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Bandsaw woes - but now fixed :)

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Bandsaw woes - but now fixed :)

Postby Steve Maskery » 23 Jun 2021, 12:43

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.

bent bandsaw.jpg
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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?
Last edited by Steve Maskery on 01 Jul 2021, 22:18, edited 1 time in total.
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Re: Bandsaw woes

Postby Mike G » 23 Jun 2021, 12:53

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.
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Re: Bandsaw woes

Postby Steve Maskery » 23 Jun 2021, 13:32

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.
Last edited by Steve Maskery on 23 Jun 2021, 13:45, edited 1 time in total.
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Re: Bandsaw woes

Postby Woodster » 23 Jun 2021, 13:43

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.
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Re: Bandsaw woes

Postby novocaine » 23 Jun 2021, 13:59

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.
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Re: Bandsaw woes

Postby AJB Temple » 23 Jun 2021, 15:34

What has caused it though? Over tensioned wide blade?
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Re: Bandsaw woes

Postby novocaine » 23 Jun 2021, 15:40

AJB Temple wrote: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.
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Re: Bandsaw woes

Postby Woodster » 23 Jun 2021, 16:11

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?
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Re: Bandsaw woes

Postby Steve Maskery » 23 Jun 2021, 16:45

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.
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Re: Bandsaw woes

Postby Doug » 23 Jun 2021, 17:15

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.
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Re: Bandsaw woes

Postby Steve Maskery » 23 Jun 2021, 17:28

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

Postby Woodbloke » 24 Jun 2021, 11:46

Steve Maskery wrote: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
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Re: Bandsaw woes

Postby Steve Maskery » 24 Jun 2021, 12:03

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

Postby Woodbloke » 24 Jun 2021, 12:13

Steve Maskery wrote: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
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Re: Bandsaw woes

Postby Andyp » 24 Jun 2021, 12:33

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.
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Re: Bandsaw woes

Postby sunnybob » 24 Jun 2021, 18:16

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.
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Re: Bandsaw woes

Postby Woodster » 24 Jun 2021, 21:07

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:

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Re: Bandsaw woes

Postby Steve Maskery » 24 Jun 2021, 21:32

"Curiouser and curiouser", said Alice.
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Re: Bandsaw woes

Postby Trevanion » 24 Jun 2021, 21:50

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.
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Re: Bandsaw woes

Postby Woodster » 25 Jun 2021, 18:13

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. ;)

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Re: Bandsaw woes

Postby Eric the Viking » 27 Jun 2021, 10:47

sunnybob wrote: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).
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Re: Bandsaw woes

Postby NickM » 28 Jun 2021, 08:50

Woodster wrote: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.
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Re: Bandsaw woes

Postby sunnybob » 28 Jun 2021, 11:05

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.
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Re: Bandsaw woes

Postby Woodster » 28 Jun 2021, 14:43

sunnybob wrote: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? ;)

NickM wrote:
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?
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Re: Bandsaw woes

Postby sunnybob » 28 Jun 2021, 15:19

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. :oops:

But I still say that frame is never going to work harden, let alone crack. 8-)
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