Help needed to lift bandsaw curse.

That's my experience with woodcutting bandsaws in schools. I became quite expert at dressing wonky teeth in one school where I couldn't stop untrained staff using the bandsaw out of hours. After resetting the offending teeth with a light hammer and a dolly, holding an oilstone at the side of a running blade and just letting it touch any high spots would trim things up quite nicely. I rescued a number of blades that way.

George B.

I was given an axminster saw that wouldn't cut true. A new blade and reset the blade support bearings and it was fine, though I had to file the bearing support to get one side right. You should have atleast 3 teeth in contact with the metal at any point, so for thin material finer blade. Keep the blade guides as close as you can to the work. If the overarm is too heavy on thin material or the blade is cutting to fast take some of the weight with your hand to ease the cut, a fast cut will often give a poor finish. Cheap blades are false ecomomy. Good Luck Noel..

Those marks suggest a bad tooth on the blade, actually two or three bad teeth that distance apart !

My bandsaw is the larger generic 4 1/2" one which was mediocre to begin with.

Don'tb know if any of what follows will be of any help.

The blade needs to be set so that it tracks correctly, (The Idler wheel does this on my saw )

One of the adjustments made was to set the each of the two guide wheels to bear firmly against the sides of the blade, and the upper one to bear against the back of the blade.

On my saw the "side" bearing are mounted on eccentric shafts which have to be rotated to set the bearing against the blade.bearings

If the blade loses any teeth it will jump!

Some time ago Engineering in Miniature carried an article on making a Blade Tension Meter.

I made one and used it to set blade tension.

Basically it is a DTI bearing against a pivoted lever clamped to the blade, whilst the other end of the frame carrying the swinging lever and DTI is also clamped to the saw blade. The blade is tensioned until the DTI shows that the blade has extended by a very small amount . From memory, on a 64" x 1/2 x 0.020" b;lade, by 0.05 - 0.06 mm.

After this "fine tuning" blades last much longer, and cuts are more accurate. One never to be repeated test showed a difference in the thickness of a 1.5 mm slice to differ by only 0.025 mm!

But that it not to be expected to happen very frequently..

Using an excess down force will cause the blade to veer, and produce a curved cut.

Some of the foregoing may be of assistance with your machine.

Howard

I have the Scheppach/Aldi saw. Looking at your" video I would suggest you are putting a lot of down pressure on the cut.This afternoon I have cut a piece of Ali 2.5 x1.5" without any feel of jump . If I increased the down pressure it did cause a jump every revolution. Slackening off the pressure to my normal "feel" stopped it. The blades that came with mine are M42 and look well finished. I cannot visually detect any sign of a weld in either of the two blades supplied.

Keith.

Thanks to everyone for your replies.

Howard, thanks for that information. I think my blade is set up pretty well even without the use of a DTI, but a DTI test of the kind you mention would certainly be useful, I'm sure. I'm also pleased with the accuracy of the cuts as things currently are. Time will tell whether the blades are long-lived in my hands; after a couple of dozen cuts in steel I can't detect any appreciable wear yet.

Keith, I can say with some confidence* I wasn't cutting with excess downward pressure; if anything I was holding the saw up in the cut; what's more, on other tests, whether I held the saw up or let it sit on the work under more of its own weight made no difference to the downwards kick. I did also mention that a change of blade improved the situation considerably, and downward pressure was the same (i.e. minimal) with the second blade as with the first.

* My right arm [the arm that was holding the saw] has functioning biceps but no functioning triceps or deltoid muscles [among others], so pressing down even remotely firmly with my right arm is something I'm physically incapable of; the outcome of a bit of a bad show on a motorbike many years ago.

John, could you explain this further? The brass was cut lying flat, so I'm not sure how a few bad teeth could have caused those marks even if there were any, which by all appearances there aren't.

The blade gets pushed sideways as the bad teeth enter making the one on the opposite side cut deeper on the side. You then get the opposite effect as the bad tooth exits and the blade goes back to it's normal tracking position. Could be a badly set tooth or more likely the teeth either side of the joint slightly out of line.

Bit like using a 4-flute cutter to cut a slot as the cutter deflects the following flute taks a bit of a cut.

Jason got it right ! 

The fact that there are two marks in the same spot tells me that the bad tooth/teeth are on the blade in one place, coming round at the same spot each blade revolution.

Also give me a clue as to how far apart the bad teeth are.

Edited By John Baron on 02/03/2021 08:11:13

Many thanks, Jason and John. Good to know this strange crop-circle-type effect has such a simple explanation.

Since this problem is with the second blade and the first is already known to be defective, I take it this means that both the blades supplied with the saw are a bit sub-standard.

Tuffsaws replacements beckon fairly soon.

Hi Bill, Guys,

Not necessarily defective, its far from uncommon, particularly if the blade weld is slightly out. More often you can bend a tooth just by letting the weight of the arm rest on the work when starting a cut. I've ripped teeth off forgetting to start the saw before lowering onto the work.

Bill,

One thing not mentioned above is that the blade may not have been welded straight. It is something that I have found on my saw when purchased. You can only really check it with the blade off the saw. Lay the back of the blade down on a dead flat surface and check that the back edges on both sides of the weld are in line, ie tight to the flat surface.

A slightly crooked weld could cause your bump.

John

Edited By Breva on 02/03/2021 20:25:52

Femi NG120 ABS bandsaw is one of the best workshop investments iv’e ever made, never had a minutes bother with it, cuts clean and square every time, no matter what the material being cut. Makes all those generic Chinese clones look like junk......and i had several different flavours of them before the Femi.

Am interested to hear why you sent yours back OP ?

Ah ok, followed your link to the Femi saga........surely that is a courier issue rather than a faulty saw ? 

Edited By Alan Waddington 2 on 02/03/2021 21:07:47

Alan, technically it was both, though the faultiness was almost certainly courier-induced rather than the manufacturer's doing. Amazon UK were also hardly blameless for sending out a saw to a UK consumer with a two-pin plug. The foul-up with the return was the icing on the cake.

I would have given a Femi another go if either Amazon or Stakesys had had a replacement in stock, but both suppliers were clean out for a long time. After a brief window of availability in the New Year, Stakesys are now out of stock again, not just of the model I bought but of virtually all 230v versions.

John B., it's useful to know how common problems of this kind are with bandsaw blades. For the record, the blade that cut the piece of brass was fresh out of the box and the teeth were definitely not brought into contact with the brass until the saw blade had reached its operating speed.

John (Breva), I have checked the first blade, which is currently removed from the saw; there is indeed a very slight though gradual dip around the weld line at the back edge of the blade.

Sadly, the bandsaw saga continues.

Earlier I was cutting a piece of 1" x "5/8" mild bright steel into T-nut sized chunks on speed 1 on my Aldi Scheppach bandsaw. I was using a Tuffsaws Vario 14-18 blade that has cut only about thirty pieces of steel and brass mostly smaller than the present piece since it was fitted new around six months ago. I cut one chunk off without any issues. I came to cut my second chunk off and the blade snapped instantaneously as the blade contacted the work, even though I contacted the work ever so gently, as I am always careful to do. The workpiece was very firmly clamped in the vice and did not move. There are no broken teeth on the blade; the blade is barely "broken in", in fact, and the teeth are virtually as sharp as they were when the blade was first fitted.

Can any one suggest how this can be avoided in future? A lifespan as short as this for a blade is clearly undesirable.

I changed the twist angle of the blade drive wheel tyre by 45 degrees to try and increase blade life

Out of the box has 90 degrees of twist

I think they should have no blade twist at all, like a vertical bandsaw, which is the best system IMO

I think things have improved but 0 degrees would be best

Edited By Ady1 on 15/03/2022 23:16:50

Thanks, Ady. I'm having a look at and slowly digesting your project.

I know what you mean about blade twist. It does seem extreme, but I assumed this was standard for portable bandsaws. Maybe it isn't.

I put a teeny bit of oil on my blades now too

Sometimes this throws the blade from the tyre at the start, but I think a little bit of lube does more good than harm

Iron tyres would be best, then you can lube it properly, some of the good italian saws have iron tyres

Bill, it might be worth reporting your experience with the Vario blade to Ian at Tuffsaws - he's very approachable, and knows a lot. He'll probably be interested. When I was struggling with setting up my own saws I emailed him and had about two pages of good advice. I buy nowhere else now!

Robin.