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How to fix Bandsaw Blade drift.

As I said bandsaws can be a nightmare. And they might be one of the most mis-understood machines in the shop as well.
Many times over the years, I've seen both horizontal and vertical saws in shops, especially maintenance shops, equipped with the highest tooth count carbon steel blades, that they use to cut everything including allen keys, etc. Machine obviously abused and zero maintenance. Mention the machine to the manager or department head, and sure enough, there will be complaints about how 'the guys' go thru blades right and left, or the machine 'eats up blades', costs them lots of money, etc. Jeeze, didn't see that comin...:crazy:
The only thing I can add is that the guides to twist the blade 45 degrees need to be in the neutral plane between the wheels. Remove the guides completely, tension the blade, tilt the wheels so the blade rides on the crown of both wheels properly, then twist the blade ... Then set the bearings or guides that support the blade to provide the cutting force.

Then after all that, then adjust the vise to cut the stock square in both planes.

I discovered this order of operations on a cheap 6x 12 bandsaw that had been broken and brazed back together with the pivot in the wrong plane, then the blade adjusted so it would cut mostly square. I had to shim the blade guide assembly to correct the error in the machine due to the brazed pivot being a little off. I'm not saying no one ever thought of that before but you have 6 degrees of freedom on two wheels and the guides. They all need to be correct..
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On old bandsaws sometimes the flanges on the wheels wear back
and this lets the band saw blade teeth ride on the wheels. This bends the teeth flat on one side taking the set out of the blade and the saw cuts crooked.
I took both wheels off my band saw put them on the lathe and cut them back so the teeth would not touch it cuts straight now.
I vote for incorrect chip load. A lower tooth count should help as should a slower feed rate. Too much pressure against the face (cutting edge) will cause the blade to move sideways. The pressure wants to push the blade backwards but because of its rigidity in that plane 1" wide vs the thickness of the blade .035" or so the blade moves sideways easier than backward.
force needs to be high. If you are guessing and not looking at what is going on during a cut everything is backwards. Force is not feed rate. Force is the ability for the saw to change feed rate under load. Our 48" hem is 1.7 tons on the post - and it is anemic for the force it needs. A 4-6 1.25" blade runs with 300-500 thrust pounds in a 1 inch cut. This is cutting on the conservative feed rate of 5.5 ipm. Funny, about the same rate and thrust of a hss drill of same surface area as blade.

The teeth have to get into the metal, if some rub then the blade gets side pressure and twist over. If your cut has a slight arc on the walk then it is guides/tension/dull blade, If it is straight then goes into arc then to tighter arc it is lack of feed rate at some point in the cut- even if temporary from lack of pressure. You can not readily recover from this once it starts. Many times your blade is ruined too.

If your saw has flanges or tires on it - either antique or not a production machine. Nothing wrong with either, I still think the 4x6 hinged vertical/horizontal imports are a good choice for many shops looking at saws. If you are making the next step up, it is a very big step.
So here is an update on my bandsaw blade woes....
I inspected the Lenox blade I had on the saw and found something quite interesting.... almost all the teeth were completely worn off, broke, or warn down. This blade has maybe made 5-6 cuts, all while I was trying to adjust the taper out when I thought the issue was in the saw itself. I checked my other two Lenox blades, purchased at the same time and they appear to have the teeth formed correctly. Since I wanted to eliminate the factor of the blade, I reinstalled the worn el-cheapo blade that originally came on the saw. The blade is extremely stretched and the teeth are worn down, but it isnt gone just yet.....and to my surprise it cut SO MUCH better than before. I should mention I was running the blade at the same SFM and down feed rate as the Lenox blade. It still wants to drift towards the clamp, but it only wants to taper .01 or .02 at MOST compared to the .06 - .200 I was seeing before. I plan to do some more investigating in the future as I have time, and I ordered another blade with a coarser pitch than the ones I currently have to see what results I get. I have a feeling that the culprit here is the blades, but I cannot say for certain.... I suppose I will look into some Morse or Wikus blades as recommended above. Thank you all for the advice, it is much appreciated.
There is the possibility the saw gremlins got to your blade some night. I think the gremlins get in when the saw is delivered and never leave. They have been in every shop I've ever been in, some much worse than others. You can leave a perfectly good saw for a little while and then when you try the next cut its junk. The gremlins are unsophisticated spirits, if you can offer them a simple saw they will often leave the intimidating looking saw alone.
Is DGI/DoAll in your area? They used to do free band saw tune ups!

The 3/6/12/24 guideline for bandsaws says 3 teeth minimum in the cut, 24 max, 6-12 ideal. So a coarser blade would help. I think otherwise the gullets get packed with chips. Good luck!
Typically when all the teeth are messed up shortly after installing a blade it its due to improper break in. Sometimes it's best to take a few REALLY slow cuts to dull the teeth a bit. Think of it as the edge prep they put on inserts or good cutting tools. The truly sharp edge is brittle and can break. If you hear any chatter when taking some of the first cuts it can break teeth because they will bite in and get too much then break off or jump out. Sometimes when this happens and the tooth breaks off and gets stuck in the material and can wipe out all the teeth behind it since they aren't made to cut such a hard metal. I've seen a blade with 2 cuts on it cutting 1/4" taper and upon inspection the teeth on that side of the cut were all broken.

I'd guess in your scenario they broke due to improper tooth pitch.
When cutting bigger materials and you aren't sure of your pitch just catch some of the chips as they come out of the cut and inspect them. If they look like they are nicely curled then you should be okay. If they are kind of bunched up you know you are overfilling the space between the teeth.
I own or have owned-sold probably 20+ Horiz-Vert bandsaws over the years. Many times it's astonishing to see guards, guides, table inserts, and tables with saw cuts in places I can't imagine how the blade got so far off track. Years ago, neighbors had a guy install a blade on a Horiz Doall with the teeth against the wheel flange, cut it completely off. How does that happen??
I own or have owned-sold probably 20+ Horiz-Vert bandsaws over the years. Many times it's astonishing to see guards, guides, table inserts, and tables with saw cuts in places I can't imagine how the blade got so far off track. Years ago, neighbors had a guy install a blade on a Horiz Doall with the teeth against the wheel flange, cut it completely off. How does that happen??
Because they are horizontals. And day shifters. Pendinghaus uses backwards blade installing (teeth towards frame, so when blade pops off it is really stuck)- maybe your friend was used to those.
...Have you ever used a PortaBand saw by hand? The secret to getting a straight cut is to cradle the saw and not let its weight go entirely on the blade. ...
I'm about to give up on a Milwaukee portable bandsaw, so I thought I'd do some research. Starett has a nice article on blade break-in. And retail blade packaging said the same thing:

One third of the portable bandsaw weight while breaking in the blade, for the first 25 to 100 square inches of cut.

If two inch square tube with eighth inch wall, that's about one square inch per 90 degree cut. Or 25 to 100 cuts.

I can't trust myself to that discipline, so...

I found a good deal on ebay for a NOS "torque reel" from govt surplus it seems (December 1952!).

Ten pounds of lift will allow the blade to see six pounds of pressure, if the saw is 16 pounds or so. Not a third, but close.

It's got ten feet of travel, should be adequate.
This could be a bit of a long shot but I would like to pick everyone's brains, especially those who had experience with correcting blade drift on a bandsaw. To give some context, I started my shop earlier this year and picked up a used WF Wells W-10-2 semi auto dual post bandsaw from a shop that was closing up shop. It is an old saw, but is still pretty solid. I got to see the saw cut in person but the owner told me I would need to replace the guide rollers and realign them if I wanted to do any amount of close or accurate cutting. Up until recently, I haven't really needed to do any accurate cutting as I have been able to feed bars on my CNC lathe and I can put the sloppy cut on the side with the remnant. However, I have a job coming up that will be machined from 3" steel bar and I cannot bar feed this material as it is a little too large for my spindle bore, so I will need to bandsaw cut them and chuck the blanks.
I set about tearing down and cleaning up the guides on the saw, replaced the rollers with new ones and did my initial adjustments checking the squareness of the blade to the table. The only thing I did not replace were the carbides on the guides as they appeared to be fine. The first few cuts I took with the saw seemed promising with only a small amount of noticeable taper in the blade feed direction, left and right were pretty square as well. I did these cuts with some scrap 1" round bar to give myself a baseline. As with any bandsaw, there is going to be a little blade drift due to the cutting forces involved, but on one properly set up it should be a consistent drift and shouldn't be very extreme. I decided since it was cutting well with the 1" bar, I would go up to a piece of 3" and test that out as well....This is where the problems start. When cutting the 3" bar, the cut starts out good until it gets about half way into the cut, at that point the blade starts to curve into the bar towards the clamp. The amount the blade drifts can be anywhere from .060" up to .200" at times and is not consistent from cut to cut. I tried to shim the guides to see if I could compensate for the drift, but all that ended up doing was creating a cut that was curved instead of just tapered. I should also mention that I was using a brand new Lenox blade for these tests and had the guides as close to the material to eliminate as much deflection as possible. I also played with the feed rate of the blade in the material and found that feeding it faster would make the blade taper more, but even slowing the feed down to almost nothing, it will still drift by an unpredictable amount. I went back to my 1 inch round bar to see if anything had changed, and it cut very consistently to the first test cuts with little to no taper at all. I also tried some square steel bar I had, and ended up with very little taper just like the smaller round bar.

I plan to contact WF Wells within the next week to see if I can solve this issue, but would anyone have any suggestions on something to try before I can get in touch with them? The part that has thrown me for a loop is the saw drifts very little, if at all when cutting small round bar or square/rectangular stock, but when I move up to the larger diameter stuff, it starts tapering off in a big way. This is a huge problem as I cannot set up a reliable machining process on the lathe if all of my slugs have tapered faces that need to be faced off. If I leave the saw as is and try to do this job, I will have to give myself at least an extra 1/4 of an inch more than I had planned for each slug to ensure that it gets cleaned up in the facing operations.

Thanks to anyone who can provide some advice.
Another thing to remember that hasn't been mentioned, don't let the blade teeth hit the concrete floor. I'll bet most of us have seen guys toss a blade on the floor to let it uncoil.
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Necro Post. Problem was resolved in December of 2022

Everything has pretty much been covered. The rule of thumb for blades is no less than 3 teeth in the material at one time and no more than 24. Less than 3 is apt to tear a tooth off, more the 24 is likely to fill the gullets and cause the blade to jam or wander.

Blade tension and down pressure are also critical. My Startrite doesn't give a tension specification other than to tighten it as much as possible with one hand. Optimal down pressure is 6 psi. Don't forget the carbide blade guides should within the .001" to .003" range to keep the blade from tilting. The blade guide arms should be as close to possible to the vise as possible.

I have also found that a blade cleaning brush is mandatory on my machine. Coolant alone doesn't clear the gullets. A brush at the exit end of the cut clears 95% of the swarf and allows the blade to cut straighter and last longer. With all the above in place I find the machine will consistently cut within +/- .005 all day long.

When changing blades don't forget the break in period. It's generally recommended to run the blade at the normal speed, but only 1/3 the down pressure for the first 10 minutes.

Here's some information on blade selection and procedures to extend longevity. As an FYI I do buy blades from these people, but I don't have one of their saws. I generally keep 4/6, 6/10, and 10/14 variable pitch bimetal blades in stock.

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An old trick among woodworkers is to gently hold a honing stone against the side of the blade that has the more aggressive cutting action and repeat the hone lightly then test cut procedure until that mounted blade cuts straight.
There's a lot of good advice on this thread...in my experience, too much downfeed pressure is the single biggest culprit to blade wandering. In fact, I'm surprised/amazed the blades cut as well as they do even with 'proper' downfeed.