Bandsaw drift

[Random Orbital Bob]

What is the actual width of the blade? Is it one of Ian's 1" 1.3 tpi "ripper" blades? If so I've also just got a couple and they're awesome. Also how green is the timber you're cutting? If very green, resins quickly build up on the left hand side of the blade as you look at it which throw the tracking off and cause drift. These resins need constant cleaning with a combo of elbow grease and white spirit. Ian has recommended greasing the blade with diesel before use to try and prevent build up but I've not tried that yet myself. The resins build up very quickly with wet wood. I cut a Laburnum log into 8 blanks yesterday and it needed cleaning.

 

[Steve Maskery]

Having the bottom of the gullet in the centre works - in some cases.
I know everyone is raving about the Youtube primer, and the guy obviously gets excellent results with his particular setup. But, as I've written before, there are some aspects that I would agree with only up to a point, and this is one of them.

The blade should be positioned so that it runs true. In many cases that means that the gullet bottom will be central, but if you have a wide blade with small gullets, then when the gullets are central the body of the blade will not be and I can see that causing all kinds of tracking problems. The whole of the blade impacts on the cut, not just the teeth itself, because all the blade is in tension and hugging the wheel, not just the teeth. So if a large part of the metal is over to one side of the crown, I don't see how it can be expected to cut straight, and that viewpoint is consistent with what you are experiencing, is it not?

 

[Random Orbital Bob]

When you say so that it runs true Steve....what specifically do you mean. No vibration and not varying in distance from the guides (ie tracks correctly)? I remember having a similar thread re planer blade setup wrt outfeed levels with you when I joined this forum over a year ago. You were the only person that could adequately explain in micro detail what was going on and therefore why blades should be set 2-4 thou below outfeed level.

This bandsaw gullet in the middle conundrum seems to have the same mystical qualities to it for me. I generally don't have problems getting my bandsaw to cut straight. If I do its almost always because the blade has gone dull and not the individual controls. I don't spend ages messing about getting the gullet bottoms centralised on the crown, I get the blade in the middle of the tyre, period. That's has always worked for my tracking needs and I use from 3/8" to 1" in widths for various operations. But I don't really understand whats going on with the crowned tyre idea. Why does a blade need to be in the middle and what is the crown of the tyre doing to assist in tensioning it? It seems to me that the crown forms a point more or less albeit very rounded over. Wouldn't that provide a fulcrum on which the blade balances? That sounds like an inherently unstable means of supporting a flimsy ribbon of metal and yet obviously it works. What I'd like to know is why does it work? What engineering principles are being employed?

 

[markturner]

Hi Bob, the blade is approx 20mm wide...not sure of the TPI or name, I went with Ian's recommendation! I am cutting kiln dried stock, no fresh timber and the blade is clean as a whistle, so no culprit there.

Steve, should I adjust the blade towards the front to adjust tracking in a particular direction or does it just depend on the saw what effect this has? What do you think re the tension? Does over tension have a negative effect as well?

cheers, Mark

 

[Random Orbital Bob]

Hi Mark....clearly not the resin thing then. I would position the blade dead central on the tyre. Forget the gullet bottom idea for the time being and just centre the blade so the points of the teeth are equi-distant from the front tyre edge as the rear of the blade is from the back of the tyre. In other words dead centred completely ignoring the gullets. With a 3/4" blade you'll never fit the gullet bottoms in the middle anyway without half the blade hanging off the end of the tyre. That clearly cant be right for supporting the blade.

Just one more question, how much wood has it cut already? I must say my experience is the number 1 cause of drift is a blunted blade. Add to that bandsaw blades go blunt pretty fast, especially deep ripping/re-sawing. So it might be worth trying to resharpen it, centralise the tracking and retry. Here is a good tutorial on sharpening if you can stomach the accent. https://www.youtube.com/watch?v=UygEQ-079Ws

Ian at Tuffsaw's also recommends this by the way

 

[Steve Maskery]

Bob
I do know what you mean about the idea that it should be inherently unstable, you'd expect it to want to fall down the slope, not ride the crest, but reality would suggest otherwise.
I'm not an engineer, but my understanding is that becasue of the angle of the blade, one edge is tensioned very slight more than the other. That tension draws the blade in that direction, which in turn increases the tension in both edges, but in the bottom edge more than the top. There comes a point where they balance and at that point, that is the direction in which the blade is going to cut. The knack is to adjust the tracking - and the thus the high point of the crown - so that this balancing point is at a position that equates with "True North" from our point of view.

I think Mathias explains it rather well here:
https://woodgears.ca/bandsaw/crowned_pulleys.html


Mark
If your blade is 20mm wide then I would not expect the gullets to be in the centre of the blade, not unless the teeth are huge and far apart. So a lot more of the blade is going to be riding on one half of the wheel than on the other half. I would expect that to drift. remember that the blade is hugging the wheel, like in the barrel demo on my DVD, and so that should tell you which way it needs to move.

HTH
Steve

 

[Random Orbital Bob]

I plan to try that sharpening method with a dremel attachment with the blade still in the saw by the way because though not horizontal it is easy to access and advance to the next set of teeth. I guess a careful abgle grinder might also work but the dremel is finer and less heavy.

Also I forgot to mention that tension on larger blades (3/4" and up) is a little notorious as being difficult to get right (sufficient tension) on certain saws. Most manufacturers publish specs with about a 1/4" exaggeration on the max blade width their saw can really handle. Now the Felder should handle a 3/4" . Is it the N3800? If so the published range is 1/4 - 3/4" In their case I don't think they're exaggerating that last 1/4" as I just cant believe a Hammer cant tension a 3/4" blade...they're too well made. But the clear advice, even from felder is that you should be winding your tension to its max amount to tension that blade properly.

 

[custard]

Most manufacturers publish specs with about a 1/4" exaggeration on the max blade width their saw can really handle. Now the Felder should handle a 3/4" . Is it the N3800? If so the published range is 1/4 - 3/4" In their case I don't think they're exaggerating that last 1/4" as I just cant believe a Hammer cant tension a 3/4" blade...they're too well made. But the clear advice, even from felder is that you should be winding your tension to its max amount to tension that blade properly.

I've got some sympathy for the manufacturers. There's a big difference in the tension requirements for an ultra thin 3/4" blade like a meat and fish blade, and a hefty M42 3/4" blade. Yet most users are just interested in a single figure...this bandsaw takes a 1" blade where as that one takes a 1 1/4" blade.

When Felder say a bandsaw is rated for a 3/4" blade they mean it will take any 3/4" blade, however when most manufacturers say their machine is rated for a 1 1/4" blade they mean it'll adequately tension a 1 1/4" blade provided it's an ultra thin one!

I use an N4400, I seem to remember that it's rated by Felder at 3/4", but the tension gauge in the machine runs up to 1 1/4" and when I've used a Starrett tension meter on it with a 1" bi metal blade it was registering at the 1" tension level when it was applying the blade manufacturers recommended level of tension.

 

[Random Orbital Bob]

Right then...so like I said to the OP. His Hammer can be relied upon to tension a 3/4" blade.

 

[markturner]

On my machine (FB610) none of the replacement blades I have used (only two so far, both from Ian) seem to tension correctly at the point indicated on the dial. The current blade ( the one I am having trouble with setting up) seems very solid and still has a few graduations to go to where it says it should be. I tried tightening it further, but was getting a rattle from inside somewhere, that I could not identify. Slackening it off a bit seemed to make this go away, but made no difference ( that I could discern anyway ) to the cut or drift, hence my question re the tension. Seems to me the correct tension must be something of a tenuous thing to achieve, as there no quantifiable way to measure it, its down to "feel", certainly on the beefier blades....

Cheers,

 

[Peter Sefton]

I have the Hammer 4400 and it will happily tension a 3/4" blade, I have never had to adjust the tracking in the 8 or so years I have owned it. I find drift is usually caused by blunt or poor quality blades, the set may be bigger on one side than the other. If the side guides are not set close enough to the blades sides or they are set to far behind the gullet they will not offer enough support. I will be demonstrating at Felder in Miton Keynes on the 5th April if any body wants to come along to see how I set my bandsaw up.
http://www.felder-group.co.uk/gb-en/events.html
Cheers Peter

 

[custard]

Seems to me the correct tension must be something of a tenuous thing to achieve, as there no quantifiable way to measure it, its down to "feel", certainly on the beefier blades....

Mark, there is a quantifiable way, but it's not particularly simple or cheap. Bandsaw blade manufacturers have recommended tensions for their blades, and you can use a tension meter to adjust the blade until it's at the recommended tension. That's how bandsaw blades are set in industrial operations or bigger workshops.

Tension meters read out in kg per square cm, which is noteworthy because what's important is the cross section of the blade, the thickness x the width expressed in square cm, so you can see just how crude is a measurement system that only uses the width and assumes some arbitrary average thickness.

The good news is that in reality sharp carbon blades on smaller machines can give excellent results across a wide range of tensions, so in practise there's other priorities apart from tension. But once you step up to 500mm or 600mm wheels or start using the more exotic blades that are becoming available then a more precise approach to setting tensions yields dividends and it's worth thinking about a Lennox or a Starrett meter. I guess if you're spending a few hundred quid for a stellite tipped bandsaw blade the price of a meter doesn't look so expensive!

 

[Random Orbital Bob]

This might help demystify the whole tension thing.

https://woodgears.ca/bandsaw/tension.html

I must say, Matthias is a real one off

 

[Alexam]

I'm not sure how much I can say openly without breaking forum rules, but the DVD will enable you to set your BS up correctly, eliminating drift and getting a good quality of cut. Just read what others have said, not just me! Money-back guarantee etc, etc.

I've only once come across a machine where the blade guides wouldn't go back far enough, and in that case it was a straightforward case of cutting away part of the blade guard with a Dremel, where it fouled the movement of the guide assembly.

EDIT - Just to be unambiguous, the specific point of using a mitre fence is covered.

This ( I've only once come across a machine where the blade guides wouldn't go back far enough, and in that case it was a straightforward case of cutting away part of the blade guard with a Dremel, where it fouled the movement of the guide assembly. ) is a very useful bit of info that I have not seen before. Thanks Steve

Alex

 

[Random Orbital Bob]

That reminds me. You might want to remove the blade guards completely from under the table. Manufacturers get a little over zealous in their blade guarding due to some serious nanny stating intervention about badge qualification so they can claim their saw satisfies some lunatic in Brussels. This is never more prevalent than in the lower blade guards. Blade guards? Blade hiding mechanism more like! In order to actually see where the gullet is with respect to the guide bearing would require X-ray vision on some saws. So if the blade guards are in the way under the table I think its safe to say its OK to remove it. Or, perhaps I've missed the massive risk that whilst standing at your bandsaw, your willy might accidentally "fall" into the moving blade, splicing ************ perfectly into bookmatched pairs!

 

[markturner]

Well, I tweaked and re set the fence. I adjusted the tracking a little to see what effect it had on the drift and which way it was correcting it, then adjusted the track until I had got rid of the drift. the blade now sits approx 5mm further forward than it did before, its not centralized, more to the front than the rear, but it does cut straight using the fence as shown here in ( admittedly crap photo) :



That's a 2mm slice taken from a 4 inch high piece of cherry....nice!

Thanks for the advice guys and interesting links - I also tensioned it up some more as the general point from various articles linked was that it was likely to be not tensioned enough, despite what you might think.

Cheers, Mark

 

[Random Orbital Bob]

Good news Mark. I forgot to mention that the built in tension meters on bandsaws are also notoriously inaccurate so don't worry what the meter is saying its at very best a rough guide only.

 

[Alder]

When I posted my query on the Kreg rip fence 3days ago I had managed to correct drift by manipulating the original fence and successfully re-sawn a 3inch timber (softwood).
As a result of a brief conversation with Steve Maskery at Peter Sefton's open day last year I had also contacted Tuff Saws and purchased 20mm blade for re-sawing work. As a result of the replies I received for which I am indebted I corrected the tracking and have successfully are-sawn a piece of (tantalised) timber 6 inches wide. The cut on the top is very good but the underneath is not quite correct. Do I need to work on the tracking again or adjust the lower blade guide.
The reason I am so cautious is that when we refurbished the house some time ago I managed to salvage some 7 inch wide pitch pine and do not want to waste what little I have by making a mess of it.
Thank you all who replied to my earlier query.
Russell Evans

 

[Random Orbital Bob]

When you say underneath not quite correct, do you mean the cut is bending from top to bottom? Also how old is the blade, what width and tpi is it?

 

[Alder]

Thank you for the reply.
The blade is a new one 20mm wide 4tpi and yes I do mean that the cut at the top is true but the cut on the underside is less so
Russell