Thread: Blade Drift - What's happening here?

See attached file re tuning out the drift.....

I should add that when you get fairly close, it only takes very small tracking adjustments to dial in a straight cut. The blade will probably end up near the centre of the wheel (by eye), but in fact will be ever so slightly off centre.

On my bandsaw I can tweak the drift easily, as the tracking is adjusted simply by turning a knob. Some older saws might not be quite so easy, i.e. reach for the spanners....

Good luck getting a straight cut !

Brilliant - exactly what I was after!

Originally Posted by Mr Brush

See attached file re tuning out the drift.....

Mr brush that is a great diagram, where did you find it?

I have two bandsaws. a 14 inch scheppach basato and a 21 inch carbatec. I run a 1 inch blade on the 21 inch saw for resawing. on this saw, a crucial part of the setup is to ensure that the top and bottom wheels are coplanar and square to the table. the ultimate test of this is if the blade is perpendicular to the table when measured from either side or from the back or front. If it isnt then not only are you going to readjust the upper bearing guides every time you adjust the depth of cut but the blade will drift to one side or the other as per the diagram posted earlier. This is because there is more distortion over a wider blade than a narrow one when the wheels arent coplanar. obviously the wider the blade the bigger the tension difference between the front and back of the blade and the more likely the blade is to cut to one side or the other.

When I am using the 14 inch saw, usually for curves or joinery with a thin blade (1/2 inch or below), I find that it is not so critical that the wheels be coplanar as long as the blade is tracking centrally on the top wheel. In this situation you normally have the top bearing guide down within 20mm of the stock anyway and if you have to move it up 30 mm or so (cabriole leg, bandsawn box, or whatever instead of flat object) the adjustment of the top bearing guide is minute if necessary at all because of the small height adjustment that is required.

There have been several disagreements over this subject on the forum over the years and it is generally because people do not differentiate between the sizes of bandsaw. I regard bandsaws over 17 inch as large and follow the guidelines I set out above for my 21 inch machine, 12 to 14 inch bandsaws as per my 14 inch model, smaller than 12 inch and you might as well use a jigsaw or scroll saw. They wont have the capacity to cut through thicker timber than the jigsaw or scroll saw has anyway. 14 to 17 inch (and there arent that many as its the grey area between free standing and mounted on a stand) are in no mans land. work them out for yourself. Once you go below 12 inches then the fatigue on the blade as a result of the tightness of the curve means they will not last long compared to their larger rivals.

anyway its past my bedtime, got to go before i turn into a pumpkin

DOug

Doug - you're probably right about the different approach for different sizes of saw/different blades/different applications.

My bandsaw is a Basato 4, and I only tend to use blades up to 1/2" for general work. I have a 3/4" bi-metal blade for resawing thicker stock, but it doesn't get much use.

For many hobby woodworkers, using smaller bandsaws, I think adjusting the tracking to correct drift is the way to go (as suggested by Michael Fortune). I suspect that the vast majority of people don't check to see if the wheels are coplanar to start with, and if they did they would find that, as delivered, most machines are miles out. I spent several hours when I got my Basato 4 trying to set the wheels up as coplanar as possible, and from that starting point the tracking adjustment to get straight cuts was fairly minor. With crowned wheels you are only moving the blade EVER so slightly off centre to get a fairly large effect on the cut direction.

Of course the tracking correction needs to be applied when you change blades, but these days I can do that in a couple of minutes and a few test cuts in scrap ply.

It sure helps to know which way to turn the tracking wheel to get the desired effect....

OK - Adjusted the tracking as per diagram: no improvement.

So I checked to see if the table was actually square to the wheels.




It wasn't


It's angled about 4-5 degrees to the left which corresponds nicely to the drift I'm experiencing. So there you go. I shall adjust that, and hopefully all will be well.

Table now adjusted and it's cutting straight as an arrow. Job done!

I had a similar problem a month or two ago. Tried all sorts of adjustments with the guide only then I checked the actual squareness of the table to the blade. Note to self .....

Glad you got it resolved too.

cheers

I've been reading through these posts just now as I am experiencing a similar problem. My bandsaw is 28 years old, its basically a no name brand, would have been an import from taiwan I guess back then, 14" throat.

It's served me well over the years. Some time ago I bought a new guide for it, to accommodate a very thin blade, 1/8" with a lot of teeth to the inch, which I used to make bandsaw boxes on. I've pretty much just left the thin blade on plus the guide.

Now I want to rip some timber down the centre, say some 12 or 12mm timber, rip it in half to say 5mm. It ripped fine but the 1/8" blade left a lot of ripply marks which I had to sand out. So I thought I would try my older blades 1/2" and 1/4" and put the original guide back on.

I have an adjustable fence fitted to my table which runs along parrallel to the mitre slot, always at right angles. But now when I put the thicker blades and original guide back on, the cut runs towards the fence and pulls the timber away from the fence.

Looking at that diagram if I am correct I should be adjusting my tracking to the rear of my tyre but when I do this the top wheel scrapes against the fixed housing cover.

Any thoughts or suggestions, I've checked my blade and it seems square to the table.

Regards
Paul

Assuming your bandsaw actually has crowned wheels (!), the tracking adjustment required to adjust blade drift should be tiny. In most cases you would only need to adjust the tracking to get the blade to run a few mm back or forward of the centreline.

I've never come across a bandsaw with so little clearance between wheel and frame that this small adjustment couldn't be performed, but maybe you've found one !

Are the wheels co-planar? It could be that the top wheel is sitting a bit back from the bottom one. You may need to shim the top wheel out slightly. I had to do that with mine too, for much the same reason...

(It is actually a really good bandsaw, it just hadn't been set up too well)

and thanks for your replies. So we are agreeing that my blade needs to be more on the rear side of the tyre. (I've actually replaced the tyres about 12 years ago).

I tend to think that I have had this scraping problem for years, but since using the tiny 1/8" blade it never worried me.

So it appears now I need to find a way to "kick" the top rear housing back a bit to allow my blade adjustment and to prevent this scraping.

Thanks again, Paul

Just rereading your post, maybe I misinterpreted you. You actually moved your top wheel out further than it was originally set up. How could I tell if it wasnt directly above the bottom wheel, just by eye sight,..?

Regards
Paul

still thinking here, which blade would you consider best for ripping of say 12mm thick timber down to two slices of around 5mm. The height of the timber might be only about 70 or 80mm high, or even much lesser.

Paul