How to make a bandsaw cut straight

I recently acquired a bandsaw that will cut wood or metal (aluminium at
3000 fpm and steel at ~100 fpm). It always cut at an angle with the
original cheapo blade. Tightened and adjusted. No dice. Gave it a 5/8
inch wide 10-12 tpi bimetal blade. Much better, but still crooked.
The bandsaw books in effect say that this is to be expected, and
describe various ways to cope with the tendency, but I could not see why.
The mitre guage that came with the saw is pretty flimsy, but even that
didn't seem to explain the degree of crookedness. Now, on table saws,
the greatest accuracy is obtained by use of a sled that carries the
stock past the blade.
So, I made a sled out of a 3/8 by 3/4 by 12 inch cold rolled mild steel
bar (that slides in the mitre slot in the table), a piece of 1/4 inch
6061 T6 aluminium plate about 6x8 inches that I had laying around, and a
piece of 3/8 by 3/4 inch aluminium bar (set vertical and accurately
perpendicular to the steel bar and thus mitre slot). The pieces are
held together with some large flat head socket cap screws. The sled
reaches to within 1/16th inch of the blade, so the stock is well
supported.
In use, the stock is held in the sled against the aluminium bar, and the
sled is pushed past the blade. On wood, this works quite well, but on
metal it still drifts a bit, the stock being held in the sled by hand.
So I drilled another hole in the sled to accept a 1/4-20 flathead socket
cap screw, and attached a small strap clamp. This allows the metal to
be clamped firmly to the sled. This works: the cuts are now
perpendicular.
So, the lesson seems to be that a significant cause of crooked cuts is
the stock drifting sideways while being cut. I don't know the source of
the sideways force, but it cannot be that large. It may be nothing more
than the vibration of the saw causing imperceptible walking.
Joe Gwinn
Reply to
Joseph Gwinn
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Apparantly it is not 'el-cheapo blades or a cheap saw that generates off-angle cuts. (or at least I assume that *this* outfit uses quality equipment) I recently got some half inch thick 6061-T6 al. plate from Online Metals. One side of a six inch square of this material has a milled and square surface. The other three sides were off by as much as 1/32" over the HALF INCH! Moral? If you really need a six inch square +?/-0 order at least 6 1/4. Also - don't assume any band saw cuts straight.
Ken.
Reply to
Ken Davey
AFAIK it results from an uneven amount of "set" in the teeth, this set being more on one side and less on the other. THe blade will "lead" or pull to the side with the more set.
This set is a product of the way blades are manufactured. More expensive blades will reduce it, but not eliminate it.
I'm talking about blades for wood here with 6-TPI and under, but I suppose the same thing would apply to blades for metal.
Reply to
LP
On my saw, I've found that the more worn the blade is, the crookeder it gets...
Jerry
Reply to
Jerry Foster
When I first made my 20 inch bandsaw, it was cutting on a slight angle and was virtuially impossible to follow a straight line without a lot of fiddling around. I changed to a bi - metal blade, and it was somewhat better. I adjusted my blade guides in so there wa virtually no clearances, it got better, and nothing else I tweaked seemed to make much difference, even changing blade brands to another brand of bi-metal. Then I remembered bimetal blades reuire a lot more tension, and since I had one blade with a few teeth missing I decided to tension it to the point it would start cutting straight or bust the blade or bend my saws frame, which would be pretty unlikely, since its 4"x 4" x 3/8" wall steel tube with gussets of 1/4" plate.......I cranked up p[retty darn hard on the tensioner, and low and behold it cut like it never cut before. I even found it cut perfectly fine with carbon steel blades. I have to think a good majority of bandsaw problems in regards to cutting straight is caused by blades that are improperly or insufficieintly tensioned
============================================== Put some color in your cheeks...garden naked!
~~~~ } ~~~~~~ } ~~~~~~~ }
Reply to
~Roy~
This sounds about right to me.
Yes. I have a 4-6 tpi bimetal blade for wood, but it is also used for thick metal, and it also drifts. I haven't tried it with the sled yet.
I forgot to mention that for really square cuts it was necessary to clamp wood to the sled as well, probably because metal on wood is still pretty low friction. I bet a sled made of hardwood (even if the rail is still metal) would allow square cuts of wood without clamping.
Joe Gwinn
Reply to
Joseph Gwinn
I suspect that you are right about insufficient tension, and I did rack the tension up to max, but it didn't quite solve the problem. The tension is still set quite high, but the sled made the difference.
Joe Gwinn
Reply to
Joseph Gwinn
[snip]
The outfit is good, but isn't industrial. The saw is a Wilton 8201 and the blades are Lenox (12-14 tpi) and Starrett (4-6 tpi).
The folk writing the bandsaw books have the best bandsaws made, and usually more than one kind, and report that all saws will drift.
If I recall, Online Metals says that their as-cut dimensions have a tolerance of up to something like 1/8 inch, and square isn't promised. Nor is clean. So, ordering oversize is necessary.
Squaring up raw stock is for me a major planned use of that bandsaw, and is why I needed to obsess on cutting straight and true. I'm going to make a larger sled that will handle (that is, clamp) pieces up to maybe 10 inches wide.
Joe Gwinn
Reply to
Joseph Gwinn
The cheapo 4x6 bandsaw guys report that a quality bimetal blade and careful tweaking yields dependable square cuts. One reports reliable .035 slices on a daily basis.
Reply to
Rex B
5 band saws here, mix of BIG wood and H+V metal, and never a blade goes on without the stretch gauge getting clamped to the blade. The blades need to be re-tensioned often. We fought long and hard with bandsaw blades...DON'T GET MOORES BLADES!!!!!!!!!! THEIR QUALITY IS INCONSISTENT, not always bad just never the same. Get the stretch specs from the mfgr., not from a table. We also use aftermarket ball bearing guides that are set-up perfectly...big difference!
Reply to
Tom Gardner
The Emerson bandsaw I scrounged up a few weeks ago cut on a hellish angle. I made up a new blade, adjusted the rollers and whatnot..and it cuts close enough now to allow just about perfect fitup when welding
Gunner
"Considering the events of recent years, the world has a long way to go to regain its credibility and reputation with the US." unknown
Reply to
Gunner
Joe..if you need Square...forget the bandsaw. They will allllllll cut off square (well..then there is Amana..but...$$$) If you need square..get a cold saw.
Gunner
"Considering the events of recent years, the world has a long way to go to regain its credibility and reputation with the US." unknown
Reply to
Gunner
Joseph Gwinn wrote: ...
You could also consider a Tenyru (sp?) style blade for your table saw. Cuts very straight, very true, and very clean. It would only cost you about $40 to try it (7 1/2" Matshushita blade from Medford Tool).
Bob
Reply to
Bob Engelhardt
[snip]
With the sled, I'm getting square to within my ability to detect out-of-square using an old Starrett combination square.
Joe Gwinn
Reply to
Joseph Gwinn
[snip]
Amana? I thought they made appliances.
I haven't quite talked myself into a cold saw, as a bandsaw is more flexible. And the sled seems to work well enough. Another poster suggested a table saw with a Tenyru (sp?) blade from Matshushita, What do you think? How do they compare?
Joe Gwinn
Reply to
Joseph Gwinn
I've had best luck with blades made from Sandvik bladestock. That seemed to be the preference of the guy who I have make my blades though he never came right out and said so. Maybe it's a Minnesota sort of deal, then.
He works out of a rather small and very old house near where the steel yards are, Nordeast by the river. The windows probably haven't been washed since WW II and the "office" looks like something out of an old movie. The welds in the blades he makes are invisible. His blades work great in my saw. His price, about $12 per blade (minimum 3 blades) is OK with me because 3 blades last me about a year.
Reply to
Don Foreman
Amana Tool Corp makes some of the finest metal cutting tools around. And they are priced like it too.
No idea. Ive used cold saws, but never used one of the blades mentioned. It should work, but it will be with much more fanfare and flying shit. Cutting speeds are far different
Gunner
"Considering the events of recent years, the world has a long way to go to regain its credibility and reputation with the US." unknown
Reply to
Gunner
[snip]
I'll look into them.
I remember seeing an industrial table saw used to cut 1/4 inch thick aluminium plate at RCA back in the late 1960s. (I don't know the max thickness it could handle.) Made a lot of noise, but the flying shit mostly went into the cabinet. Just like when cutting wood I suppose.
Judging by the pitch of the noise, the blade was going a few thousand fpm at the teeth.
The operator didn't use goggles or hearing protectors, and seemed a bit hard of hearing. But he was old, so who knows if it was noise or age or a combination. But that was one LOUD saw.
When and where was this published? Even George Washington cautioned against "entangling alliances" in the late 1700s, and he was worrying about the US getting too involved in European politics, and getting dragged into European wars.
Joe
Reply to
Joseph Gwinn
Accurate bandsaws exist in sawmills, ganged bandsaws to slice the cant (squared-off log) into rough lumber. They use the bandsaw to minimize loss to the kerf, and have to cut to a minimum thickness to keep the planing losses down, too. Wide blades, heavily tensioned, close guides, and no tolerance for tooth damage. Most of my bandsawing has been OK except for blades that get worn on one side more than the other; they will steer toward the sharper side.
Dan
Reply to
Dan_Thomas_nospam
It might be nice to say bandsaws are used to minimize loss - but the were developed for BIG Cants. Only in recent years kerf has been important as it brought some more profit and less waste. The waste was used to heat and boil and make other products.
The story tall blades had to go away with the Giant Redwoods. They were first cut to length that a long team could pull then quartered to make it over the mountains and through the round blades. This quartering was really tough and took time. The band saw has ruled since. Much like the wire saw for stone. Once started, the industry never looks back.
Martin
Reply to
lionslair at consolidated dot

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