I bought a Powermatic 14″ bandsaw with a riser block about a year ago. It was on sale and I was setting up a small shop. I assembled it according to the directions and there it sat. I am a carpenter, and was busy, and I didn’t have much call for the bandsaw until recently. I went to set up the saw and I noticed that there was about 1/16″ of drift in the blade front to back. I wasn’t able to adjust it with the tracking knob. I decided to strip the table off the saw and check the wheels with my level and combination square. First I found the wheels to be out of parallel, so I drilled out one of the holes for the post of the riser block and I was able to pivot the top back to parallel. Then, once parallel, I found the top wheel to be in back of the bottom wheel. I shimmed the top wheel out with washers having read about this solution from Mark Duginsky, though Powermatic recommended against this fix. Having brought the wheels parallel and in plane I am still having movement in the blade, about a 1/32″. The wheels seem to be round having checked them with my combination square held in a fixed position. The wheels were also pretty true, though there was a run out of about a 1/64″ or less in the top wheel. Is this run out my problem? Is this drift a real problem or am I being too anal? My concern is with the thrust bearing and its placement. Should I set the distance when the gap with the blade is at its greatest or least? Could the tires be a problem even though they haven’t seen much use? I leave the saw in the mid tension position when not in use, as recommended.The tracking knob doesn’t seem to help. The blade also seems fine, I have the same problem with different blades. I am just throwing it all out there since I haven’t been able to come up with a solution. Hope you can help. Thanks.
Edited 1/12/2008 10:28 am ET by paoloi
Replies
Two things up front:
Being you asked, yes, you are being a bit anal, but it is your shop and you can be as fussy as you want. To me a tool is a means to an end. In the case of a band saw, you want it to saw wood and it probably would have done that quite well even if the blade had a bit of front to back motion, it happens all of the time.
Second, everything you did would have no real effect on the problem you were trying to solve. Powermatic was correct in saying you shouldn't shim their upper wheel, you can damage the bearings that way, and drilling out the casting alignment holes was definitely not called for.
If you are going to work on machinery the basic rule is the same as the oath doctors take: "First do no harm." The second rule is "If it ain't broke, don't fix it." You can't fix a machine without thoroughly understanding how it works and then you need to use that knowledge to figure out what is wrong, if anything is wrong, before you start in with the wrenches.
Enough with the rant, I apologize if I have offended.
Now to the blade movement. There are only a couple of likely reasons why a blade would move back and forth, either the blade has a slight misalignment in it, and/or one, or both, of the wheels are out of flat. Here's how to figure out what is going on:
Unplug the machine. Pull back all of the guides, upper and lower, both side and thrust. Install a fresh 1/2" blade on the machine. Tension the blade according to the scale, and get it tracking as close to the midpoint of the wheels as possible. If it won't track in the center of both wheels at the same time split the difference.
If you spin the blade by turning the top wheel by hand it shouldn't be rubbing on anything, you will be able to hear if it is scraping on a bearing or anything else. Now set the upper guide assembly so it is 3 inches above the table, 6 inches if you have a riser block installed. Move the upper thrust bearing in until it is about 1/16" away from the back of the blade.
Now rotate the upper wheel by hand and watch the space between the blade and the bearing. If the gap closes up, or reaches it's widest point once or twice with each revolution of the wheel, and always when the wheel is in the same position, then the wheels are causing the blade to move back and forth. If needed, move the thrust bearing in or out a bit to get it where the blade is just kissing the bearing when the blade is furthest back, this will make it easier to judge the spot of greatest movement.
If the movement of the blade doesn't seem to be coordinated with the position of the wheels, then the problem is probably with the blade. To test this, rotate the wheels until the blade comes to the point where it kisses the thrust bearing. Now put a small spot of masking tape on the blade even with the bearing. Continue to rotate the upper wheel. If the gap keeps closing up each time the tape mark comes around to the bearing, then the blade isn't quite straight.
It is possible that both the wheels and the blade are contributing to the movement in which case you will be getting the gap to move in and out in a more complex pattern.
Run the test and let me know what you find out.
John White
Edited 2/7/2008 4:41 pm ET by JohnWW
Hey John thanks for the reply. I did what you said prior to getting your response and it seemed as though the movement was due to the blade. I marked the wheels and the blade at its contact points with the thrust bearings, and consistently touched the bearing at close to the same points without relation to the wheel position. It has done this with several blades however, both 1/2", but a 1/4" blade had much less movement. About the adjustments that I made I do take some issue. The drilling out of the riser block was done at the suggestion of Powermatic's tech support. The shimming of the wheels and concern over their being parallel and in plane with one another came after reading Mark Duginske's book on the bandsaw, which I believe Taunton published. I know that there are many ways to do most anything in woodworking but I would think machine set up would be universal. Perhaps there should be a discussion among the experts, at least within the Taunton family, about proper set up of machinery so there is not so much confusion. As for now I will leave the bandsaw the way I have it.
Mark Duginske made a career out of getting band saws perfectly set up, but I am not convinced that slight misalignments of the saw make any real difference when it comes to cutting wood. Since I responded to you, I have found out that Powermatic apparently had a batch of defective riser blocks that did cause some more serious alignment problems and that is why they told you to drill out the riser block, but that was a unique situation.John White
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