Bandsaw woes - but now fixed :)

[Steve Maskery]

I've been having trouble tracking my bandsaw blade for a while now. Turning the tracking know was getting to be a very stiff operation and it wasn't moving the wheel as I would expect it to. "I must get around to find out what's happening, one day".

Well last week my BS did not sound happy and a moment later there wwas a bang and the blade came off. It wasn't snapped, it had just jumped off. Strange.

With more dificulty that I expected I did get the blade back on, but everything was wrong, so I decided to strip it down to see what was going on. I wish I'd taken a better picture of what I found, this was just to remind me how to put it back together.



The vertical grey bit in the middle is a casting which carries the wheel. That casting is pulled up by the black saddle when I tighten the top wheel. The same casting is pressed upon by the tracking rod from the rear of the machine (the side visible in the photo) in order to tilt the axis of the top wheel.

For scale, it is about 18mm square in section and about 100mm long. That nut in the middle is M8, IIRC, I don't have it in front of me.

Still with me? Good.

That casting has a 15 degree bend in it. It should be straight. And where the tracking rod presses on it, there is now a hole right the way through, largely hidden by the BR end of the saddle in the photo). The casting is hollow on the side we can't see.

So I guess the bang was the sound of the tracking rod puncturing the casting.

A call to Scheppach reveals that a replacement part is available from Germany. Guess how much?

 

[Mike G]

Are you sure it's a casting, Steve? It looks somewhat like a bit of box section (so an extrusion). If so, getting it straightened and strengthened. or having a replacement made, won't be very hard.

OK, I'll play. £125.

 

[Steve Maskery]

It's a casting, Mike, there is a stepped hole and raised flange on the side you can't see.

Scheppach want £65, +VAT, +P&P from Germany. My guess is that I'll have small change out of a ton.

Instead, I sent it along to my mate Stuart who is going to try to fit it. He's straightened it, opened up the fracture in the process, of course, and is now busying himself repairing and strengthening it so that it doesn't happen again in a hurry.

Personally I was hoping he would suggest machining a new one out of steel square section. I'm no engineer, but it doesn't seem too big a job to me, but I trust Stuart, so if says he can fix it, then he can fix it.

 

[Woodster]

Strange indeed. Castings normally snap rather than bend. I’ve just checked the mechanism on my RP BS300E and it looks much more solid with all the parts being made of steel. The actual adjustment knob on mine though was a very poor design, easily improved by making a crank handle and fitting a thrust washer. Good luck with the repair Steve.

 

[novocaine]

that would be a very very very expensive casting, especially given it's hollow in nature so couldn't be sintered metal. it would be considerable cheaper to billet fabricate parts and weld together. to get the profile I can see, it would have to be investment cast and there is no casting relief which would be a dead give away. sorry Steve, but I still question it being a cast part. things like the shoulder flange could be spot welded or sil brazed, that cross shaft in the picture appears to have a fillet brazed root.

the fact it failed on being bent back would also point to it not being a casting. there are other reasons that I don't think it's a casting, but that should be enough for now.

if your good man can fix it, let him, it's already fubar, it can't be broken anymore. worst case it's a fab job to make one, nothing to difficult from the picture, the biggest issue would be the stepped hole which would need to be machined then brazed in.

 

[AJB Temple]

What has caused it though? Over tensioned wide blade?

 

[novocaine]

What has caused it though? Over tensioned wide blade?

looking at how it has bent I'd say it's excessive dust removal. :lol:

now in serious mood, it's possibly due to fatigue from cycling related to general usage but it could also be from a bearing failure under load resulting in excessive strain. A bit like a stuck blade but less noticeable. might be worth new bearings as a belt and braces type affair Steve. this is all conjecture though as it isn't sat in front of me.

 

[Woodster]

Looking at the picture closely it does look much like a casting. I should add that Steve didn’t say it was hollow as such, just “hollow at the back” so it would be easy enough to cast. Castings can slowly deform over the years so maybe that’s what’s happened?

 

[Steve Maskery]

I can only assume it is caused by being under constant pressure from the tracking knob. The saw does usually have a 3/4" blade on it. which means tensioning it to the max. I think that this has been a long time coming, actually, as it's not been easy to fettle the saw for quite a long time.

The other casting that has moved is the table. There is a blade access slot that runs from the user to the throat. The tqable used to be level each side of that slot, now there is a step. Some saws have an alighnment pin to stop that from happening, but this one doesn't

Good point about the bearings, I'll ask Stuart if he thinks they are on the way out. I think that there is a bearing supplier in Mansfield, somewhere.

I'll post some photos of the fix when I get it back.

 

[Doug]

Cassells do bearings Steve they are on Littleworth in Mansfield NG18 2SH
https://www.ciponline.co.uk/bearings-an ... rings-c574

If your blade is still sharp I can try rewelding it, the welders maximum size is 5/8 but it might stretch to 3/4.

 

[Steve Maskery]

Thanks Doug, yes, I know where they are.
The blade didn't snap, it just jumped off.

 

[Woodbloke]

I can only assume it is caused by being under constant pressure from the tracking knob. The saw does usually have a 3/4" blade on it. which means tensioning it to the max.

Steve, just a query on this one; do you leave the tension on the blade all the time, even when the ‘shop isn’t in use?…say at night. I used to do that but now unwind the tension at the end of each working day in the ‘shop. I also only use a 1/2” 3tpi blade on my big Ax saw for everything, inc deep sawing (200mm+) which really does mean that the blade can be wound up righty-tighty - Rob

 

[Steve Maskery]

Yes, it's always tensioned. Quite possibly that might be a bad idea...

 

[Woodbloke]

Yes, it's always tensioned. Quite possibly that might be a bad idea...

In no way being critical here Steve as I used to do the same thing for donkey’s years, but when I worked at Ax a few years ago, Keith Thompson (nice bloke btw) one of the guys responsible for sorting out their machinery etc mentioned to me in conversation one day over a mug of tea (and I’ve never seen anywhere drink as much tea as Axminster :shock: :shock that the tension should be removed at the end of each working day. That got me thinking and it’s something I do religiously now at the end of the day before I lock up - Rob

 

[AndyP]

I am seriously considering cutting a hole in the BS door and inserting a bit of clear perspex so that I can tension and detension and know that I am back to the same mark.

On the other hand as I use it so infrequently it is probably just as well if I open the door and give it a good clean and inspection before each use.

 

[sunnybob]

When I first got my bandsaw, I unwound the blade everyday, because thats what i read I should do. I just turned the tension knob four turns, and made a little wooden tag to hang over the bearing block saying "4 turns loose" to remind me to retension the next day.
After a few years, 2 maybe 3, my attention span wandered and I just stopped bothering.
Now, once the new blade is set, I leave the thing completely alone. I have not seen any evidence of a problem in the last 4 years. Admittedly the widest blade I use is 3/8".
I have the axminster 350, and the top wheel carrier is vastly more substantial than Steves sheppach seems to be.

 

[Woodster]

I’m just throwing this out there, but just wondering why a Bandsaw would have a quick release lever unless the manufacturers expected you to follow the instructions in the manual? This is from Axminster’s current top of the range trade Bandsaw:

 

[Steve Maskery]

"Curiouser and curiouser", said Alice.

 

[Trevanion]

I only ever de-tension the bandsaw with the 2" blade on it as it will tend to crack the blades in the gullets if left under pressure and not running for a long period of time. Each blade is £120 and costs about £60 to re-weld and sharpen, so if it cracks prematurely it becomes quite an expensive endeavour.

Narrower blades I leave tensioned for months without any real noticeable problems, eventually, they do go pop but by that point, they've done their fair share of work.

 

[Woodster]

Not very scientific, more out of my own curiosity really. I mounted and zeroed a Dial gauge with a 3/8” blade at rest. I then tensioned it to its normal setting. Bandsaw frame deflection was 0.08mm. Not very much but I wonder what this would have been with a blade double the size? Could leaving the blade like this put a permanent bend in the frame? Maybe over time both the frame and blade will stretch. Not worth the risk on my modest RP BS300E for the sake of a few turns on the crank.

 

[Eric the Viking]

When I first got my bandsaw, I unwound the blade everyday, because thats what i read I should do. I just turned the tension knob four turns, and made a little wooden tag to hang over the bearing block saying "4 turns loose" to remind me to retension the next day...

I do just the same with mine - a bit pf paper gripped under one of the adjustment wheels that says "5 half-turns!"
Easier for me to remember (and the tension screw is fairly coarse).

 

[NickM]

Not very scientific, more out of my own curiosity really. I mounted and zeroed a Dial gauge with a 3/8” blade at rest. I then tensioned it to its normal setting. Bandsaw frame deflection was 0.08mm. Not very much but I wonder what this would have been with a blade double the size? Could leaving the blade like this put a permanent bend in the frame? Maybe over time both the frame and blade will stretch. Not worth the risk on my modest RP BS300E for the sake of a few turns on the crank.

I guess the trade-off is between creating a permanent bend in the frame by leaving it under strain, versus repeatedly flexing the frame by de/re-tensioning. Would the latter cause metal fatigue?

I suppose if there is a permanent bend put into the frame, then, over time, you will need to bend it more and more to get the same tension and the bend will get bigger.

 

[sunnybob]

I can not see how frame deflection could weaken the bandsaw. Even if the deflection was 1 mm (over 100 times more than you measured :shock: ), 1 mm over a 1 metre length frame, how many million, million times would that have to happen to work harden that steel? :eusa-naughty:

It would be more informative if a strain gauge was fitted to the blade itself to measure tension and stretch.
From my experience with smaller blades, I know its been my fault when a blade snapped, by pushing too fast through the wood.
I did snap a 1/8th blade. Again, my fault, I turned the adjuster as though there was a 3/8" in there. It pinged before could start the machine.

 

[Woodster]

Even if the deflection was 1 mm (over 100 times more than you measured :shock: )

You need new batteries in your calculator bob :lol: 0.08 x 12.5 = 1


I think Nick has a better handle on the issue, at least with modest size bandsaws that many folks have?

I suppose if there is a permanent bend put into the frame, then, over time, you will need to bend it more and more to get the same tension and the bend will get bigger.

But as I said earlier, maybe the blade just stretches over time?

 

[sunnybob]

I've mentioned many times that maths is a closed book to me :lol:

But I actually thought I had got it right that time. First decimal is 10's, second decimal is 100's. So move the decimal 2 to the left is 100?

Awcrap. As I wrote that I realised that we were starting with 8, not 1.

But I still say that frame is never going to work harden, let alone crack.

 

[Trevanion]

But I still say that frame is never going to work harden, let alone crack.

I would agree with this, I've never seen a noticeably bent bandsaw frame nor one that was broken (or at least, one that wasn't dropped from height) either made from welded steel or cast iron. After 200 years or so of bandsaw technology, you'd think there would at least be one case if it was a design flaw.

Likewise, with "flat spots" on the band wheels, has anyone actually ever seen this happen themselves? With the blade bearing on half the wheels and the tyres being quite stout I can't really see it ever being a big issue in the short term. I've definitely seen (and I'm sure some of you have also) bandsaws that have been abandoned with a tensioned blade for many years with no use and they get put into service without any "flat spot" issues.

Just those "engineer" types with too much time to bloody think about problems that are absolutely non-consequential, same with those daft "Carter" bandsaw guides, they cost a small fortune and they will not improve the cut of the machine, extend the life of your blades, or make you a magical woodworking wizard once installed despite claims. I've had the good fortune to have used pretty much all kinds of bandsaws from the little Burgess three-wheelers, to the middle of the line Startrite 352s, all the way up to the big Stenner re-sawing bandsaws, the thing that made the biggest difference across the board to the cut quality was how sharp your blade was, with tooth geometry and feed rate coming in close behind, differing types of blade guides make very little to no difference, a sharp blade is absolutely key.

Rant over... :lol:

 

[Woodster]

But I still say that frame is never going to work harden, let alone crack.

I would agree with this.

So do I. I don’t know why Bob has suggested work hardening and cracking. Probably just a slight over exaggeration to support his position?

What’s with the rant about Carter products?

 

[Trevanion]

What’s with the rant about Carter products?

It was more of a general rant about people who overthink bandsaws to the Nth degree. The Carter guides being a prime example of said overthinking, it's a solution looking for non-existent problems.

 

[sunnybob]

No, its a very clever marketing ploy
But the single wheel guide does actually have some effect with super thin blades cutting sharp curves in bandsaw boxes.
No, I cant afford them :eusa-naughty: , but I knew a boxmaker who had a single wheel and spoke highly of it.

My reference to the frame cracking was an extrapolation of the quote from the axminster comment about the frame not taking kindly to constant changes in stress. the only way a steel box section frame can not take kindly to anything, is to bend and subsequently crack. Either of which I find very hard to believe, except on the smallest and cheapest bandsaws.
Even the truly awful Fox machine that was my first bandsaw was stronger than that.

 

[RogerS]

Yes, it's always tensioned. Quite possibly that might be a bad idea...

Nope...if it's good enough for Peter Sefton to leave tensioned up then it's good enough for me.

 

[Eric the Viking]

My little SIP saw is similar to probably hundreds of others from China over the last few decades. It has huge annoyances, one of which is that it _does_ bend with big blades, so that the top guide support goes significantly out of alignment when a big blade is well tensioned. One thing that has always annoyed me is that, although it ought to be strong enough, the frame is only tack-welded in places up the main column (a pair of rectangular-section steel tubes side-by-side), and it's not continuous. Given the paint is getting a bit manky now (it's old!), I am tempted to grind it off and fill in with weld between the tacks, to see if that improves matters.

But Trevanion is spot-on - with a sharp blade and decent tension it still cuts really well. I just have to double check squareness to the table, if that matters for the job in hand.

That said, I changed the bearings (top + bottom wheels) recently, and that's brought it back to nice smooth kerfs again - it was getting a bit ragged, which I think was wear. A cheap "upgrade" though, likewise the guide bearings too, but with a big blade only the back bearing ever touches whe it's cutting, and even then only if I push too hard.

 

[sunnybob]

out of curiosity only, have you tried reducing the tension until the cut visibly deteriorates?
I have a theory (substantiated by nothing other than my own feelings) that most people over tension bandsaw blades because they feel they should.
I was recently cutting a block of walnut 18 cm thick for a bandsaw box, and got a really nice cut surface, then 2 days later while cleaning the machine I realised the blade was quite poorly tensioned.
I wound it up three turns to make it "ping", and the cut became rough. :shock:

 

[Woodster]

My little SIP saw is similar to probably hundreds of others from China over the last few decades. It has huge annoyances, one of which is that it _does_ bend with big blades, so that the top guide support goes significantly out of alignment when a big blade is well tensioned. One thing that has always annoyed me is that, although it ought to be strong enough, the frame is only tack-welded in places up the main column (a pair of rectangular-section steel tubes side-by-side), and it's not continuous. Given the paint is getting a bit manky now (it's old!), I am tempted to grind it off and fill in with weld between the tacks, to see if that improves matters.

Modern hobbyist bandsaws simply aren’t as rigid as they could be, a consequence of being affordable. As you’ve noticed most are just welded mild steel sheet. Provided you don’t use overly large blades on them though and take the tension off when you’re finished they can work very well with a good blade. Some of the modestly sized American bandsaws of the recent past seem to have cast iron frames so I expect they may be better in some respects.

 

[Eric the Viking]

out of curiosity only, have you tried reducing the tension until the cut visibly deteriorates?
I have a theory (substantiated by nothing other than my own feelings) that most people over tension bandsaw blades because they feel they should.
I was recently cutting a block of walnut 18 cm thick for a bandsaw box, and got a really nice cut surface, then 2 days later while cleaning the machine I realised the blade was quite poorly tensioned.
I wound it up three turns to make it "ping", and the cut became rough. :shock:

Well I usually don't fuss too much about tension, but do what you say - try a test cut to see. I like it tight enough to not need much from the guide bearings. Proportionally, I probably tension small blades more than big ones.

But I think there's a bit of 'no free lunch' about frame rigidity. The few bigger Stenners etc. that I have been up close to (annoyingly I cannot remember the detail of my grandfather's one, which I think was Wadkin, as all the other mill machines were), seem to have a suspension arrangement (springs) for the top wheel axle, to allow some give - wouldn't be there if it wasn't needed. I would think frame elasticity helps on smaller saws, although mine also has a spring...

 

[Doug]

Yes, it's always tensioned. Quite possibly that might be a bad idea...

Nope...if it's good enough for Peter Sefton to leave tensioned up then it's good enough for me.

But Peters will be used very frequently isn’t the point that it’s a good idea to release the tension if the saw is going to stand idle for a while?
I imagine flat spots on a tyre also has a lot to do with the quality of the tyre.

 

[sunnybob]

My axminster 350 does have a spring on the top adjusting wheel support.
Sadly it seems to be there for looks only as its utterly useless. It fully compresses way before the blade gets even close to tension.

If I could find a spring with double the strength it might just be useful.

 

[Steve Maskery]

Mines the same, actually.

I'm just off out to pick up the repaired casting.

 

[Woodster]

I’m pretty sure the spring is the same on mine. Strange design?

But the single wheel guide does actually have some effect with super thin blades cutting sharp curves in bandsaw boxes.

 

[Steve Maskery]

Well I've got it back.



You can see how the hairline fracture has opened up as he straightened it. That was invisible when I took it off. Stuart has filled the cavity with a 2-part metal epoxy amd an aluminium bar, then plated it front and back and pinned it top and bottom. The bottom bolt also now acts as a bearer for the tracking thrust knob. It weighs a ton, now.

It may not be the prettiest job in the world, but I bet it is 10x stronger than it was originally and, as I've had the saw 20-odd years, I fully expect it to see me out.

The saw is up and running again and I can get on with my project, yippee!
S

PS - On a Facebook group yesterday, someone was saying that their BS was drifting and what could they do about it. I explained how the tracking knob tilts the top whell, alters the position of the blade and therefore changes the cutting direction.

Another gentleman said you just need a sharp blade and it will be all good. When I pointed out that you needed both, he said that I should watch "the American guy" who "knows what he's talking about".

I maintained a dignified silence, at least online.

 

[Woodster]

Glad you’re sorted Steve.

I wonder which American guy he was referring to?