Bandsaw throwing bands - forwards!

[Stubby]

If thats the saw teeth that has done that to the outer race then it will blunt it pretty quick even if it stays on ! ....

[MattyF]

I had a woodmizer and remember once a band had come of or been knocked off then it would need to be reset even if still sharp. Once it's been off its a waste of time reusing. There was several adjustments on my band saw to stop this happening but I found the way to set it up was start at the begining and follow the manual. Trying to tweak a problem out used to make things worse.

 

 

Pretty much my finding on my Norwood , once they have come off they will keep on coming off unfortunately. Keeping them correct in tension and topped up with coolant and reading what the logs going to do as some times they will have tension and need a wedge or two other wise they pinch the blade... But this pulls them back not forward but basically you want to do every thing possible to stop it from skipping in the first place or it will keep on doing it like you described.

[gensetsteve]

I found the blades on the smaller bandsaws were more likely to cause problems. The deeper wider blades seem to control the wood not the other way round. I had loads of problems in the early days and advice on here helped lots. I found I had to turn the log regularly as the tension in the wood was capable of throwing the band of track and it would start climbing or dropping. The other thing that threw me was I had a few sticks that had been felled next to the root plate it took hours of changing blades swapping sticks before it dawned on me. It was all great fun and a huge learning curve. I cringe when a novice post on here wants to hire a machine to plank 40 tonnes in a day. A good skill to learn and you can't beat experience.

[agg221]

It was the back of the blade which wore the groove. I think once it started it must have had a tendency to catch and jam - it looks like the band wheel also caught the ridge brought up on the surface so plenty of opportunities to create friction, slackening the band on the lead in.

 

My experience is also that heavier bands make for smoother cutting on the wood, but it's a three-way thing between wood, band and wheels. With a light band and some thin wedges the machine drives, pulling the band under control at the cost of a bit of accuracy once the band has lost its initial perfect edge. With a heavier band, the cut is more accurate but the machine can't pull out any slight deviations so if it is thrown then it's scrap.

 

I have both, but tend to run light bands when I am trying to figure out problems, heavy ones when the machine is working well as this is more cost-effective. Note, these are much lighter than Norwood or Woodmizer bands - they are 3/4" and the light ones are 0.6mm, heavy ones are 0.9mm cobalt steel.

 

Alec

[agg221]

OK, some more info.

 

I've changed the two guide bearings, had the wheels off and checked the bearings, which are perfect.

 

I put it back together, first five feet of 12" wide oak like a hot knife through butter, then jumped the band off forward again.

 

Second band, set up and did about 20', then jumped at the very end of the board, but I caught it doing it. It's very odd - the band is rolling off at the top of the drive wheel where it feeds in. Either it's coming in slightly too far forward, or the wheel is tipping slightly forward. I tried rotating the wheel by hand, backwards and forwards, and with the band starting from properly on the wheel to starting to come off was 1/4 turn. Then after about 15 or 20 times doing this, suddenly it started tracking in the middle of the wheel. Of course it was dull by then but I checked it for true running and it did about another 8'.

 

I then changed over to another band, which did about 20' and then snapped (it was an old band, so this doesn't worry me as such). Fourth band on and it would only track at the front of the wheel. After about 15' it jumped again and it is currently back to running right off the wheel again as above.

 

Any ideas where to look for this intermittent fault? Fortunately I can resharpen the bands because otherwise I would have got through four bands for about 4cu.ft of timber, which is rather unrealistic!

 

Alec

[gensetsteve]

On my woodmizer there was an adjustment of the drive wheels left to right but also top to bottom. Sounds like the pressure of the cut keeps the band in place but as you get near the end you reduce the cutting pressure so the band rides forward. The other thing to check is are the bands tensioned right. I may have completely the wrong end of the stick here as can't actually see what's going on

[cornish wood burner]

Just a thought but were the bearings tight on their mounting shafts and in their housings.

[agg221]

Just a thought but were the bearings tight on their mounting shafts and in their housings.

 

Yes - I didn't dismantle the wheels, just took them out. There is no play or roughness and they run forever if you hold the shaft on the ends and spin it up.

 

They are secure in their housings - the drive wheel shaft has to be drawn back in with a bolt and the front of the shaft is the adjustment for tracking, which holds it tight when screwed in (and does not work loose). The idle wheel shaft again has to be drawn in with a bolt and the wheel is tensioned against this shaft by pivoting the wheel backwards, so it would naturally locate at the inner edge even if there was any play on the outer face of the shaft (I can't feel any).

 

Steve - I think you are right that it is pressure on the band in the cut which stops it jumping even more frequently - I do notice that it jumps faster with sharper bands, which is consistent with this. However, when I enter the cut it is tracking properly (you can rev it up and it doesn't jump). When it goes wrong it is tracking clean off the front of the wheel as it enters, so much so that it is jumping the rim. The issue is that I don't seem to do anything to it to get from one state to the other, and back again. No top to bottom adjustment on mine unfortunately.

 

Alec

[Wendelspanswick]

Have you tried putting a straight edge on the edge of the wheels when the band is tensioned, it would show if your frame is flexing or twisting under load.

[agg221]

Have you tried putting a straight edge on the edge of the wheels when the band is tensioned, it would show if your frame is flexing or twisting under load.

 

I haven't - I did think about this but can't see how to do it as the wheels are pretty much fully enclosed by the casing, which also forms part of the tensioning system so you can't take it off to examine it. I'll have another think about whether I can jig something up with some pins though, set them to depth against the wheel edges through the casing and then and then rest that on a straight edge afterwards - cheers for the thought.

 

Alec