tipped) give that a try. Very expensive blade though. These are touchy saws. They can work really well for the money but can also be frustrating machines.
The saw has to be set up properly - it took me a long time to adjust it correctly. Also, Stellite blades will cut for a long time after they are dull, just not well. That might account for the rippling you are seeing.
My machine and the others that he has used have the 3 horse motor on it, and he thinks that the wobbly cut may be due to the machine being slightly under powered for what we are doing but it makes no sense to me because the saw will cut wobbly more it seems when we are cutting narrower pieces. This leads me to think tension or guides. You can actually watch the blade as its cutting and as it enters the cut for the first inch or two it will wander all over the place and make a high pitched screaming sound while the blade is vibrating when you take the cut piece and turn it so you can see the cut and take a speed square and draw a line across the rippled portion of the cut each ripple is exactly the same distance apart as the tip of the blade. I am stumped as to why this is happening but am more worried about the tracking issue than anything else. Any help or suggestions would be very helpful.
If I remember correctly the tire on the top wheel of the Hitachi is flat as versus crowned as on most band saws. Check this out as well. If you've developed an overly tall center crown in the tire then that might result in no front edge support for the blade, and subsequently, drift in the lead edge. Band saws are tricky beasts. It doesn't take much for them to get all out of whack.
The only other thing that seems kind of weird is that without a blade on it the upper wheel seems to have a lot of play. Not in the bearing but in the tracking linkage. On the tracking knob shaft there is a collar that is held in place by a roll pin that rests against a frame piece. That is where the play is like there should be a shim or washer under the collar. I do not know if this makes any sense, perhaps I should be talking to Hitachi but they have not responded to emails I have sent them trying to figure this out by going through tech support.
Make sure your plastic blade guides are pressing the full width of the blade, spaced away about the thickness of a folded piece of paper on each side. Make sure your blade teeth are just in front of the upper tire. If I remember correctly those wheels are about 3" deep.
I would not bother emailing Hitachi tech support. See if you can get them on the phone. You could also have a bad blade. I believe band saw blades are supposed to be a tad longer along the back edge to put more tension on the front edge.
I have learned that the better the drying and stabilizing process the better the saw cuts. If you have a good moisture meter you will probably be able to nail down the suppliers that get it and the ones that don't. Also check for case hardening in the wood that you are getting (most good meters will only measure in about 3/4 of an inch, so take a few cuts and measure again.) I also learned that the relative humidity, temperature and wind speed (open air shop) all make a difference.
Most guitar makers (Gibson, ect.) all re-saw in a controlled environment of around 50% relative humidity, living in Hawaii I do not have this option as the relative humidity is around 90%, although I try to only cut guitar parts when it drops below 70%. I seem to have better results when I do this. I only have to cut this good for one particular customer. So for the most part I really like this saw for the power and speed that it has.
The only issue really is the wobbly cut it makes as you are starting in on a cut and sometimes randomly during a cut. I am fairly sure that it is because the saw really needs a five horse motor to cut well, or it is a nature of the beast thing with the wide thin blade. I have three questions. Tom, do you get a very pronounced wobble to the 3 inch blade as you are starting a cut that leaves an "s" shaped pattern in the wood? The pattern should match the t.p.i. of the blade? Contributor H - do you know the kerf of the Lennox blades that you use? This saw is driving me nuts and I am open to new ideas about re-sawing! Also, do these Lennox blades work on the Hitachi cb75 or are you running these on a different saw?
I've tried 2" blades but they don't seem to work as smoothly as the 1" blades. I wish I had thought to try narrower blades on the Hitachi as I had the complete smaller blade bearing sets. I was thoroughly convinced that re-sawing required a very wide blade though. I suspect that if I had tried a 1" blade on it I never would have sold it and bought the Laguna Resaw Master.
The Resaw Master is a decent saw, but it took a long time and a lot of parts replacements from Laguna to get it going properly. It is only an 18" wheel though (granted that's larger than the 16" Hitachi wheels) and I don't think I'd ever get another re-saw smaller than 20" - I'd prefer a 24". We do not get full life out of the blades before we get stress cracking. I've tried just about everything to fix this but have become convinced it is the small diameter wheel. Other than that the saw works adequately well. We typically cut 6" to 10" poplar, oak, cherry, mahogany, pine etc.
Comment from contributor R:
Could the wobbly cut pattern have anything to do with the initial feed speed of the material into the band when it begins to enter the wood? I recently re-programmed a large resaw for a reduced speed when the wood enters the band. The feedworks speeds up to production speed for the rest of the cut. The old experienced sawyer believed if it could be done that it should be helpful in band life and due to the dryer nature of the end of the material and start angles, help get the band on started on the right track.
