Bandsaw woes.

I may have posted about this before in a 'which bandsaw should I buy' context. A Femi would be nice, but it's not going to happen for a while. So I have to live with what I've got.

Here is a cut in 1.5" aluminium square:

At this point the blade jumped off the wheels (I was hoping to get all the way though, hence the redundant 'top' reminder). So two problems, which I think are linked: (a) the cut is way out of square and (b) the blade jumps from the wheels. Probably relevant is that the cut starts smoothly, but the machine makes a clunking noise and the arm 'hops' a little in time with the clunk before the blade jumps the wheels. I've watched the weld and it isn't catching in the workpiece, it happens when the weld is somewhere inside the machine.

Here's a pic of the machine:

and another with the arm set at an angle to make it clearer how the castings fit together:

Obviously there are many variables here. What I'm after is advice on systematic diagnosis of the problem(s). Everything is fixable with a lathe and a mill!

Robin.

Edited By Robin Graham on 19/12/2019 00:37:00

Hi Robin, I have a Femi and there's nothing special about them, there's no reason your saw shouldn't cut as well, try checking the bearings that guide the blade, sometimes a chip can get wedged between the blade and the roller, and the small bearing shatters, not that noticeable until some sideways force is put on the blade, I'd check those first.

If all four of those are OK, they might need adjustment, one side of the blade should have the bearings on a cam to adjust.

It was aluminum solid, not tube right?

(just in case).

Yes, solid - why is that relevant?

Robin.

I believe that you are picking up small bits of aluminium in the teeth of the blade causing the problem, when the clunking starts stop the saw and look closely at the teeth and you will see chips of ally stuck there. I had the same experience and once you have cleared the teeth you are back to normal. Regards Pat

We know, the size, we now know the section, but there are still several parts/settings that may be relevant.

Play at all pivoting/rotating points, type and condition of blade, tooth size, condition of wheel bands, and whether you usually cut wet or dry (seems dry in this case) compared to the manufacturer advice. All these things, and perhaps others, may have relevance to your problem - no point everyone unnecessarily offering advice on the current details only to find something important has been overlooked/ignored.

Further, it appears that the band support has not been adjusted to minimise the “free length” of the band. I’m sure there are other owners of this supplier that have been very satisfied with the operation of their saw, with (or without) regular corrective actions.

Certainly, if the band is distorted between front and back of cut, poor efficiency could follow. Even the source of bands has been known to make a considerable difference.

When cutting Alu. on my saw I run a piece of Bees wax along the line which seems to ease the cut.

How much use has the blade had? They don't last forever particularly if just carbon steel.

Any signs of small cracks starting from the gullets of the teeth which may be your clicking.

Had any snatches recently when small work has moved in the chuck? can kink blade

Easiest way to eliminate a lot of guessing and time spent looking would be to try a new blade, if still a problem then it's the saw, if not then it was the blade.

Edited By JasonB on 19/12/2019 07:34:17

What pitch blade were you using ? Wider cuts require a coarser pitch blade to prevent the gullets getting clogged - clogged gullets give rise to a wandering blade.

If you can't fit a blade with a coarser pitch, reducing the feedrate to the point that the gullets don't clog will also help prevent the blade from wandering. On the bandsaws at work we had similar problems (600mm deep cuts in graphite) & enlisted the assistance of the blade manufacturers. The blades were changed to the coarsest we could get (2 / 3 TPI vari-pitch) & reducing the feedrates to the point that the gullets didn't get filled largely solved the problem. That on top of ensuring the blade tension was correct (the saw blade rep used a tension gauge to determine that, on our machines, correct tension was with the adjuster as tight as we could get it) & that the moving guide was set close to the block.

HTH

Nigel B

Please forgive this opportunistic post, but someone amongst you bandsaw users may be interested in my “For Sale” Advert.

MichaelG.
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Please delete if it is considered inappropriate.

<edit> Inappropriate asterisk deleted as requested.

Edited By Neil Wyatt on 21/12/2019 10:09:49

Robin - I have that same model from the same supplier. I would rate the chances of obtaining a 'straight' cut (in anything) as close to zero. In fact my particukar machine was sold at a discount as being "incapable of adjustment to correct cut by our engineers"! I occasionally manage a vague vertical but there's never going to be a 'no-fettling required' result. It is, therefore a muscle saver for crude approximations only - matches my skill level!

I wish you well with your endeavours and will follow closely

rgds

Bill

I suspect the alignment of the blades guides. the brutal twist back onto the powered wheel is very demanding.

I had similar trouble with my saw and it was compounded with blade breakage. I put it right in the following way

Take the blade right out and dismantle the guide wheel heads. Mine were badly made with cast surfaces that fitted where they touched, re-machine all those so that they can be relied upon to guide the blade correctly. Now stretch a wire or fishing line round the blade wheels with it snugly into the rim groove and rebuild the blade guides.

The aim is to only just support the back of the blade, the wire should therefore just graze those wheels. Take the wire out and refit the blade. Grip it at the low end with a tool makers clamp where it runs out of the guide to twist the blade and set it upright with respect to the vice and held like that refit the side wheels to support it. Next set the guide blocks is to hold the twist before screwing it down to the support beams. Be sure the side wheels allow the blade to run through without gripping it tightly.

Tension the blade to a mid musical tone by plucking the free section at the back of the bow, a dull thud is far too slack it does need to ping.

Tooth count is important. I use 10 tpi for everything other than tube which I cut at 14 tpi. One last point, avoid cutting welds with hard spots, that can take the edge off teeth on one side and lead to curved cuts.

My saw has behaved impeccably after that treatment for more that 8 years now. It has had other problems but not blade throw off or breakage.

Regards Brian

Thanks for replies.

Bill - (Cornish Jack) maybe you got the first one I bought from them and sent back! It was even worse on vertical alignment than the replacement, and as you know there is no provision for adjustment.

I'll fit a new blade and see if that helps. When I bought the machine I also ordered a small stock of replacement blades from Axminster. They are 1470mm x 1/2" 14tpi carbon steel - I think I might still have one left, However it may be better to fit a third party blade. My Record woodworking BS certainly works better with Tuffsaw blades than the Record offerings.

I'll go for bimetal with M42 teeth. Ian at Tuffsaws stocks these with various pitches - from what's been said here it seems 8/12 or 10/14 Vari-Tooth might be a reasonable choice.

Having said that there is a fundamental problem with the machine which I'll have to address at some point if I want to get it to cut true:

Apologies for it being sideways - I forgot that if I want things to come out the right way up on this forum I have to turn my camera 90 degrees.

Robin.

Edited By Robin Graham on 19/12/2019 23:22:25

Edited By JasonB on 20/12/2019 07:03:16

Because if it's tube you are cutting a relatively thin section whose width may be of the same order as the blade tooth spacing. At least, there may be only a few teeth in contact. It's common for the blade to snag and jump off the wheel under those circumstances. If I have to do it I usually support the saw by hand to give only light pressure.

Without all the relevant detail, most of which does not seem to be readily available, my only suggestion for a solution might be to tilt the vise. Perhaps that is the fundamental problem - or maybe it is not. I can think of other fundamental issues with problems such as this.

I think the vice is an integral part of the base casting. Though the blade is pulling in the cut so would do the same whatever angle the work were held at eg blade not inline with plane that the arm moves in.

You are right Jason. The vice is indeed integral with the base casting. I'm now pretty sure that there are several problems with this machine. I think the pics of a square in the vice show that the axis on which the arm swings is not parallel to the vice base. Maybe I could fix this by making a 'sub base' with an arrangement of fixing/jacking screws to allow adjustment. The blade pulling might also a be problem, but perhaps secondary. This is becoming a challenge! I'll get a better saw when finances are better, but I don't like chucking stuff without having a go at fixing it.

Postie delivered a package with the Zoro logo on it today - my wife confiscated it immediately. What can it be I wonder? Do they sell socks?

Merry Xmas, and thanks to all who have helped me out with advice and entertaining engineering chat over the years I've been on this forum.

Robin

Posted by Robin Graham: "the axis on which the arm swings is not parallel to the vice base".

This was essentially the same problem I had with my Aldi metal bandsaw, which I sent back only a few days after buying it.

I am presently without any metal bandsaw, and my view is that unless a metal bandsaw of this type has at least a few degrees of adjustable sideways tilt at the pivot point, wear between moving parts at the pivot point will eventually cause cuts to stray from dead vertical - that is if they were vertical to begin with, i.e. when the saw was new.

I don't know whether metal bandsaws with adjustable tilt at the pivot point exist, because I've not really looked into it, but if they don't surely they should.

Edited By Bill Phinn on 21/12/2019 02:36:51

When I got my Chester H110 bandsaw, I had a lot of problems with the blade jumping off. The cause turned out to be the guide bearings!

3 out of 6 collapsed within 3 months, since then I have had no trouble at all!

Jim

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Fundamental rule of Engineering to a price :

If you can’t make it ‘right’ ... make it adjustable.

MichaelG.