Metabo bas260. Blade off when reversed and bearing issue

[Eric The Viking]

Basic: have you checked the tyres are in good nick, and not loose on the wheels or lumpy anywhere?

The machine will move the blade backwards by itself for one of three reasons (there must be more, but hey...):

1. The motor has "issues". They often get depressed around this time of year, usually after doing a tax return... Seriously, it just might be because of a failed start winding or centrifugal switch failing or the run capacitor (simple mains synchronous motors can be made to run in either direction, but not by reversing the polarity of the power connection). One of the symptoms of motor problems is (surprisingly) very little motor power, AND the motor getting hot quickly (you'll feel it on the outside of the case fairly quickly (tens of seconds) arter startup).

If this is the case, you need to stop trying to use it and fix the motor - it may be repairable but it won't be if you let it run extremely hot. They all have cooling fans (induction motors for this sort of machine), and shouldn't get more than hand-heat warm in use. If it does, you have a problem. It obviously won't be the ONLY problem, but you need to fix everything!

2. If the bearings are good, and the bandsaw blade is a small one, imbalance in the wheels might cause it to tip backwards under gravity, as it stops. Check both wheels, with the blade and the drive belt (bottom wheel) completely removed. They will probably have a 'favourite' spot they settle at. For each wheel, mark the bottom of the wheel when they stop at this point. Turn the wheel so the mark is level with the centre (i.e. 90 degrees) and let go. Note how fast the wheel picks up speed, and if it oscillates to and fro. If the oscillation is a lot, it may be significantly out of balance. If that's weight, you might rebalance it by adding some to a spoke. If the wheel is distorted (see 3), you'll need to replace it (and that'll be a reason it sheds the blade).

3. The wheels themselves could be oval or warped. Adjust the guides so none of them touch the blade when it's properly tensioned. It should run by hand happily both forwards and backwards without problems, There's no advantage to turning it fast by hand - go slowly and see if/how it moves across the tyres. If it starts to "walk" something's up with the wheel alignments, and/or one of them is damaged.

Moving along...

4. check the wheel bearings: this is hard to describe, but any granular feel, or wobble, or noise (one wheel sounding different to the other when turned by hand) is a sign something's up. They're usually a standard size, and cheap from bearing suppliers (there's usually a code on one face of the bearing's outer shell). Vastly overpriced from the machine's spares stockist usually. Check without the motor belt in place, as it'll colour your perception of how they differ.

5. Run the machine with the guides NOT quite touching the blade when the blade isn't cutting. There are plenty of descriptions, write-ups, youtube essays, etc., on all this. I recommend Steve Maskery's as the most straightforward. The biggest nuisance will be the back (thrust) guides putting too much pressure on the blade when you're cutting. They're a long stop in small bandsaws - if they do engage, the blade can wobble around when it's cutting, with not-straight results. The same generally applies to the side bearings, but it depends if you're cutting straight or curves. In all cases, they're a 'safety net' rather than how the blade should be controlled. It should happily cut by itself running just on the wheels alone (that's UNSAFE - you need the guides - but I hope you can see what I mean). If you apply too much forward pressure when cutting that won't help either - there's an optimum speed, based on blade size, stock type and thickness, and how you're cutting, and you have to find it.

Hope that makes a little sense,

E.

 

[CHJ]

To me you are chasing two unrelated things, The belt/motor tension reversing the wheels is of little consequence.

I think that your main problem is the alignment of your upper rear blade support.
This would appear to be too far forward in relation to the upper wheel, when going forward the blade is leaving the upper guide wheel in more or less the correct plane but is being pushed forward by the blade rear guide.
As soon as you reverse the motion the upper rear guide is feeding the blade forward on the upper drive wheel.

Somewhat exaggerated sketch.

Whichever components are not in the same plane I think your problem lies because of the above effect.

 

[Lard]

Morning all,

I think I've cracked it! .......probably should write i haven't really done anything but it's working".

Thanks again for everyone who gave their thoughts, opinions and suggestions. I slept on a few and then went back to basics.

1. Took off the blade and completely removed both wheels, mounted wheels on a shaft and spun......neither were warped or 'oval' although I noticed that the bottom one had a 'balancing' weight fitted onto one part of the rim (assume like a car wheel etc). This appeared to rule out any major casting issues and so I remounted the wheels.

2. Spun the wheels and found that both started turning backwards on running out of their forward energy......not too much but too obvious to miss.......however this movement seemed somewhat sporadic and so occurred in somewhat random spots along the rim.......so I accepted this as normal.

3. Fitted the blade and took up the loose tension only.....spun the wheels and same thing happened (as in 2 above) but because the blade was on, it immediately started to come off the track.....and so within a few inches of backward movement the blade was obviously close to being off......spent ages pondering this and happened to notice that the lower wheel track (cleaning) brush was not particularly putting many bristles onto the rim and could actually be swivelled, so I tightened this up and repositioned and hey presto (rightly or wrongly) this immediately reduced, as one would expect, the backward movement (didn't remove it just reduced it).

4. Removed the blade and fitted the motor drive belt and made sure it was a lot tighter than I'd had it previously. This, again as you may expect, reduced the backward effect even more (still there but very small).

5. Refitted blade and re tensioned to what I think is the proper setting????? and set all 6 bearings......tried all out with hand turning of wheels as per usual.

6. No other option left so Powered her up and let her run......all fine.

7. Tried a proper cut of firstly softwood and then hardwood and no problems whatsoever!!!!

In summary.....1. I believe I must have had the drive belt too slack originally and so by trying to make a cut simply stopped the blade because it was causing the wheel to spin on the slack drive belt.
2. I think I was a little tentative in my tensioning of the blade. Even though I thought I had it tight I now believe it's much tighter.

My bearing sets and still not equally set (left and right - as in earlier photos) but that doesn't make any difference to the untouched unaffected plane of the blade......manufacturing issue perhaps??
Rear thrust bearings are still bewildering as even though they obviously stop me from pushing the blade backwards they do nowt else....ie they do not spin at all. When I revolved the wheels in 3 above I set the rear bearing to rub against the blade and it did not move one bit!! It would therefore appear that even though it is able it turn by hand it is designed to simply be a stop? to the blade should it touch it in operation???

Sorry for ranting but wondered if any of you would now humour me and tell me if your blade has any backward movement if you turn either wheel by hand and let go? I would appreciate knowing that it's not just me?

I've made quite a few cuts now and it's running (and cutting) lovely.

Dq

 

[Eric The Viking]

Pleased it's working for you, BUT deeply unconvinced you found or cured the problem. The blade simply should not come off, forwards or backwards.

I strongly recommend Steve Maskery's videos, as he explains well a systematic approach to setting up any small bandsaw. If you go through that procedure, it will be OK.

E.

PS: check condition and fixedness of the tyres - should be secure and obviously crowned. It's important. The blade should be running fairly centrally on both wheels.

 

[dickm]

With EtV on this - there is something still amiss. By the basic laws of physics, the wheels should not turn backwards at all after they have initially stopped, unless something, probably something springy, is storing rotational energy on the last movements of the wheel to then force it backwards. If whatever is doing this stores enough energy to make the blade plus wheels system go backwards, that must be offering serious resistance during normal running.
Without becoming obsessional about this, you may still need to look for additional "spriings" as well as the brush.