bandsaw drift

[marty shultz]

I was resawing some 3" thick alder last weekend and the blade always drifted away from the fence in the first 3-4 inches of the cut then maintained the line after that. what causes the drift?

[George Bokros]

The grain in the wood can cause it along with blade flutter. I am not familiar with alder so I know nothing about the grain of that wood.

George

[marty shultz]

I cut more about 20 pcs. Alder is very similar to Pine in terms of hardness.

[ed vitanovec]

Theres some videos on the internet that shows how to compensate for blade drift by adjusting your fence.

[Steve Juhasz]

The grain in the wood can cause it along with blade flutter. I am not familiar with alder so I know nothing about the grain of that wood.

George

If the wood grain is the boss of the cut, the bandsaw is simply not set up properly. Could even be that the blade is not sharp enough, but something needs to be adjusted. Perhaps even the user's feed technique/speed.

[Jerry Thompson]

Alex Snodgrass on Youtube set me straight. No pun intended.

[Jim Finn]

I re-saw a lot of 8" red cedar. I went to carbide blades to avoid drift. After the blade dulls a bit it starts to wander. I replaced these dull blades a few times, but kept them. Last week I tried sharpening one and it did not help, but I then put a knife sharpening stone against the side of the blade as it was running and this took the drift out of that blade. You might try that.

[glenn bradley]

Since the saw cut fine after a few inches I imagine it is setup reasonably. My first thought would be the blade. Like a chainsaw, a bandsaw blade gets really damaged really quick if you encounter something irregular. I would try a new blade. For 3" and taller I would go to a 2-3 tpi skip or similar. You do not want too many teeth in the cut as it is difficult to clear the chips. JMHO.

[Joe Hillmann]

How dry was the piece of wood. If it was fairly wet the ends would be dryer and harder than the rest of the wood. It is common on sawmills when cutting logs that have been down for a while for the blade to rise or fall in the first and last 6 inches of the log because it is dryer than the rest.

[Myk Rian]

Since the saw cut fine after a few inches I imagine it is setup reasonably. My first thought would be the blade. Like a chainsaw, a bandsaw blade gets really damaged really quick if you encounter something irregular. I would try a new blade. For 3" and taller I would go to a 2-3 tpi skip or similar. You do not want too many teeth in the cut as it is difficult to clear the chips. JMHO.

^^^THIS^^^
Teeth on one side of the blade have been damaged.
The band can only bend out so far, then it cuts straight, but there is still tension to the side it is resisting.

[Gus Dundon]

Must be the fence or the feed rate. Recheck!

[ian maybury]

Once a saw is set up right (wheels coplanar, blade tension roughly right, guides right and a new or definitely good and correctly specified blade tracking consistently before cutting) it should basically be OK with little need to fuss.

An unbalanced blade (differing sets/sharpness or whatever one side to other), a wider blade than the saw can properly tension, and oddball grain seem all to be capable of causing problems.

Another issue (especially on smaller saws with high wheel camber) may be the blade moving to one side of the wheel or the other under cutting forces (going around the corner to one side or the other - which alters the line of cut - one set up option is to track the cut line to the fence by altering the position the blade tracks at on especially the upper wheel), a flexible saw chassis twisting under the cutting force (likely compounding with the going around the corner issue), or perhaps a spring which isn't stiff enough to more than oppose the cutting force. (leaving the blade slack and free to wander in the cut - massive blade tension isn't necessarily required, but the spring has to be stiff enough to be able to oppose the cutting force without much deflection).

One or other of this last lot of issues seem quite likely if the tracking changes shortly after the cut starts. Easing up on the feed force may help in these cases - although deep resawing and the self feeding action of the rake on the teeth can bite/cause pretty high cutting forces in hardwood.

Badly set guides can't help, but guides once more or less right may be less of an issue than is often thought. Badly made and unbalanced/bent jointed blades are very common (wear can have the same effect), even from some well known makers. Too fine a tooth/too small a gullet for the depth of cut so there isn't enough space to carry the dust out without it spilling between the sides and the wood (causing lots of friction/jamming) is also a common issue - and one reason (with accuracy of set etc) why the very coarse carbide blades often do such a good job on saw with wheels big enough to run them. Carbides can run a wide tooth spacing and deep gullet, while still retaining a toooth form that gives a decent finish. The maximum pitch on steel blades because of the tooth form and typically heavy set seems to be limited as much by the poor finish they leave as they get coarser as anything else.

There's set up and technique stuff that can help or hinder the situation, but there isn't really any mystique. Like in many situations to do with woodworking machines - if it's set up correctly but still not working right then there's likely something wrong with the design of the machine. Often down it it being underspecified/oversold/too cheap for the job. I'm (while not a long term expert) firmly of the belief (based on an extended period of playing with the variables while trying to get an under specified saw working right) that all else being equal there's plenty of especially lightweight DIY saws out there that simply are not strong enough to handle re-sawing. A weak spring and/or chassis is especially problematical - a metallic squealing and or chattering coming in as the cutting forces increase can suggest this.

Switching to something like a good heavy duty Italian can be a bit of an eye opener - the issues and the set-up sensitivity just evaporate and the saw laughs at most of what its asked to do...

[marty shultz]

The bandsaw is a Felder FB 540 with a 1-1/4" woodslicer blade cutting through 3" - 6" thick dry alder. I watched the blade closely as the wood made contact with the blade. The blade rotates slightly away from the fence for about 2" then cuts a consistent path parallel to the fence.

[John TenEyck]

I've had the same thing happen on my little 14" Delta with a blade that has the same specs. as a Woodslicer. Your Felder is a whole different class of saw, yet the same thing happened. I suspect you know how to set up your saw correctly and believe I do too, yet the same problem happened. In my case the blade angled towards the fence and then straightened out after about 4 inches.

Ian offered some interesting insights. With respect to those I don't think it's inadequate spring tension, at least not in my case. You can't get much tension on a 14" Delta in any case, but with this narrow kerf blade I have more tension than on the thicker blades I normally use which have never wandered in this fashion. When those blades have wandered they don't straighten out again, and I've always attributed the underlying reason to be a blade that's dull on one side or not positioned correctly on the wheels (with all due respect to Alex Snodgras, who apparently knows nothing about saw mechanics and doesn't think it's necessary). Of course, the beam strength of the Woodslicer type blade is probably still less than my other blades, even at higher tension, so you could be right. It's just odd why the cut straightens out after a few inches.

To whoever made the comment that it could be caused by the wood being dryer at the end of the board than in the middle, that couldn't have been the case for me because I was resawing drawer stock from lengths of wood that I had just cut from a longer board.

I don't know the answer as to why this happens, but it appears like it can happen with saws at opposite ends of the spectrum.

[marty shultz]

I played around with the position of the blade gullet with respect to the wheel's centerline but surprisingly it didn't make an appreciable difference in the cut. I thought I could reverse the trend and have the blade cut towards the fence. Finally moved the fence to be in line with the angle the blade wanted to cut at the beginning of the cut and it appears to have worked. I haven't cut but one test pc so I'm not positive I've cracked the code.