Bandsaw wanders

R

rscoffey

Joined
Sep 12, 2006
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I just managed to set myself up with a Milwaukee porta band saw on a Swagg stand. I'm awaiting delivery on some blade steel, but meantime I was cutting a kickplate for a door. The material was very thin steel (Ala Lowes). The blade on the saw wanted to wander off to my left. Fortunately, this was not a critical cut and I was able to "twist" the stock and pretty much follow the cut line. I would like to figure out what causes this. Is it me? Am I trying to feed the saw too fast? This also happens on my Ryobi bandsaw but that saw has a very narrow (3/16") blade. On the Ryobi, I have the top and bottom guides set as close to the blade as I can get them. If any of you more experienced guys can give me some advice, I'd really appreciate it. I don't want to screw up the steel that Aldo is sending me. :confused:

Many thanks

Bob
 
Bandsaws do not necessarily cur straight lines. Now...that being said...you can help yourself a bit. First, be sure all guides are positioned properly with proper clearances. Second..take a pc of wood or something realtivley soft an mark a straight line on it. Begin sawing this line and see which way you must feed the stock to follow the line. Stop the saw in mid cut without moving the stock. Readjust your fence parallel to the stock. This is about as close as you will get.
 
My Milwaukee does the same. I only use when I need a portable saw. Both my Horizontal and Vertical bandsaws have adjustable blade guides that allow for very precise cuts. Typically you adjust the guide for the thickness of material so that the blade flex is minimized. thus a straight cut. I have not seen a portable with this feature.
 
Portable Band Saws are made to cut bars of metal in pieces..the straightness of the cut is not a major design issue.

The main reasons a blade on a band saw ( wood or metal) wanders is due to several related things:
1) Blade tension - set the tension as tight as you can make it for metal cutting. The design of most smaller metal cutting band saws is to have a blade that runs straight as it goes around the rollers and then twists as it goes through the guides. This allows a larger clearance throat, but can make the blade want to track back toward the left. The blade is made so it is flexible enough to take this twist...but that allows it to wander ,too.
2) Tooth wear - If you try and cut a curve with a metal cutting band saw, you will be cutting with only one corner of the teeth. This will quickly ( often in seconds) make the blade sharper on one side than the other...and make it cut in a curve from then on. Cheap blades do this faster. The way to avoid this and make blades last longer is to cut straight lines and grind in the curves. Cut the profile in straight slices, meeting at angles as needed. Trying to cut the blade edge curve is a fruitless task, and will destroy the blade soon.
3) Guide throat height - The guide rollers on a metal cutting band saw are not nearly as precise or tight as a wood saw. Adjust them as needed to get a good tracking. Most metal cutting band saws only allow the guide rollers to come down to within about 4" of the table. This is way too large a gap for preventing the blade from twisting when cutting 1/4" flat stock. If you have the skills, weld on an extension of the upper roller arm so it can come down closer to the table. An alternative is to build up the table with several inches of MDF and put a sheet metal table top on that. This doesn't change the distance between the upper and lower guides, but it does make the cut much closer to the upper guide, and that will help a lot.
 
Another thing that makes a bandsaw wander is sideways pressure at the cut will cause the back of the blade to act like a windsock that points the cutting part of the blade *towards* the direction the pressure is coming from, also if the stock is not perfectly perpendicular to the blade that will cause the windsock tracking effect as well, in addition to the factors listed above. Bandsaws, especially cheap ones, are not really a precision tool. They are used to remove bulk material before a precision tool is used

-Page
 
The most likely cause would be your blade is getting dull. Both of the wood cutting band saws in my wood shop, a 14" Craftsman and a 24" Jet, will do the same thing when the blade begins to get dull. When I start resawing lumber to make book-matched veneer a fresh sharp blade is most important.

The causes the other members have mentioned are distinct possipilities, but I would start with a new blade and then look at the other issues.
 
A few things... As a commercial plumber I've used Milwaukee Porta-Band Saws almost daily for 15 years. Almost every saw cuts differently.
Is your saw new? Or used? The roller guide bearings wear out allowing the blade to flex causing cuts to go askew even if adjusted in as much as possible.
The tension lever when rotated fully is less tension than if you pull the lever back slightly, increasing the tension some times helps.
Sharp blades fed at a speed that allows easy cutting will help keep the cut straight.
I had one saw with a bent frame that no matter what I did would always cut crooked, after a few days I just adjusted the angle of my cuts. :mad:

Repair parts are usually easily available from local tool repair shops.

Hope this helps!:D
 
Thank you very much for the insight. I will take your advice to heart and see where we go. To answer Brians question, no the saw is used, but it doesn't appear to have be overly used or abused. Thanks again.

Bob
 
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